The diagenetic history of the giant Lacq gas field, witness to the apto-albian rifting and the Pyrenean orogeny, revealed by fluid and basin modeling

https://doi.org/10.1016/j.marpetgeo.2021.105250Get rights and content

Highlights

  • Combining several equations of state allows the P-T modeling of H2S-bearing fluids.

  • The rifting and the orogenic stages influenced the diagenesis of the Deep Lacq reservoir.

  • Hydrocarbon maturation, dolomitization and calcite precipitation were controlled by the rifting event.

  • The reservoir was infilled with gas during the Pyrenean orogeny.

  • TSR did not occur in-situ.

Abstract

The link between fluid circulation schemes and basin histories remain one of the most valuable tools to understand the diagenetic evolution of petroleum reservoirs. This study proposes a diagenetic model for the Deep Lacq reservoir constrained by petrography, geochemistry, fluid inclusions studies and basin modeling analyses. Drill cores penetrating the 3000 m deep Late Jurassic to Early Cretaceous “Deep Lacq” reservoirs, in the Aquitaine basin SW France, were used to investigate how the geodynamic evolution of the basin influenced the diagenesis of petroleum reservoirs. This basin experienced a phase of rifting during the Lower Cretaceous followed by inversion and compression during the Paleogene. Petrographic and geochemical results indicate that early diagenesis involved bacterial activity and early dolomitization. Fluid thermodynamic modeling, coupled with the reconstruction of the basin history provided insight into the timing of diagenetic fluid circulations. Burial diagenesis involved a rift-related dolomitization episode linked mainly to the recrystallization of earlier dolomites and the circulation of deep hot fluids connected to the Triassic evaporites. The dolomitizing fluids circulated at temperatures close to 136–144 °C and pressures of 338–386 bars, during the Aptian (120-116 Ma). During the post-rift uplift and its subsequent thermal re-equilibration, multiple fluid pulses precipitated coarse blocky calcites. These Ca-rich fluids circulated between 109 and 97 Ma, at high-pressure conditions at around of 704–766 bars and with temperatures of 146–156 °C. The circulation of another fluid pulse that resulted in the precipitation of anhydrite cements is linked to the onset of the Pyrenean orogeny. No evidence that support in-situ TSR reactions were found, which suggests migration of TSR-related H2S from a kitchen in the deeper parts of the basin. This multi-modeling approach shows how the detailed thermodynamic analyses of fluid inclusions can add valuable constraints on a diagenetic model and eventually link it to the larger-scale basin's history.

Introduction

The circulation of diagenetic fluids in petroleum reservoirs can be strongly influenced by the geologic history of the basin (Beaudoin et al., 2014, Beaudoin et al., 2015; Salardon et al., 2017; Renard et al., 2019; Elias Bahnan et al., 2020). In the Aquitaine foreland basin, north of the Pyrenees Mountains (SW France), several hydrocarbon fields are located in Jurassic and Cretaceous reservoirs (Biteau et al., 2006). The giant Lacq field is part of the Lacq petroleum system with productive reservoirs extending over 320 km2, a gas column reaching 3100 m and reserves in the order of 8.9 trillion cubic feet (Biteau et al., 2006). The exploitation of this gas field was a pioneering achievement at the time of its discovery in 1951. The high pressure (675 bar) and temperature (135 °C) with a dangerous gas composition (15,2% H2S, 9,7% CO2; 69,2% C1, 5,3% C2+) (Le-vot et al., 1996) made it necessary to build an innovative desulfurization plant in 1957, still operational till present day.

The anticlinal structure of Deep Lacq is the result of the superposition of Jurassic rifting and Early Cretaceous rifting events, later inverted during the Late Cretaceous and the Paleogene (Sibuet et al., 2004; Jammes et al, 2009, 2010; Clerc and Lagabrielle, 2014; Mouthereau et al., 2014; Corre et al., 2016; Teixell et al., 2016; Vacherat et al., 2016). These events had significant control on the types, sources, chemistries and circulation mechanisms of the diagenetic fluids in the Aquitaine basin, as previously documented in the Rousse field (Renard et al., 2019), in the Upper Lacq oil reservoir (Elias Bahnan et al., 2020) and in the Chaînons Béarnais (Incerpi et al., 2020; Motte et al., 2021; Salardon et al., 2017). However, despite its importance as the most strategic reservoir in France during the 1970s (Biteau et al., 2006), no models were yet proposed to explain the diagenesis of Deep Lacq.

