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  • The impact of grain-coating chlorite on the effective porosity of sandstones
    Mar. Petrol. Geol. (IF 3.538) Pub Date : 2020-01-16
    Haoran Xia; Elizabeth Hernandez Perez; Thomas Dunn

    Chlorite grain coatings in sandstones can inhibit quartz overgrowths and preserve porosity in hot reservoirs, but coatings may also introduce high irreducible water saturation and therefore reduce effective porosity. In order to derive a quantitative model to predict microporosity and effective porosity, five sets of sandstone samples with well-developed chlorite grain coatings were studied. Scanning electron microscopy and X-ray diffraction results on each set indicate various types of chlorite morphology and a broad range of chlorite abundance, though the ratio of the average size to the average thickness of chlorite platelets is constant in all samples. Microporosity, defined in this study as the product of total porosity and irreducible water saturation, is correlated to chlorite by volume content and chemical composition: ϕmicro = 7.08 × Vchl/(0.39 × Vchl + 2.26) + 0.927 for iron-rich chlorite, and ϕmicro = 7.08 × Vchl/(1.88 × Vchl + 7.83) + 0.927 for magnesium-rich chlorite, where ϕmicro is microporosity in porosity units (p.u.) and Vchl is volume percentage (%) of chlorite in the bulk sample. When the total porosity for a sample is known, its effective porosity is the difference between the total porosity and the microporosity.

    更新日期:2020-01-16
  • Organofacies composition of the upper Jurassic – Lowermost Cretaceous source rocks, Danish central graben, and insight into the correlation to oils in the Valdemar field
    Mar. Petrol. Geol. (IF 3.538) Pub Date : 2020-01-15
    L. Ponsaing; A. Mathiesen; H.I. Petersen; J.A. Bojesen-Koefoed; N.H. Schovsbo; H.P. Nytoft; L. Stemmerik

    The organic-rich marine shales of the Upper Jurassic - lowermost Cretaceous Farsund Formation are the main hydrocarbon source rocks for the Cretaceous chalk reservoir of the Valdemar Field (Danish North Sea). Geochemical analyses of oil extracts from core samples across the greater Valdemar Field show substantial heterogeneity of the reservoir oils, suggesting contribution from kitchen areas with source rocks of variable organofacies and thermal maturity. In order to better understand the source rock facies that charged the field, a refined organofacies characterization of the Upper Jurassic - lowermost Cretaceous marine shale source rock succession (Farsund Formation) in the Danish Central Graben was established. This organofacies characterization is based on integration of petrographic and geochemical data and demonstrates large variations in both the regional and local distribution of the organofacies at the sequence level in the shales within the Danish Central Graben. In addition, the organofacies characterization shows that the respective sequences in the succession may be represented by several organofacies at the same time. Part of the explanation to the heterogeneity in the oil types accumulated within the Valdemar Field may lie in the presence of different organofacies within the uppermost sequences (Vol-3 to Ryaz-1) in the three kitchen areas. Each organofacies presumable generates different types of oils and the variation in the relative proportions of the different organofacies likely determines the composition of the generated oils. One dimensional (1-D) maturity modelling at three pseudo-well locations, each representing a potential Farsund Formation kitchen, shows that all kitchens are in the main oil window and that mainly oil was expelled from the Volg-3 to Ryaz-1 sequences. Modelling indicates that (i) average values of TOC, HI, thickness and the kinetic model are the main controls on generation and expulsion of hydrocarbons; and (ii) by increasing these parameters, expulsion could also occur from the lower part of the succession.

    更新日期:2020-01-15
  • 更新日期:2020-01-15
  • Cenozoic structural history of the Gippsland Basin: Early Oligocene onset for compressional tectonics in SE Australia
    Mar. Petrol. Geol. (IF 3.538) Pub Date : 2020-01-15
    Elizabeth M. Mahon; Malcolm W. Wallace

    The Gippsland Basin contains some of the largest hydrocarbon accumulations in Australia, and has been in production since the 1920's. These hydrocarbons are trapped by large growth anticlines offshore, in reservoirs of the Cretaceous to Eocene-aged Latrobe Group. Despite the obvious importance of these growth anticlines, the timing of their formation, and the overall Cenozoic tectonic history of the basin is not well understood. Here, we present a detailed growth strata analysis of the faults and anticlines within the Cenozoic sediments of the Gippsland Basin. This indicates two major phases of tectonism in the basin: 1. Late Cretaceous to Eocene extension, and 2. Oligocene to Holocene compression. Detailed analysis of the extensional phase indicates the development of numerous normal growth faults, which display an overall reduction in the magnitude of extension from the Late Cretaceous to the Eocene, commonly terminating at the top of the Latrobe Group. The shift to compressional tectonism occurred at approximately the Eocene-Oligocene boundary (∼34 Ma). A major and widespread episode of compression then occurred, with evidence of growth on anticlines and reverse faults beginning in the early Oligocene. This previously unrecognized early Oligocene event produced significant growth (20–50% total growth) of the major anticlines which host hydrocarbon accumulations. The early Oligocene event represents the first phase of the compressional tectonic regime that continues to the present day in SE Australia. It appears likely that this Oligocene event affected other basins in SE Australia and probably contributed to uplift of the Eastern Highlands. The underlying tectonic cause for this Oligocene compressional regime is enigmatic and may be related to far field tectonic processes. A second pulse of compressional tectonism and anticline growth occurred during the mid-Miocene and is generally more significant in the onshore regions of the basin. The youngest phase of compressional tectonism beginning in the Late Miocene (∼10 Ma) is also more intense in onshore regions and is marked by an unconformity that is widespread in SE Australia.

    更新日期:2020-01-15
  • Sequence stratigraphy of deep-water systems
    Mar. Petrol. Geol. (IF 3.538) Pub Date : 2020-01-15
    Octavian Catuneanu

    Stratigraphic cyclicity in the deep-water setting reflects the interplay of accommodation and sedimentation on the shelf, which controls shoreline trajectories, sediment supply to the shelf edge, and the timing of all elements of the sequence stratigraphic framework. Stratigraphic trends defined by changes in the types, volume, and composition of gravity flows during the shoreline transit cycles on the shelf provide the diagnostic criteria for the identification of deep-water systems tracts and bounding surfaces. Non-diagnostic variability in the sedimentological makeup of systems tracts reflects the unique tectonic and depositional settings of each sedimentary basin, and needs to be rationalized on a case-by-case basis. Contour currents may further modify the sedimentological makeup of deep-water sequences, but do not provide diagnostic elements for the definition of systems tracts and bounding surfaces. The application of sequence stratigraphy to the deep-water setting relies on the construction of composite profiles that illustrate the relative chronology of the different types of gravity-driven processes at regional scales. The cyclicity relevant to the definition of sequences is described by the composite rather than local profiles. The place of accumulation of depositional elements depends on the location of sediment entry points along the shelf edge, the types of gravity-driven processes, and the seafloor morphology. The allocyclic and/or autocyclic lateral shifts of deep-water depositional elements further enhance the offset between local trends and the regional composite profile in terms of timing and frequency of cycles, timing of coarsening- and fining-upward trends, and timing of the coarsest sediment. The sedimentological cycles defined by local trends must not be confused with the stratigraphic cycles defined by regional composite profiles.

    更新日期:2020-01-15
  • Origin of sulfate-rich fluids in the early Triassic Montney Formation, Western Canadian Sedimentary Basin
    Mar. Petrol. Geol. (IF 3.538) Pub Date : 2020-01-11
    Mastaneh H. Liseroudi; Omid H. Ardakani; Hamed Sanei; Per K. Pedersen; Richard A. Stern; James M. Wood

    This study investigates diagenetic and geochemical processes that control regional distribution and formation of sulfate minerals (i.e., anhydrite and barite) in the Early Triassic Montney Formation in the Western Canadian Sedimentary Basin. The generation of H2S in hydrocarbon reservoirs is often associated with the dissolution of sulfate minerals, as a major source of sulfate required for sulfate-reducing reactions. The formation of pervasive late diagenetic anhydrite and barite in the high H2S zone of the Montney Formation is therefore contrary to the normal paragenetic sequence of sour gas reservoirs. Petrographic observations revealed early and late anhydrite and barite cement. The early fine-crystalline anhydrite cement is dominant in northeastern British Columbia (low H2S zone), while the late-stage coarse-crystalline cement and fracture/vug-filling anhydrite are dominant in Alberta (high H2S zone). The bulk isotopic values (δ34S: +2.9 to +24.7‰ V-CDT, δ18O: −11.2 to +15.7‰ V-SMOW) suggest that sulfate-rich fluids originated mainly from modified Triassic connate water was the origin of early anhydrite. In contrast, the SIMS isotopic values of late anhydrite (δ34S: +18.5 to +37‰ V-CDT, δ18O: +12 to +22‰ V-SMOW) and barite cement (δ34S: +23.3 to +39‰ V-CDT, δ18O: +13.2 to +18.7‰ V-SMOW) as well as fracture/vug-filling anhydrite (δ34S: +23.5 to +24.7‰ V-CDT, δ18O: +13.3 to +14.7‰ V-SMOW) from Alberta represents a mixed isotopic signature of Triassic connate water and contribution of dissolved sulfate-rich fluids derived from dissolution of Devonian evaporites. The 87Sr/86Sr isotope ratios of the fracture/vug-filling anhydrite (0.7092–0.7102) are highly radiogenic suggesting extensive water/rock interactions between sulfate-rich fluids and siliciclastic and basement rocks. The similar isotopic composition of the late anhydrite/barite and fracture/vug-filling anhydrite in western Alberta with Devonian evaporites isotopic signature, and the highly radiogenic 87Sr/86Sr ratio further supports sulfate-bearing fluids were mainly originated from underlying Devonian evaporites and migrated upwards through deep-seated faults/fractures to the Montney Formation.

    更新日期:2020-01-13
  • Origin, composition and relative timing of seaward dipping reflectors on the Pelotas rifted margin
    Mar. Petrol. Geol. (IF 3.538) Pub Date : 2020-01-11
    Caroline Harkin; Nick Kusznir; Alan Roberts; Gianreto Manatschal; Brian Horn

    The mechanism by which seaward dipping reflectors (SDRs) are formed is a topic of debate. Two contrasting models exist for their formation, the volcanic-faulting model and the volcanic-loading model. Each of these models has important implications for the processes which control the structure and formation of magma-rich rifted continental margins. We have examined high-quality deep-seismic reflection data across the Pelotas Basin, offshore Brazil. These data reveal a remarkable set of SDRs, for which we have investigated the likely nature of their formation. The total package of SDRs has an across-strike width of ∼200 km and a variable vertical thickness of ∼10–17 km, previously interpreted as volcanic flows. Detailed observations, however, show changes in seismic character and geometry within the SDR package, which suggest a complex and varied evolution. We have used gravity anomaly inversion and seismic observations together to investigate the likely composition of the SDRs by determining the proportion of basaltic material to sedimentary/volcaniclastic material (basalt fraction) within the SDRs. This has been achieved by minimising the difference between the depth of the gravity Moho and seismic Moho in order to quantify the lateral variation in basalt fraction, taken to be proportional to the bulk density of the package. The density of the SDR package together with seismic interpretation is then used to infer the composition, depositional environment, source and time of formation relative to breakup. Our analysis suggests that the overall SDR basalt fraction and bulk density decrease oceanwards, possibly due a change in the type of volcanic deposits from predominantly subaerial to volcaniclastics, possibly deposited subaqueously. The SDRs can be split into three sub-packages. The two inner SDR packages are interpreted to consist of lava flows sourced from syn-tectonic, subaerial eruptions, associated with the onshore Paraná Large Igneous Province, flowing eastwards into an extensional basin. The outer SDR package shows reflector geometries that progressively offlap oceanwards, interpreted as extrusives sourced from an eastwards-migrating, newly formed ocean ridge. Our analysis suggests that both the volcanic-faulting and volcanic-loading models for SDR formation are applicable to the Pelotas rifted margin, recording distinct syn-rift and syn-breakup magmatic events. We show that both SDR formation models can be recognised in a naturally occurring example and can coexist on the same margin.

