Experimental Study and Field Application of CO2 Huff-And-Puff for Enhanced Oil Recovery in Fractured Volcanic Reservoirs

To address the challenges of rapid production decline and low recovery efficiency in fractured volcanic reservoirs caused by low matrix permeability and complex fracture networks, this study systematically investigates the development characteristics and key controlling factors of CO2 huff-and-puff(HnP) in such reservoirs through integrated long-core physical simulations and field tests. The research shows that CO2 HnP can effectively improve the oil recovery of volcanic rock reservoirs. However, the development effect mainly depends on the first three cycles, with the oil production accounting for 89.8% of the total output, showing an obvious production decline characteristic. CO2 injection volume and production rate are the major factors affecting the oil recovery. However, when the CO2 injection volume exceeds 0.2 pore volume(PV) reduces the oil-CO2 exchange ratio below 0.2, diminishing economic viability. An optimal soaking time of 24 h was identified, beyond which additional recovery gains are marginal. The field test results show that CO2 HnP can effectively supplement formation energy. The incremental oil production well during the stage reaches 935 tons, the effective period is 285 days, and the oil displacement efficiency is 1.33, indicating good technical and economic performance.