Abstract
Fiber-optic gyroscopes (FOGs)-based Measurement While Drilling system (MWD) is a newly developed instrument to survey the borehole trajectory continuously and in real time. However, because of the strong vibration while drilling, the measurement accuracy of FOG-based MWD deteriorates. It is urgent to improve the measurement accuracy while drilling. Therefore, this paper proposes an innovative scheme for the vibration error of the FOG-based MWD. Firstly, the nonlinear error models for the FOGs and ACCs are established. Secondly, a 36-order Extended Kalman Filter (EKF) combined with a calibration method based on 24-position is designed to identify the coefficients in the error model. Moreover, in order to obtain a higher accurate error model, an iterative calibration method has been suggested to suppress calibration residuals. Finally, vibration experiments simulating the drilling vibration in the laboratory is implemented. Compared to the original data, compensated the linear error items, the error of 3D borehole trajectory can only be reduced by a ratio from 10% to 34%. While compensating for the nonlinear error items of the FOG-based MWD, the error of 3D borehole trajectory can be reduced by a ratio from 44.13% to 97.22%. In conclusion, compensation of the nonlinear error of FOG-based MWD could improve the trajectory survey accuracy under vibration.
Highlights
Accurate borehole trajectory information could help the automatic drilling tool to hit the target [1]
Wang et al [11,12] and Zhang et al [13] analyzed the influence of downhole vibration on Fiber-optic gyroscopes (FOGs)-based Measurement While Drilling system (MWD) measurement accuracy
In order to improve the measurement accuracy of the FOG-based MWD under conditions of drilling vibrations, this paper proposed an innovative scheme for the vibration error of FOGs-based MWD
Summary
Accurate borehole trajectory information could help the automatic drilling tool to hit the target [1]. A fiber-optic gyroscope (FOG) based on an inertial navigation system has been used in aeronautics and astronautics field, such as in airplanes, missiles, and satellites [4]. It can offer realtime position, velocity, and altitude information of the aircraft without relying on other information [5]. The FOGs and ACCs measure the angular rate and acceleration of the automatic drilling tool, respectively They utilize the inertial navigation algorithm to calculate the three-dimensional (3D) borehole trajectory. Wang et al [11,12] and Zhang et al [13] analyzed the influence of downhole vibration on FOG-based MWD measurement accuracy.
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