Abstract: To address the issues of high production decline rate and low recovery rate in the early stage of tight oil development,considering the rock and fluid properties of Fuyu tight oil reservoir, numerical simulation methods were used to study the effects of injection timing and injection pressure on the effect of CO₂ huff-n-puff.The engineering parameters were optimized, the characteristics of reservoir pressure distribution and interfacial tension distribution are analyzed,the operability of CO₂ huff-n-puff development of tight oil is studied.The results indicate that CO₂ huff-n-puff should be implemented when the oil reservoir pressure coefficient drops to around 0.65.At this time,CO₂ can fully contact with crude oil,which is beneficial for the dissolution,thereby improving the recovery efficiency.As the injection pressure approaches the minimum miscible pressure,CO₂ in a separate phase enters the matrix,making full contact with the tight oil deep within.The dissolved miscible phase improves the development effect.After reaching dissolution equilibrium,the interfacial tension between CO₂ and tight oil increases rapidly over time,the time of well shut-in can be determined at this moment.The optimal engineering parameters for CO₂ huff-n-puff recovery in this study are:the injection volume is 8000 t,the injection rate is 120 t/d, the injection pressure is 27 MPa,and the time of well shut-in is 30 d. According to this scheme, the increase of crude oil production is calculated to be 3 084 t,and the oil replacement ratio is calculated to be 0.39. The in-situ test of horizontal well also confirms that the application of CO₂ huff-n-puff technology in Fuyu tight oil reservoir increased the recovery rate by 1.38 to 3.33 percentage points.The research results are of great significance for further expanding the application of CO₂ huff-n-puff technology in tight oil reservoirs.

Key words: tight oil, CO₂ huff-n-puff, parameter optimization, pressure distribution, interfacial tension, Fuyu Reservoir