    更新日期:2020-01-13
  • A new approach to discern the hydrocarbon sources (oil vs methane) of authigenic carbonates forming at marine seeps
    Mar. Petrol. Geol. (IF 3.538) Pub Date : 2020-01-11
    Yuedong Sun; Shanggui Gong; Niu Li; Jörn Peckmann; Meng Jin; Harry H. Roberts; Duofu Chen; Dong Feng

    Numerous marine hydrocarbon seeps have been discovered in the past three decades, the majority of which are dominated by methane-rich fluids. However, an increasing number of modern oil seeps and a few ancient oil-seep deposits have been recognized in recent years. Oil seepage exerts significant control on the composition of the seep-dwelling fauna and may have impacted the marine carbon cycle through geological time to a greater extent than previously recognized. Yet, distinguishing oil-seep from methane-seep deposits is difficult in cases where δ13Ccarb values are higher than approximately −30‰ due to mixing of different carbon sources. Here, we present a comparative study of authigenic carbonates from oil-dominated (site GC232) and methane-dominated (site GC852) seep environments of the northern Gulf of Mexico, aiming to determine the geochemical characteristics of the two types of seep carbonates. We analyzed (1) major and trace element compositions of carbonates, (2) total organic carbon (TOC), total nitrogen (TN) and carbon isotope (δ13CTOC) of residue after decalcification, (3) sulfur isotope signatures of chromium reducible sulfur (CRS, δ34SCRS) and residue after CRS extraction (δ34STOS), as well as (4) sulfur contents (TOS) of residue after CRS extraction. Carbonates from the studied oil seep are dominated by aragonite and exhibit lower δ34SCRS values, suggesting carbonate precipitation close to the sediment surface. In addition, oil-seep carbonates are characterized by higher TOC and TOS contents and higher TOC/TN ratios, as well as less negative δ13CTOC values compared to methane-seep carbonates, probably reflecting a contribution of residual crude oil enclosed in oil-seep carbonates. Very low δ13CTOC values (as low as −68.7‰, VPDB) and low TOC/TN ratios of methane-seep carbonates indicate that the enclosed organic matter is derived mainly from the biomass of methanotrophic biota. This study presents new geochemical data that will allow the discrimination of oil-seep from methane-seep deposits. Although some of the geochemical patterns are likely to be affected by late diagenesis, if applied with caution, such patterns can be used to discern the two end-member types of seepage – oil seeps and methane seeps – in the geological record.

    更新日期:2020-01-13
  • Shallow gas in the Holocene mud wedge along the inner East China Sea shelf
    Mar. Petrol. Geol. (IF 3.538) Pub Date : 2020-01-10
    Yufeng Chen; Bing Deng; Jing Zhang

    High-resolution seismic surveys were carried out in the inner shelf of the East China Sea to investigate the distribution of shallow gas in Holocene sediments. Shallow gas is distributed extensively in the Holocene strata of the shelf which is dominated by the Yangtze River. Organic-rich, fine-grain sediments deposited throughout the Holocene are essential for gas generation and accumulation. The thickness of the Holocene sediment is the main controlling factor determining the distribution of shallow gas. Gas seepages were found mostly at a water depth up to 20 m, where sediment erosion mainly occurs. Coincidence between shallow gas seepage and high methane concentration in the water column suggests that gas emission from these sediments is a potentially significant source of greenhouse gas. The interaction between shallow gas migration and coastal erosion would therefore potentially lead to increased greenhouse gas emission and accelerated sediment erosion. Such results can be applied to other costal locations around the world.

    更新日期:2020-01-11
  • The Baiyun Slide Complex, South China Sea: A modern example of slope instability controlling submarine-channel incision on continental slopes
    Mar. Petrol. Geol. (IF 3.538) Pub Date : 2020-01-09
    Wei Li; Tiago M. Alves; Michele Rebesco; Jie Sun; Jian Li; Shuang Li; Shiguo Wu

    The Baiyun Slide Complex is one of the largest submarine landslides on the northern margin of the South China Sea. Newly acquired high-resolution bathymetric data, 2D and 3D seismic data permitted the systematic investigation of the Baiyun Slide Complex in terms of its seafloor morphology and associated sedimentary processes. The headwall region of the Baiyun Slide Complex, located at a water depth between 1000 m and 1700 m, is U-shaped and opens towards the east. It was efficiently and almost completely evacuated, generating pronounced headwall and sidewall scarps. Submarine channels, sediment waves, migrating channels, sediment drifts and moats are observed within and around the headwall region, illustrating the effects of both downslope and along-slope sedimentary processes. Submarine channels are 16–37 km-long 800-1500 m-wide, and 20 to 50 m-deep. As a modern example of the interplay between slope instability and subsequent incision, submarine channels were generated after the formation of the Baiyun Slide scar to suggest intensified downslope sedimentary processes after the slope collapsed. The initiation and formation of these submarine channels result from the evacuation of the Baiyun Slide scar, which provided the necessary space of the continental slope to accommodate subsequent turbidity and mass wasting flows. Our results are an important example of how submarine landslides can influence erosional and depositional processes on continental margins.

    更新日期:2020-01-09
  • Catalytic hydropyrolysis of asphaltenes in marine oil from the Tarim Basin, NW China: Implications to complicated oil charging histories in an old composite basin
    Mar. Petrol. Geol. (IF 3.538) Pub Date : 2020-01-09
    Jian Chen; Wanglu Jia; Zhongyao Xiao; Ping'an Peng

    Oil asphaltenes have been used to characterize the source(s) and timing of expulsion of early charged oils. However, the application on asphaltene in a complex petroleum basin have been limited. Marine oils from the Tarim Basin, NW China, were selected to release asphaltene-bound molecules by the catalytic hydropyrolysis technique (Hypy). The analyzed samples were 10 heavy oils from two major oil-production regions (the Tabei and Tazhong uplifts) in the basin. The asphaltenes may be mixed products from multiple hydrocarbon charging stages, if we consider the main oil filling events and the regional geothermal histories of corresponding reservoirs. However, the similar molecular and isotopic characteristics of the hydropyrolyzates indicate contributions from one major source rock (possibly lower Cambrian mudstone) during relatively early periods, based on the presently known source characteristics. The preservation of asphaltenes probably reflects a low reservoir temperature after charging. The asphaltenes were derived from marine algae deposited in a strongly reducing environment, given the biomarker data (e.g., relatively abundant aryl isoprenoids and low Pr/Ph) and carbon isotopic data (−35.5‰ to −34.4‰). Asphaltenes were expelled around the oil generation peak. Moreover, molecular ratios indicative of maturity (e.g., tricyclic terpanes/hopanes), derived by Hypy of asphaltenes, suggest that the asphaltenes of the Tazhong Uplift are generally more mature than those of the Tabei Uplift. Moreover, this is mainly related to different maturities when the oil was expelled. The free hydrocarbons in the Tazhong Uplift show greater molecular and isotopic variations than those in the Tabei Uplift. This might be attributed to more complex accumulation processes in the former. Late oils with a range of maturities, mixing proportions with early biodegraded oils, and degrees of alteration by thermochemical sulfate reduction could all have played a role in generating this variability. The results indicate that the hydrocarbons released from oil asphaltenes by Hypy can provide insights into multiple charging processes in an old composite petroleum basin.

    更新日期:2020-01-09
  • How to deal with missing overburden - Investigating exhumation of the fragment of the Mid-Polish Anticlinorium by a multi-proxy approach
    Mar. Petrol. Geol. (IF 3.538) Pub Date : 2020-01-09
    Katarzyna Łuszczak; Michał Wyglądała; Michał Śmigielski; Marta Waliczek; Bronisław A. Matyja; Andrzej Konon; Mirosław Ludwiniak

    Tectonic inversion and erosion conceal basin geological history. As simple stratigraphic reconstructions can be inaccurate, thermal modelling techniques are often applied. In this paper, we show the advantages of a multi-proxy approach for exhumation studies, which explores full range of all possible solutions. The part of the Mesozoic Central European Basin that was inverted into the Mid-Polish Anticlinorium in the Late Cretaceous is chosen as a case study. The analysis consists of three steps: First, a wide range of possible geological scenarios is constructed, accounting for two alternatives of the overburden sequence, southern and northern, that result from the impact of the Holy Cross Fault on Mesozoic deposition. The second stage comprises apatite fission track and vitrinite reflectance analyses carried out on a ∼1500 m long vertical profile, inverse modelling of these data to obtain thermal histories, and 1D thermal modelling of burial-erosion using the PetroMod software. In the third step, results of modelling exercises are combined with probabilities of the overburden variants to define an ensemble of the most likely geological scenarios. By applying this workflow we conclude that exhumation of the Mid-Polish Anticlinorium began in the latest Turonian–early Campanian and that ∼1.7–2.3 km of uppermost Triassic–Cretaceous rocks were removed. The heat flow was similar or slightly higher than the present-day value and during the Jurassic the study area was located on the northern side of the Holy Cross Fault, where deposition was faster. We also investigate the impact of elevated Late Palaeozoic heat flow on our samples and find that it was overprinted by high Late Cretaceous temperatures. All this is achieved by presenting the results as an ensemble of the most likely solutions within the wide modelling space.

    更新日期:2020-01-09
  • Origin of chert nodules in the Ediacaran Doushantuo Formation black shales from Yangtze Block, South China
    Mar. Petrol. Geol. (IF 3.538) Pub Date : 2020-01-07
    Ping Gao; Zhiliang He; Gary G. Lash; Shuangjian Li; Rongqiang Zhang

    Chert nodules are widely developed in Ediacaran deposits of South China, yet the mechanism responsible for their formation remains disputed. Petrological and geochemical studies of chert nodules and host shale of the Ediacaran Doushantuo Formation of the Yangtze Block, South China, were carried out to more fully assess silicification of these deposits. Doushantuo chert nodules display a concentrically layered internal structure dominated by quartz and lesser concentrations of calcite, carbonate fluorapatite, organic matter, pyrite, and sphalerite. Individual layers become thinner from nodule centers to edges. Our results suggest that (1) Doushantuo host black shale accumulated under persistent anoxic bottom water conditions and (2) chert nodules formed as a consequence of the anaerobic oxidation of methane focused along sulfate-methane transition zones at shallow burial depth. Nodules likely originated from porous proto-nodules that consisted of 13C-depleted authigenic calcite produced by the anaerobic oxidation of methane. Decaying of organic matter within nodules helped to create porosity that was filled by authigenic calcite and also released phosphate and zinc ions to pore water, thus favoring precipitation of carbonate fluorapatite and sphalerite. Silica supplied principally from the diagenesis of clay minerals of the host shale cemented the nodules and replaced early formed calcite. The progressive infilling of residual porosity by 18O-depleted pore fluids associated with increasing burial depth is reflected in the strongly negative δ18Ocarb values documented from the nodules. Thus, the formation of Doushantuo chert nodules reflects a protracted diagenetic history initiated by bacterial sulfate reduction and anaerobic oxidation of methane close to and within the sulfate-methane transition zone and continued in association with the diagenetic release of silica from host shale as well hydrocarbon generation with increasing burial depth.

