A damage mechanics approach to the simulation of hydraulic fracturing/shearing around a geothermal injection well

Pogacnik, Justin; Elsworth, Derek; O’Sullivan, Michael; O’Sullivan, John

doi:10.1016/j.compgeo.2015.10.003

Cited by 43 publications

(13 citation statements)

References 27 publications

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“…where k 0 is the initial permeability, and k is the current permeability under non-zero stress conditions. In this study, the stress-permeability relationship is developed based on indoor tests and the combination of Equations (15) and 17yields:…”

Section: Flow Equationmentioning

confidence: 99%

“…Conversely, numerical methods provide an alternative approach to study the development and evolution of cracks in geotechnical materials. Many researchers applied several different numerical methods to investigate the crack propagation in rocks and the macroscopic scale effect in permeability of discontinuous jointed rock masses [13][14][15][16][17][18][19]. The finite element method (FEM) is popular and generally accepted in rock mechanics problems due to its convenient and maturity in handling nonlinear solutions and rock heterogeneity.…”

Section: Introductionmentioning

confidence: 99%

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Three-Dimensional Numerical Investigation of Coupled Flow-Stress-Damage Failure Process in Heterogeneous Poroelastic Rocks

Chen¹,

Wei²,

Yang³

et al. 2018

Energies

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The failure mechanism of heterogeneous rocks (geological materials), especially under hydraulic conditions, is important in geological engineering. The coupled mechanism of flow-stress-damage should be determined for the stability of rock mass engineering under triaxial stress states. Based on poroelasticity and damage theory, a three-dimensional coupled model of the flow-stress-damage failure process is studied, focusing mainly on the coupled characteristics of permeability evolution and damage in nonhomogeneous rocks. The influences of numerous mesoscale mechanical and hydraulic properties, including homogeneity, residual strength coefficient, loading rates, and strength criteria, on the macro mechanical response are analyzed. Results reveal that the stress sensitive factor and damage coefficient are key variables for controlling the progress of permeability evolution, and these can reflect the hydraulic properties under pre-peak and post-peak separately. Moreover, several experiments are conducted to evaluate the method in terms of permeability evolution and failure process and to verify the proposed two-stage permeability evolution model. This model can be used to illustrate the failure mechanics under hydraulic conditions and match different rock types. The relation of permeability with strain can also help confirm appropriate rock mass hydraulic parameters, thereby enhancing our understanding of the coupled failure mechanism in rock mass engineering.

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Section: Flow Equationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Three-Dimensional Numerical Investigation of Coupled Flow-Stress-Damage Failure Process in Heterogeneous Poroelastic Rocks

Chen¹,

Wei²,

Yang³

et al. 2018

Energies

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“…This approach is expected to show poor convergence properties and smaller timestep requirements during hydromechanical loading of stress‐sensitive rocks, compared to establishing convergence directly on the poroelastic solution of pressure and stress or displacement. In another implementation, a damage‐based updater for permeability is used to model permeability enhancement during injection for enhanced geothermal applications. However, in that implementation, the flow problem ignores the mechanical coupling arising from the change in volumetric stress, and therefore, it is not clear how the damage‐induced permeability enhancement interacts with the volumetric deformation‐induced porosity and permeability changes, especially when the two types of coupling act against each other.…”

Section: Introductionmentioning

confidence: 99%

Coupled poromechanics‐damage mechanics modeling of fracturing during injection in brittle rocks

Bubshait¹,

Jha²

2019

Numerical Meth Engineering

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Summary Subsurface injection of fluids in a stress‐sensitive naturally fractured rock faces the problem of near‐wellbore fracture evolution and associated changes in rock properties. Numerical modeling of the changes in permeability and poroelastic properties of the near‐wellbore region is challenging due to the coupling between fracture dynamics and poromechanics across multiple length scales of fractures and the host rock. We present a numerical framework to model anisotropic and dynamic evolution in rock properties based on a coupled formulation of fluid flow, rock mechanics, and fracturing, where fracturing‐induced damage is used to update the rock properties. A generalized fixed‐stress method, which accounts for damage‐induced anisotropy in flow and deformation processes, is developed to sequentially solve the equations of flow, mechanics, and fracture evolution. We demonstrate the usefulness of our framework in quantifying the effects of injection rate variability, initial fracture distribution, and in‐situ stress state on the evolution in permeability, elastic stiffness, and the Biot parameters. Our framework does not require the computational mesh to conform to existing or future fractures, allows simultaneous growth of multiple randomly distributed fractures, and can be implemented relatively easily in existing coupled flow‐geomechanics simulators to extend them to model fracturing at the reservoir scale.

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“…The mechanical and hydraulic properties of rock joints are of great significance in rock engineering, including near-field modeling of activated faults [1][2][3], petroleum, shale, and geothermal reservoirs [4][5][6][7][8][9]. Shear stimulation of existing fracture networks is considered a method for permeability enhancement in geothermal systems [10][11][12]. Similar to fault zones (Figures 1(a) and 1(b)) with continuous infilled gouge layers [13,14], weathered joints (Figure 1(c)) are generally filled with undeformed minerals, which can significantly influence the mechanical properties and permeability of rock masses [15].…”

Section: Introductionmentioning

confidence: 99%

Numerical Simulation of Shear Behavior and Permeability Evolution of Rock Joints with Variable Roughness and Infilling Thickness

2018

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The mechanical properties and permeability evolution of sand-infilled rock joints during the shear process is an important issue in rock engineering, such as it pertains to hydraulic fractures filled with proppant. Shear can disrupt the preexisting hydraulic and mechanical equilibrium conditions, thus affecting fluid flow. In this study, we simulate the shear behavior of rock joints with variable roughness and sand infilling thickness using the discrete element code PFC2D. Rock joint roughness is evaluated by the joint roughness coefficient (JRC), and sand infilling thickness is evaluated by a thickness ratio (i.e., ratio of infill thickness to rock height) ranging from 0.02 to 0.20. The results show that peak shear strength decreases with the thickness ratio in a relation that can be expressed by a hyperbolic function. We also measure the permeability evolution during shearing and find that the permeability of infilled rock joints increases with both the thickness ratio and JRC.

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A damage mechanics approach to the simulation of hydraulic fracturing/shearing around a geothermal injection well

Cited by 43 publications

References 27 publications

Three-Dimensional Numerical Investigation of Coupled Flow-Stress-Damage Failure Process in Heterogeneous Poroelastic Rocks

Three-Dimensional Numerical Investigation of Coupled Flow-Stress-Damage Failure Process in Heterogeneous Poroelastic Rocks

Coupled poromechanics‐damage mechanics modeling of fracturing during injection in brittle rocks

Numerical Simulation of Shear Behavior and Permeability Evolution of Rock Joints with Variable Roughness and Infilling Thickness

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