This study focuses on the Kimmeridigian-Barremian Deep Lacq gas field and aims to present a diagenetic model describing the different types, sources and circulation schemes of diagenetic fluids at different phases of the complex geological history that the Aquitaine basin has experienced. The diagenetic events described in this research are placed in a geodynamic perspective that allows a better understanding of fluid activity during a complete Wilson cycle. Starting from a tectonic quiescence state and proceeding to early rifting, hyperextension, post-rift subsidence and ending with orogenesis, fluid-rock interactions are examined at each step. The case study presented in this work can be used as an example to compare diagenetic models of petroleum reservoirs in basins that experienced a similar geodynamic history as the Aquitaine. Examples include the Dengying reservoirs of the SW Sichuan basin (Wu et al., 2016), the Jurassic carbonates of Mount Lebanon (Nader, 2003), the Mobile Bay Jurassic Norphlet Formation of the Gulf of Mexico (Mankiewicz et al., 2009), the Níspero deeply buried Lower Cretaceous carbonate reservoir in the Gulf of Mexico (Bourdet et al., 2010), the Devonian Southesk-Cairn carbonate complex in Alberta, Canada (Machel and Buschkuehle, 2008), etc … The significance of this work is the use of multi-scale modeling approaches to extrapolate μm-scale fluid inclusions to basin-scale geodynamic events of the Aquitaine basin.

Section snippets

Geology and stratigraphy

The Deep Lacq reservoir is part of the Lacq petroleum system in the Arzacq sub-basin, south of the Aquitaine basin (Fig. 1). The Upper Lacq reservoir (Elias Bahnan et al., 2020) is separated from Deep Lacq by the Sainte Suzanne Marls. Since the target of this work is Deep Lacq, only the Jurassic to Early Cretaceous formations will be discussed. The genesis of the Aquitaine basin and the complete stratigraphic column of Lacq have been extensively described and detailed in a previous work (Elias

Sampling

The studied core samples of Deep Lacq were obtained from wells LA-101 (Latitude: 43.420648°; longitude: −0.619980°) and LA-104 (Latitude: 43.420421°; longitude: −0.638811°) (Fig. 1, Fig. 3). Additional public data on these wells can be found at the French national geological survey website (BRGM: infoterre. brgm.fr). Following the same strategy as that described by Elias Bahnan et al. (2020) for Upper Lacq, these wells were selected after a preliminary evaluation of nearly 600 thin sections

Basin modeling

The geodynamic history of the Lacq petroleum system was modeled using Petromod 1D software. A synthetic well combining the entire stratigraphy of wells LA-101 and LA-104 was prepared from drilling reports and used as the main input source for the model. Boundary conditions were set by using the paleowater depths (PWD), sediment-water interface temperatures (SWIT) and basal heat flow (HF) as discussed by Elias Bahnan et al. (2020). Vitrinite data were collected from TOTAL archives and were used

Petrography of diagenetic phases

Precursor limestones consist of chalky mudstones, wackestones to bioclastic packstones (Fig. 4-A and B). Bioclastic material consists of microforaminifera, shells of mollusks, sponges, echinoderms and annelids, with sizes reaching up to 2 mm.

Fluid modeling

Fig. 9 gives strong petrographic evidence of primary aqueous and oil inclusions entrapment in the studied phases. The location of fluids between growth zones or in clusters limited to individual crystals indicate a primary origin of the inclusions. Also, microthermometry results provide additional supporting evidence that can complement petrographic observations. Fig. 10 shows different homogenization temperatures and salinities between the different cement phases. This difference indicates

Conclusions

This work highlights the power of applying a multi-modeling approach to reveal the diagenetic history in a complex geodynamic setting. After a detailed petrographic analysis of all the phases present, the multitude of equations of states used in AIT-PIT modeling provided valuable insight into the fluids P-T conditions. These in turn were then validated against the basin history to place age constraints on the timing of fluids circulation.

The diagenesis of the giant Deep Lacq reservoir has been

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

This work was funded by TOTAL EP-R&D and the Center de Recherches sur la Géologie des Matières Premières Minérales et Energétiques (CREGU), contract number FR00008500 - CREGU/T25. Sylvain Calassou and the colleagues from the Center Scientifique et Technique Jean Féger de TOTAL (CSTJF-TOTAL) are warmly thanked for providing access to their facilities and data archives to conduct this research. Olivier Fonta from GEOPETROL is thanked for providing access to the core samples. Pierre Cartigny from

References (66)

  • A. Elias Bahnan et al.

