Volume 33: CCUS Technologies for the Carbon Neutrality: Part I

Characterization of CO2 Sequestration and Enhanced Oil Recovery in Near-depleted Edge-Bottom Water Reservoirs Zhi Liu, Jianchun Xu



Geological sequestration sites for CO2 include depleted oil and gas reservoirs, deep aquifers, coal seams and deep-sea strata, etc. Among them, near-depleted oil and gas reservoirs are ideal sites for long-term CO2 storage due to complete and safe trap closure and clear understanding. As the production of typical edge-bottom water reservoirs entered the high water cut stage, it becomed more difficult to further increase the recovery rate in conventional water drive development. We investigated the control factors of the CO2 enhanced oil recovery and storage. Firstly, the typical characteristics of the reservoir were extracted to establish a conceptual model for numerical simulation and fit the reservoir production dynamics. We have studied the modes of CO2 enhanced oil recovery (EOR), including water drive, gas drive, gas-top drive, water alternating gas (WAG) and bi-directional drive. The highest recovery was obtained with 39.04% for the bi-directional drive. Different injection pressures were then tested, combined with recovery and storage, we controlled the injection pressure close to the initial reservoir pressure at 14,000 kPa. Secondly, we have analysed the characteristics of the storage stage, including reservoir pressure maintenance and injection rates. It was assumed that the reservoir fracture pressure was 1.4 times the initial pressure, beyond which the CO2 would leak. The maximum storage weight obtained in this case is 25.683 million tonnes. Meanwhile, the slower the injection rate, the more CO2 can be stored. We proposed a production scheme for near-depleted edge-bottom water reservoirs and analyzed the main parameters for CO2 storage, providing some guidance for the siting and development of similar reservoirs.

Keywords CO2 storage, CO2-EOR, Near-depleted edge-bottom water reservoir, Numerical simulation

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