Experimental Study on Factors Affecting Oil Recovery in Sandstone-Buried Hill Superimposed Reservoirs

Sandstone-buried hill superimposed reservoirs, characterized by the coexistence of the sandstone matrix and the fracture pore matrix, present unique challenges in integrated development due to their connectivity and physical properties. Currently, research on the factors affecting the recovery of sandstone-buried hill superimposed reservoirs with both porous and fractured media is limited. In this study, a more realistic method for preparing fractured cores and calculating fracture permeability was proposed, and the effect of confining pressure on fracture permeability was investigated. Additionally, a three-tube experimental apparatus was designed to study the effects of connectivity, different permeability contrasts between sandstone and buried hills, and various development strategies on recovery. The results indicate that fracture permeability is significantly affected by the confining pressure. When sandstone and buried hills are not connected, the total recovery is the highest. As connectivity increases, the recovery from sandstone gradually decreases, while the recovery from the buried hill gradually increases, leading to a decrease in the overall recovery. The permeability contrast between sandstone and buried hill has a minimal impact on the overall recovery; however, a higher permeability contrast leads to increased sandstone recovery and decreased buried hill recovery. The highest overall recovery was achieved with injection solely into the sandstone, followed by general injection, with the lowest recovery from injection solely into the buried hill. This study provides new insights into the integrated development of sandstone-buried hill reservoirs.