| Title | Simulation of Slip-Induced Permeability Enhancement Accounting for Multiscale Fractures |
|---|---|
| Authors | Eren UCAR, Inga BERRE, Eirik KEILEGAVLEN |
| Year | 2015 |
| Conference | Stanford Geothermal Workshop |
| Keywords | numerical simulation, discrete fracture matrix, hydraulic stimulation, shear dilation, matrix permeability |
| Abstract | In geothermal systems, permeability of fractured rocks is one of the most crucial parameters for the reservoirs’ performance. The permeability of rocks can be increased by hydraulic stimulation, which is performed by injecting pressurized fluid into low permeability rock. The increase in fluid pressure induces slip and shear dilation in the fracture surfaces and it leads to a permanent permeability enhancement. In the present study, we subdivide a fractured rock into two parts as fractures and matrix. Fractures are large-scale discontinuities that contribute dominantly to flow through the rock. The remaining media is represented as matrix, which possibly includes small-scale fractures, but has relatively low permeability. Literature on hydraulic stimulation has previously disregarded matrix-fracture interaction, applying either discrete fracture network models or continuum representations of the reservoir. Ignoring the flow in the matrix may result in an overestimate of the permeability enhancement, while continuum models fails to represent the heterogeneity of the flow pattern. This paper presents a model for slip-induced permeability enhancement that couples a joint deformation model for slip of existing fractures to a model for fluid flow that accurately represents flow in dominating fractures while also incorporating the effect of the permeability of the surrounding medium. The flow simulations are based on applying the Discrete Fracture Matrix module of MATLAB Reservoir Simulation Toolbox. Motivated by realistic scenarios, several fracture networks are generated and discretized. The impact of matrix permeability on the shear dilation of fractures and the global flow of the fractured porous medium is investigated by numerical experiments based on realistic reservoir parameters. It is shown that including the effect of small-scale fractures may result significantly different global flow behavior and fracture dilation in the fractured porous medium. Therefore, our simulation approach to model hydraulic stimulation would provide a more realistic prediction of permeability enhancement in the geothermal reservoirs. |