Study Of Non-orthogonal Coordinate Measurement Technology For Vertical Tool

In the real-time drilling, accurate measurement of downhole position parameters is the key factor to realize steering drilling downhole at all angles, such as deviation angle, tool face angle and azimuth. The output signal of sensor is very weak in the orthogonal coordinate system under vertical and little inclination attitude. It still exists great error after the subsequent processing of AD sampling and numerical calculation, which impacts the calculation accuracy of parameters. It is unable to avoid the inherent problems of small original signal using same or different type of sensors combination to improve measurement method and establish compensated error model.Automatic drilling technology, domestic and international automatic vertical drilling technology are introduced briefly, and the direction cosine method of the updating attitude algorithm is presented in detail. In addition, basic principles of attitude measurement are analyzed and output formulas of the quartz flexible accelerometer sensors are deduced. Also normal calculation method of attitude measurement parameters is studied and internal reason of insufficient precision of vertical measurement in conventional orthogonal coordinate system is analyzed. In order to improve the original signal amplitudes and their SNRs, a non-orthogonal coordinate system is presented. Meantime theoretical model and its measuring error are investigated and tested. A compensation technique is presented to correct the position error, which is originated from the misalignment of each axis for the inclinometer and the ideal coordinate system in drilling.The experimental signals and computational results show that this non-orthogonal coordinate system can increase the original amplitude more than ten times, and improve overall accuracy of vertical attitude measurement greatly. After correcting attitude parameters by coefficient compensation method, the fitting degree of each tool face angle between the actual values and the estimate of the trend line is higher than before. The relative error of each deviation angle is reduced obviously, which achieves equal precision and ideal correction effects.