Study on the imbibition recovery trends in low-permeability cores under high-pressure CO2

Abstract

Imbibition plays a crucial role in extracting crude oil from low-permeability reservoir matrices. After CO2 is injected into the low-permeability reservoirs for development, both CO2 and surfactants often coexist in the imbibition fluid. While previous studies have mainly focused on the individual presence of CO2 or surfactants, limited research has been conducted on their coexistence. In this paper, the imbibition recovery trends in low-permeability cores under high-pressure CO2 are investigated by measuring the imbibition efficiency, the three-phase contact angle (CA), and the oil-water interfacial tension (IFT). The findings of this research indicate that the surfactant significantly enhances the interface characteristics, substantially increases the imbibition rate, and improves recovery by more than 14 %. Temperature has a greater impact on the interface characteristics compared to pressure, directly influencing the distribution of SDS molecules at the interface. Despite temperature elevation leading to increased IFT and reduced concentration of charged ions, it still enhances the rock hydrophilicity and improves imbibition efficiency. Pressure affects the interface characteristics mainly by modifying CO2 solubility. With increasing pressure, the IFT decreases, the concentration of charged ions increases, and the electrostatic repulsion between ions is enhanced, ultimately enhancing rock hydrophilicity and significantly boosting imbibition efficiency. The coexistence of CO2 and SDS further improves the interface characteristics, exhibiting synergistic effects in reducing IFT and enhancing rock hydrophilicity. These research findings contribute to a deeper understanding of the imbibition mechanism and provide theoretical support for the development and application of CO2 injection in the field.