Influencing Factors Analysis and Parameters Optimization of CO2 Huff and Puff for Shale Oil

To reveal the main controlling factors of enhanced oil recovery by CO2 huff-n-puff in shale oil reservoirs and determine reasonable CO2 huff-n-puff development parameters, a compositional numerical simulation was performed to evaluate the enhanced oil recovery effects. The study investigated the influence of various development parameters on the CO2 huff-n-puff process, including the CO2 injection volume, injection rate, soaking time, number of huff-n-puff cycles, and injection methods. The results demonstrate that the CO2 injection volume represents varying degrees of reservoir energy enhancement, with the recovery rate increasing more slowly as the injection volume rises. The gas injection rate reflects the speed of energy replenishment in the reservoir; compared to low-speed injection, high-speed injection leads to an earlier transition to the soaking phase, but excessively high rates may result in insufficient contact between CO2 and crude oil. The production enhancement effect improves with longer soaking times, but the rate of increase slows down after 30 days of soaking. The recovery rate continuously increases with more huff-n-puff cycles, with the highest initial recovery observed during the first cycle. Subsequent cycles exhibit a gradual reduction in incremental recovery, eventually stabilizing. Based on numerical simulation optimization, the optimal CO2 injection volume is 600,000 cubic meters, the optimal injection rate is 20,000 cubic meters per day, the optimal soaking time is 30 days, and the optimal number of huff-n-puff cycles is four. The research provides significant guidance for improving shale oil recovery through CO2 huff-n-puff operations, as well as for the design and effective implementation of gas injection development strategies.