Improving Fracture-Matrix Recovery in Low-Permeability Reservoirs: An Experimental Study of Huff-n-Puff Imbibition Using Active Carbonated Water

Summary Imbibition oil recovery is crucial for enhancing fossil energy production in fractured low-permeability reservoirs. However, traditional methods, such as water flooding and CO2 injection, face significant challenges in improving oil recovery due to issues like early gas breakthrough, high transportation costs, and insufficient oil mobilization. This study aims to investigate the mechanism of active carbonated water (ACW) imbibition between fractures and the matrix in low-permeability fractured reservoirs. The interfacial tension (IFT) and contact angles of various imbibition fluids were measured, followed by one-dimensional 1D Huff-n-Puff (HnP) experiments using long core samples. The effects of CO2 concentration, fracture number, and soaking time on oil recovery were analyzed. The results indicate that ACW HnP imbibition achieves a recovery factor of 39.41%, primarily due to its low IFT, strong wettability reversal, and efficient mass transfer. The imbibition mechanism includes soaking-static imbibition and production-dynamic imbibition stages. CO2 diffusion causes oil expansion, increasing pressure during soaking. Nuclear magnetic resonance (NMR) analysis revealed recovery factors of 42.33% and 41.46% for small and large pores, respectively. These findings provide insights into enhancing fracture-matrix imbibition efficiency in low-permeability fractured reservoirs and offer a promising method for improving oil recovery.