Anisotropic Response Characteristics of Array Induction Logging in Laminated Shale and Its Correction Methods

Summary The lamination characteristics of shale are one of the sources of anisotropy in shale reservoir resistivity, with significant differences in horizontal and vertical resistivity, and usually with vertical resistivity greater than horizontal resistivity. Therefore, the resistivity anomaly caused by anisotropy in horizontal wells of shale reservoirs seriously interferes with the logging evaluation of shale reservoirs. Based on the 3D finite element method, the electromagnetic field distribution of array induction logging was simulated, and the influence of resistivity, anisotropy, and well inclination angle on resistivity in laminated shale formations was analyzed. A resistivity correction chart was constructed using the sensitivity differences of each subarray of array induction logging in anisotropic formations. Finally, resistivity anisotropy correction is achieved based on actual logging data. Research has shown that in anisotropic formations of horizontal wells, the effects of formation resistivity, anisotropy, and well inclination angle on each subarray of array induction logging are different, resulting in significant deviations between the measured resistivity values and the actual formation resistivity values. Through the construction of resistivity correction charts with different sensitivities of each subarray, anisotropy correction was performed on the actual well data. The corrected resistivity can approximately represent the horizontal resistivity of the reservoir, laying the foundation for evaluating shale reservoirs using resistivity data.