    Impact of geodynamics on fluid circulation and diagenesis of carbonate reservoirs in a foreland basin: example of the Upper Lacq reservoir (Aquitaine basin, SW France)

    Mar. Petrol. Geol.

    (2020)
  • J. Horita

    Oxygen and carbon isotope fractionation in the system dolomite–water–CO2 to elevated temperatures

    Geochem. Cosmochim. Acta

    (2014)
  • Y. Kitayama et al.

    Co-magmatic sulfides and sulfates in the Udachnaya-East pipe (Siberia): a record of the redox state and isotopic composition of sulfur in kimberlites and their mantle sources

    Chem. Geol.

    (2017)
  • H. Machel

    Bacterial and thermochemical sulfate reduction in diagenetic settings — old and new insights

    Sediment. Geol.

    (2001)
  • G. Motte et al.

    Rift and salt-related multi-phase dolomitization: example from the northwestern Pyrenees

    Mar. Petrol. Geol.

    (2021)
  • S. Renard et al.

    Diagenesis in Mesozoic carbonate rocks in the North Pyrénées (France) from mineralogy and fluid inclusion analysis: example of Rousse reservoir and caprock

    Chem. Geol.

    (2019)
  • E. Roedder

    Fluid inclusion analysis—prologue and epilogue

    Geochem. Cosmochim. Acta

    (1990)
  • R. Salardon et al.

    Interactions between tectonics and fluid circulations in an inverted hyper-extended basin: example of mesozoic carbonate rocks of the western North Pyrenean Zone (Chaînons Béarnais, France)

    Mar. Petrol. Geol.

    (2017)
  • A. Teixell et al.

    The crustal evolution of the west-central Pyrenees revisited: inferences from a new kinematic scenario

    Compt. Rendus Geosci.

    (2016)
  • R. Thiéry et al.

    Individual characterization of petroleum fluid inclusions (composition and P–T trapping conditions) by microthermometry and confocal laser scanning microscopy: inferences from applied thermodynamics of oils

    Mar. Petrol. Geol.

    (2002)
  • J. Veizer et al.

    87Sr/86Sr, δ13C and δ18O evolution of Phanerozoic seawater

    Chem. Geol.

    (1999)
  • Y.-G. Zhang et al.

    Determination of the homogenization temperatures and densities of supercritical fluids in the system NaClKClCaCl2H2O using synthetic fluid inclusions

    Chem. Geol.

    (1987)
  • P. Angrand et al.

    Lateral variations in foreland flexure of a rifted continental margin: the Aquitaine basin (SW France)

    Tectonics

    (2018)
  • Nicolas Beaudoin et al.

    Crustal-scale fluid flow during the tectonic evolution of the Bighorn Basin (Wyoming, USA)

    Basin Res.

    (2014)
  • J. Biteau et al.

    The Aquitaine basin

    Petrol. Geosci.

    (2006)
  • D.D. Blackwell et al.

    Thermal conductivity of sedimentary rocks: measurement and significance

  • J. Bourdet et al.

    Petroleum type determination through homogenization temperature and vapour volume fraction measurements in fluid inclusions

    Geofluids

    (2008)
  • M.-C. Caumon et al.

    Raman spectra of water in fluid inclusions: I. Effect of host mineral birefringence on salinity measurement

    J. Raman Spectrosc.

    (2015)
  • C. Clerc et al.

    Thermal control on the modes of crustal thinning leading to mantle exhumation: insights from the Cretaceous Pyrenean hot paleomargins

    Tectonics

    (2014)
  • C. Clerc et al.

    High-temperature metamorphism during extreme thinning of the continental crust: a reappraisal of the North Pyrenean passive paleomargin

    Solid Earth

    (2015)
  • J. Connan et al.

    The origin of the Lacq superieur heavy oil accumulation and of the giant Lacq inferieur gas field (Aquitaine basin, SW France)

  • R. Curnelle et al.

    Evolution mesozoique des grands bassins sedimentaires français; bassins de Paris, d'Aquitaine et du Sud-Est

    Bull. la Société Géologique Fr.

    (1986)
  • Z. Duan et al.

    An equation of state for the CH4-CO2-H2O systems: II. mixtures from 50 to 1000°C and 0 to 1000 bar

    Geochem. Cosmochim. Acta

    (1992)
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