Abstract
The effect of geomechanics is crucial in the modeling of fractured reservoirs since fractures can be more stress-sensitive than the rock matrix. In fractured reservoirs, the microscale fractures are often homogenized into the matrix continuum leading to matrix permeability anisotropy. The embedded discrete fracture model (EDFM) is becoming increasingly popular for numerical simulation of fractured reservoirs and has been successfully employed in the simulation of coupled geomechanics and flow systems. However, the anisotropic permeability of matrix cannot be considered in traditional EDFM. An approach of coupled geomechanics and flow modeling is proposed for fractured reservoirs considering anisotropic matrix permeability. In order to calculate the fluid exchange between fractures and rock matrix in an anisotropic formation, an integrally embedded discrete fracture model (IEDFM) is used. The geomechanics model of the proposed approach uses an equivalent continuum approach, which introduces an equivalent material to represent the overall deformation of the fractured rock under normal and shear stresses. The constitutive relations of the equivalent continuum are derived rigorously from stress-strain analysis, where the stress-dependent moduli of natural fractures are included. The coupled geomechanics and flow system is solved using the fixed-stress split iterative coupling strategy with the dynamic hydraulic parameters of matrix and fractures updated separately. Several examples are performed to demonstrate the applicability of the proposed approach for modeling the coupled geomechanics and flow system in fractured reservoirs considering anisotropic permeability. The effect of anisotropy is investigated, which indicates that the dynamic behavior of a fracture is highly orientation-related due to initial stress anisotropy and matrix permeability anisotropy. Simulations also show that the anisotropic matrix permeability affects the compaction in the reservoir domain, which reflects on the performance of production.
Highlights
During the exploitation of hydrocarbon reservoirs, pore pressure changes caused by production can lead to rock compaction, which in return affects the hydraulic properties such as porosity and permeability
The effect of geomechanics is more crucial since fractures can be more stress-sensitive than the rock matrix
Based on the dual continuum concept, a dual porosity poroelastic theory (DPP) is proposed [5,6,7], where the Geofluids effective stress law is modified to capture different extents of deformation of the rock matrix and fractures. en, Wittke [8] rigorously derived the constitutive model for a fractured rock using the concept of equivalent continuum
Summary
During the exploitation of hydrocarbon reservoirs, pore pressure changes caused by production can lead to rock compaction, which in return affects the hydraulic properties such as porosity and permeability. Series of attempts to simulate coupled geomechanics and flow problems in fractured reservoirs using the dual continuum concept and the dual porosity poroelastic theory are performed [9,10,11,12,13,14,15]. A coupled geomechanics and flow model for the simulation of fractured reservoirs considering matrix anisotropy is proposed in this study. E flow simulation uses the IEDFM to account for the fluid exchange between fracture control volumes and the rock matrix with anisotropic permeability. An equivalent continuum approach is used to derive the stiffness matrix required in the finite element method, where an equivalent material is introduced to represent the overall deformation of fractured rock. Validation and detailed discussion of the IEDFM in anisotropic formations can be found in the work of Shao et al [32]
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