A Coupled Geomechanics and Flow Model for Enhanced Gas Recovery and CO2 Storage in Shale Reservoirs

Abstract

Summary A fully coupled multicomponent flow and geomechanics model, which incorporates viscous flow, Kundsen diffusion, molecular diffusion, multi-component adsorption/desorption and geomechanics effect, is developed to study the enhanced gas recovery and CO2 storage in fractured shale reservoirs. Specifically, an efficient hybrid model, which consists of single porosity model, multiple porosity model and Embedded Discrete Fracture Model (EDFM), is adopted to model multiscale fractures. In flow equations, the Peng-Robinson EOS, extended Langmuir isotherm and Fick’s Law are adopted. In geomechanical portion, the proppant nonlinear deformation is considered. Then, the mixed space discretization (i.e., finite volume method for flow and stabilized XFEM for geomechanics) and modified fixed stress sequential implicit methods are applied to solve the proposed model. The robustness of the proposed method is demonstrated through several numerical examples, and a comprehensive analysis of the mechanisms for enhanced gas recovery and CO2 storage in fractured shale gas reservoirs is carried out, which takes into account Kundsen diffusion, molecular diffusion, multi-component adsorption/desorption, proppant nonlinear deformation, and different injection strategies including huff-n-puff scenario. Results show that CO2 injection is an effective approach for enhancing shale gas recovery, and the injected CO2 can be stored as free, adsorbed, and dissolved state. Besides, we can also find that stimulated reservoir volume, natural/induced fractures, hydraulic fractures, various transport/storage mechanisms and injection strategies have significant effects on enhanced gas recovery and CO2 storage in fractured shale reservoirs.