Abstract: This study aims to address the challenges in characterizing pressure falloff test curves during the shut-in period of fracturing-flooding water injection wells in low-permeability reservoirs, and the difficulty in determining reservoir heterogeneity and fracture properties. Based on the black-oil model and displacement discontinuity method (DDM), in combination with the reservoir characteristics such as threshold pressure gradient and stress sensitivity effects, a fracturing-flooding well testing model was developed and solved to account for dynamic fracture variations. Application of the model to a typical fracturing-flooding geological model revealed the fracturing-flooding well testing curve characteristics. The results show that the fracturing-flooding well testing curve can be divided into six typical flow stages: I. wellbore storage stage; Ⅱ. first transitional flow stage; Ⅲ. fracture-dominated flow stage; Ⅳ. second transitional flow stage; Ⅴ. radial flow stage; Ⅵ. boundary reflection stage. Among these, the differences in flow regime during Stage Ⅲ are mainly governed by the fracture length, aperture, and conductivity. With a gradual decrease in the permeability of heterogeneous reservoirs near the water injection well, Stage Ⅲ undergoes a transition from pseudo-radial flow to bilinear flow, and then to linear flow. A well testing curve fitting was performed on a fracturing-flooding water injection well in a target block, and the inversion results indicate that the well is located at the center of the permeability transition zone, with the fracturing-flooding fracture semi-length and maximum conductivity of the fracture being determined. This research offers technical support for the analysis of fracturing-flooding well testing curves and the formulation of post-stimulation development strategies.

Key words: low-permeability reservoirs, heterogeneous reservoirs, fracturing-flooding, numerical well testing, facture propagation, displacement discontinuity method

摘要： 针对低渗透油藏压驱注水井关井压力降落测试曲线特征认识不清、储层非均质和裂缝属性难以确定的问题,基于黑油模型和位移不连续法,考虑启动压力梯度、应力敏感效应等储层特性,建立并求解了裂缝动态变化的压驱试井模型。将其应用于压驱典型地质模型,得到压驱试井的曲线特征。研究结果表明,压驱试井曲线可被分为6个典型流动阶段:井筒储集阶段、第一过渡流动阶段、裂缝流动阶段、第二过渡流动阶段、径向流动阶段和边界反映阶段;其中,裂缝流动阶段流动形态的差异主要与裂缝的长度、开度和导流能力有关;随着非均质储层中注水井附近渗透率逐渐降低,裂缝流动阶段经历了拟径向流、双线性流、线性流的转变。选取实际区块压驱注水井开展试井曲线拟合的反演结果表明,实例井位于渗透率渐变带中心,反演可得到该井的压驱裂缝半长和最高裂缝导流能力。

关键词: 低渗透油藏, 非均质储层, 压驱注水, 数值试井, 裂缝扩展, 位移不连续法