When do fractures initiate during the geological history of a sedimentary basin? Test case of a loading-fracturing path methodology

https://doi.org/10.1016/j.jsg.2022.104683Get rights and content

Highlights

  • •

    An interdisciplinary methodology is proposed for a geological loading -fracturing path.

  • •

    A loading path is established numerically under geological constraints.

  • •

    Failure conditions are applied to material with increasing strength.

  • •

    Jointing and faulting fracturing windows are defined under minimum overpressure.

  • •

    Fracturing initiates early in incompletely lithified/buried material.

Abstract

We propose a methodology to determine the initiation and reactivation of fracturing during the geological history of a sedimentary basin. The data input is derived from the Eagle Ford unconventional play (Texas, USA) and includes stratigraphy, burial and exhumation, tectonic regimes, regional fractures and faults, in situ stresses, and present-day mechanical properties of rocks. Based on this dataset and mechanical simulations, we build a stress history (the loading path). Using this path and criteria for the tensile and shear failure, we evaluate the temporal intervals when fracturing is possible during the geological history of a sedimentary basin for different scenarios of the associated strength evolution of its material. We conclude that most probably fracturing is initiated in early (shallow) burial conditions, at a post-compaction stage, with no or limited overpressure, when the cohesion of the material is still low.

Introduction

Constraining the geological context and the timing of fracture formation (the fracturing history) is a fundamental objective for structural geologists, especially those involved in subsurface operations like fluid and gas recovery, reservoir characterization, caprock integrity, and hydraulic fracturing. A large amount of research on fractured reservoirs or reservoir analogs has been carried out in different rock types: in sandstones (e.g., Laubach and Ward, 2006; Olson et al. 2009; Becker et al., 2010; Laubach et al., 2010; Fall et al., 2014, 2015), in carbonates (e.g., Hooker et al., 2012; Lamarche et al., 2012, Lavenu et al., 2014; La Bruna et al., 2020), and mainly, in organic-rich mudstones known as oil or gas shales (e.g., Engelder, 1985, Laubach and Ward, 2006; Engelder and Whitaker, 2006; Becker et al., 2010; Evans et al., 2014; Gale et al. 2014; Wilkins et al., 2014; Hooker et al., 2018, Laubach et al., 2019; Minisini et al. 2020).

Fracturing history is addressed using structural geology methods, including tectonic, microtectonic, and petrographic analyses (e.g., Price and Cosgrove, 1990; Fossen, 2016), but most often, on the basis of thermobarometric measurements (e.g. Becker et al.,2010; Fall et al., 2015; Hooker et al., 2015) and studies of the evolution of mineral deposits in both host material and fractures (e.g., Taron and Elsworth, 2009; Laubach et al., 2009, 2019). Different methods may lead to contradictory conclusions. For example, numerous studies based on thermobarometric measurements and analysis of multistep mineralizations in fractures (e.g., Beaudoin et al., 2011), often in oil and gas reservoirs (e. g. Laubach and Ward, 2006; Evans et al., 2014; Fall et al., 2015; Becker et al., 2010; Hooker et al., 2015), show that fractures (essentially veins) generally start forming at ∼ >3 km during burial, regardless of the tectonic or structural context (see a synthesis in Fig. 9 in Laubach et al. 2019). The primary triggering mechanism invoked for fracturing is overpressure generated by thermocatalytic effects during the hydrocarbon maturation, although several other causes of overpressure exist (Grauls, 1999; Swarbrick et al., 2002) and unloading can also trigger fracturing (Hooker et al., 2018). These studies imply that the formation of mineralized fractures in intact (unfractured) rocks is initiated when diagenetic evolution was well advanced or completed (e.g., Laubach and Ward, 2006; Engelder and Whitaker, 2006; Evans et al., 2014; Becker et al., 2010). It follows, that a considerable time span should exist between the deposition of sediment and the onset of fracturing (up to several tens of million years).

A contradictory conclusion follows from an increasing number of regional and outcrop studies showing that fractures (intended as planar discontinuities in rocks, namely porosity/dilatancy bands or joints, barren or mineralized joints, veins, deformation bands, or small faults) can form in very shallow conditions during the early burial history when diagenesis evolution was not advanced. For example, pre-diagenetic polygonal faulting can occur in just deposited clay- and smectite-rich sediments due to their volumetric contraction. (e.g., Baudon and Cartwright, 2008; Cartwright, 2011; Gay et al., 2021).