    更新日期:2020-01-07
  • Facies associations, detrital clay grain coats and mineralogical characterization of the Gironde estuary tidal bars. A modern analogue for deeply buried estuarine sandstone reservoirs
    Mar. Petrol. Geol. (IF 3.538) Pub Date : 2020-01-07
    Maxime Virolle; Hugues Féniès; Benjamin Brigaud; Raphaël Bourillot; Eric Portier; Patricia Patrier; Daniel Beaufort; Isabel Jalon-Rojas; Hervé Derriennic; Serge Miska

    Estuarine tidal bar sandstones are complex reservoir geobodies commonly exploited by the oil and gas industry. In order to better predict the reservoir potential of these geobodies, this study provides a modern-day reservoir analogue, describing tidal bars in the inner and outer Gironde estuary from the microscopic to the macroscopic scale. The originality of this work lies in the multi-scale study of modern estuarine tidal bars based on numerous piston cores extracted in a high-energy environment. This work demonstrates that these tidal bars are composite sedimentary bodies made up of individual reservoir sand units separated by thick muddy layers. Their vertical facies associations and internal architectures are controlled by local hydrodynamic variations and seasonal river influxes. Detrital clay grain coats are notably characterized using a portable and handheld mineral spectrometer from the base to the top of the tidal bars. X-ray diffraction and electron microscopes reveal that these coats are mainly composed of di-octahedral smectite, illite, chlorite and kaolinite associated with other components such as diatoms or pyrite. The best reservoir geobodies are those with the minimum clay permeability barriers at the macro and mesoscale. An optimum coated grain content and clay fraction volume is also needed for generating authigenic clay coatings and inhibiting quartz overgrowth. These conditions are met within the tidal sand bars of the outer estuary funnel that are expected to be the best reservoir geobodies in deeply buried sandstones.

    更新日期:2020-01-07
  • The pore structural evolution of the Marcellus and Mahantango shales, Appalachian Basin
    Mar. Petrol. Geol. (IF 3.538) Pub Date : 2020-01-07
    Liaosha Song; Timothy R. Carr

    The generation and primary migration of hydrocarbons in organic-rich shale leaves void space in organic matter, which is the porosity associated with organic matter commonly observed under scanning electron microscope (SEM). In this study, Middle Devonian black shale core samples were collected from three wells penetrating the organic-rich Marcellus Shale and the organic-lean Mahantango Formation in Pennsylvania and West Virginia. Pyrolysis, ion milled SEM and low-pressure nitrogen adsorption analysis were conducted to investigate the organic richness and the properties of the pore system. Vitrinite reflectance (Ro) values in the range of 1.36%–2.89% represent a maturity spectrum covering the wet-gas to post-mature zones. In general, the pore system is composed of organic matter-hosted pores and mineral-hosted pores. However, the dominant pore types and pore sizes vary stratigraphically across lithology and abundance of organic matter. All the organic matter observed in this study shows an amorphous occurrence. Pore space between mineral grains (both silt-size and clay-size) can be filled by organic matter, which contains secondary porosity generated by thermal cracking of kerogen. Mineral-hosted pores are concentrated in organic-lean samples in which secondary organic matter could not fill most of the primary pore space. The destruction of primary mineral-hosted pores and the generation of secondary organic matter-hosted pores were observed. TOC values show positive correlations with the porosity, specific surface area, and the abundance of micropores. Increasing thermal maturity correlates with a significant decrease of pore volume and surface area, primarily through diminishing or vanishing of micropores. The richness and thermal maturity of organic matter in organic-rich Devonian shale can be effective parameters for evaluation of reservoir quality and upscaling the appraisal.

    更新日期:2020-01-07
  • Insights in the pore structure, fluid mobility and oiliness in oil shales of Paleogene Funing Formation in Subei Basin, China
    Mar. Petrol. Geol. (IF 3.538) Pub Date : 2020-01-07
    Xiaoping Liu; Jin Lai; Xuechun Fan; Honglin Shu; Gaocheng Wang; Xiaoqiang Ma; Mengcai Liu; Ming Guan; Yufeng Luo

    Pore structure is an important factor influencing reservoir properties of oil shales. Routine core analysis, thin section, scanning electron microscope (SEM), mercury injection capillary pressure (MICP) tests, Nuclear Magnetic Resonance (NMR), and computed tomography (CT) were used to provide insights into the pore throat distribution in oil shales of member 2 of Paleogene Funing Formation (E1f2) in Subei Basin, China, with the special aim to unravel the effect of pore structure on fluid mobility and oiliness. The relationships between NMR parameters, petrophysical property and capillary parameters are investigated. The results show that rock composition in the oil shales consist of quartz, feldspar, carbonate particles, clay minerals and organic matters. Pore systems consist of large-scale interparticle pores, intragranular dissolution pores, and small-scale micropores within clay minerals and the organic matter pores. Four types of pore structure (Type Ⅰ, Type Ⅱ, Type Ⅲ and Type Ⅳ) are divided according to the patterns of capillary curves, capillary parameters, NMR T2 (transverse relaxation time) spectrum and BVI (bulk volume of immovable fluid) values. From Type Ⅰ to Type Ⅳ pore structure, the maximum mercury saturation (SHgmax) and mercury extrusion efficiency are decreasing, and the SHgmax are less than 50% averagely, indicating the oil shales are characterized by very poor pore connectivity. The T2 spectrum changes from bi-modal behavior to uni-modal and the right peaks become lower or even disappearing from Type Ⅰ to Type Ⅳ pore structure. Fluid mobility is not primarily controlled by pore size, but dependent on the content of short T2 components (<1 ms). The micro-fractures as well as particles (mainly dolomites) filling them emit strong blue fluorescence. The edges of particles emit strong blue fluorescences indicate that the interparticle pores are oil bearing. The carbonate particles are oil-wet, and intragranular dissolution pores within carbonate particles are fluorescent. Authigenic clay minerals abundant in intercrystalline pores, and organic matters abundant in organic pores, emit scattered strong blue fluorescence. Pore structure controlled fluid mobility and determined the microscopic oiliness and macroscopic oil bearing property or hydrocarbon productivity. The comprehensive study above gains insights into the microscopic pore structure and their controls on fluid mobility and oiliness in shale oil reservoirs, and this may have implications for resource potential evaluation and effective exploitation of oil shales.

    更新日期:2020-01-07
  • Organic geochemical characteristics and organic matter enrichment of mudstones in an Eocene saline lake, Qianjiang Depression, Hubei Province, China
    Mar. Petrol. Geol. (IF 3.538) Pub Date : 2019-12-19
    Xiangxin Kong; Zaixing Jiang; Youheng Zheng; Meng Xiao; Chen Chen; Hao Yuan; Fengling Chen; Shiqiang Wu; Jianguo Zhang; Chao Han; Shengqian Liu

    The Qianjiang Depression is a typical Eocene hypersaline lake basin developing good source rocks in the Qianjiang Formation, which have recently been identified as a potential target for saline lacustrine shale oil exploration. Previous studies have only focused on estimates of source rock potential and reservoir quality. However, studies on organic matter enrichment mechanisms in evaporative environments are limited. Based on organic geochemical and mineralogical data, as well as sedimentological analyses, we researched the factors controlling differences in organic matter enrichment in the basin. The results show that total organic carbon (TOC) contents are closely associated with lithofacies with distinct variations. Three main lithofacies associations (LAs) were identified: (1) glauberite-rich LA1 with medium TOC; (2) carbonate-rich LA2 with high TOC; and (3) anhydrite-rich LA3 with low TOC. The distribution of biomarkers from 14 samples indicate both higher land plants and aquatic organisms were involved in the organic matter accumulations. Combining experimental results on gammacerane/C30 hopane, extended tricyclic terpane ratio (ETR), Sr/Ba, V/Ni, and sedimentary characteristics, we analyzed the sedimentary environments of the three LAs. LA1 was deposited in a salinity stratified waterbody with strong evaporation, LA2 was deposited in a still, stratified deep waterbody, whereas LA3 was deposited in a disturbed, saline waterbody. Sedimentary environments not only controlled the formation of the lithofacies, but also influenced the organic matter sources and preservation. Relatively low salinity, strong anoxic condition without physical disturbance, appropriate nutritional terrigenous material inputs, and algal blooms produced the best organic matter enrichment in the saline lake system.

    更新日期:2020-01-04
  • Quantitative evaluation of the transporting capacity of unconformities: A Case Study from the Zhongguai Area, Junggar Basin, NW China
    Mar. Petrol. Geol. (IF 3.538) Pub Date : 2019-12-19
    Kuaile Zhang; Zhenliang Wang; Yiqin Jiang; Aiguo Wang; Changyu Fan; Baoli Xiang; Ni Zhou

    Unconformities are special geologic bodies with a three-layer structure including the rock above the unconformity, a weathered clay layer, and a leached rock. The Upper Wuerhe (Upper Permian) bottom unconformity in Northwest Junggar Basin is the main pathway system linking the Zhongguai (ZG) lift with hydrocarbon source kitchens. Based on the log response characteristics of the unconformity's vertical structure and core calibration, a principal component analysis (PCA) was applied to extract and identify the evaluation parameters of the unconformity's vertical structure. On the basis of Darcy's Law, the quantitative characterization formula of the unconformity's transport capacity with an actual geological significance was established after taking several factors into consideration. The migration probability of the unconformity was used to evaluate the possibility that the unconformity acted as a migration pathway. Consequently, a relationship between the migration probability and the evaluation parameters was developed to analyze the effectiveness of these parameters in characterizing the transporting capacity of the unconformity. This study shows that the quotient of the two principal components extracted from the conventional logging curves (Pc1/Pc2) have different reference values in the leached and parent rocks. The distribution of thicknesses of the weathered clay layer and the leached rock is well matched with the distribution of paleogeomorphology. The parameters representing only a single geological factor are not enough to determine whether the unconformity acted as a migration pathway. The flow coefficient (Cf) containing multiple factors can effectively and clearly identify the transporting capacity of the unconformity, considering the positive correlation between the parameter Cf and the migration probability of the unconformity. The oil and gas shows of the area with a parameter Cf greater than 10 × 10−4 cm2/s are abundant, which is the superior transporting area of the unconformity, and there is a good matching relationship between the distribution of the superior transporting area of the unconformity and that of the hydrocarbon distribution.

    更新日期:2020-01-04
  • Fine-grained volcanic-hydrothermal sedimentary rocks in Permian Lucaogou Formation, Santanghu Basin, NW China: Implications on hydrocarbon source rocks and accumulation in lacustrine rift basins
    Mar. Petrol. Geol. (IF 3.538) Pub Date : 2019-12-23
    Xin Jiao; Yi-qun Liu; Wan Yang; Ding-wu Zhou; Bin Bai; Tian-shu Zhang; Min-ru Zhao; Zhe-xuan Li; Zi-yuan Meng; Yi-yao Yang; Zhi-xin Li

    Subaqueous volcanic-hydrothermal field is a complex hybrid geological system, where sediments originated from volcanic, hydrothermal, lacustrine, terrestrial, and biotic sources are mixed. Recent petrological studies on such sediments have indicated a potential relationship between volcanic-hydrothermal activities and oil generation and accumulation. Here, we explore the mechanisms of sedimentation and oil accumulation in well-laminated organic-rich fine-grained sedimentary rocks in Permian Lucaogou Formation deposited in the lacustrine Santanghu rift basin, NW China. We conducted petrographic, carbon and oxygen isotopic, and organic geochemical analyses of fifty-four core samples from three wells (forty-eight samples from Well W1, two from W2, four from W3) designed for tight oil exploration. Four main observations and interpretations are: 1) The fine-grained sediments are a mixture of volcanic-hydrothermal detrital feldspar grains, authigenic quartz crystals, and primary lacustrine dolomite, forming interbedded tuffaceous shale and dolostone; 2) authigenic quartz crystals were precipitated from acidic hydrothermal fluids, whereas fine-grained angular alkaline feldspars were derived from subaqueous volcanic eruption; 3) the TOC content and oil generation potential increase with increased mixing of feldspars and carbonate minerals. Hence, the dolomite-bearing tuffaceous shale and tuffaceous dolostone are the best source rocks; and 4) the fine-grained sedimentary rocks are interpreted as a subaqueous volcanic-hydrothermal deposit that controls the source potential. The sedimentary processes of an ancient sediment-hosted geothermal system and its implications on hydrocarbon source rocks and accumulation were first identified. Algal bloom induced by subaqueous eruptions is the main cause for episodic deposition of organic matter and extreme heterogeneity in both lithofacies and source-rock distribution. The results suggest that cone-shaped buildups on seismic sections, which were formed by volcanic-hydrothermal deposits and contain highly-mixed feldspar and carbonate sediments, are the best hydrocarbon reservoirs, and demonstrate a strong relationship between volcanic-hydrothermal activities and hydrocarbon accumulation in an extensional tectonic setting.

