Modeling branched and intersecting faults in reservoir‐geomechanics models with the extended finite element method

Liu, Chuanqi; Prévost, Jean‐Hérve; Sukumar, N.

doi:10.1002/nag.2949

“…The comparison shows that, even when the cracks are intersecting, the phase-field method provides a numerical solution very similar to an XFEM solution. The simulation result is also qualitatively correct in that the intersection inhibits the slip of the inclined crack, which has also been observed by Liu et al 69 .…”

Section: Biaxial Compression On a Rock With Two Intersecting Crackssupporting

confidence: 84%

Phase‐field modeling of rock fractures with roughness

Fei

¹

,

Choo

²

,

Liu

³

et al. 2022

Num Anal Meth Geomechanics

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Phase-field modeling-a continuous approach to discontinuities-is gaining popularity for simulating rock fractures due to its ability to handle complex, discontinuous geometry without an explicit surface tracking algorithm. None of the existing phase-field models, however, incorporates the impact of surface roughness on the mechanical response of fractures-such as elastic deformability and shear-induced dilation-despite the importance of this behavior for subsurface systems. To fill this gap, here we introduce the first framework for phase-field modeling of rough rock fractures. The framework transforms a displacementjump-based discrete constitutive model for discontinuities into a strain-based continuous model, without any additional parameter, and then casts it into a phase-field formulation for frictional interfaces. We illustrate the framework by constructing a particular phase-field form employing a rock joint model originally formulated for discrete modeling. The results obtained by the new formulation show excellent agreement with those of a well-established discrete method for a variety of problems ranging from shearing of a single discontinuity to compression of fractured rocks. It is further demonstrated that the phase-field formulation can well simulate complex crack growth from rough discontinuities.Consequently, our phase-field framework provides an unprecedented bridge between a discrete constitutive model for rough discontinuities-common in rock mechanics-and the continuous finite element method-standard in computational mechanics-without any algorithm to explicitly represent discontinuity geometry. K E Y W O R D Sphase-field modeling, rock fractures, rock discontinuities, roughness, rock masses, shearinduced dilation INTRODUCTIONRock fractures are pervasive in natural and engineered subsurface systems. The mechanical behavior of rock fractures not only controls the performance of many geotechnical structures such as slopes and tunnels (e.g., [1][2][3] ), but it plays an important role in the operation of subsurface energy technologies such as hydraulic stimulation, nuclear waste disposal, enhanced geothermal systems, and geologic carbon storage (e.g., [4][5][6][7][8] ).

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“…The comparison shows that, even when the cracks are intersecting, the phase-field method provides a numerical solution very similar to an XFEM solution. The simulation result is also qualitatively correct in that the intersection inhibits the slip of the inclined crack, which has also been observed by Liu et al [55].…”

Section: Biaxial Compression On a Rock With Two Intersecting Crackssupporting

confidence: 84%

Phase-field modeling of rock fractures with roughness

Fei,

Choo,

Liu

et al. 2021

Preprint

0

View full text Add to dashboard Cite

Phase-field modeling-a continuous approach to discontinuities-is gaining popularity for simulating rock fractures due to its ability to handle complex, discontinuous geometry without an explicit surface tracking algorithm. None of the existing phase-field models, however, incorporates the impact of surface roughness on the mechanical response of fractures-such as elastic deformability and shear-induced dilation-despite the importance of this behavior for subsurface systems. To fill this gap, here we introduce the first framework for phase-field modeling of rough rock fractures. The framework transforms a displacement-jump-based discrete constitutive model for discontinuities into a strain-based continuous model, and then casts it into a phase-field formulation for frictional interfaces. We illustrate the framework by constructing a particular phase-field form employing a rock joint model originally formulated for discrete modeling. The results obtained by the new formulation show excellent agreement with those of a well-established discrete method for a variety of problems ranging from shearing of a single discontinuity to compression of fractured rocks. Consequently, our phase-field framework provides an unprecedented bridge between a discrete constitutive model for rough discontinuities-common in rock mechanics-and the continuous finite element method-standard in computational mechanics-without any algorithm to explicitly represent discontinuity geometry.

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“…XFEM is widely applied to solve crack problems in reservoir engineering, including branched and intersecting faults [15,18,21,22], cohesive crack propagation [23][24][25], and 3-D thermal crack propagation [26,27]. The contact problem is a highly nonlinear constrained problem, so generally, it can be solved using XFEM with both primal and dual formulations.…”

Section: Introductionmentioning

confidence: 99%

Fracture Reactivation Modeling in a Depleted Reservoir

Cao¹,

Yin²,

Liang³

et al. 2021

Computer Modeling in Engineering &Amp; Sciences

0

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Injection-induced fracture reactivation during hydraulic fracturing processes in shale gas development as well as coal bed methane (CBM) and other unconventional oil and gas recovery is widely investigated because of potential permeability enhancement impacts. Less attention is paid to induced fracture reactivation during oil and gas production and its impacts on reservoir permeability, despite its relatively common occurrence. During production, a reservoir tends to shrink as effective stresses increase, and the deviatoric effective stresses also increase. These changes in the principal effective stresses may cause Coulomb fracture slip in existing natural fractures, depending on their strength, orientation, and initial stress conditions. In this work, an extended finite element model with contact constraints is used to investigate different fracture slip scenarios induced by general reservoir pressure depletion. The numerical experiments assess the effect of Young's modulus, the crack orientation, and the frictional coefficient of the crack surface on the distribution of stress and displacement after some reservoir depletion. Results show that the crack orientation significantly affects the state of stress and displacement, particularly in the vicinity of the crack. Slip can only occur in permitted directions, as determined by the magnitudes of the principal stresses and the frictional coefficient. Lastly, a larger frictional coefficient (i.e., a rougher natural fracture surface) makes the crack less prone to shear slip.

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Modeling branched and intersecting faults in reservoir‐geomechanics models with the extended finite element method

Cited by 13 publications

References 20 publications

Phase‐field modeling of rock fractures with roughness

Phase‐field modeling of rock fractures with roughness

Phase-field modeling of rock fractures with roughness

Fracture Reactivation Modeling in a Depleted Reservoir

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