Reconciliation of contrasting theories for fracture spacing in layered rocks

Schöpfer, Martin; Arslan, Arzu; Walsh, John J.; Childs, Conrad

doi:10.1016/j.jsg.2011.01.008

Cited by 116 publications

(74 citation statements)

References 47 publications

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“…This is the effect of three different aspects of the model:The heterogeneity in the particle packing of the veins produces local weaknesses that allow fractures to crosscut the vein or reactivate either the vein or the interface (see chapter 4.1.2).Fractures in the DEM Model exhibit a higher degree of sinuosity and roughness than the straight, parallel veins in the conceptual model due to the intrinsic heterogeneity of the models and the structural dimension of the particle packing [ Hull , ]. A higher degree of interaction is therefore inevitable.The loading mechanism produces fractures with a characteristic spacing that results from the geometry of the setup as well as the ratio of tensile strength of the brittle layer and interface shear strength [ Schöpfer et al ., ]. Fractures have therefore a tendency to form in the same sequence at approximately the same position along the extension direction in each model.…”

Section: Discussionmentioning

confidence: 99%

The evolution of crack seal vein and fracture networks in an evolving stress field: Insights from Discrete Element Models of fracture sealing

2014

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Veins are ubiquitous in upper and middle crustal rocks. Due to strength and stiffness contrast to the host rock, veins can influence crack propagation. Here we present Discrete Element Models to investigate crack-vein interactions by simulating cycles of fracturing of a rock mass, sealing the cracks to form veins, and refracturing the rock mass after rotating the stress field. We observe different styles of interaction between new fractures and existing veins, depending on the strength ratio between vein and host rock and on the changes in the stress field between the different deformation stages. If the orientation of stress field does not change between deformation stages, ataxial crack seal veins are produced if the veins are weak and a bundle of subparallel microveins if the veins are strong. If the stress field is rotated between deformation stages, the interactions include reactivation, fracture deflection, and crosscutting. Reactivation of weak veins occurs even if the vein orientation is highly unfavorable relative to the stress field. Relays of fractures between reactivated veins form at a higher angle to the veins than expected. This demonstrates that the orientation of secondary veins does not reflect the regional stress field in a simple manner and that veins can strongly influence fracture connectivity, with implications for paleostress analysis and basin modeling. Simulation results compare well with field examples of multiphase vein networks in carbonates from Jebel Akhdar, Oman.

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Section: Discussionmentioning

confidence: 99%

The evolution of crack seal vein and fracture networks in an evolving stress field: Insights from Discrete Element Models of fracture sealing

2014

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“…BPMs with smooth joints have been applied to study: confinement-dependent rock strength degradation in hard rock (Bahrani, Valley, Kaiser, & Pierce, 2011) and fracture spacing in layered rocks (Schöpfer, Arslan, Walsh, & Childs, 2011).…”

Section: Development and Applicationmentioning

confidence: 99%

The bonded-particle model as a tool for rock mechanics research and application: current trends and future directions

Potyondy

2015

Geosystem Engineering

319

129

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We generalize our view of a bonded-particle model (BPM) to consist of a base material (that is a packed assembly of rigid grains joined by deformable and breakable cement at grain -grain contacts) to which larger-scale joints can be added and whose mechanical behavior is simulated by the distinct-element method using the two-and three-dimensional discontinuum programs PFC2D and PFC3D. The micromechanical processes that control brittle fracture, and thus, should inform any micromechanical theory or model, are summarized. The rich variety of microstructural models that can be produced by the bonded-particle modeling methodology are described and classified with respect to their microstructural and larger-scale features. These models provide a wide range of rock behaviors that encompass both compact and porous rock at both an intact and rock-mass scale, and examples are provided of how BPMs are being used to model rock at these scales. The examples include an intact anisotropic material that may swell and contract in response to changes in saturation, the behavior of two alternative BPMs that can match both the uniaxial and tensile strengths of compact rock and the embedding of an intact BPM within a larger continuum model to study fracturing around a gold-mine stope in quartzite.

