Fractures widely exist in rocks and are one of the controlling factors for the formation and distribution of hydrocarbon reservoirs. Electrical surveys are effective means for the quantitative detection and characterization of fractures. However, although all rocks experience pore pressure, the deformation of fractures with pore pressure and its effects on the anisotropic electrical properties of fractured rocks, which can help for the improved interpretation of electrical survey data, remain poorly understood. We bridge this knowledge gap in this work. We first implement dedicated laboratory measurements of the anisotropic electrical conductivity of artificial sandstone samples with and without aligned penny-shaped fractures as a function of pore pressure. We then invert from the experimental data for the fracture parameters that characterize the deformation of the fractures. We finally theoretically model the effects of pore pressure-induced fracture deformation on the anisotropic electrical properties of fractured rocks. The results show that the inverted porosity and aspect ratio of the fractures increases exponentially with pore pressure and exhibit linear correlation with each other as an implicit function of varying pore pressure. We also demonstrate that the variations in the fracture porosity caused by the varying pore pressure are the first-order parameter affecting the pore pressure-dependent electrical properties of fractured rocks. The results not only reveal the deformation of aligned fractures with pore pressure and its effects on the anisotropic electrical properties of fractured rocks, but also provide new insights for the detection and prediction of overpressure in fractured rocks.

中文翻译：

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裂缝参数随孔隙压力的变化及其对裂缝岩石各向异性电学性质的影响

岩石中广泛存在裂缝，是油气藏形成和分布的控制因素之一。电测是定量检测和表征裂缝的有效手段。然而，尽管所有岩石都会经历孔隙压力，但裂缝随孔隙压力的变形及其对裂缝岩石各向异性电学性质的影响（有助于改进电测数据的解释）仍然知之甚少。我们在这项工作中弥合了这一知识差距。我们首先对具有和不具有对齐的便士形裂缝的人造砂岩样品的各向异性电导率作为孔隙压力的函数进行专门的实验室测量。然后，我们根据实验数据反演表征裂缝变形的裂缝参数。最后，我们从理论上模拟了孔隙压力引起的断裂变形对断裂岩石各向异性电特性的影响。结果表明，裂缝的反孔隙度和纵横比随着孔隙压力呈指数增加，并且作为变化孔隙压力的隐函数，彼此呈现线性相关性。我们还证明，由孔隙压力变化引起的裂缝孔隙度的变化是影响裂缝岩石与孔隙压力相关的电学性质的一阶参数。研究结果不仅揭示了孔隙压力对排列裂缝的变形及其对裂隙岩石各向异性电学特性的影响，而且为裂隙岩石超压的检测和预测提供了新的见解。