Detection Performance and Grading-Selection-Based Inversion of Low-Frequency Alternating Current Resistivity Logging in Moderate-High Resistance Formations

Abstract

Summary With the development of high-angle/horizontal well technology, unconventional tight reservoirs with moderate/high resistivity have gradually become the focus of exploration and development. However, in moderate-high-resistance reservoir environments, distorted responses can be observed regularly in the array laterolog curves, which will lead to misjudgment for the oil-gas reservoirs. Therefore, the detection performance of the array lateral instrument powered by low-frequency alternating current urgently needs to be clarified and the true resistivity of the formation is necessary to be analyzed and extracted. In this paper, the reasons for distorted responses are investigated as well as the qualitative and quantitative assessments of the detection performance of low-frequency alternating current lateral instrument in moderate-high resistance formations. Moreover, a rapid inversion method is proposed based on the initial value grading optimization strategy to invert the anisotropic resistivities from the observed data with outliers. Numerical simulation results show that the current flow characteristics vary significantly across stratigraphic models and the distorted responses are primarily caused by the high-resistance characteristics and borehole enlargement. The combination of the initial value grading optimization strategy and the regularization inversion algorithm improves the accuracy of the inverted resistivities even further. Synthetic and field examples are analyzed to illustrate the detailed implementations and the performance of the proposed inversion method.