    更新日期:2020-01-04
  • The heterogeneity of pore structure in lacustrine shales: Insights from multifractal analysis using N2 adsorption and mercury intrusion
    Mar. Petrol. Geol. (IF 3.538) Pub Date : 2019-12-13
    Ming Guan; Xiaoping Liu; Zhijun Jin; Jin Lai

    A series of parameters from a variety of techniques, such as pore size distribution, surface area, pore volume, etc., have been used to characterize the pore structure of unconventional shale reservoirs. However, the investigation on the quantification of pore structure heterogeneity is still scarce. In this aspect, a multifractal theory combined with N2 adsorption and mercury intrusion was used to obtain pore structure characteristics and quantify the heterogeneity of pore size distribution of nine lacustrine shale samples from the second member of Kongdian Formation (Ek2) in Cangdong Sag, Bohai Bay Basin, China. The results show that the Ek2 shale contains complex pore network, and pores with small pore size predominate in pore system. Both N2 adsorption branches and pore throat size distributions from mercury intrusion demonstrate multifractal nature. The width of singularity spectra from multifractal analysis is used to quantitatively characterize the heterogeneity degree of pore size distribution and shows good consistency with pore size distributions derived from N2 adsorption and mercury intrusion. The pore structure from mercury intrusion is much heterogeneous than that from N2 adsorption, indicating that an increased number of large pores will increase the heterogeneity of pore size distributions. Compared with other rock compositions, TOC has an obvious impact on the heterogeneity of pore structure in small pore size range.

    更新日期:2020-01-04
  • Alternating of aggradation and progradation dominated clinothems and its implications for sediment delivery to deep lake: The Eocene Dongying Depression, Bohai Bay Basin, east China
    Mar. Petrol. Geol. (IF 3.538) Pub Date : 2019-12-19
    Jianping Liu; Benzhong Xian; Youliang Ji; Chenglin Gong; Junhui Wang; Zhen Wang; Peng Chen; Delin Song; Wenzong Wei; Ximeng Zhang; Luxing Dou

    Sediment routing in deep-water settings can be significantly different in lacustrine basins from their well-studied marine counterparts, which has been largely overlooked during the past decades. The seismically well-imaged lacustrine clinothems in the Eocene Dongying Depression provide a good opportunity to bridge the deep-water sediment partitioning with clinothem architecture and shelf-edge trajectories, which have been studied through the integration of 3D seismic data and well-logging data. In the study area, the Eocene delta-complexes are architecturally manifested as alternating aggradation dominated (AC) and progradation dominated clinothems (PC). The Eocene Dongying clinothem architecture has been documented in terms of shelf–edge trajectory angle (θsht), edge-to-toe distance (ETT), aggradation height (Ah), progradation distance (Pd) and maximum foreset angle (γmfa). Aggradation dominated clinothems are characterized by ascending shelf-edge trajectories with thick and widespread sand-prone bottomsets, suggesting higher efficiency of sediment delivery into the outlying lake floor. Progradation dominated clinothems, in contrast, are characterized by flat to slightly descending trajectories and generally by a lack of bottomsets. Alternations of rising and flat to slightly descending trajectories accompanied with different clinothem types probably indicate frequent relative lake level changes (on time-scales of 100s of kyr). Further analysis of seismic images and extensive well-logs suggest the distal aggradational bottomsets are generally consist of sub-lacustrine channel-lobe systems, whereas sediment slide, slump blocks occur in slope to slope toe areas of progradation dominated clinothems, which indicate varied processes of deep-water sediment transport associated with different clinothem types and shelf-edge trajectories. Lake-level, sediment supply, water salinity and density change induced by humid-arid climate cycle are suggested to be main factors controlling clinothems stacking pattern and sediment dispersal into deep-lacustrine. Humid climate are considered to be related with strongly aggradational clinothems, during which sediment can be directly transported to the distant bottomset areas due to increased sediment concentration and energy in river discharge. Whereas during dry periods, progradation dominated clinothems start to build under stillstand or falling lake level conditions, sediment generally accumulates at river mouth and collapses due to sediment overload or fault activity. Therefore, a relationship between deep-lacustrine depositional process and climatic signature was established which may provide new thoughts in both the study of deep-water sequences and deep-water exploration in lacustrine basins.

    更新日期:2020-01-04
  • Geological and geophysical features of and controls on occurrence and accumulation of gas hydrates in the first offshore gas-hydrate production test region in the Shenhu area, Northern South China Sea
    Mar. Petrol. Geol. (IF 3.538) Pub Date : 2019-12-16
    Wei Zhang; Jinqiang Liang; Jiangong Wei; Jing'an Lu; Pibo Su; Lin Lin; Wei Huang; Yiqun Guo; Wei Deng; Xiaolu Yang; Zhifeng Wan
    更新日期:2020-01-04
  • Seafloor depressions on the Nigerian margin: Seabed morphology and sub-seabed hydrate distribution
    Mar. Petrol. Geol. (IF 3.538) Pub Date : 2019-12-14
    F. Taleb; M. Lemaire; S. Garziglia; T. Marsset; N. Sultan

    Gas hydrate quantification using acoustic data requires proper knowledge of the mineralogy of their host sediment. In this paper, a petrophysical model allowing GH quantification at sites where mineralogy profiles are absent is proposed. This approach is applied to a high gas flux pockmark system in the Gulf of Guinea where in-situ acoustic and geotechnical measurements together with core measurements could have been correlated and tied to seismic data. Projections of the in-situ measurements on seismic profiles have shown that the study area not only accommodates zones of shallow and dense GH; but also zones where solid hydrate and free gas coexist as well as pockets of free gas. Further analysis of several seismic profiles has allowed illustrating the detailed GH occurrence zone within the study area, estimate its volume and its occupancy ratio of the pockmark. Correlations between GH content and 3D bathymetry sections have allowed to draw a link between different GH contents and the morphology of the pockmark, which also shares similarities with the morphology of the GH occurrence zone it accommodates.

    更新日期:2020-01-04
  • The influence of variable progradation to aggradation ratio and facies partitioning on the development of syndepositional deformation in steep-walled carbonate platforms
    Mar. Petrol. Geol. (IF 3.538) Pub Date : 2019-12-13
    Andrea Nolting; Christopher K. Zahm; Charles Kerans; Yaser Alzayer

    One of the remaining questions in carbonate geology and reservoir studies is the origin of steep-walled carbonate platform margins and the role of gravity versus other structural processes in controlling the distribution of fracture networks and failure surfaces. This study is an attempt to document the role of gravity, interacting with stratigraphic architecture in controlling fracture patterns and margin collapse. We employ finite-discrete element models to illustrate that progradation/aggradation (P/A) ratio and facies tract partitioning in steep-walled carbonate platforms affects the development, distribution, and intensity of syndepositional deformation. All models are under the influence of only gravitational loading, where pore pressure is held constant. We utilize a modified Mohr-Coulomb constitutive law with a Rankine Rotating crack tensile corner to capture both tensile and shear brittle failure. Our results illustrate that P/A ratio affects the distribution and intensity of discrete fractures that form in steep-walled carbonate platforms. Our results suggest that deformation is more extensive in a progradational carbonate platform, where shelf edge angles are greatest and the clinoform is thickest. Alternatively, aggradational carbonate platforms experience localized deformation in front of the antecedent shelf edge where the clinoform is thickest and steepest. The introduction of mechanical heterogeneity associated with facies tract partitioning affects the intensity of fracturing in both progradational and aggradational models, with the greatest number of fractures developing in reef facies in both scenarios. Development of brittle deformation under the sole application of gravity and lack of seaward lithostatic confinement is consistent with the syndepositional nature of deformation in these settings. This work illustrates the interplay between carbonate platform geometry, facies distribution, and the resulting syndepositional deformation.

    更新日期:2020-01-04
  • Petrofacies prediction and 3-D geological model in tight gas sandstone reservoirs by integration of well logs and geostatistical modeling
    Mar. Petrol. Geol. (IF 3.538) Pub Date : 2019-12-26
    Binfeng Cao; Xiaorong Luo; Likuan Zhang; Yuhong Lei; Jinsong Zhou

    These effective reservoir rocks that can have sufficient porosity and permeability and hydrocarbon accumulations determine economic reserves and high yield of tight oil and gas. Understanding the origin and distribution of these effective reservoir rocks is important for sorting out “sweet spots” in tight reservoirs. Multiple-scale analyses from the microscopic, via drill core to single wellbore have been conducted to examine reservoir heterogeneity of the Upper Paleozoic Shanxi Formation in the southeastern Ordos Basin. Five sandstone petrofacies have been defined in terms of texture and framework composition, detrital matrix, diagenesis and pore types: quartz arenite, tuffaceous quartz arenite, ductile lithic-lean sub-litharenite, ductile lithic-rich sandstone and tightly carbonate-cemented sandstone. The various petrofacies show fundamentally different pathways of diagenetic and reservoir-quality evolutions, due to the complexity of texture and detrital composition in the Shanxi Formation, directly related to the provenance and depositional environment. Quartz arenites and ductile grain-lean sub-litharenites both form effective reservoir rocks. By translating petrofacies to well-log signatures corrected from petrographic and core analysis data, a model based on factor analysis has been built to predict petrofacies at the well scale. For investigating the distribution of each petrofacies at the field scale, sequential indicator simulation method has been used to construct a 3-D petrofacies model with facies conditioning. The isopach maps of quartz arenites and ductile lithic-lean sub-litharenites have been made from the 3-D petrofacies model to quantify their areal distributions, and to define the “sweet spots” by combining isopach maps of these effective reservoir rocks and gas production data from well tests. The concept of reservoir petrofacies is an important tool for the characterization of tight sandstone reservoirs.

    更新日期:2020-01-04
  • Influence of fracture stratigraphy on hypogene cave development and fluid flow anisotropy in layered carbonates, NE Brazil
    Mar. Petrol. Geol. (IF 3.538) Pub Date : 2019-12-27
    F. Balsamo; F.H.R. Bezerra; A.B. Klimchouk; C.L. Cazarin; A.S. Auler; F.C. Nogueira; C. Pontes
    更新日期:2020-01-04
  • Constraining the timing and evolution of hydrocarbon migration in the Bight Basin
    Mar. Petrol. Geol. (IF 3.538) Pub Date : 2019-12-19
    Julien Bourdet; Richard H. Kempton; Vanessa Dyja-Person; Jacques Pironon; Se Gong; Andrew S. Ross

    Micron-sized fluid inclusions within quartz grains from Late Cretaceous sandstones, recovered from drill cuttings from four wells in the Great Australian Bight, contain palaeo-fluids such as brine, black oil, light oil, gas condensate, and N2 and CO2-rich hydrocarbon gas, providing evidence of multiple palaeo-hydrocarbon migration in the Bight Basin. A series of microscopic, spectroscopic and thermometric characterisation techniques were applied to the petroleum fluid inclusions in Gnarlyknots-1A, Potoroo-1, Greenly-1 and Duntroon-1 in order to estimate fluid types, palaeo-pressures and palaeo-temperatures (PT) of hydrocarbon entrapment, and to provide constraints on the age of petroleum migration in the central and eastern parts of the Ceduna Sub-basin. The Coniacian interval (Tiger Supersequence) in Gnarlyknots-1A trapped a variety of petroleum fluid types (black oil, light oil and gas-condensate) over an extended period. The earliest phase of oil entrapment recorded in quartz grains took place at a minimum of 58 °C as light oil and, together with pressure, constraints this to the end of the Cretaceous (circa 75 Ma). Source rocks capable of light oil generation at this time occur in the Blue Whale Supersequence. Petroleum compositions evolved toward more gas-rich fluids during the Cenozoic. This, together with some late oil constrained to Miocene age migration, implies generation from at least two source rocks. Source rocks capable of generating gas at this time are interpreted to be in the Blue Whale and White Pointer supersequences, while late oil may have been expelled from the Tiger Supersequence in the central basin depocentre. The palaeo-PT evolution recorded by the fluid inclusions in Gnarlyknots-1A closely follows the modelled burial curve, suggesting that the petroleum fluids were in thermal equilibrium with the rock. In contrast, the oil and gas inclusion assemblages found at Potoroo-1, Greenly-1 and Duntroon-1 were trapped later, with some at temperatures higher than the formation temperatures predicted from burial models. Whilst there are several potential mechanisms that explain these observations, we suggest that these wells are located near major extensional faults that have the potential for conducting fluids upwards. Additionally, gases such as CO2 and N2 associated with hydrocarbons possibly relate to mixing with mantle-derived fluids, which may also have contributed to the aforementioned thermal anomalies.

