Impact of Fracturing Fluid Fluid-Loss Characteristics on Oil Displacement Efficiency and Underlying Mechanisms

In previous studies, efforts regarding fracturing fluid fluid loss have predominantly aimed at "fluid loss reduction." This study, however, focuses on shifting from "fluid loss reduction" to "fluid loss promotion." This paper combines orthogonal experimental design with nuclear magnetic resonance (NMR) technology to reveal the mechanism by which fracturing fluid fluid loss distance affects displacement efficiency in unconventional reservoirs. Experiments found significant correlations between fluid loss distance and injection pressure differential, reservoir permeability, and fracture morphology parameters. Among these, permeability has the highest influence factor at 62.3%, making it the key factor affecting seepage distribution. Three different types of fracturing fluids were selected for this study—LGF-80 fracturing fluid, CNI fracturing fluid, and bio-based nano-oil-displacement fracturing fluid—to conduct research from a multi-factor, multi-level perspective, exploring the optimal conditions for each factor. The bio-based fracturing fluid system developed based on nanotechnology demonstrates significant advantages over traditional LGF-80 and CNI systems, achieving markedly improved displacement efficiency in low-permeability core experiments. The dynamic imbibition-NMR coupling measurement method proposed in this work overcomes the limitations of traditional fluid loss volume evaluation and provides important reference value for improving field displacement efficiency.