Response Characteristics of Logging While Drilling System with Multi-Scale Azimuthal Electromagnetic Waves

In order to detect changes in stratigraphic structures in time, and accurately evaluate formation while avoiding drilling risks, logging while drilling (LWD) instruments are required with adequate depth of detection (DOD) and higher resolution. However, the measurement results of a single scale LWD cannot simultaneously satisfy the stated requirements. Therefore, the detection characteristics of ultra-deep azimuthal electromagnetic wave LWD and a conventional one were simulated and investigated, and the boundary detection ability and resolution of the system were analyzed as well. Meanwhile, the detection effect of undrilled formation interface was also explored. Moreover, the quasi-Newton method was used to perform accurate and fast inversion of data from LWD with multi-scale azimuthal electromagnetic waves. The study results showed that by increasing the coil spacing and reducing the frequency, the LWD with ultra-deep azimuthal electromagnetic waves could have a boundary detection ability of tens of meters. Combined with a small-scale azimuthal electromagnetic wave LWD, the real-time resistivity profile of reservoirs through inversion could be obtained, so as to bring about geological prediction, geosteering, and reservoir characterization in the vicinity of wellbore and farther away.