Performance Analysis of Tactical Grade Inertial Systems for MWD Process

Abstract

A complete knowledge of the drill bit direction and orientation during the drilling process is essential to guarantee accurate directional drilling procedure. Presently, three accelerometers and three magnetometers are typically used as a part of the Measurement-While-Drilling MWD equipment. In some cases, the use of magnetometers has deleterious effect on the accuracy of the surveying process. This is due to the magnetic interference of the drill string, downhole ore deposits and other geomagnetic effects. Recently, gyroscopes have been proposed to aid the magnetometers in environments of high magnetic interference. This paper describes the development of a reliable MWD surveying technique utilizing Inertial Navigation Systems (INS) as a replacement of magnetometers. Tactical grade INSconsisting of three gyroscopes and three accelerometers to be miniaturized inside the bottom-hole assembly is adopted in this study. The proposed system offers station-based surveying for monitoring of azimuth, inclination and tool face angles. Additionally, it provides continuous surveying by applying Kalman filtering to optimally integrate the sensor measurements and to provide both the drill bit position and orientation in realtime. This study also offers accurate modeling of INS long-term errors in order to achieve the desired accuracy for horizontal drilling applications. Pre-filtering using wavelet multi-resolution analysis is utilized in this study to improve the performance of both gyroscopes and accelerometers. This procedure removes most of the short-term and high frequency errors to separate the motion dynamics from the sources of vibration and shocks experienced downhole.The performance of the proposed system is examined using a special experimental setup that performs rotations similar to that experienced by the drill bit. The results showed that reliable MWD surveying performance can be achieved. The suggested INS-based MWD surveying technique eliminates the costly nonmagnetic drill collars for the magnetometers, survey the borehole continuously without interrupting the drilling process and improve the overall accuracy by utilizing real-time digital signal processing techniques.

A Long-Term Performance Enhancement Method for FOG-Based Measurement While Drilling

“…Therefore, we choose the MCM to calculate the trajectory. MCM [ 24 , 25 ] assumes the two surveying stations lie on a circular arc, and the arc is located in a plane for which the orientation is known at both ends by knowing the inclination and azimuth angles. Figure 7 illustrates the MCM.…”

“…The MCM fits a spherical arc between the two stations by calculating the curvature “ DL ” from the 3D vectors and scaling by a ratio factor ( RF ). When the first station positions are known, the second station positions is computed using the following expressions [ 25 ]: where is the difference in the true vertical depth between the two stations with and being the difference in the north and east directions, respectively. Δ MD is the drilling pipe length.…”

Continuous Wellbore Surveying While Drilling Utilizing MEMS Gyroscopes Based on Kalman Filtering

“…This can be further translated to the continuous velocity measurements' update of the inertial sensor measurements. Additionally, a continuous position is applied based on the position computed by the MCM [ElGizawy et al, 2006]. The second external update scheme is based on stationary measurements taken when the drilling operation stops on a regular basis to connect a new stand of pipes.…”

“…Based on this information, the Kalman filter estimates the random errors within the INS output. In turn, it enhances the performance of the surveying system while drilling by removing the estimated errors from the MEMS inertial sensor measurements[ElGizawy et al, 2006]. The observation vector k…”

IMU/Magnetometer-Based Azimuth Estimation with Norm Constraint Filtering

“…To weaken magnetic interference from metallic drilling equipment, a magnetometerbased MWD system is typically mounted inside an expensive non-magnetic drill collar [6]. This can effectively remove magnetic interference, due to the metallic materials of the drill collar; however, use of a non-magnetic drill collar imposes the problem of high cost [7].…”