The primary objective of this study is to address all known causes of productivity declines in unconventional shale gas formations with horizontal multifractured wells and to develop a fully coupled geomechanical/flow simulation model to simulate these production conditions. The model mimics the effect of depletion-induced in-situ stress variations on productivity by taking into account several phenomena, such as stress-dependent matrix and natural-fracture permeability and reduction in fracture conductivity because of fracture-face creep and proppant crushing, deformation, and embedment.
Model Formulation
Reservoir Matrix. The gas-storage mechanism in a shale gas reservoir is conceptually different from that of a conventional reservoir. Natural gas is adsorbed on the organic matter present in shales and, in some cases, on certain clay minerals. This adsorbed-gas layer further constricts the area for flow through the pore structure, thus reducing the effective pore radius.
