Application of Complex Image Theory in Geosteering

With the development of horizontal drilling technology and application of the logging while drilling tool, geosteering systems have been widely applied in precision and adaptive drilling. The geosteering system controls the direction, in real time, of the drilling bit in horizontal or deviated well. The position information of both drilling bit and bed boundary is provided to the system for the determination of drilling directions in real time. In this paper, the complex image method (CIM) is applied to speed up the boundary detection process. The proposed method reduces the simulation time and improves the real-time performance of the control system. This method is implemented in both two-layer and three-layer cases. The accuracy of the proposed method is tested in different frequencies and conductivity contrasts. The simulation results show that the complex image theory works well in most geosteering situations. Compared with the results from the full solution, the complex image theory has satisfactory accuracy. Error only exists in areas within 2 ft away from boundaries. When there are 600 000 logging points, the CIM method is 160 times faster than a full solution.