Volume 57

ECPA Module: An Advanced Compositional Model for Enhanced Gas Recovery and CO2 Storage in Porous Media Using an Association Equation of State Wei Xiong, Yu-Long Zhao, Shao-Mu Wen, Li-Li Liu, Zheng-Lin Cao, Xin Huang, Lie-Hui Zhang

Abstract

Compositional simulation plays a vital role in understanding the behavior of multiple components within the captured CO2, such as impurities or various injection scenarios, helping optimize the storage process and ensure its long-term safety and effectiveness. A new ecpa module in MATLAB Reservoir Simulation Toolbox (MRST) has been developed based on the electrolyte cubic-plus-association equation of state (e-CPA) to simulate enhanced gas recovery and CO2 storage with CO2 injection. The ecpa module combines Fickian diffusion, Langmuir adsorption, and the e-CPA equation of state to accurately describe phase equilibria and transport phenomena in complex systems such as CO2-CH4-H2O-NaCl system. The e-CPA equation of state demonstrates superior accuracy over conventional models (e.g., PR EoS) in predicting vapor-liquid equilibria and phase behavior across a wide range of pressures and temperatures. For the CO2-H2O system, the e-CPA model achieves lower average absolute relative deviations (AARD: 5.93% for CO2 solubility, 9.54% for H2O content in gas) compared to Tsivintzelis’s model (AARD: 8.52% and 15.55%, respectively). In the Barnett shale case study, accounting for sorption and diffusion increases CHâ‚„ mass flow rates by 15-20%, highlighting their critical role in unconventional reservoir simulations. Comparisons with ECLIPSE and CMG (GEM) reveal strong agreement in CO2-CH4 mixing behavior, recovery factors, and breakthrough times. MRST (e-CPA) matches CMG’s predictions for CH4 production and CO2 storage, validating its matrix-fracture coupling and thermodynamic consistency. The ecpa module, consolidated into the MRST framework, provides an open-source, state-of-the-art tool for simulating multicomponent flow in geological carbon storage, shale gas recovery, and enhanced hydrocarbon extraction. Its release in MRST 2025a will enable broader academic and industrial adoption, fostering advancements in subsurface energy systems.

Keywords CCUS, enhanced gas recovery, CO2 storage, brine, dual-permeability, e-CPA equation of state