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“…Important aspects of understanding fracture networks, these properties include: mechanical layer thicknesses (e.g. Pollard & Aydin 1988;Wu & Pollard 1995;Schöpfer et al 2011); contrasts in physical properties at layer interfaces, especial in Young's modulus (e.g. He & Hutchinson 1989;Cooke et al 2006;Lézin et al 2009); and the bonded strength of interfaces between mechanical layers (e.g.…”

Section: An Integrated Interdisciplinary Approachmentioning

confidence: 99%

Advances in the study of naturally fractured hydrocarbon reservoirs: a broad integrated interdisciplinary applied topic

Spence

Couples

Bevan

et al. 2014

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Naturally fractured reservoirs, within which porosity, permeability pathways and/or impermeable barriers formed by the fracture network interact with those of the host rock matrix to influence fluid flow and storage, can occur in sedimentary, igneous and metamorphic rocks. These reservoirs constitute a substantial percentage of remaining hydrocarbon resources; they create exploration targets in otherwise impermeable rocks, including under-explored crystalline basement, and they can be used as geological stores for anthropogenic carbon dioxide. Their complex fluid flow behaviour during production has traditionally proved difficult to predict, causing a large degree of uncertainty in reservoir development. The applied study of naturally fractured reservoirs seeks to constrain this uncertainty and maximize production by developing new understanding, and is necessarily a broad, integrated, interdisciplinary topic. Some of the methods, challenges and advances in characterizing the interplay of rock matrix and fracture networks relevant to fluid flow and hydrocarbon recovery are reviewed and discussed via the contributions in this volume.Global estimates of conventional hydrocarbon resources are typically subdivided based on lithological reservoir types for example, carbonate or siliciclastic (e.g. Roehl & Choquette 1985). However, many of these sedimentary rock reservoirs may contain fractures to a greater or lesser degree. The recent boom of unconventional reservoirs highlights once again the key role that natural fractures can play in helping production of fluids. It also requires an improved understanding of the geology and physics of natural fracture networks to meet public expectations regarding safety issues. Moreover, fracture networks can be present in otherwise impermeable crystalline basement rocks (e.g. Sanders et al. 2003;Murray & Montgomery 2012;Slightam 2012) and igneous intrusions (e.g. Gudmundsson & Løtveit 2012), also allowing these rocks to form potential fractured reservoirs. Historically, fractured crystalline basement rocks have been under-explored as potential hydrocarbon reservoirs. Naturally fractured reservoirs constitute a substantial percentage of remaining hydrocarbon resources. Naturally fractured reservoirsA reservoir fracture is a general term used to describe a 'naturally occurring macroscopic planar discontinuity in rock due to deformation, or physical diagenesis' (Nelson 2001). Reservoir fractures encompass both extensional ( joints) and shear (faults) structures. Fractures formed by brittle tectonic deformation are the most common focus for studies of naturally fractured reservoirs. However, reservoir fractures may also include structures that formed by desiccation (e.g. shrinkage cracks) and syneresis (e.g. chickenwire texture) in sediments, and structures that formed by thermal , as used here. Naturally fractured reservoirs are generally defined as such when the fracture network has a significant influence on fluid flow in the reservoir such that: (1) the fracture networ...

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Reconciliation of contrasting theories for fracture spacing in layered rocks

Cited by 116 publications

References 47 publications

The evolution of crack seal vein and fracture networks in an evolving stress field: Insights from Discrete Element Models of fracture sealing

The evolution of crack seal vein and fracture networks in an evolving stress field: Insights from Discrete Element Models of fracture sealing

The bonded-particle model as a tool for rock mechanics research and application: current trends and future directions

Advances in the study of naturally fractured hydrocarbon reservoirs: a broad integrated interdisciplinary applied topic

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