Syn-compaction fracturing marked by folded (ptygmatic) veins can occur in soft, very hydrated sediments like mudstones (de Joussineau et al., 2005; Wilkins et al., 2014; Gale et al., 2014; Hooker et al., 2018) or in different structural and sedimentological settings where the synchronous formation of diffuse fracture networks formed during the early burial stages (at less than 1000 m-depth) before any major tectonic influence (Lavenu and Lamarche, 2017; La Bruna et al., 2020). Post-compaction ductile (hydroplastic) early faulting in the siliciclastic Triassic basins in the High Atlas (Morocco) occurred in a syn-depositional context (Laville and Petit, 1984). In sandstone layers, shear deformation associated with this faulting is accommodated by the hydrated clay between quartz grains in unfolded deformation bands. Faults have specific shapes and surface morphologies (Petit and Laville, 1987) and are characterized by a high displacement gradient (Wibberley et al., 1999). Recent early jointing in shallowly buried compacted and low-cohesion sediments has been documented in Quaternary glacial sands (Meier and Kronberg, 1989), in late-Quaternary mudstones of the Nankai accretionary prism (Chamot-Rooke et al., 1992), in the Pliocene porous marly limestone of la Scala dei Turchi in Sicily (Cita and Pillians, 2009; Petit, personal observation).

The aforementioned and many other examples indicate that during burial, the relation between fracturing and diagenetic strengthening is complex and driven by many different factors like the physical and chemical depositional environment (Gale et al. 2014; Lander and Laubach, 2014; Laubach et al., 2019; La Bruna et al., 2020), the nature and heterogeneity of the sedimentary material (Laubach and Ward, 2006; Laubach et al., 2009; Frost and Kerans, 2010), the conditions of burial, etc.

Whatever the complexity, a generic question remains: when do fractures initiate (are created in an intact material) during the geological history of a sedimentary basin? Also, are there some specific physical or geological conditions that may favor early shallow fracturing initiation? Clearly, the geological approach and available information are not sufficient to answer these questions. Geomechanical constraints, that are central in the analysis here, must be considered as well.

The mechanical basis for fracture formation presented in structural geology textbooks (faults, shear fractures, hybrid fractures, joints, deformation bands) (e.g., Price and Cosgrove, 1990; Fossen, 2016) mainly refers to the results of rock mechanics tests (e.g., Paterson and Wong, 2005; Jaeger et al., 2007; Turner et al., 2017) and the Mohr-Coulomb theory.

Attempts to use these tools to predict failure conditions from a temporal perspective are scarce (Voight and St. Pierre, 1974; Narr and Currie, 1982; Engelder, 1985; Price and Cosgrove, 1990; English, 2012) and based on simplistic, purely theoretical burial-exhumation scenarios.

The most popular approach to fracture formation consists in the numerical modeling based on linear elastic fracture mechanics, LEFM (Lawn and Wilshaw, 1975). This approach has allowed to obtain important insights into the mechanics of jointing and fault/crack propagation problems (e.g., Segall and Pollard, 1983; Atkinson, 1987; Pollard and Aydin, 1988; Petit and Barquins, 1988; Barquins et al., 1992; Olson, 1993; Gross, 1993; Bai and Pollard, 2000; Cosgrove and Engelder, 2004; Savalli and Engelder, 2005; de Joussineau and Petit, 2007; Scholz, 2007; Olson et al., 2009). However, the existing models ignore the temporal (historical) aspect, except through contrasting loading conditions (de Joussineau and Petit, 2021). Furthermore, these models do not consider inelastic straining preceding and accompanying fracture formation, which is taken into account within the framework of elastoplasticity and damage theories using different numerical techniques (Schöpfer et al., 2011; Tang et al., 2008; Li et al., 2012; Guo et al., 2017; Chemenda 2019). This approach allowed especially to reveal different modes of fracture initiation (including through dilation banding) and obtain the so-far unexplained nonlinear relation between bed thickness and fracture spacing (Chemenda, 2019; Chemenda et al., 2021, 2022). However, these models were not designed to address the temporal (historical) aspects of fracture formation either. This is our focus here. We use a simplified elastoplastic framework and do not address the details of the processes of fracture initiation, evolution, and structuring of the fracture networks. We simply evaluate whether and when fracturing is possible during the basin history. This is done by constraining first the evolution of both the material strength and the effective subsurface stress state, taking the mudstone-dominated Eagle Ford unconventional play (Texas, USA) as the test case. Then we evaluate the periods (fracturing windows) when fracturing is possible, using simple criteria for tensile and shear failure. We obtain that fracture initiation is likely to occur under early burial conditions, with no or limited overpressure when the material is already compacted but still has low cohesion.

