Accelerating geological gas storage simulations: A novel and efficient gases-brine phase equilibrium calculation algorithm

Geological carbon sequestration (GCS) and gas energy storage in water-bearing formations, one of the most promising methods of Carbon Capture, Utilization, and Storage (CCUS), offers a permanent and reliable solution for mitigating climate change. Although reservoir simulation is widely employed to evaluate GCS projects, its high computational cost, driven by the complexity of phase equilibrium calculations, poses a challenge to obtain timely assessments. To address this, we propose an innovative Adaptive Saturated Composition (ASC) algorithm to bypass unnecessary stability analyses, therefore reducing the computational expenses of gases-brine phase equilibrium calculations in GCS simulation. The ASC algorithm relies on pre-calculated binary gas-brine data and is extended to multicomponent systems (CH₄, N₂, H₂S, CO₂) through a mixing rule. We performed extensive tests under varying underground conditions, demonstrating that the proposed ASC algorithm offers superior efficiency, accuracy and scalability compared to existing algorithms. It eliminates over 99.9 % of unnecessary stability analyses in binary systems and reduces their frequency by over 93 % in multicomponent gas systems. Remarkably, the ASC algorithm achieves accurate detection of phase transitions across all tested scenarios. Moreover, it is widely applicable in most of water-bearing geological gas storage scenarios, including natural gas storage, geological CO₂/air energy storage, and CO₂-based geothermal systems.