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 analyzed the advantages and disadvantages of rock resistivity measurements of cylindrical and cubic samples. To overcome the difficulties above, we developed a core holder for radial resistivity measurements and proposed a radial resistivity measurement method for cylindrical samples. Based on the conformal transformation of the complex variable function theory, we established a mathematical model of radial resistivity. We developed a measurement method of radial resistivity according to the mathematical model and verified this approach with isotropic cores. The theoretical calculation results agree with the experimental results. With the radial resistivity measurement method, we effectively tested 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.

Mechanism of Forming Low Resistivity in Shale Reservoirs

“…Even a bit of pyrite and overmature organic matter can greatly affect the resistivity. Experiments also verify [59,61] the anisotropic resistivity in shale and large resistivity discrepancy among rocks with different directions.…”

“…To verify the effectiveness of the above numerical simulation method for resistivity, the shale sample S5 was selected for experimental testing [59]. Figure 3(a) shows the axial lamination of the sample.…”

“…Fractures with formation water are also involved in the context of low-resistivity lamination. In 2020, He et al [59] developed an experimental method on the radial resistivity characterizing plug anisotropy. The resistivity under different water saturations may be calculated by means of this method (Figure 16).…”

Method to Measure Radial Thermal Conductivity for Cylindrical Samples

“…Because the plane has become a curved surface, such a problem cannot be solved directly using a simple formula involving elementary calculations. Researchers have used conformal transformation in complex variable functions to solve the abovementioned issues and successfully applied seepage and electric conduction problems in the past. , Fortunately, the thermal conductivity also satisfies the partial differential equation ∂ u /∂ t = k ∇ u . As long as the properties of the sample in a certain direction are the same and the Cauchy–Riemann condition is satisfied in the 2D plane, conformal transformation similar to that used in seepage and electricity conduction can be adopted.…”

“…The vast majority of cores are cylindrical as they are sampled via drilling . Different from rocks that can be cut into various shapes, the cylindrical batteries only as the whole may have their own functional characteristics.…”