Optimization of CO2 flooding under dual goals of oil recovery and CO2 storage: Numerical case studies of the first-ever CCUS pilot in Changqing oilfield

Abstract

CCUS (CO2 capture, utilization, and storage) is an important way to reduce carbon emissions and is increasingly applied in the development of hydrocarbon resources. It is crucial to develop proper engineering parameters to achieve the dual goals of enhanced oil recovery (EOR) and CO2 storage. This paper reports systematic numerical case studies of the first-ever CCUS pilot project at Changqing Oilfield to identify further improvement opportunities compared to the current development strategy. The targeted reservoir is located in the Huang 3 (H3) block and is characterized by ultra-low permeability (<1 mD), low oil production (<5 tons/day), and miscible and near-miscible flooding. A three-phase compositional reservoir model is established and a typical well group, consisting of one injector and eight producers, is selected to perform the numerical case studies. We investigate the influence and sensitivity analysis of engineering parameters on oil production and CO2 storage in ultra-low permeability sandstone reservoirs. The results indicate that the well pattern, the timing of switching to water-alternating-gas injection, the gas-water slug size ratio, and the injection rate are controlling factors to achieve favorable performance. The simulation results show that by using optimized engineering parameters, the oil recovery factor of the target reservoir is significantly increased by 25% and the CO2 storage efficiency is increased by 60%. Finally, an optimized development plan is obtained based on the actual conditions of the target reservoir. The reported case studies are supposed to provide insights into the optimal design and operation of CO2 utilization and storage in hydrocarbon reservoirs.