Radial resistivity measurement method for cylindrical core samples

Abstract

Electrical resistivity is one of the fundamental physical properties of rocks, and its relationship with fluid saturation is widely used in reservoir evaluation. The interpretation of electrical logs usually relies on the results of rock resistivity tests of cores in the laboratory. In the laboratory, core samples are commonly cut into cylinders, and the resistivity is measured along the axial direction. To determine the rock resistivity along different directions, samples are cut into cubes and tested along three perpendicular directions to obtain resistivity data. The expensive and complicated preparation process of cubic samples and the custom holder requirements limit the use of these tests. We have analyzed the advantages and disadvantages of rock resistivity measurements of cylindrical and cubic samples. To overcome the abovementioned difficulties, we develop a core holder for radial resistivity measurements and a radial resistivity measurement method for cylindrical samples. Based on the conformal transformation of the complex variable function theory, we establish a mathematical model of radial resistivity. We develop a measurement method of radial resistivity according to the mathematical model and verify this approach with isotropic cores. The theoretical calculation results agree with the experimental results. With the radial resistivity measurement method, we effectively test the resistivity anisotropy of shale. This method has more advantages than existing methods in terms of the sample preparation and realization of various displacement levels and angles. Hence, the proposed method can be widely used.