Enhanced CO2 Use and Storage in Water-Invaded Gas Reservoirs: Insights from Innovative In-Situ Experimental Investigations

Abstract This study investigates the injection of CO2 into gas reservoirs for enhanced methane recovery and long-term CO2 storage. It aims to understand fluid migration and the evolution of CO2 post-injection under in-situ reservoir conditions. By analyzing these dynamics, the study provides insights into optimizing CO2 use and improving storage efficiency. We developed an innovative experimental method to distinguish CO2 from methane under reservoir conditions using X-ray to detect n-butane iodide, extracted in superficial CO2, to indicate the concentration of CO2. Using this approach, experiments were conducted to examine gas-liquid migration patterns, CO2 mass transfer and diffusion, and the impact of gravity. The method enabled precise measurement of CO2 concentration profiles under varying injection volumes and conditions, allowing for a comprehensive understanding of fluid behavior in water-invaded gas reservoirs. In water-invaded gas reservoirs, gas expansion during depletion (pressure reduction from 14 to 7 MPa) discharged 40% of the movable water, increasing to 79% with CO2 injection. Although gravity contributed to uniform water invasion profiles, it also reduced the efficiency of gas displacement by 8%. During CO2 displacement of methane, a distinct mixing zone formed, expanding with increasing injection, but ended with a fixed maximum length moving forward as injection proceeds. This highlighted the effectiveness of CO2 in displacing methane while simultaneously facilitating storage. Gravity played a crucial role in fluid distribution, significantly altering CO2 diffusion, CO2 plume behavior and water migration patterns after injection. This study introduces a novel experimental approach for tracking CO2 and fluid migration under realistic reservoir conditions. By quantitatively measuring the length of the mixing zone and migration of its concentration profile, the findings provide insights into optimizing CO2 injection strategies, enhancing methane recovery, and improving the long-term efficiency of CO2 storage. By offering practical guidance for field applications, this work contributes to the advancement of CO2 utilization in gas reservoirs.