Optimization of Gas Huff-n-Puff for Enhanced Oil Recovery in Shale Condensate Reservoirs in Jiyang Depressions, China

Abstract

The shale condensate reservoirs hold vast reserves, suggesting significant development potential, yet low recovery remains a major industry obstacle. Based on a field case from the Jiyang depression, a method using gas cycling to improve the recovery rate of shale condensate gas reservoirs has been proposed. By integrating EDFM (embedded discrete fracture model) and nonequilibrium initialization technique, a model for shale condensate reservoir was established. The study conducted a comprehensive analysis of the impact of various pressure control strategies on production capacity, compared the effects of different gas injection medium and modes on enhancing recovery factor, and on this basis, optimized the CO₂ huff-n-puff parameters. The research results demonstrated that (1) from the perspective of choke management, it is most appropriate to control BHP drop rate at 200 kPa/month. (2) By comparing different injection medium and mode, the CO₂ huff-n-puff serves as the optimal gas injection design. (3) The optimal CO₂ injection scheme is as follows: injecting after the third year of depletion development, with a single injection volume of 360 × 10⁴ m³, a gas injection rate of 10 × 10⁴ m³/d, a soaking period of 10 days, 6 huff-n-puff cycles. After parameter optimization, the recovery rate increased by 17.63%. It comprehensively analyzes and optimizes the parameters of the gas injection scheme through numerical simulation methods, providing valuable guidance and reference for the development of gas injection techniques in shale condensate reservoirs.