    更新日期:2020-01-04
  • Emergence of a submarine canyon, Crotone Basin, southern Italy
    Mar. Petrol. Geol. (IF 3.538) Pub Date : 2019-12-26
    Massimo Zecchin; Mauro Caffau

    The Serra Mulara canyon is a middle Pleistocene submarine canyon developed along the Ionian coast of Calabria, southern Italy, now exposed on land due to the long-term regional uplift of the area. New data have allowed recognizing three depositional sequences in the upper part of the succession, probably glacio-eustatic in origin, documenting an evolution of depositional systems that reflect the emergence of the canyon. Sequence 1 shows a rapid shift from turbidites and hemipelagites accumulated in the upper part of the canyon fill to forced regressive deltaic deposits, which reflect a marked shallowing of the area. Sequence 2 consists of estuarine transgressive and deltaic highstand deposits, whereas Sequence 3 is fully composed of fluvial deposits, testifying the emergence of the area. The upper part of the Serra Mulara succession is an useful example showing the transition from submarine canyon to continental settings, a situation that is not adequately documented in the literature, and is also relevant to better reconstruct the timing of the uplift of this part of Calabria.

    更新日期:2020-01-04
  • Provenance and sedimentary evolution from the Middle Permian to Early Triassic around the Bogda Mountain, NW China: A tectonic inversion responding to the consolidation of Pangea
    Mar. Petrol. Geol. (IF 3.538) Pub Date : 2020-01-03
    Yanqing Shi; Hancheng Ji; Jingwei Yu; Pengfei Xiang; Zhibo Yang; Dongdong Liu

    The tectonic attribute and evolution of the Bogda Mountain are crucial to understand the Palaeozoic development of the Tian Shan and Central Asian Orogenic Belt (CAOB). In this work, we combined sedimentological and geophysical methods such as field section measurements, cores analysis, well logs and seismic sections interpretation to study the sedimentary evolution from the Middle Permian to Early Triassic. In addition, provenance analysis was performed for the sediments from both flanks of the Bogda Mountain. This set of data allows to improve the constraint on the tectonic attribute and evolution in this area. The facies studies indicate abrupt changes in depositional environments from the lacustrine-alluvial fan and fan delta from the Middle Permian to Upper Permian, as well as the migration of subsidence centres from the Bogda Mountain to piedmonts. Based on detrital zircon U-Pb geochronology, the North Tian Shan (NTS) as well as the Early-Middle Permian post-collisional magmatic activities are identified as the main provenances of the Middle Permian deposits from both flanks. The Late Permian sample shows a strongly concentrated unimodal age peak of ∼305–320 Ma, indicating a single source from the NTS and Bogda Mountain for sediments. The Lower Triassic samples in the Chaiwopu Depression (CWD) in the south flank of the Bogda Mountain show obvious sources from the Central Tian Shan (CTS) but these are absent in all samples from the north flank of Bogda Mountain. Meanwhile, the Early Permian peaks of ∼280–295 Ma are consistent with the bimodal volcanism in the Bogda Mountain dominate in samples from both flanks. According to the comprehensive geological evidence, the deposition of the Lower Permian–Middle Permian strata probably occurred in a rift extension and expansion setting. A tectonic inversion happened at the beginning of the Late Permian, which resulted in the initial uplift of the Bogda Mountain. The uplift also occurred in the NTS and CTS in the Late Permian. This tectonic inversion happened for the whole Junggar Basin and was an important intracontinental tectonic movement, which might result from the consolidation of the Pangea supercontinent.

    更新日期:2020-01-04
  • Shale pore structure characteristics of the high and low productivity wells, Jiaoshiba shale gas field, Sichuan Basin, China: Dominated by lithofacies or preservation condition?
    Mar. Petrol. Geol. (IF 3.538) Pub Date : 2020-01-02
    Shang Xu; Qiyang Gou; Fang Hao; Baiqiao Zhang; Zhiguo Shu; Yangbo Lu; Yuxuan Wang

    Both the characteristics of lithofacies and tectonic movements are important factors in controlling the development, destruction, and preservation of pores in shale reservoirs. However, the main factors that control the structure of shale pores are complex and highly disputed, restricting the understanding of the mechanisms that lead to the accumulation of shale gas. In this study, mineral composition and geochemical analyses, high resolution field emission scanning electron microscopy (FE-SEM), and low-pressure gas adsorption (N2 and CO2) were conducted to evaluate the pore systems of different types shale in the Jiaoshiba area, Sichuan Basin. A total of three shale groups, including silica-rich high production shales, clay-rich low production shales, and silica-rich low production shales were identified on the basis of lithofacies and gas-bearing characteristics. The highest values of TOC, pore volume, and specific surface area are found in the silica-rich high production shales, with an average of 4.182%, 33.04 × 10−3 cm3/g, and 38.71 m2/g, respectively. The total pore volume and specific surface area in the clay-rich low production shales are 19.85% and 28.62% lower than that of silica-rich high production shales. This suggests that the types of lithofacies have a more prominent influence on the specific surface area of the shales, while the pore volume plays a smaller role. However, the pressure in silica-rich low production shales is often released due to strong tectonic deformation. The OM pores in the silica-rich low production shales therefore tend to be both compressed and closed, with low surface porosity and of round shape. The total pore volume and specific surface area of silica-rich low production shales are 34.63% and 22.0% lower than that of the silica-rich high production shales. This indicates that tectonic movement has a significant influence on the shale pore volume, while specific surface area has a smaller influence.

    更新日期:2020-01-04
  • Tectono-sedimentary signature of the second rift phase in multiphase rifts: A case study in the Lufeng Depression (38–33.9 Ma), Pearl River Mouth Basin, south China sea
    Mar. Petrol. Geol. (IF 3.538) Pub Date : 2020-01-02
    Jiawang Ge; Xiaoming Zhao; Xiaomin Zhu; Jijia Liao; Bingshan Ma; Brian G. Jones

    Compared to first rift phase (RP1) or single rift basins, the relationship between fault behaviours and depositional architecture during the second rift phase (RP2) remains insufficiently understood in multiphase rifts. This study attempts to provide implications for tectono-sedimentary signatures during the RP2 in multiphase rift evolution, according to an integrated analysis of 3D seismic reflections, wire logs and cores from the Lufeng Depression in the Pearl River Mouth Basin, South China Sea. The four recognised third-order sequences, ESQ1-4, define a two-stage tectono-sedimentary evolution, including an early (ESQ1-2) and a late stage (ESQ3-4) of the RP2 (38–33.8 Ma) in the Lufeng Depression. Fan-deltaic, braided deltaic sandstone-prone and lacustrine mud-prone deposits are interpreted from the basin margin towards to the central areas. During the early stage of the RP2, two relatively steep dipping E-W striking faults in the northern area were very active, undergoing rapid reactivation with a high displacement, while other faults were less active, had low displacements with respect to the extension direction and possibly represent pre-existing fault geometries. Two tectono-depositional signatures are identified during the early stage of the RP2: 1) facilitation of newly captured axially-dominated deltaic systems in the rapidly reactivated fault propagated areas, as a more uniform distribution of connected and elongated depocentres establishes an axial-supply drainage catchment; 2) sustained previous drainages from the end of the RP1 showed an increase of dip-slope sourced systems in low-displacement faulted-controlled areas, i.e. these areas lack fault-controlled topographic re-organisation but show establishment of a hanging dip-slope. The late stage of the RP2 is characterised by a low-accommodation basin as faulting activities totally waned, and thus large-sized shallow-water deltaic systems and long-distance transported sandstones are promoted. This study highlights the distinctive stratigraphic architectures and associated sediment dispersal patterns induced by progressive fault activity during the RP2 cycle. Furthermore, the proposed depositional signatures may be used as a reference when studying less data-rich multiphase rifts elsewhere.

    更新日期:2020-01-04
  • 1D and 2D Nuclear magnetic resonance (NMR) relaxation behaviors of protons in clay, kerogen and oil-bearing shale rocks
    Mar. Petrol. Geol. (IF 3.538) Pub Date : 2020-01-01
    Pengfei Zhang; Shuangfang Lu; Junqian Li; Xiangchun Chang

    Few 1D T2 and 2D T1-T2 Nuclear magnetic resonance (NMR) studies have focused on oil-bearing shales with complex constituents and a deeper understanding of the NMR relaxation behaviors of oil confined in shale is needed. In this paper, a series of T2 and T1-T2 NMR experiments were performed on oil-bearing shale and its components (clay minerals and kerogen) to obtain the T1-T2 fluid typing chart and analyze the adsorbed and free oil in shale. The results were as follows: five types of water (bound, adsorbed, free, crystal and structural water) in clay minerals were qualitatively identified and described by the specific T2 to T1/T2 ratio values, and T1-T2 maps were used to qualitatively indicate the clay type. The T1-T2 fluid typing chart containing the signatures of 8 proton populations in oil-bearing shale was defined and included bulk liquid, macropore (>1000 nm) oil, nanopore (<1000 nm) oil, and free water in clay minerals or kerogen, shale pore water, bound water in clay minerals, kerogen and crystal water. Adsorbed oil was mainly confined in nanopores, especially micropores smaller than 100 nm, while free oil composed of movable and irreducible oil was predominant in mesopores (100–1000 nm) and macropores. Furthermore, the proportion of irreducible oil gradually decreased and that of movable oil gradually increased from mesopores to macropores. The results demonstrate that the T1-T2 NMR technique may be an effective method for the assessment of fluid distributions and proton mobility and has potential applications for the characterization of shale oil occurrence states.

    更新日期:2020-01-04
  • Permeability distribution and scaling in multi-stages carbonate damage zones: Insight from strike-slip fault zones in the Tarim Basin, NW China
    Mar. Petrol. Geol. (IF 3.538) Pub Date : 2019-12-31
    Guanghui Wu; Kuanzhi Zhao; Haizhou Qu; Nicola Scarselli; Yintao Zhang; Jianfa Han; Yifeng Xu

    Architecture and permeability of fault damage zones are important for understanding fault mechanisms and fluid flow in fractured rocks. Nevertheless, this understanding is often hindered by limited availability of data, especially in the subsurface. A comprehensive suite of cores, logs and production data is here presented to unravel petrophysical properties and fracture characteristics of deep (>6000 m) Ordovician limestones within strike-slip fault zones of the Tarim intracratonic basin (NW China). The results show that (1) the carbonate porosity is mainly secondary dissolution porosity and comprises low porosity (<5%) and low permeability (<0.5 mD) of the matrix reservoirs, and the “sweet spots” in fractured reservoirs with high permeability (>5 mD) and high porosity (>8%); (2) the fault damage zones are generally tight with fracture aperture < 0.05 mm that formed during multiple genetic events and were successively affected by marked diagenesis; (3) the fracture porosity is negligible, but fracture related dissolution is of critical significance and enhance permeability by more than two orders of magnitude higher than the tight matrix reservoirs in fault damage zones; (4) fracture attributes (frequency and aperture), permeability and production across fault zones display a distinct dichotomy between the inner and outer damage zones, with high permeability and production mainly within 500 m of inner damage zones; (5) the permeability had no distinct logarithmic or power-law scale to distance to fault, but a large scatter and slow decrease in inner damage zones. The results indicate that in deep subsurface carbonate reservoirs along fault zones of the Tarim basin, (1) permeability can be characterized by integrating cores, log and production data at different scales; (2) multi-stages fracture diagenesis, particularly of the late stage fracturing and fracture related dissolution, dominated the permeability in the carbonate damage zones; (3) an increased cementation and fracture diagenesis of fault cores led to a scattered permeability distribution in the inner damage zones; (4) “sweet spots” of fractured reservoirs are main exploitation targets along the fault damage zones.

