Abstract
Dual-permeability models were developed to simulate the permeability of fractured reservoirs, including connected fracture networks, fracture corridors, unconnected fractures, and nonconductive fractures. The opening of nonconductive fractures was simulated based on either fracture dilation caused by shearing or fracture opening caused by tensile failure. In this way, the permeability change of all fractures (both conductive and nonconductive) can be simulated responding to the change in the effective stresses caused by reservoir depletion and/or injection. It is assumed that the conductive fractures possess a base-level permeability before production and injection, which corresponds to the residual permeability of the fractures. This implies that the apertures of fractures have closed to their irreducible limit at the reservoir depth and initial conditions, but minimum hydraulic apertures still exist.
The newly developed dual-permeability modeling technique was applied to an areal model of a fractured/faulted reservoir containing 49 wells, which simulated 36 months of production with waterflooding in the presence of fracture sets and faults. This study was to understand the geomechanical influences on flow rates at individual wells, which were assessed with the spatial and temporal correlations in flow rates at pairs of wells. This example revealed the ongoing interaction between pressure, production/injection rate, permeability, and deformation in the fractured reservoir. The stress direction has an important effect on the evolution of fracture permeability. The sliding of faults induced significant permeability enhancement of the fractures around the faults. Long-range rate correlations were predominantly related to geomechanical links; short-range rate correlations were mainly related to high permeable channels.
