Multiple Physicochemical Process-Coupled Numerical Simulation for CO2 Storage in Depleted Oil Reservoirs

Summary CO2 storage in depleted oil reservoirs plays a vital role in sequestering greenhouse gases and enhancing the recovery of remaining underground oil. However, this process exhibits complex behaviors, involving multiple physicochemical processes. Although existing simulators have been used to study CO2 storage, they have limitations in addressing the complexities involved, such as phase equilibrium, chemical reactions, and heat transfer. To address these limitations, we present the development of a novel numerical simulator for CO2 storage in depleted oil reservoirs. First, we derive the governing equations for phase equilibrium and the thermo-hydro-chemical (T-H-C)-coupled model, then outline in detail the corresponding solution method. We present several cases to validate the accuracy and reliability of the developed simulator, then apply the simulator to a case study of CO2 storage in depleted oil reservoirs to assess its practical application. Based on the simulation results, we analyze the evolutions of the flow field, CO2 storage efficiency, and crude oil recovery. In addition, we analyze the effects of key controlling factors, such as pressure difference, reservoir temperature, and well spacing, on CO2 storage efficiency and crude oil recovery. The results indicate that reasonably increasing the pressure difference between injection and production wells can enhance both CO2 storage and crude oil recovery. Low-temperature reservoirs are preferable for enhancing CO2 storage, whereas high-temperature reservoirs are more effective for improving crude oil recovery. Increasing the well spacing significantly enlarges the sweep zone, which benefits both CO2 storage and crude oil recovery. Finally, we present a 3D case to demonstrate the developed simulator’s capability for 3D simulations and to analyze the effects of gravity. The 3D simulation results also imply the necessity of considering gravity in CO2 storage.