Field observations and analytical modeling of fracture network permeability in hydrocarbon reservoirs

Abstract Faults, and composite fault and joint networks are common structural and hydrologic elements in reservoirs. The structural and hydrologic architecture of faults is complicated by the formation of striated slip surfaces, cataclasite and gouge, deformation of the adjacent wall rock, and hydrothermal mineralization. A prototype, analytical computer algorithm is presented to model faults as anisotropic fluid conduits, and joints as isotropic conduits. The permeability tensor of the rock mass is determined by the volume averaged contribution of each fault and joint in the population via tensor rotation from the local coordinate system of each fracture to the global, geographic reference frame. Permeability across the fracture walls and the permeability of the rock matrix are also considered in the algorithm. Application to a synthetic network of conjugate fractures illustrates that the anisotropic surface texture of faults is a fundamental feature determining the permeability of the rock mass. Modeling is also conducted to illustrate how changes in the stress tensor affect permeability anisotropy.