Insights into Enhancing Shale Oil Recovery Postfracturing with CO₂ Huff and Puff and Elastic Depletion Development Strategies

Abstract

After hydraulic fracturing, shale reservoirs often undergo rapid production declines during depleted development, resulting in a low cumulative production. CO 2 huff and puff emerges as a promising method to enhance shale oil recovery postfracturing. This study conducted independent experiments to investigate multistage depressurization elastic depletion development and the CO 2 huff and puff method in shale oil. The effects of injection pressure, temperature, fractures, and other parameters on the CO 2 huff and puff recovery were analyzed using nuclear magnetic resonance (NMR). The impact of the CO 2 huff and puff on crude oil in different pores was elucidated. The results show that the fluid mobility of the shale reservoir is poor, with the recovery rate of elastic depletion development being less than 10%. Conversely, a CO 2 huff and puff can enhance the recovery rate by up to 20%. The recovery rate of shale oil through a CO 2 huff and puff correlates positively with injection pressure and temperature. The initial cycle of huff and puff contributes the most to crude oil recovery, reaching up to 50%. Under equivalent parameter conditions, the presence of fractures can increase the CO 2 huff and puff efficiency by 20% compared to the matrix core. Combined with NMR experiments, the lower limit of pores that oil can be produce in matrix and fracture cores in elastic depletion development is 200 and 150 nm, respectively. In the context of CO 2 huff and puff development, these values decrease to 30 nm for matrix cores and 15 nm for fractured cores.