Downhole Magnetic Compass Interference Compensation
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Solution Overview
Problem
Magnetic measurements of the earth's magnetic field in a borehole are inaccurate due to interference from the magnetic field of the drill bit, affecting the steering of the drill string.
Innovation Solution
A method and system that involve obtaining sensor readings of the drill bit's magnetic field at multiple positions around the bit, determining the magnetic dipole moment of the drill bit, and using this information to correct downhole measurements of the local earth magnetic field, thereby improving the accuracy of drill string orientation determination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a magnetic sensor is located near the drill bit to obtain earth's magnetic field measurements, then the measurement location is improved (closer to bit for better steering control), but the measurement precision deteriorates due to interference from the drill bit's magnetic field
Solution Approach 1:
The patent performs preliminary characterization of the drill bit's magnetic field by taking measurements at multiple positions around the bit before actual drilling operations. This pre-acquired magnetic field data is stored and later used to compensate for interference during downhole measurements, allowing the sensor to be positioned close to the bit while maintaining accuracy through software-based correction
Solution Approach 2:
The patent introduces an intermediary computational process that acts as a mediator between the contaminated raw measurement and the desired clean earth's magnetic field value. The compensation algorithm uses the pre-characterized bit field model to subtract the bit's magnetic interference from the sensor readings, effectively filtering out the harmful magnetic field components
2Measurement precision
If multiple sensor readings are taken at various positions around the drill bit, then the measurement precision of the bit's magnetic field characterization is improved, but the loss of time increases due to multiple measurement positions
Solution Approach 1:
The magnetic field characterization is performed as a preliminary one-time operation during drill bit manufacturing or before first use, rather than repeatedly during each drilling operation. This pre-characterization data is stored and reused for multiple drill bits or extended periods, making the time investment negligible compared to the operational benefits
Solution Approach 2:
The patent transforms the complex spatial magnetic field distribution into a simplified set of parameters (magnetic dipole moment components) that capture the essential characteristics of the bit's magnetic field. This parameter reduction allows accurate representation of the magnetic field using minimal measurement data, reducing the number of required measurement positions and time
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
The solution effectively compensates for the drill bit's magnetic field interference, enhancing the accuracy of downhole magnetic field measurements and improving the precision of drill string steering.
Implementation Method 1
A plurality of sensor readings of a magnetic field of a drill bit are obtained at a location on the earth surface using a magnetic field sensor
Implementation Method 2
A measurement of a local earth magnetic field is obtained using a downhole magnetic field sensor located in the drill string, wherein the measurement is affected by the magnetic field of the drill bit
Data Source
AI summary
A drilling system includes a method of determining an orientation of a drill string in a borehole. Sensor readings of a magnetic field of a drill bit are obtained at a plurality of positions along a curve extending around the drill bit along a longitudinal bit axis from a first location to a second location. A drill string includes the drill bit and a downhole magnetic field sensor that obtains a measurement of a local earth magnetic field, wherein the measurement is affected by the magnetic field of the drill bit. A processor determines a magnetic dipole moment of the drill bit from the plurality of sensor readings, calculates a second measurement of the local earth magnetic field downhole using the magnetic dipole moment of the drill bit, and determines the orientation of the drill string from the calculated correction of the measurement of the local earth magnetic field.