Abstract: To address the decline in single-cycle recovery and the slowdown in cumulative recovery increase during the later stage of gas huff-n-puff,CO₂,methane,ethane,and propane were selected to carry out extraction experiments using a high-temperature and high-pressure reactor,and gas chromatography was employed to determine the oil components extracted with different gases.Combined with the viscosity changes of the remaining oil after extraction,the molecular mass selectivity of different gases was compared.Moreover, CO₂ huff-n-puff and CO₂-alternating-alkane huff-n-puff experiments were conducted to evaluate the recovery enhancement effects of different injection methods.The experiments revealed that propane has the highest extraction rate,reaching 62.60% at 30 MPa,ethane andCO₂ achieve 53.07% and 49.25% respectively at 30 MPa,and methane has the poorest extraction ability,only 20.47% at 30 MPa.Propane shows the most uniform molecular mass selectivity,extracting all oil components,and ethane preferentially extracts light and medium components,mainly those within C₂₅,while CO₂ and methane mainly extract light components within C₁₅.The huff-n-puff experimental results showed that CO₂-alternating-alkane huff-n-puff enhances recovery by over 10% compared to CO₂-only huff-n-puff,with significant improvements in later-stage recovery per cycle.This research offers valuable insights for enhancing tight oil recovery.

Key words: tight oil, gas huff-n-puff, molecular mass selectivity, recovery enhancement, extraction rate