Variation of Fracture Parameters With Pore Pressure and Its Effects on the Anisotropic Electrical Properties of Fractured Rocks

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.