When the reservoir pressure is decreased lower than the dew point pressure in shale gas condensate reservoirs, condensate would be formed in the formation. Condensate accumulation severely reduces the commercial production of shale gas condensate reservoirs. Seeking ways to mitigate condensate in the formation and enhance both condensate and gas recovery in shale reservoirs has important significance. Very few related studies have been done. In this paper, both experimental and numerical studies were conducted to evaluate the performance of CO₂ huff-n-puff to enhance the condensate recovery in shale reservoirs. Experimentally, CO₂ huff-n-puff tests on shale core were conducted. A theoretical field scale simulation model was constructed. The effects of injection pressure, injection time, and soaking time on the efficiency of CO₂ huff-n-puff were examined. Experimental results indicate that condensate recovery was enhanced to 30.36% after 5 cycles of CO₂ huff-n-puff. In addition, simulation results indicate that the injection period and injection pressure should be optimized to ensure that the pressure of the main condensate region remains higher than the dew point pressure. The soaking process should be determined based on the injection pressure. This work may shed light on a better understanding of the CO₂ huff-n-puff- enhanced oil recovery (EOR) strategy in shale gas condensate reservoirs.

The exploitation of tight oil faces significant challenges due to their low permeability, complex pore structures, and rapid production decline rates. Water-based enhanced oil recovery (EOR) methods hold great promise due to their low cost and wellbore safety. However, their effectiveness is significantly constrained by low injectivity and clay swelling. The water huff-n-puff strategy has demonstrated success in the Tuha Oilfield achieving economic production. Nevertheless, deeper mechanistic understanding is needed to elucidate the underlying recovery mechanisms. In this study, the effectiveness of two water-based EOR methods—asynchronous huff-n-puff (ASHNP) and synchronous huff-n-puff (SHNP)—was investigated using core flooding experiments on tight cores from the Santanghu Basin, China. Nuclear magnetic resonance was utilized to analyze oil recovery, characterize water front movement, and evaluate displacement dynamics across multiple huff-n-puff cycles. Results indicate that ASHNP exhibits a water front advancement pattern like power function with a power exponent of 0.67, while all the swept cores exhibited a recovery as high as 40%. In contrast, SHNP demonstrated rapid initial advancement in water front, which is twice that of ASHNP. However, the oil recovery of the rock not adjacent to the inlet is less than 30% and it decreases sharply with increasing depth. The reservoir fluid between two wells would be locked due to the symmetrical injection. Comparative analysis suggests that ASHNP is a more effective water injection strategy for water-wet tight oil reservoirs with deeper water penetration depth and higher sweeping efficiency. These findings provide insights into optimizing water-based EOR methods for tight oil reservoirs.