Application of CO₂/N₂ Compound Huff ‘n’ puff Technology in Deep Heavy Oil Reservoirs

Lukqin Triassic heavy oil reservoir belongs to deep heavy oil reservoir. After more than 20 years of technical research and field test, a ‘combination of secondary and tertiary oil recovery’ technique series for heavy oil extraction has been established. In the past several years, large-scale implementation of N 2 huff ‘n’ puff for enhanced oil recovery has yielded positive results. However, the diminishing effectiveness of multiple cycles of huff ‘n’ puff has become increasingly prominent. To improve development efficiency, PVT phase behavior experiments (including gas injection swelling experiment and pseudo-bubble point pressure test), numerical simulation and field test were conducted. Additionally, parameters of huff ‘n’ puff process has been optimized. The experimental results of PVT phase behavior show that CO 2 significantly enhances the volume expansion of heavy oil and demonstrates superior viscosity reduction compared to N 2 ; In comparison to N 2 , CO 2 injection into heavy oil provides a larger foam oil range, facilitating the formation of foam oil during huff ‘n’ puff. Numerical simulation results indicate that the optimal parameters for CO 2 /N 2 compound huff ‘n’ puff after multiple cycles of N 2 huff ‘n’ puff are: the ratio of N 2 :CO 2 :N 2 is between 1:4:1 and 1:10:1, the injection sequence is N 2 -CO 2 -N 2 , the injection volume is 4×10 5 m 3 , the injection speed is greater than 5×10 4 m 3 /d, and the soaking time is 20 d. A total of over 20 wells have implemented CO 2 /N 2 compound huff ‘n’ puff in this reservoir, resulting in significant water control and oil enhancement, effectively improving the development performance of multiple cycles of huff ‘n’ puff. The research verifies the feasibility of implementing CO 2 /N 2 compound huff ‘n’ puff and provides practical guidance for optimizing CO 2 /N 2 compound huff ‘n’ puff in industrial applications.