Characterization of CO2 Huff-n-puff Recovery from Dual Horizontal Wells in Shale Matrix-Fractured Reservoirs

Shale reservoirs are characterized by high heterogeneity and ultra-low permeability. For most shale reservoirs with insufficient formation energy, CO2 injection is one of the most economical and effective extraction technologies to improve the shale oil recovery factor. At the same time, fractures also have a significant impact on the oil recovery factor of shale reservoirs. This work uses a high-temperature and high-pressure three-dimensional physical simulation experimental device to restore the realistic conditions of shale reservoir reservoirs during the huff-n-puff process. The results show that the CO2 huff-n-puff and puff recovery factor of shale oil reservoirs are mainly concentrated in the first four rounds, and the effect of improving the oil recovery factor decreases with the increase of production rounds. Compared to non-fracture CO2 huff-n-puff, the presence of fractures significantly affects CO2 huff-n-puff in shale reservoirs, with an 8.95% increase in the oil recovery factor after fracture creation. Fractures can expand the coverage area of CO2 and effectively increase the range of CO2 production. This study reveals the pressure field variation pattern during CO2 huff-n-puff and puff in shale oil reservoirs under different matrix-fracture patterns, providing theoretical guidance for large-scale field application of CO2 huff-n-puff injection and extraction optimization.