Optimization of Oil Recovery and CO2 Sequestration in Tight Reservoirs During CO2 WAG Flooding With Hydraulic Fracture

Tight oil reserves are of great significance in oil exploration and development in China. CO2 flooding is promising in tight reservoirs due to its high mobility and better injectivity, and water alternative gas (WAG) flooding could improve sweep efficiency and oil recovery, which is extensively used. However, its injectivity in tight reservoirs is limited. The feasibility of improving CO2-water alternations performance in tight reservoirs by hydraulic fracturing was investigated in this study. In this paper, numerical reservoir simulation was conducted to simulate CO2 WAG flood process with typical reservoir characteristics and hydraulic fracture properties of the YC formation. The optimization of hydraulic fracturing during CO2 alternative water injection process were performed with numerical simulation, response surface and multiple response optimization method, which could be done with acceptable accuracy by performing a limited number of runs, hence, reducing the engineering time, effort and money. With the simplified equation between the NPV or CO2 storage and different hydraulic fracture parameters, operators can determine the best combination of all the factors for different objectives. The results show that moderate fracture length, large fracture height and small water-gas ratio could achieve the optimal economic benefits and CO2 storage in low permeability reservoirs. This work can provide a better understanding of the physical mechanisms and key parameters affecting the effectiveness of CO2 WAG flooding for enhanced oil recovery in the tight formation.