A Finite-Volume Discretization for Deformation of Fractured Media

Uçar, Eren; Keilegavlen, Eirik; Berre, Inga; Nordbotten, Jan Martin

doi:10.48550/arxiv.1612.06594

Cited by 3 publications

(5 citation statements)

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“…We use a recently developed cell-centered finite volume method, Multi-Point Stress Approximation (MPSA) [Keilegavlen and Nordbotten, 2017;Nordbotten, 2014], to approximate the solution of the linear momentum balance equation because it enables the use of the same data structure applied in the fluid flow discretization. MPSA enables the efficient inclusion of fractures by modeling them as internal boundary conditions, including fracture deformations in both the normal direction (change in the mechanical aperture) and the shear direction (caused by excess shear stress) [Ucar et al, 2016].…”

Section: Multi-physics Couplingmentioning

confidence: 99%

Postinjection Normal Closure of Fractures as a Mechanism for Induced Seismicity

Uçar

Berre

Keilegavlen

2017

Geophysical Research Letters

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Understanding the controlling mechanisms underlying injection‐induced seismicity is important for optimizing reservoir productivity and addressing seismicity‐related concerns related to hydraulic stimulation in Enhanced Geothermal Systems. Hydraulic stimulation enhances permeability through elevated pressures, which cause normal deformations and the shear slip of preexisting fractures. Previous experiments indicate that fracture deformation in the normal direction reverses as the pressure decreases, e.g., at the end of stimulation. We hypothesize that this normal closure of fractures enhances pressure propagation away from the injection region and significantly increases the potential for postinjection seismicity. To test this hypothesis, hydraulic stimulation is modeled by numerically coupling flow in the fractures and matrix, fracture deformation, and matrix deformation for a synthetic reservoir in which the flow and mechanics are strongly affected by a complex three‐dimensional fracture network. The role of the normal closure of fractures is verified by comparing simulations conducted with and without the normal closure effect.

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Section: Multi-physics Couplingmentioning

confidence: 99%

Postinjection Normal Closure of Fractures as a Mechanism for Induced Seismicity

Uçar

Berre

Keilegavlen

2017

Geophysical Research Letters

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“…Future models might also include fracture roughness and solve the full equilibrium equations to estimate aperture changes that influence permeability. Recently, progress in this direction has been made using boundary element methods, multi-point stress approximations (MPSA) and the novel extended finite volume method (XFVM) (Norbeck et al, 2016;Ucar et al, 2016;Deb and Jenny, 2016). However, these models are not yet as computationally efficient as to allow an adaption for THERMAID.…”

Section: Discussionmentioning

confidence: 99%

THERMAID - A matlab package for thermo-hydraulic modeling and fracture stability analysis in fractured reservoirs

Jansen¹,

Valley²,

Miller³

2018

Preprint

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Understanding the dynamics of naturally fractured systems and fractured reservoirs in terms of flow, heat transport and fracture stability (e.g. induced seismicity) is important for a range of applications associated with waste water injection, renewable energy (e.g. geothermal systems), and greenhouse gas mitigation (e.g. geological sequestration of CO2). Here we present the implementation and validation of an open source MATLAB package for efficient numerical simulations of the coupled processes in fractured systems. We take advantage of the embedded discrete fracture model that efficiently accounts for discrete fractures. We perform a series of numerical benchmark experiments to validate the implemented approach against analytical solutions and established numerical methods. Finally, we use a simplified geomechanical model and an integrated fracture stability analysis that allows estimating the potential for shear stimulation, and thus a mechanistic assessment of induced seismic risk during stimulation. The open source distribution of the source code and results can be used as a blue print for the re-implementation of the method in a high performance computing (HPC) framework or as a standalone simulation package for investigating TH(m) problems in geothermal reservoirs.

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“…In line with previous studies (Aagaard et al, 2013;Crouch & Starfield, 1982), the two surfaces of fracture are modeled as face pairs that have positive and negative sides. The face pairs are integrated as internal boundary conditions to the momentum balance equations, which are introduced in Section 2.3, by using the method developed by Ucar et al (2016). The discontinuity relations due to the fracture deformation (equation ( 2), (5), and ( 6)) are defined as 𝒖 + − 𝒖 − = ∆𝒖 𝑓 on 𝛤 where ∆𝒖 𝑓 = 𝒏 + (𝛥𝐸 𝑛,𝑟𝑒𝑣 + 𝛥𝐸 𝑛,𝑖𝑟𝑟𝑒𝑣 ) + 𝜻 + 𝛥𝑑 𝑠 .…”

Section: Mechanics Of Fracturesmentioning

confidence: 99%

“…Here, the primary variable, displacement, is defined at the face centers of the fracture faces as illustrated in Figure 2b. The details about the grid structure can be found in Ucar et al (2016). For illustration purposes, we show a gap between two red dots, but there is no gap between the duplicated faces and the face centers in the computational mesh.…”

Section: Grid Structurementioning

confidence: 99%

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Three‐Dimensional Numerical Modeling of Shear Stimulation of Fractured Reservoirs

2018

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Shear-dilation-based hydraulic stimulations can enable commercial exploitation of geothermal energy from reservoirs with inadequate initial permeability. While contributing to enhancing the reservoir's permeability, hydraulic stimulation processes may also lead to undesired seismic activity. Here we present a three-dimensional numerical model aiming to aid increased understanding of shear-dilation based hydraulic stimulation and its consequences. The fractured reservoir is modeled as a network of explicitly represented large-scale fractures immersed in a permeable rock matrix. The numerical formulation is constructed by coupling three physical processes: fluid flow, fracture deformation, and rock matrix deformation. For flow simulations, the discrete fracture-matrix model is used, which allows fluid transport from high-permeable conductive fractures to rock matrix and vice versa. The mechanical behavior of the fractures is modeled with reversible and irreversible deformations corresponding to elastic deformation and slip. Linear elasticity is assumed for mechanical deformation and stress alteration of the rock matrix. Fractures are modeled as lower-dimensional surfaces embodied in the domain, subjected to specific governing equations for their deformation along the tangential and normal directions. Both the fluid flow and momentum balance equations are approximated by finite volume discretizations. The new numerical model is demonstrated considering a three-dimensional fractured formation with a network of 20 explicitly represented fractures. The effects of fluid exchange between fractures and rock matrix on the permeability evolution and the generated seismicity are examined for test cases resembling realistic reservoir conditions. Numerical modeling of the shear stimulation can be a powerful tool for estimating the potential performance of the stimulated reservoir, for understanding governing mechanisms, and/or for forecasting possible undesired by-products of the stimulation process. However, due to the complex structure of the fractured rock and the number of coupled physical processes involved in the stimulation process, many modeling aspects remain unresolved. Challenges include the description of the mechanical and hydraulic behavior of the UCAR ET AL. 3891

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A Finite-Volume Discretization for Deformation of Fractured Media

Cited by 3 publications

References 0 publications

Postinjection Normal Closure of Fractures as a Mechanism for Induced Seismicity

Postinjection Normal Closure of Fractures as a Mechanism for Induced Seismicity

THERMAID - A matlab package for thermo-hydraulic modeling and fracture stability analysis in fractured reservoirs

Three‐Dimensional Numerical Modeling of Shear Stimulation of Fractured Reservoirs

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