Microscopic mechanism of fracturing fluid imbibition in stimulated tight oil reservoir

Abstract

The imbibition of fracturing fluid is of great significance to improve the development of fractured tight oil reservoirs. Understanding the micro-characteristics of fracturing fluid imbibition is necessary to improve the imbibition efficiency. In this work, the experiments of the spontaneous imbibition under simulated in-situ condition is conducted to understand the micro-characteristics of fracturing fluid imbibition, and the Nuclear magnetic resonance (NMR) and high-resolution X-rays computed tomography (CT) scanning are applied to monitor the process and the liquid distribution of spontaneous imbibition. The experimental results indicate that the spontaneous imbibition is mainly occurred in macropores at the initial stage, and the velocity of fracturing fluid is lower than that of formation water in spontaneous imbibition due to the weaker motivity generated from the lower oil-fracturing fluid interfacial tension. The fracturing fluid can promote the spontaneous imbibition due to it can decrease the kinetic energy loss when it transforms into the interfacial free energy. Thus, the oil recovery obtained from the fracturing fluid imbibition increased to 20.7% from 15.8% by formation water imbibition. The main reason accounts for it is that the wettability of fracturing fluid is stronger than that of formation water, thus can promote the whole process of spontaneous imbibition, and the lower viscosity would reduce the flow resistance at the latter stage. A higher oil-water interfacial tension (IFT) can accelerate the velocity of spontaneous imbibition at the initial stage, while a proper interfacial tension is favorable at the latter stage.