Section snippets

Previous and our geomechanical approaches in more detail

Several studies have attempted to relate faulting–fracturing episodes to stress evolution in rock volumes during a simple, theoretical burial-exhumation cycle (e.g., Voight and St. Pierre, 1974; Narr and Currie, 1982; Warpinski, 1989; Price and Cosgrove, 1990; English, 2012). Most of these studies assume that the rocks experienced oedometric loading–unloading corresponding to uniaxial vertical straining with fixed vertical/lateral boundaries. Elastic or visco-elastic rock behavior is assumed,

Geological context and constraints on tectonic regimes and axes in the Eagle Ford Group and Del Rio region, Texas USA

The LFP methodology (Table 1) is applied to the case of the Eagle Ford Group which presents excellent regional reservoir analog outcrops and accessible reservoir data (burial exhumation curves, representative rock properties, and in situ stress). The Eagle Ford Group deposited between ∼97 and 90 Ma. It is composed of limestones, organic-rich mudstones, and bentonites, alternating stratigraphically every 1–40 cm. The 60–130 m thick Eagle Ford Group is underlain by the Buda Limestone and overlain

Outcrop-scale faults and shear fractures

In the area of study, these structures are observable in Buda Limestone, Eagle Ford Group, and Austin Chalk, with rather similar geometries (Fig. 4). The most frequent normal faults and shear fractures (conjugate or not) are not dense and have dominantly NE-SW (y-parallel) strike as in the Balcones Fault Zone (Ferrill et al., 2014, 2017) (Fig. 2) and as the lineaments observed on the seismic images in the Chittim Ranch (Treadgold et al., 2011).

Both SE and NW dipping faults are present (Fig. 3

Burial-exhumation and mechanical data

The vertical stress history (path) in Fig. 7 is obtained from the evolution of both total lithostatic pressures (the total vertical stress σvtot) and hydrostatic pore pressure pw (typical of the upper crust, Towned and Zoback, 2000) during burial and exhumation of the Eagle Ford Group in the Chittim Ranch. The effective vertical stress σv, σv=σvtot−pw, is also shown in this figure, along with the red line approximating the σv points. This line is assumed to be the vertical effective (at p=pw)

Construction of the reference loading path with the geological and geomechanical constraints

To focus on the main purpose of the paper, the methodological steps for the construction of a reference loading path are presented in Appendix 3, but to facilitate the task for the interested reader, the figures cited in Appendix 3 (Fig. 8 to Fig. 9, Fig. 10) are kept in the main text.

We focus here on the principles for the construction of the reference loading path shown in Fig. 10, Fig. 11.

  • -

    Stresses σx, σy, and σv are effective, calculated for pore pressure p equal to the hydrostatic pressure p

Failure conditions

Tensile failure occurs when the least effective stress is negative (tensile) and reaches the tensile strength σtσ3+=σ3−p+=−σtwhere σ3=σ3tot−pw; p+ is the pore overpressure since σ3 is already effective stress at hydrostatic pore pressure pw. The obvious drawback of this criterion is that it does not depend on the stress state and notably the mean stress σm. The rock mechanics data from triaxial extension tests of porous geomaterials show that σt (or the magnitude of the tensile stress σ3 at

Evolution of mechanical properties during the basin history

To define the fracturing windows, the loading path and failure conditions are not enough; the evolution of mechanical properties is needed as well. Both the material stiffness and strength increase with burial (e.g., Laubach et al., 2019; Chang et al., 2006). The variation in elastic stiffness can be ignored in our model as is discussed in Appendix 3, but the variation of the strength parameters such as material cohesion k and tensile strength σt play a fundamental role. This becomes obvious if

Loading-fracturing path models without and with evolving mechanical properties

In Fig. 11, the present-day rock strengths (given in Table 3) are imposed over the entire time history. The p+ curve in Fig. 11 shows the overpressure needed to reach tensile rupture and generate Mode I joints. The loading-fracturing path models with evolving properties and the loading path from Fig. 10c are presented in Fig. 15a and c. These models coincide with that in Fig. 11 after σm (green line on the plots) reaches its maximum value around 45 Ma, after which the properties do not change

Fracturing windows and conditions during early burial

Fig. 15e shows that with the Prop2 model, the normal faulting window is wide (∼15 Ma) due to the slow increase in cohesion k over time (see curve k=f(t) in Fig. 14d). Normal faulting (middle sketch top, Fig. 15e) occurs before the onset of jointing predicted at ca. 68 Ma in the strike-slip regime when σt∼<1/3 of the maximum (present-day) σt value (5 MPa). Present-day rock cohesion k is reached at ca. 55 Ma at a burial depth of ca. 1100 m (dashed lines on Fig. 7) well before the maximum burial.

