Coupled hydro-mechanical-chemical simulation of CCUS-EOR with static and dynamic microscale effects in tight reservoirs

Abstract

Tight reservoir can be potentially stimulated via CO2 injection and serves as potential sites for CO2 storage. However, simplifying flow mechanisms in hydro-mechanical-chemical coupling simulations can cause significant deviations in forecasting productivity and storage performance. In this study, a coupled hydro-mechanical-chemical model with both static and dynamic microscale effects was established for the first time. We characterized the impact of micro- and nanopores on the multicomponent thermodynamics and multiphase flow of CO2 and in-situ oil by considering the critical property shift, capillary pressure, and boundary slip. The matrix and hydraulic fracture system were constructed based on the embedded discrete fracture model (EDFM). The effect of mineral reaction in the matrix and time-varying width and permeability of propped fractures were also involved in the model to address practical field-scale problems. An iteratively coupled scheme was used in a more comprehensive model to compute the flow and mechanical parameters at each time step, with the impact of different degrees of microscale effects studied by changing the proportions of micropores and nanopores. Two fluid models with different minimum miscible pressures (MMPs) were used to simulate the miscible and immiscible production processes. The stress sensitivity was analyzed based on the Biot poroelasticity theory and time-varying fracture conductivity, with the results suggesting that stress sensitivity can reduce overall production by slower outward pressure movement but can inhibit gas channeling and breakthrough to a certain extent. The detailed analysis of microscale effects, miscibility, and stress sensitivity in this work is of practical significance for tight reservoir development and CO2 geological storage.