Regular Article

Co-optimization of oil recovery and CO₂ storage for cyclic CO₂ flooding in ultralow permeability reservoirs

¹ CNPC Technology and Economics Research Institute, Beijing 100724, China
² School of Energy Resources, China University of Geosciences, Beijing 100083, China
³ Research Institute of China National Offshore Oil Corporation, Beijing 100027, China
⁴ Research Institute of Petroleum Exploration and Development, Beijing 100083, China

^* Corresponding author: 149658753@qq.com

Received: 29 July 2017
Accepted: 17 July 2018

Abstract

Cyclic CO₂ flooding is an efficient method to enhance oil recovery in ultralow permeability reservoirs. As the demand for low carbon economy development, co-optimization of CO₂ storage and utilization should be considered. In this research, initially a comprehensive optimization method was proposed, which co-optimize oil recovery and CO₂ storage by different weighting factors. Then, a series of core flooding experiments were performed using the core samples collected from Changqing oilfield, which is a ultralow permeability reservoir with heterogeneity and micro-cracks, CO₂ injection parameters of slug size and Injection-Soaking Time Ratio (ISR) were optimized. The results revealed that the optimal injection parameters changed for different optimization objectives. In the case where equal important to oil recovery and CO₂ storage were considered, the optimum CO₂ injection parameters in the ultralow permeability reservoirs were 0.03PV for slug size and 1:1 for ISR. Comparing the method of oil recovery optimization (ω ₁ = 1) to co-optimization of oil recovery and CO₂ storage (ω ₁ = ω ₂ = 0.5), oil recovery was reduced by 8.93%, CO₂ storage was significantly increased by 25.85%. The results provide an insight into parameter optimization of CO₂ enhanced oil recovery design.