Study on multiphase flow behavior and parameters for CO2 storage in depleted oil and gas reservoirs

In CO₂ storage within depleted oil and gas reservoirs, the primary focus is on increasing production, aiming to achieve higher oil recovery with the least amount of CO₂ injection, which contradicts the purpose of carbon storage. The research on improving the performance of CO₂ enhanced oil recovery and storage has not addressed the optimization of CO₂ migration range, neglecting the impact of CO₂ migration on injection and well placement design. This article aims to improve the CO₂ storage and migration as the primary objective, establishing a three-phase seepage-heat transfer coupling numerical model, revealing the fluid distribution patterns in reservoir. Comparing the effects of injection and well parameters on CO₂ storage capacity, oil recovery and CO₂ migration. The results indicate that low-temperature and high-speed injection is beneficial for CO₂ storage, increasing well spacing is advantageous for CO₂ migration, and horizontal wells should be preferred during well placement, followed by the up-injection down-production 3 wells pattern. On the basis, multi-objective optimization is carried out for CO₂ storage capacity, oil recovery and CO₂ migration range. In research conditions, with the same amount of CO₂ injected, the storage capacity and migration range increase by 95.2 % and 12.1 %, respectively, while the decline in oil recovery is effectively mitigated. This study expected to provide a theoretical basis for CO₂ storage in depleted oil and gas reservoirs.