Conclusion

  • •

    The proposed methodology for the evaluation of the periods of probable fracturing (fracturing windows) is based on models of the evolution of the stress state (loading path) and the material strength during the basin history.

  • •

    The loading path is defined using data on the regional succession of tectonic regimes. The mechanical modeling takes into account as much tectonomechanical data as possible. For our case study of the mudrocks of the Eagle Ford Group (Texas, USA), the burial exhumation data,

Author statement

Jean-Pierre Petit: Conceptualization, methodology, field observations and data collection, validation, original draft writing, visualization, project administration, funding acquisition. Alexandre Chemenda: Conceptualization, methodology, field observations, physical modeling, formal analysis, original draft writing, visualization, validation. Daniel Minisini: Field observations, writing, review and editing, project administration. Pascal Richard: Project administration, supervision. Steve

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 conducted within the Geo-FracNet consortium initially sponsored by Shell and Total Energy and was essentially developed with Shell Technology Center Houston,. We thank Andrew Madiarov and Taixu Bai from Shell (Houston) for providing the mechanical data on the Eagle Ford samples. Many thanks to the five reviewers and to S. Laubach, who considerably helped improving this interdisciplinary paper.

References (111)

  • G. de Joussineau et al.

    Mechanical insights into the development of fracture corridors in layered rocks

    J. Struct. Geol.

    (2021)
  • T. Engelder

    Loading paths to joint propagation during a tectonic cycle: an example from the Appalachian Plateau

    U.S.A.: J. Struct. Geol.

    (1985)
  • D.A. Ferrill et al.

    Hybrid failure: field evidence and influence of fault refraction

    J. Struct. Geol.

    (2012)
  • D.A. Ferrill et al.

    Deciphering thrust fault nucleation and propagation and the importance of footwall synclines

    J. Struct. Geol.

    (2016)
  • D.A. Ferrill et al.

    Fault zone processes in mechanically layered mudrock and chalk

    J. Struct. Geol.

    (2017)
  • E.L. Frost et al.

    Controls on syndepositional fracture patterns, Devonian reef complexes, Canning Basin, Western Australia

    J. Struct. Geol.

    (2010)
  • M. Gross

    The origin and spacing of cross joints: examples from the Monterey Formation, Santa Barbara Coastline, California

    J. Struct. Geol.

    (1993)
  • L. Guo et al.

    A numerical study of fracture spacing and through-going fracture formation in layered rocks

    Int. J. Solid Struct.

    (2017)
  • C. Jorand et al.

    Formation of parallel joint sets and shear band/fracture network in physical models

    Tectonophysics

    (2012)
  • J. Lamarche et al.

    Relationships between fracture patterns, geodynamics and mechanical stratigraphy in Carbonates (South-East Basin, France)

    Tectonophysics

    (2012)
  • S.E. Laubach et al.

    Diagenesis in porosity evolution of opening-mode fractures, middle triassic to lower Jurassic la Boca formation, NE Mexico

    Tectonophysics

    (2006)
  • S.E. Laubach et al.

    Structural diagenesis

    J. Struct. Geol.

    (2010)
  • A.P.C. Lavenu et al.

    Relating background fractures to diagenesis and rock physical properties in a platform–slope transect

    Example of the Maiella Mountain (Central Italy): Mar. Petrol. Geol.

    (2014)
  • T.M. Lehman

    Sedimentation and tectonism in the Laramide Tornillo basin of west Texas

    Sediment. Geol.

    (1991)
  • J.-P. Petit et al.

    Crack-seal, slip': a new fault valve mechanism?

    J. Struct. Geol.

    (1999)
  • J.-P. Petit et al.

    Paleostress superimposition deduced from mesoscale structures in limestone: the Matelles exposure, Languedoc, France

    J. Struct. Geol.

    (1995)
  • M.P. Schöpfer et al.

    Reconciliation of contrasting theories for fracture spacing in layered rocks

    J. Struct. Geol.

    (2011)
  • B.K. Atkinson

    Fracture Mechanics of Rocks

    (1987)
  • M. Barquins et al.

    Paths and kinetics of branching from defects under uniaxial and biaxial compressive loading

    Int. J. Fract.

