摘要: 油气主要储集在岩石孔隙和缝洞内，深部复杂应力环境下储层岩石裂隙渗透演化直接影响油气的运移规律，是油气勘探开发的重要研究对象。为了解复杂应力路径下含裂隙岩石的渗透演化特性，利用高精度渗流-应力耦合三轴实验设备，对含随机分布裂隙泥岩开展了单试样-复杂应力路径加卸载过程中的渗透性演化试验研究，试验方案依次为 (i) 围压递增条件下渗透性测试；(ii) 渗透压力递增条件下渗透性测试；(iii) 偏应力循环加卸载条件下渗透性测试；(iv) 围压、偏应力同步增长条件下渗透性测试。结果表明裂隙泥岩中的渗流可视为低渗流速度的层流；裂隙发育丰富岩样（R2）渗透率及应力敏感性明显较高。渗透率随渗透压力、围压分别呈正、负的指数函数变化。偏应力加载导致渗透率降低，卸载引起渗透率上升，但整体呈不可逆降低；围压、偏应力同步增长引起渗透率呈下降趋势，并逐步趋于稳定；围压10.3MPa作用下，渗透率基本保持恒定。由此基于裂隙双重介质模型，考虑泥岩变形过程中裂隙系统和基质系统的相互作用以及外部应力作用下的裂隙膨胀变形，构建了裂隙泥岩渗透率演化力学模型；模型模拟结果与试验结果具有较好的一致性。相关成果可为裂隙泥岩渗透性演化预测和油气高效开采提供重要的理论依据。
EXPERIMENTAL STUDY ON PERMEABILITY EVOLUTION OF FRACTURED MUDSTONE UNDER COMPLEX STRESS PATHS
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Abstract: The main reservoirs of oil and gas are in the pores and fractures of rocks. Under the deep and complex stress environment, the reservoir rock fracture permeability evolution directly affects the flow of oil and gas, which is an important research object of oil and gas exploration and development. In order to study the permeability evolution of fractured rock under complex stress paths, the permeability test of a single sample in the process of loading and unloading complex stress paths was performed using high precision hydro-mechanics coupled triaxial experimental equipment. The experimental scheme is (i) permeability test under increasing confining pressure; (ii) permeability test under increasing fluid pressure; (iii) permeability test under cyclic loading and unloading deviatoric stress; (iv) permeability test under increasing confining pressure and deviatoric stress synchronously. The results show that fluid flow in fractured mudstone can be regarded as laminar flow with low velocity; The sample contained more fracture (R2) has a significantly higher permeability and stress sensitivity. The permeability changes with the fluid flow pressure and the confining pressure as a function of positive and negative exponential functions. The increase of the deviatoric stress leads to a decrease in the permeability, and the unloading causes the permeability to increase. The whole evolution of permeability is irreversibly reduced. During the stage of the increase of confining pressure and deviatoric stress, the permeability also decrease, and tends to stable. Under the confining pressure of 10.3 MPa, the permeability is basically constant. Therefore, based on the double medium model of fracture, the permeability evolution model of fractured rock is proposed considering the interaction among fracture system, matrix system and the expansion deformation of fracture under external stress. The simulation results of the model are in good agreement with the experimental results. These results can provide an important theoretical basis for the prediction of permeability evolution of fractured mudstone and efficient oil and gas exploitation.