Coupled multiphase poroelastic analysis of reservoir depletion including surrounding strata

Field observations suggest that although pressure depletion is a local process that only occurs inside aquifers or reservoirs, it results in volume changes that trigger a redistribution of effective stresses in a more extensive domain, which involves the entire overburden and surrounding rocks, extending out to considerable distances. A tabular petroleum reservoir in an infinite or semi-infinite domain is viewed as a macroscopic displacement discontinuity, allowing use of the efficient displacement discontinuity mathematical method to calculate stresses and displacements that arise due to pressure changes. A three-dimensional (3-D) finite element method (FEM) using a multiphase poroelastic formulation is applied to the reservoir. By coupling the displacement discontinuity and FEMs, a 3-D large-scale multiphase poroelastic reservoir can be simulated within an infinite or semi-infinite domain. Numerical examples are given, and results indicate that the influence of the surrounding rocks is an essential coupling factor for the analysis of multiphase flow-induced pressure changes, saturation evolution and reservoir deformation arising from injection or production activities.