    更新日期:2020-01-04
  • Tectonic evolution of Tianshan-Bogda-Kelameili mountains, clastic wedge basin infill and chronostratigraphic divisions in the source-to-sink systems of Permian-Jurassic, southern Junggar Basin
    Mar. Petrol. Geol. (IF 3.538) Pub Date : 2019-12-31
    Rui Zhao; Jinyu Zhang; Chuanmin Zhou; Zhijie Zhang; Si Chen; Daniel F. Stockli; Cornel Olariu; Ronald Steel; Hua Wang

    Continuous Paleozoic-Mesozoic sediment records within Junggar Basin, Northwestern China, provide details on tectonic evolution of the surrounding Tianshan, Bogda, and Kelameili orogenic belts. We compiled 5250 zircon U-Pb ages from 58 samples (602 new and 4648 published ages) and integrated with published paleo-current directions, paleo-geography, and well core data to reconstruct the uplift timing and provenance for source-to-sink systems of southern Junggar Basin from Permian to Jurassic. This reconstruction strongly suggests that the Kelameili area, middle Southern Tianshan, and western Northern Tianshan had been uplifted before the Permian. However, the uplift of southern Central Tianshan, eastern Bogda, and western Bogda initiated in middle Permian, late Permian, and early Jurassic, respectively. In addition, maximum depositional age calculated from youngest zircon U-Pb ages modes provides new constrains on the chronostratigraphy of southern Junggar Basin, including the Jingjingzigou Fm., Karamay Fm., Haojiagou Fm., Shirenzigou Fm., Lucaogou Fm., Toutunhe Fm., and Qigu Fm. This study provides a basis for a larger reconstruction of the stratigraphic and tectono-sedimentary evolution in response to the tectonic interactions between southern Junggar Basin and surrounding ranges during Permian through Jurassic times.

    更新日期:2020-01-04
  • 更新日期:2020-01-04
  • Sedimentological and stratigraphic signature of the Plio-Pleistocene tectonic events in the Southern Apennines, Italy: The Calvello-Anzi Basin case study
    Mar. Petrol. Geol. (IF 3.538) Pub Date : 2019-12-27
    Pitts Alan; Jablonska Danica; Di Donato Valentino; Mazzoli Stefano; Spina Vincenzo; Di Celma Claudio; Tondi Emanuele

    The Plio-Pleistocene Calvello-Anzi Basin (CAB) represents a synorogenic shallow marine to alluvial succession deposited during the late phase of the Apennine Orogenic event. While the stratigraphy and sedimentary cycles are well known, the precise role and timing of the tectonic phases affecting this area are unclear. In this paper we report the major findings from a study aimed at unraveling the signatures of the Plio-Quaternary tectonic events affecting the CAB and this portion of the Southern Apennines by using a field integrated approach characterized by facies analysis, structural surveying, and basin architecture. The CAB is located in the axial portion of the Southern Apennine chain and has a roughly E-W orientation which is at a high angle with respect the main NW-SE striking regional tectonic structures controlling the foreland-directed migration of the compression. In the study area, an approximately 1,200-meter-thick package of Zanclean (early-middle Pliocene) to Santernian (middle Pleistocene) shelf, shallow marine, and alluvial deposits accumulated during the late stages of the Apennine orogenic evolution. Within the CAB deposits we recognize two main depositional motifs which roughly correspond to previously established regional cycles that are genetically linked to two corresponding tectonic phases of the Southern Apennine chain. Our results reveal how these two main tectonic phases played a primary role in controlling the depositional architecture, facies, depocenter distribution, and the basin shape throughout the CAB's lifespan. In the proposed model, during the first depositional stage (Zanclean), the CAB formed as a wedge-top basin, controlled by the subsurface propagation of NW-SE-trending thrusts related to the main NE-SW directed shortening of the Apennines. This stage is recorded in the basal units of the CAB infill by progressive unconformities, the development of syn-tectonic shallow marine sedimentary wedges along a high gradient tectonically controlled depositional surface, and a marked SE migration of the main depocenter. During the second depositional stage (upper Piacenzian to Santernian), the CAB was controlled by a series of roughly E-W-trending normal faults which crosscut the preexisting compressional structural fabric. Syndepositional activity along these faults played a direct role in creating an E-W oriented tectonic depression and controlling the accommodation space for the upper portion of the CAB infill. This second stage is marked by two points of evidence. The first point is revealed by a southwestward migration of the CAB depocenter driven by ∼90-degree rotation from a roughly NW-SE elongated pattern to roughly elongated W-E transverse to the Pliocene regional structural fabric. This depocenter drift also coincides with an abrupt change in depositional regime from shallow marine to continental sedimentation. The second and most important point of evidence is the presence of several basin-bounding extensional fault zones which cut the lower Pliocene basin-fill units. We relate these features to the middle upper Pleistocene transition to along-strike extension, widely reported in the Southern Apennines, which is related to the overall extensional regime that is acting on the chain also at present. Data from this study provide additional insight into the evolution of the Southern Apennine chain, the formation of the Plio-Pleistocene CAB, and the debated role of Quaternary tectonics on the basin's development during the post-collision orogenic phases. Given the proximity of the study area with several oil fields and considering that hydrocarbon traps in Southern Apennines are Plio-Quaternary in age, the constraints provided on the timing and the style of the regional deformation may improve the definitions of hydrocarbon traps in the buried Apulian platform.

    更新日期:2020-01-04
  • A conceptual model for glaciogenic reservoirs: From landsystems to reservoir architecture
    Mar. Petrol. Geol. (IF 3.538) Pub Date : 2019-12-27
    Bartosz Kurjanski; Brice R. Rea; Matteo Spagnolo; David G. Cornwell; John Howell; Stuart Archer

    Glaciogenic sediments are present in many hydrocarbon-producing basins across the globe but their complex nature makes it difficult to characterise the reservoir-quality sedimentary units. Despite this, Ordovician glacial deposits in North Africa, and Carboniferous-Permian glaciogenic sequences in the Middle East, have been proven to host significant, economical, hydrocarbon accumulations. Additionally, discoveries have been made in the shallow (<1000 m below seabed), glacial, Pleistocene sedimentary succession of the North Sea (e.g. Peon and Aviat). This paper provides a predictive exploration framework in the form of a conceptual model of glaciogenic sediment-landform distributions. The model is based on the extensive onshore glacial sedimentary record integrated with available offshore data. It synthesises the published knowledge, drawing heavily on glacial landsystem models, glacial geomorphology and sedimentology of glaciogenic deposits to provide a novel conceptual model allowing for the efficient description and interpretation of glacial sediments and landforms in the subsurface. Subsequently, land-terminating and water-terminating ice sheet depositional systems are described and discussed, with respect to ice advance and retreat cycles. This detailed description focuses on the macro-scale stratigraphic organisation of glacial sediments with relation to the ice margin, aiding the prediction of glaciogenic sediment distributions, and their likely geometry, architecture and connectivity as reservoirs.

    更新日期:2020-01-04
  • 更新日期:2020-01-04
  • Quantitative analysis of stylolite networks in different platform carbonate facies
    Mar. Petrol. Geol. (IF 3.538) Pub Date : 2019-12-24
    Elliot Humphrey; Enrique Gomez-Rivas; Joyce Neilson; Juan Diego Martín-Martín; David Healy; Shuqing Yao; Paul D. Bons

    Stylolites are rough surfaces that form by pressure solution, and present variable geometries and spatial distributions. Despite being ubiquitous in carbonate rocks and potentially influencing fluid flow, it is not yet clear how the type and distribution of stylolite networks relate to lithofacies. This study investigates Lower Cretaceous platform carbonates in the Benicàssim area (Maestrat Basin, Spain) to statistically characterise stylolite morphology and stylolite network distributions in a selection of typical shallow-marine carbonate lithofacies, from mudstones to grainstones. Bedding-parallel stylolite networks were sampled in the field to quantify stylolite spacing, wavelength, amplitude, intersection morphology and connectivity. Grain size, sorting and composition were found to be the key lithological variables responsible for the development of rough anastomosing stylolite networks. Poorly-connected stylolites with large vertical spacings were found to be dominant in grain-supported lithofacies, where grains are fine and well sorted. Anastomosing stylolite networks appear well developed in mud-supported lithofacies with poorly-sorted clasts that are both heterogenous in size and composition. Mud-supported facies feature stylolites that are closely spaced, have high amplitudes and intersection densities, and predominantly present suture and sharp-peak type morphologies. Larger grains and poor sorting favour the formation of stylolites with small vertical spacings, low wavelengths and high amplitudes. This statistical analysis approach requires only limited information, such as that from drill core, and can be used to characterise stylolite morphology and distributions in subsurface carbonate reservoirs.

    更新日期:2020-01-04
  • Physical properties and core-log seismic integration from drilling at the Danube deep-sea fan, Black Sea
    Mar. Petrol. Geol. (IF 3.538) Pub Date : 2019-12-24
    M. Riedel; T. Freudenthal; M. Bergenthal; M. Haeckel; K. Wallmann; E. Spangenberg; J. Bialas; G. Bohrmann

    Drilling, coring, and geophysical logging were performed with the MARUM-MeBo200 seafloor drilling rig to investigate gas hydrate occurrences of the Danube deep sea fan, off Romania, Black Sea. Three sites within a channel-levee complex were investigated. Geophysical log data of P-wave velocity, electrical resistivity, and spectral gamma ray are combined with core-derived physical properties of porosity, magnetic susceptibility, and bulk density. Core- and log physical property data are used to define a time-depth conversion by synthetic seismogram modeling, which is then used to interpret the seismic data. Individual polarity reversed reflectors within the stratigraphic column drilled are linked to reduction in P-wave velocity and bulk density. Those reflectors (and associated reflection packages) are accompanied by distinct and systematic changes in sediment porosity, magnetic susceptibility, and electrical resistivity. Overall, the sediments at drill site GeoB22605 (MeBo-17) represent the younger (upper) levee sequence of the channel, that has been eroded at drill site GeoB22603 (MeBo-16). Splicing seismic data across the channel from the East (MeBo-16) to the West (MeBo-17) demonstrates the continuation of reflectors underneath the channel. The upper ∼50 m below seafloor (mbsf) at site MeBo-16 do not stratigraphically belong to the same sequence of the (deeper) levee-deposits. Above the marked erosional unconformity, sediments at Site MeBo-16 are likely derived by a mixture of repeated slump-events (identified as seismically transparent units) interbedded with hemi-pelagic sedimentation. Similarly, sediments within the upper ∼20 mbsf at Site MeBo-17 are not stratigraphically the same levee-deposits, but are derived by a mixture of slump-events (also seen in the marked seafloor amphitheatre architecture of a large failure complex extending further upslope) and hemi-pelagic sedimentation. All observations combined show that the seismically observed stratigraphic pattern represents a reflectivity sequence mostly driven by variations in density (porosity) and correspondingly by changes in P-wave velocity and electrical resistivity. All observations from the geophysical log- and core, as well as geochemical data do show no evidence for the presence of any significant gas hydrates within the drilled/cored sequences.

