IMPROVING WELLBORE SURVEYING ACCURACY OF HORIZONTAL WELLS BY UTILIZING A DUAL-AXIS OPTICAL GYRO SYSTEM

Abstract Measurement-while-drilling (MWD) surveying systems utilizing fiber optic gyroscopes (FOGs) have been suggested as a replacement for the present magnetic surveying techniques in order to avoid the imperfections associated with magnetic monitoring devices. A gyroscopic surveying methodology incorporating a single FOG with its sensitive axis along the central axis of the drill pipe and three mutually orthogonal single-axis accelerometers was suggested to survey horizontal wells. This method suffered from some limitations and an increase in the surveying errors at certain orientations. This article aims at overcoming these limitations by suggesting a dual FOG system using an additional FOG with its sensitive axis normal to the central axis of the drill pipe. The proposed dual FOG system has been tested using a custom designed experimental setup that can simulate several orientations similar to those experienced by the bottom hole assembly downhole. The results showed significant improvement in the accuracy of the surveying parameters with no specific limitations. This study suggests that gyroscopic surveying utilizing a dual FOG system can be a reliable solution for MWD surveying of horizontal wells.

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