Identifying the carbonate interlayer using the horn response of electromagnetic wave resistivity logging while drilling combined with drilling and mud-logging data during geo-steering

Abstract

Abstract The electromagnetic wave propagation resistivity (EWPR) and natural gamma rays (GR) are commonly used in logging while drilling (LWD) to identify the formation interface and for geo-steering. Because the GR logging value of a carbonate reservoir does not change significantly or not change at all, the horn effect of the EWPR is the main basis for identifying the formation interface. However, many factors influence the horn effect, so it is sometimes difficult to determine whether the sharper response of the EWPR is the horn signal or the real value of the thin interlayer. Therefore, based on a review of existing research results, in this paper, the EWR-PHASE4 LWD tool is taken as an example, and using a numerical forward simulation, the influences of different resistivity ratios of the surrounding rock to the target layers, the different transmitter spacings on the EWPR for different angles between the borehole trajectory and formation are investigated. The conditions required to generate horn signals at the formation interfaces and the influencing rules of the main influencing factors are summarized, providing a theoretical basis for correctly determining the formation occurrence. Since the drilling and mud-logging data can be used to determine the formation's properties directly, through application examples, this study provides a reference for identifying the carbonate interlayer and formation occurrence using a combination of EWPR with drilling and mud-logging data, which has a smaller uncertainty than the application of only EWPR.