    更新日期:2020-01-04
  • A synthesis of the sedimentary evolution of the Demerara Plateau (Central Atlantic Ocean) from the late Albian to the Holocene
    Mar. Petrol. Geol. (IF 3.538) Pub Date : 2019-12-20
    Anne-Sophie Fanget; Lies Loncke; France Pattier; Tania Marsset; Walter Roest; Cédric Tallobre; Xavier Durrieu de Madron; F. Javier Hernandez Molina

    The Demerara Plateau, off the French Guiana and Surinam margin, corresponds to a prominent sub-horizontal marginal plateau. The interpretation of a large set of seismic data acquired along the Demerara Plateau and integration with previous seismic stratigraphy and drill studies enables a better understanding of the sedimentary evolution of the outer Demerara marginal plateau. Since the end of the transform activity (late Albian), three sedimentary evolutionary stages have been identified. 1) The Pre-contourite Stage (late Albian to early Miocene) is strongly controlled by the structure of the margin that influences the distribution pattern of post-transform deposits through differential thermal subsidence between transform and divergent segments. 2) The Transitional Stage (middle Miocene to early Pliocene) is expressed as a current-controlled erosive surface resulting from the onset of bottom-current interactions due to the establishment and strengthening of the modern thermohaline circulation that is coeval with the progressive closure of the Isthmus of Panama. 3) The Contourite Stage (middle Pliocene to Holocene) is characterized by the development of a contourite depositional system that is linked to the activity of the North Atlantic Deep Water circulation and by a complex interaction between alongslope and downslope processes. Our study highlights that marginal plateaus might be particularly prone to develop contourite features since they regionally influence ocean current dynamics in guiding and accelerating bottom contour currents. Marginal plateaus should thus be considered as a key target to study bottom current dynamics and paleocirculation patterns.

    更新日期:2020-01-04
  • Biomarkers of Oligocene lacustrine source rocks, Beibuwan-Song Hong basin junction, offshore northern Vietnam
    Mar. Petrol. Geol. (IF 3.538) Pub Date : 2019-12-20
    Hans Peter Nytoft; Michael Bryld Wessel Fyhn; Jussi Hovikoski; Malgorzata Rizzi; Ioannis Abatzis; Hoang Anh Tuan; Nguyen Thanh Tung; Nguyen Thu Huyen; Trinh Xuan Cuong; Lars Henrik Nielsen

    Highly oil prone source rocks containing sapropelic Type I and mixed Types I and III kerogen are found in 233 m of the 500 m deep, fully cored ENRECA-3 well drilled on Bach Long Vi Island, located at the junction between the Beibuwan and the Song Hong basins offshore northern Vietnam. The cored succession is made up entirely by Oligocene, deep lacustrine deposits. The origin of the organic matter (OM) in 62 samples is evaluated on the basis of gas chromatography-mass spectrometry (GC-MS and GC-MS/MS). OM in 55 samples is sourced primarily from lacustrine organisms and contains abundant 4-methylsteranes, tetracyclic polyprenoids (TPP) and lycopane, and no markers for marine organic matter. The proportion of triterpanes derived from angiosperms is low in most saturated fractions and only traces of gymnosperm diterpanes are detected. In contrast, all aromatic fractions have a high proportion of compounds having an origin from both gymnosperms and angiosperms. Very high concentrations of hopanoids in both fractions suggest significant bacterial alteration of the original OM. Most samples have a high concentration of rare C31 diaromatic 8,14-secohopanes with a fluorene moiety. Low pristane/phytane (Pr/Ph) ratios indicate that anoxic/suboxic bottom water conditions existed during OM accumulation. The presence of β-carotane, gammacerane and traces of arylisoprenoids could indicate a stratified water column. OM in a few samples with lower than average hydrogen index (HI) is mainly of terrestrial origin with a higher proportion of C29 steranes, diterpanes and oleanoids and lower concentrations of both saturated and aromatic hopanes. Higher Pr/Ph, a higher C34 isohopane ratio (IHR34) and a lower homohopane index (HHI) indicate that this low-HI OM was originally deposited under more oxic conditions and subsequently transported to deeper water. Low sterane and hopane isomerization ratios show that no samples have reached the oil-window. Some novel maturity parameters for immature lacustrine samples are proposed.

    更新日期:2020-01-04
  • Testing reproducibility of vitrinite and solid bitumen reflectance measurements in North American unconventional source-rock reservoir petroleum systems
    Mar. Petrol. Geol. (IF 3.538) Pub Date : 2019-12-18
    Paul C. Hackley; Carla V. Araujo; Angeles G. Borrego; Antonis Bouzinos; Brian J. Cardott; Humberto Carvajal-Ortiz; Martha Rocio López Cely; Vongani Chabalala; Peter J. Crosdale; Thomas D. Demchuk; Cortland F. Eble; Deolinda Flores; Agnieszka Furmann; Thomas Gentzis; Paula A. Gonçalves; Carsten Guvad; Mária Hámor-Vidó; Iwona Jelonek; Julian Esteban Jaramillo Zapata

    An interlaboratory study (ILS) was conducted to test reproducibility of vitrinite and solid bitumen reflectance measurements in six mudrock samples from United States unconventional source-rock reservoir petroleum systems. Samples selected from the Marcellus, Haynesville, Eagle Ford, Barnett, Bakken and Woodford are representative of resource plays currently under exploitation in North America. All samples are from marine depositional environments, are thermally mature (Tmax >445 °C) and have moderate to high organic matter content (2.9–11.6 wt% TOC). Their organic matter is dominated by solid bitumen, which contains intraparticle nano-porosity. Visual evaluation of organic nano-porosity (pore sizes < 100 nm) via SEM suggests that intraparticle organic nano-pores are most abundant in dry gas maturity samples and less abundant at lower wet gas/condensate and peak oil maturities. Samples were distributed to ILS participants in forty laboratories in the Americas, Europe, Africa and Australia; thirty-seven independent sets of results were received. Mean vitrinite reflectance (VRo) values from all ILS participants range from 0.90 to 1.83% whereas mean solid bitumen reflectance (BRo) values range from 0.85 to 2.04% (no outlying values excluded), confirming the thermally mature nature of all six samples. Using multiple statistical approaches to eliminate outlying values, we evaluated reproducibility limit R, the maximum difference between valid mean reflectance results obtained on the same sample by different operators in different laboratories using different instruments. Removal of outlying values where the individual signed multiple of standard deviation was >1.0 produced lowest R values, generally ≤0.5% (absolute reflectance), similar to a prior ILS for similar samples. Other traditional approaches to outlier removal (outside mean ± 1.5*interquartile range and outside F10 to F90 percentile range) also produced similar R values. Standard deviation values < 0.15*(VRo or BRo) reduce R and should be a requirement of dispersed organic matter reflectance analysis. After outlier removal, R values were 0.1%–0.2% for peak oil thermal maturity, about 0.3% for wet gas/condensate maturity and 0.4%–0.5% for dry gas maturity. That is, these R values represent the uncertainty (in absolute reflectance) that users of vitrinite and solid bitumen reflectance data should assign to any one individual reported mean reflectance value from a similar thermal maturity mudrock sample. R values of this magnitude indicate a need for further standardization of reflectance measurement of dispersed organic matter. Furthermore, these R values quantify realistic interlaboratory measurement dispersion for a difficult but critically important analytical technique necessary for thermal maturity determination in the source-rock reservoirs of unconventional petroleum systems.

    更新日期:2020-01-04
  • Ichnological signatures from wave- and fluvial-dominated deltas: The LA Anita formation, upper Cretaceous, austral-magallanes basin, Patagonia
    Mar. Petrol. Geol. (IF 3.538) Pub Date : 2019-12-14
    Damián Moyano Paz; Sebastián Richiano; Augusto N. Varela; Alejandro R. Gómez Dacál; Daniel G. Poiré

    Depositional processes operating in deltaic shorelines create a variety of physico-chemical stressful conditions that impact directly on benthic fauna. The ichnological signatures of deltaic successions reflect these physico-chemical stresses, such as rapid sediment influx, elevated water turbidity, periodically reduced oxygenation, salinity fluctuations, and wave- and tidal-energy. In the Campanian La Anita Formation of the Austral-Magallanes Basin, two examples of deltaic successions, each showing different relative dominance of wave and fluvial processes, are described in detail, allowing the recognition of contrasting stresses that acted differentially in a wave-dominated, fluvial-influenced delta and a fluvial-dominated delta. Variations in the burrowing intensity and ichnodiversity allowed us to discriminate the different physico-chemical stresses. In the wave-dominated, fluvial-influenced deltaic deposits, the alternation between fair-weather waves and storm events acted as the main controlling factor on benthic fauna in the facies of the prodelta and distal delta front, displaying facies-crossing and horizontal elements attributable to the Skolithos and Cruziana Ichnofacies, such as Arenicolites isp., Chondrites isp., Cylindrichnus isp., Diplocraterion isp., Gyrochorte isp., Ophiomorpha isp., Palaeophycus isp., Planolites isp., Rhizocorallium isp., Rossellia isp., Schaubcylindrichnus isp. and Skolithos isp. Water turbidity and periodically reduced bottom water oxygenation conditions also played an important but subordinate role. The proximal delta front, and distributary and terminal distributary channel deposits show low burrowing intensities and ichnodiversities with structures attributable to the depauperate Skolithos Ichnofacies with few Diplocraterion isp., Gordia isp., Lockeia isp., Macaronichnus isp., Ophiomorpha isp., Schaubcylindrichnus coronus and Siphonichnus isp., showing stress conditions associated with rapid sediment influx, high energy and reduced salinity conditions related to fluvial discharges as the most important controlling factors. Periodically, fluctuations in salinity conditions due to river discharges and channel avulsion may have also played important roles. The fluvial-dominated deltaic deposits show that the controlling factors were associated with fluvial discharge and river-sediment influx with no clear influence of wave or tidal action. The facies of the distal delta front were controlled by episodic sedimentation, elevated water turbidity, periodically reduced oxygenation and salinity fluctuations, the associated trace fossil suite consists of a monospecific assemblage of Ophiomorpha isp. and sparse Palaeophycus isp. The proximal delta front and the distributary channel deposits are mostly unburrowed, locally displaying a few Arenicolites isp., Lockeia isp., Ophiomorpha isp., Psilonichnus isp. and Teredolites isp. The development of these suites was controlled mainly by heightened sedimentation rates influx triggered by high fluvial discharges, elevated water turbidity due to heightened suspended load and buoyant plumes, periodic fluctuations in salinity conditions caused by river discharges and channel avulsion. Interdistributary areas are characterized by facies preserving evidence that reduced oxygenation was the most important controlling factor in this subenvironment. Fluvial processes generate the most extreme stressful conditions for benthic colonization by tracemakers. Wave processes tend to buffer the stresses produced by river discharge. The effect of waves on fluvial stress is reflected in the higher bioturbation intensities and ichnodiversities that the wave-dominated deltaic deposits of the La Anita Formation delta show in relation to the fluvial-dominated ones.

    更新日期:2020-01-04
  • Characterization of microseepage-induced diagenetic changes in the Upper-Red Formation, Qom region, Iran. Part I: Outcrop, geochemical, and remote sensing studies
    Mar. Petrol. Geol. (IF 3.538) Pub Date : 2019-12-04
    Saeid Asadzadeh; Carlos Roberto de Souza Filho

    This article explores the footprints of hydrocarbon microseepage in the Upper-Red Formation overlying the Alborz petroleum reservoir located in the Saveh-Qom basin, Iran. It involves a multidisciplinary investigation including field observation and sampling, detailed petrographical and geochemical analysis, and remote sensing mapping using Sentinel-2 and ASTER data. The study revealed significant changes in the microseepage-affected zones when contrasted to unaffected lithofacies and helped to develop a novel array of mineralogical and geochemical indicators for microseepage phenomenon. These comprise partial bleaching of the red-beds, secondary goethite coatings, diagenetic clay minerals (e.g. illite-smectite, chlorite), and pervasive calcite, silica, and gypsum cementations. In geochemical terms, the major oxides, particularly the ratio of CaO + K2O/Na2O + MgO + CaO + K2O proved to be a reliable index for distinguishing microseepage-prone zones. Based on isotopic studies, a combination of three sources of carbon, comprising oxidized hydrocarbons, was recognized in the carbonate cements; yet the strata were shown to be moderately flushed by percolating fluids. Satellite remote sensing was successful in mapping reservoir-scale footprints of the microseepage systems. It indicated that the extent of the induced alterations, and thereby the outline of the underlying reservoir, is much larger than previously known. Overall, the secondary changes were shown to be a function of the geochemistry of the host-rock, the local environmental variables (i.e. climate and hydrogeology), and the 3D architecture of the trap. The substantiated indicators carry direct implications for onshore microseepage targeting and hold high potential to help reduce the exploration and development risks in frontier and mature basins.

