The Analysis and Application of Formation Interface Response Characteristics of the Resistivity LWD Tool

During resistivity logging while drilling (resistivity LWD) in highly deviated or horizontal wells, the resistivity is significantly affected by the formation interface and dramatic polarization effects can occur. According to the fundamental theory of electromagnetic fields, a model for layered formations was established, and numerical simulations were used to simulate the response when the resistivity LWD tool was horizontally penetrating the interface among formations with different resistivity. In this way, the response patterns of the resistivity LWD tool were analyzed and the preconditions and influencing factors of polarization effects were summarized. The results show that more significant polarization effect will be shown under larger coil spacing and higher working frequency of the tool. Comparing the amplitude difference resistivity, phase difference resistivity is more susceptible to polarization effects. Taking Well A in Yong-X Fault Block as an example, the applications of formation interface response characteristics from resistivity LWD tool were presented. It was indicated that polarization effects of resistivity LWD logs can be used to identify formation interfaces at given specific geological models to facilitate geosteering.