In tight oil reservoirs, water huff and puff serves as an effective recovery technique by replenishing formation energy and stabilizing production of volumetric fractured horizontal wells. However, fully coupled flow–geomechanics models currently available are limited in accounting for nonlinear flow characteristics and impose strict mesh constraints under complex geometry conditions. To address these challenges, a numerical model integrating fully coupled flow and geomechanics is established. The model incorporates nonlinear flow behavior and is constructed on the three-dimensional projection-based embedded discrete fracture model (3DpEDFM) to characterize four-dimensional in situ stress evolution during long-term waterflooding and water huff and puff processes in tight reservoirs. Notably, this study presents the first integration of 3DpEDFM with the virtual element method for coupled flow and geomechanics, enabling accurate simulation of complex fracture–matrix interactions without relying on conforming grids. The governing flow and mechanical equations are, respectively, discretized by the finite volume and virtual element methods, leading to a fully coupled nonlinear system that is solved using Newton–Raphson iterations. The model's reliability is demonstrated by benchmarking against the classical Mandel problem and numerical outputs from the commercial simulator tNavigator under idealized scenarios. A case study is further designed according to the geological features of a representative tight reservoir in China, involving long-term waterflooding and water huff and puff implemented via a volumetric fractured horizontal well injection–production system. The simulation results are used to investigate changes in flow behavior and in situ stress evolution. A reduction in horizontal principal stress differences within the stimulated reservoir volume is achieved through the application of water huff and puff, which in turn promotes the development of a complex fracture network and boosts horizontal well productivity.
Zhou et al. (Fri,) studied this question.