    更新日期:2020-01-04
  • Palynological analysis of the late Ordovician - Early Silurian black shales in south China provides new insights for the investigation of pore systems in shale gas reservoirs
    Mar. Petrol. Geol. (IF 3.538) Pub Date : 2019-11-22
    Jingqiang Tan; Ruining Hu; Wenhui Wang; Jeffrey Dick

    The late Ordovician Wufeng and early Silurian Lungmachi formations are primary targets for shale gas exploration in the southeastern marginal area of the Sichuan Basin, Southwest China. In this research, different groups of micro-fossils (large numbers of taxonomically unrelated organic- and inorganic-walled fossil groups) from the two formations were analyzed in order to investigate their pore characters under the evaluation of shale gas reservoirs. A large number of biological autologous micro-nano pores in radiolarians, sponge spicules, acritarchs, conodonts, chitinozoans, and scolecodonts were analyzed. The results show that most pores are densely and randomly distributed with honeycomb or irregular shapes. Although the samples are over mature and were deeply buried, micro-fossils remain in a large number of biological micro-nano pores. Pore diameter varies from 20 to 4000 nm but differs among micro-fossil groups. The widely distributed siliceous micro-fossils, such as radiolarians and sponge spicules, could enhance the brittleness of shales. They may promote the development of natural fractures during diagenesis or artificial fractures during stimulation. When fractures are connected with micro-nano pores in the shale, they could provide effective storage space and improve the overall connectivity. In most of the analyzed shale samples, micro-fossils show positive correlation with high TOC strata. Considering the importance of micro-fossils and their pores in the perspective of hydrocarbon generation, connectivity, accumulation, and production of shale gas, we suggest that micro-fossil pores should be included in the classification of pore systems.

    更新日期:2020-01-04
  • Pore-scale modeling of carbonates
    Mar. Petrol. Geol. (IF 3.538) Pub Date : 2019-11-20
    Ayaz Mehmani; Rahul Verma; Maša Prodanović

    Carbonate rocks display complex pore textures with heterogeneities that extend over several length scales. Identifying and capturing the significant pore space properties in a computationally tractable model is therefore nontrivial. Pore-scale models bridge predictions of transport properties from sub-pore to core scale and attempts have been made to render such methods cost-effective. This chapter reviews several methods for fabricating pore-scale models of carbonate rocks and discusses approaches to simulating their fluid flow and solute transport properties. The advantages and limitations of each method in reducing the reservoir development uncertainties are explained. We argue that pore-scale models can play an important role in predicting the petrophysical properties of carbonate rocks. Even more importantly, they provide sensitivity analyses of pore-scale features on macroscopic transport observations and offer explanations for anomalous flow behaviors.

    更新日期:2020-01-04
  • Stratigraphically controlled silicification in Danian chalk and its implications for reservoir properties, southern Danish Central Graben
    Mar. Petrol. Geol. (IF 3.538) Pub Date : 2019-11-19
    Kasper H. Blinkenberg; Kresten Anderskouv; Emma Sheldon; Christian J. Bjerrum; Lars Stemmerik

    The effect of silica on reservoir quality in chalk is subject to continuing debate. In particular, the stratigraphic variations in silica content within the chalk matrix have not been addressed sufficiently. In this study, a new approach is applied to constrain silica variability in reservoir chalk utilizing hand-held X-ray fluorescence (HH-XRF) on samples from four Maastrichtian–Danian cores from hydrocarbon-producing fields in the southern Danish Central Graben. The results indicate a significant lateral and stratigraphic variability in silica concentrations across the study area; data display a common stratigraphic signature in all wells, however, with maximum silica concentrations and minimum porosities occurring in the lower part of the Danian Ekofisk Formation. Correlation between HH-XRF quantified silica concentrations and biostratigraphic data indicates the synchronous onset of an at least semi-regional silica event during the mid-Danian, nannofossil zones NNTp2F–G to NNTp4A–D, whereas the upper boundary of the peak silica unit is poorly constrained. Generally, stratigraphic trends in silica concentrations appear to be negatively correlated with porosity trends. However, comparison between the HH-XRF quantified silica content and reservoir data (porosity, permeability, estimated pore radius and calculated specific surface area) shows poor correlation indicating that silica content within the Ekofisk reservoir is not the only factor controlling the reservoir quality. Unknown complex diagenetic interactions between calcite, silica and clay probably influence the reservoir properties by promoting calcite cementation in stratigraphically controlled zones, making the Ekofisk reservoir much less predictable than the underlying Maastrichtian Tor Formation.

    更新日期:2020-01-04
  • Comment to “More than ten years of Lusi: A review of facts, coincidences, and past and future studies” by Miller and Mazzini (2018): Taking the trigger debate above ground
    Mar. Petrol. Geol. (IF 3.538) Pub Date : 2019-10-09
    Phillip Drake

    Since erupting in 2006, the “Lapindo” mudflow (or “Lusi,” as it is known by scientists) has released a constant flow of mud that has devastated communities and environments in East Java's Sidoarjo regency. The mudflow also has spawned countless formal and informal scientific reports that dispute what initiated the eruption: drilling for gas or a distant earthquake. A 2018 special issue in Marine and Petroleum Geology by the “Lusi Lab” is devoted entirely to the mudflow, which includes an article by Miller and Mazzini (2018) that presents one perspective of the current status of the trigger debate. This discussion article draws attention to a series of inaccuracies and misrepresentations within Miller and Mazzini’s (2018) article. These concerns include (1) the promotion of erroneous drilling and geological data, (2) the inaccurate and unprofessional characterization of scientists who posit opposing interpretations of drilling and geological data, (3) the use of deceptive rhetoric, (4) the dissemination of misleading and unsubstantiated claims about unnamed stakeholders, and (5) the lack of knowledge of – and sensitivity toward – social contexts. After providing an overview of these issues, this article focuses on items (3), (4) and (5), which tend to be overlooked in ongoing geological discussions on the disaster, but have a significant impact on the production, circulation, and reception of geoscience in both professional and non-professional arenas. This commentary on Miller and Mazzini (2018) does not challenge the credibility or integrity of the authors or any scientist associated with the Lusi Lab, but rather argues for a version of geoscience that stays above ground by being conscientious to the social dynamics that impact, and are impacted by, scientific inquiry. Without the appropriate care and scholarly caution, even the most neutral scientist's work can be perceived as compromised to both scholarly and non-scholarly audiences.

    更新日期:2020-01-04
  • Comment on “Correlation analysis of element contents and mechanical characteristics of shale reservoirs” by Liu et al. (2018)
    Mar. Petrol. Geol. (IF 3.538) Pub Date : 2019-06-08
    Ye Zhang; Y.Z. Ma; Ernest Gomez

    We found the article and conclusion by Liu et al. (2018) interesting, as the authors conducted a correlation analysis between element contents and rock mechanical characteristics of an organic rich shale in southern China. When analyzing data obtained from logging shale gas wells, non-parametric methods for calculating correlation coefficients were employed along with statistical significance tests that utilize confidence levels. The authors' conclusion suggests that mechanical properties cannot be solely determined based on the elemental composition of shale, while mineralogy (quartz vs. clay fractions) can explain some of the effects observed in their correlation analysis. In our opinion, a couple of points regarding the correlation analysis and the brittleness index, as introduced by Liu et al. (2018), were not clearly presented. Further elucidations are needed to clarify these points for the readers of this journal. Herein, we present a discussion on the two following issues: The first issue on correlation analysis impacts the second issue of constructing a mathematical model of brittleness index, and thus is slightly more extensively discussed.

    更新日期:2020-01-04
  • Ice-sheet dynamics through the Quaternary on the mid-Norwegian continental margin inferred from 3D seismic data.
    Mar. Petrol. Geol. (IF 3.538) Pub Date : 2017-02-28
    A Montelli,J A Dowdeswell,D Ottesen,S E Johansen

    Reconstructing the evolution of ice sheets is critical to our understanding of the global environmental system, but most detailed palaeo-glaciological reconstructions have hitherto focused on the very recent history of ice sheets. Here, we present a three-dimensional (3D) reconstruction of the changing nature of ice-sheet derived sedimentary architecture through the Quaternary Ice Age of almost 3 Ma. An extensive geophysical record documents a marine-terminating, calving Fennoscandian Ice Sheet (FIS) margin present periodically on the mid-Norwegian shelf since the beginning of the Quaternary. Spatial and temporal variability of the FIS is illustrated by the gradual development of fast-flowing ice streams and associated intensification of focused glacial erosion and sedimentation since that time. Buried subglacial landforms reveal a complex and dynamic ice sheet, with converging palaeo-ice streams and several flow-switching events that may reflect major changes in topography and basal thermal regime. Lack of major subglacial meltwater channels suggests a largely distributed drainage system beneath the marine-terminating part of the FIS. This palaeo-environmental examination of the FIS provides a useful framework for ice-sheet modelling and shows that fragmentary preservation of buried surfaces and variability of ice-sheet dynamics should be taken into account when reconstructing glacial history from spatially limited datasets.

    更新日期:2019-11-01
  • Deformation bands evolving from dilation to cementation bands in a hydrocarbon reservoir (Vienna Basin, Austria).
    Mar. Petrol. Geol. (IF 3.538) Pub Date : 2013-05-01
    Ulrike Exner,Jasmin Kaiser,Susanne Gier

    In this study we analyzed five core samples from a hydrocarbon reservoir, the Matzen Field in the Vienna Basin (Austria). Deformation bands occur as single bands or as strands of several bands. In contrast to most published examples of deformation bands in terrigeneous sandstones, the reduction of porosity is predominantly caused by the precipitation of Fe-rich dolomite cement within the bands, and only subordinately by cataclasis of detrital grains. The chemical composition of this dolomite cement (10-12 wt% FeO) differs from detrital dolomite grains in the host rock (<2 wt% FeO). This observation in combination with stable isotope data suggests that the cement is not derived from the detrital grains, but precipitated from a fluid from an external, non-meteoric source. After an initial increase of porosity by dilation, disaggregation and fragmentation of detrital grains, a Fe-rich carbonate fluid crystallized within the bands, thereby reducing the porosity relative to the host sediment. The retention of pyrite cement by these cementation bands as well as the different degree of oil staining on either side of the bands demonstrate that these cementation bands act as effective barriers to the migration of fluids and should be considered in reservoir models.

    更新日期:2019-11-01
  • Dilatant shear band formation and diagenesis in calcareous, arkosic sandstones, Vienna Basin (Austria).
    Mar. Petrol. Geol. (IF 3.538) Pub Date : 2015-08-25
    Marco Lommatzsch,Ulrike Exner,Susanne Gier,Bernhard Grasemann

    The present study examines deformation bands in calcareous arkosic sands. The investigated units can be considered as an equivalent to the Matzen field in the Vienna Basin (Austria), which is one of the most productive oil reservoirs in central Europe. The outcrop exposes carbonate-free and carbonatic sediments of Badenian age separated by a normal fault. Carbonatic sediments in the hanging wall of the normal fault develop dilation bands with minor shear displacements (< 2 mm), whereas carbonate-free sediments in the footwall develop cataclastic shear bands with up to 70 cm displacement. The cataclastic shear bands show a permeability reduction up to 3 orders of magnitude and strong baffling effects in the vadose zone. Carbonatic dilation bands show a permeability reduction of 1-2 orders of magnitude and no baffling structures. We distinguished two types of deformation bands in the carbonatic units, which differ in deformation mechanisms, distribution and composition. Full-cemented bands form as dilation bands with an intense syn-kinematic calcite cementation, whereas the younger loose-cemented bands are dilatant shear bands cemented by patchy calcite and clay minerals. All analyzed bands are characterized by a porosity and permeability reduction caused by grain fracturing and cementation. The changed petrophysical properties and especially the porosity evolution are closely related to diagenetic processes driven by varying pore fluids in different diagenetic environments. The deformation band evolution and sealing capacity is controlled by the initial host rock composition.

    更新日期:2019-11-01
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