MWD Accelerometer Auto-Calibration for Drilling Navigation
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Solution Overview
Problem
Current directional drilling methods face challenges in accurately determining wellbore position due to errors in magnetometer and accelerometer measurements, particularly from magnetization of drill strings and accumulated drift errors, leading to uncertainties in wellbore trajectory and increased production costs from frequent calibration needs.
Innovation Solution
The implementation of redundant accelerometers with voltage measurement-based auto-calibration and fault diagnosis within the drilling measurement system, using temperature and voltage readings from orthogonally placed accelerometers to compute bias, sensitivity, and orthogonality error coefficients, which are then used to improve navigation accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If magnetometers are used to measure earth's magnetic field for wellbore azimuth determination, then navigation capability is provided, but drill string magnetization causes bias errors in magnetometer measurements leading to azimuth errors
Solution Approach 1:
The patent separates the magnetic field measurement function from the drill string by using a non-magnetic drill string section. This extracts the harmful magnetization effect from the system, allowing magnetometers to measure only the earth's magnetic field without contamination from drill string magnetization, thereby resolving the azimuth measurement accuracy problem
Solution Approach 2:
The patent introduces a non-magnetic drill string section as an intermediary element between the ferromagnetic drill string sections. This intermediary prevents the transmission of magnetic interference from the ferromagnetic sections to the magnetometers, enabling accurate magnetic field measurements while maintaining the structural integrity of the drill string
2Reliability
If accelerometers are used for wellbore position determination and attitude measurement, then redundant measurement capability is provided, but accumulated drift error degrades measurement performance over time
Solution Approach 1:
The patent implements a feedback mechanism where accelerometer measurements are continuously monitored and corrected using reference data from magnetometers and other sensors. This feedback loop compensates for accumulated drift errors by comparing accelerometer-derived position with independently measured position data, maintaining long-term measurement accuracy while preserving the redundancy benefit
Solution Approach 2:
The patent combines multiple sensor types (accelerometers, magnetometers, gyroscopes) into an integrated navigation system. By merging the strengths of different sensors and using their measurements complementarily, the system achieves both redundancy and long-term accuracy, as each sensor type compensates for the weaknesses of others over time
3Measurement precision
If laboratory calibration is performed for accelerometers at various temperatures, then scale factor and bias errors are corrected, but calibration must be stopped during drilling operations when errors occur
Solution Approach 1:
The patent enables the accelerometer system to perform self-calibration during normal drilling operations using internally available reference data from magnetometers and other sensors. This self-service calibration mechanism continuously corrects drift errors without requiring external intervention or stopping drilling operations, maintaining both measurement precision and productivity simultaneously
Solution Approach 2:
The patent implements continuous calibration functionality that operates throughout the entire drilling process rather than requiring periodic interruptions. By maintaining continuous calibration using real-time sensor data and reference measurements, the system ensures ongoing measurement accuracy while preserving uninterrupted drilling productivity
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances the reliability and accuracy of drilling navigation by reducing temperature and measurement errors, allowing for continuous operation without the need for frequent tool replacement, thereby reducing production losses and costs.
Implementation Method 1
MWD tools containing sets of three orthogonal accelerometers, thermometers, and magnetometers that are disposed about the drill string and used to measure the orientations of the local gravitational and magnetic field vectors
Implementation Method 2
To measure the earth's magnetic field, which is used as a north reference from which wellbore azimuth may be computed
Data Source
AI summary
A method for obtaining accuracy gravity coefficients out of three orthogonally oriented accelerometer devices and a thermometer by computing, using a pre-programmed micro-control unit processor, temperature errors, bias error coefficients, sensitivity error coefficients, and orthogonality error coefficients during measurement while drilling operations. Particularly, the method uses voltage data values of the three orthogonally oriented accelerometers to compute said error coefficients which provides for zero-error positioning of the MWD tool during long-term downhole surveying as well as while facing high-shock, vibrations, and high temperatures.