Semi-Analytical Modeling of Multi-Mechanism Gas Transport in ShaleReservoirs with Complex Hydraulic-Fracture Geometries by the BoundaryElement Method

摘要

This work proposes a novel boundary-element based approach to model fluid transport in unconventionalshale gas reservoirs with complex hydraulic fracture networks.The fluid flow model employed in this workconsiders multiple fluid transport mechanisms identified in in gas transporting process in shale nanoporesincluding diffusion,sorption Kinetics,Knudsen diffusion,and sorbed-phase surface diffusion.Accordingly,two governing partial differential equations(PDEs)are written for free and sorbed gases.In the proposedmethod,boundary integral formulations are analytically derived using the fundamental solution of theLaplace Equation for two governing nonlinear PDEs and Green's second identity.The domain integralsconsidering the nonlinear terms due to multi-mechanism effects,are transformed into boundary integralsemploying the dual reciprocity method(DRM).The resulting boundary integral equations for free andsorbed gas later are solved in terms of a series of discrete nodes after coupling with fracture flow model.Thevalidity of proposed solution is verified using several case studies through comparison with a commercialfinite-element numerical simulator COMSOL.