    (1992)
  • F. Bassinot et al.

    Variations of porosity in calcareous sediments from the Ontong Java plateau

  • Z.P. Bažant et al.

    Fracture and Size Effect in Concrete and Other Quasibrittle Materials

  • N. Beaudoin et al.

    Fracture‐controlled paleohydrogeology in a basement‐cored, fault‐related fold: sheep Mountain Anticline, Wyoming, United States, Geochem

    Geophys. Geosyst.

    (2011)
  • S.P. Becker et al.

    A 48 m.Y. History of Fracture Opening, Temperature, and Fluid Pressure: Cretaceous Travis Peak Formation, East Texas Basin

    (2010)
  • P. Bird

    Kinematic history of the Laramide orogeny in latitudes 35°-49°N

    Western United States: Tectonics

    (1998)
  • J.K. Bobich

    Experimental Analysis of the Extension to Shear Fracture Transition in Berea Sandstone (Doctoral Dissertation

    (2005)
  • J.A. Bryer et al.

    Evidence for late cretaceous volcanism in Trans-Pecos Texas

    J. Geol.

    (2007)
  • S.M. Cather

    Stress and volcanism in the northern Mogollon-Datil volcanic field, New Mexico: effects of the post-Laramide tectonic transition

    Geol. Soc. Am. Bull.

    (1990)
  • A.I. Chemenda et al.

    Mode I cracking versus dilatancy banding : experimental constraints on the mechanisms of extension fracturing

    J. Geophys. Res.

    (2011)
  • A.I. Chemenda

    Origin of regular networks of joints: experimental constraints, theoretical background, and numerical modeling

    J. Geophys. Res. Solid Earth

    (2019)
  • A.I. Chemenda et al.

    Origin of strong nonlinear dependence of fracture (joint) spacing on bed thickness in layered rocks: mechanical analysis and modeling

    J. Geophys. Res. Solid Earth

    (2021)
  • R.C. Cobb et al.

    Superposed Deformation in the Santiago and Northern Del Carmen Mountains, Trans-Pecos, Texas: New Mexico Geological Society Guidebook, 31st Field Conference

    (1980)
  • P.G. DeCelles

    Late Jurassic to Eocene evolution of the Cordilleran thrust belt and foreland basin system, western USA

    Am. J. Sci.

    (2004)
  • M. Dokur et al.

    Reservoir Characterization of the Upper Cretaceous Woodbine Group in Northeast Texas Field, Texas

    (2012)
  • G.P. Eberli et al.

    Factors controllingelastic properties in carbonate sediments and rocks

    Lead. Edge

    (2003)
  • T. Engelder et al.

    Early jointing in coal and black shale: evidence for an Appalachian-wide stress field as a prelude to the Alleghanian orogeny

    Geology

    (2006)
  • J.M. English

    Thermomechanical origin of regional fracture systems

    AAPG (Am. Assoc. Pet. Geol.) Bull.

    (2012)
  • J.M. English et al.

    Opening-mode fracture systems: insights from recent fluid inclusion microthermometry studies of crack-seal fracture cements

  • M.A. Evans et al.

    Deformation conditions for fracturing in the middle devonian sequence of the central Appalachians during the late Paleozoic Alleghenian orogeny

    AAPG (Am. Assoc. Pet. Geol.) Bull.

    (2014)
  • A. Fall et al.

    Natural hydraulic fracturing of tight-gas sandstone reservoirs, Piceance Basin, Colorado

    Bulletin

    (2014)

    • Cited by (4)

    • Fracture-pattern growth in the deep, chemically reactive subsurface

      2023, Journal of Structural Geology

    • Bed thickness-dependent fracturing and inter-bed coupling define the nonlinear fracture spacing-bed thickness relationship in layered rocks: Numerical modeling

      2022, Journal of Structural Geology

    • Introduction: Faults and fractures in rocks: mechanics, occurrence, dating, stress history and fluid flow

      2022, Geological Magazine

    • Evidence for Regional Fluid Migration in the Eagle Ford Formation, Austin Chalk, and Buda Limestone of South-Central and West Texas, USA

      2023, SSRN
    1

    Present address: 210 Route de Durfort, 30350, Canaules et Argentières, France.

    2

    Present address: Lotissement les Dryades, 56370, Sarzeau, France.

    3

    Present address: Chautauqua Beach Rd. SW, Vashon, WA 98070, USA.

    View full text
    © 2022 Elsevier Ltd. All rights reserved.