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US 12,742,380 B2Granted
Interference compensated cross-axial magnetometer measurements
AssigneeSchlumberger Technology Corporation
InventorsMakito Katayama, Edward Richards
Life of this patent
Estimating the term…
Abstract
A method for making cross-axial magnetic field measurements in a downhole tool includes evaluating cross-axial magnetic field measurements to determine a magnetic interference bias and removing the magnetic interference bias to obtain compensated cross-axial magnetic field measurements.
Claims17
A method for compensated magnetic field measurements in a wellbore, the method comprising:
- deploying a downhole tool in the wellbore, the downhole tool including first and second cross-axial accelerometers and first and second cross-axial magnetic field sensors positioned such that the first and second cross-axial magnetic field sensors are configured to detect an intermittent source of electromagnetic (EM) interference;
- using the cross-axial accelerometers and the cross-axial magnetic field sensors to obtain cross-axial gravitational field measurements and cross-axial magnetic field measurements while the downhole tool is deployed in the wellbore;
- computing an angle X from the cross-axial gravitational field measurements and the cross-axial magnetic field measurements made during a first time period during which there is no EM interference;
- monitoring an operational state of the intermittent source of EM interference to identify:
- inactive periods when the intermittent source is inactive;
- and
- active periods when the intermittent source is active;
- estimating magnetic tool face values for the cross-axial magnetic field measurements made during a second time period during which there is EM interference, the estimating using the computed angle X and corresponding cross-axial gravitational field measurements made during the second time period;
- extracting a corresponding plurality of interference signals using the estimated magnetic tool face values for each of a plurality of the magnetic field measurements made during the second time period;
- averaging the plurality of extracted interference signals to estimate an interference bias in the magnetic field measurements made during the second time period;
- removing the interference bias from the magnetic field measurements made during the second time period to compute compensated cross-axial magnetic field measurements;
- computing a wellbore azimuth using the compensated cross-axial magnetic field measurements;
- and
- changing a direction of drilling in response to the computed wellbore azimuth.
11 more elements
A downhole tool, comprising:
- first and second cross-axial accelerometers and first and second cross-axial magnetic field sensors deployed in a downhole tool body, the first and second cross-axial magnetic field sensors positioned such that the first and second cross-axial magnetic field sensors are configured to detect magnetic flux emanating from an intermittent source of electromagnetic interference;
- and
- a processor configured to:
- cause the cross-axial accelerometers and the cross-axial magnetic field sensors to obtain cross-axial gravitational field measurements and cross-axial magnetic field measurements while the downhole tool is deployed in a wellbore;
- compute an angle X from the cross-axial gravitational field measurements and the cross-axial magnetic field measurements made during a first time period during which there is no EM interference;
- monitor an operational state of the intermittent source of electromagnetic interference;
- estimate magnetic tool face values for the cross-axial magnetic field measurements made during a second time period during which there is EM interference using the computed angle X and corresponding cross-axial gravitational field measurements made during the second time period;
- extract a corresponding plurality of interference signals using the estimated magnetic tool face values for each of a plurality of the magnetic field measurements made during the second time period;
- average the plurality of extracted interference signals to estimate an interference bias in the magnetic field measurements made during the second time period;
- remove the interference bias from the magnetic field measurements made during the second time period to compute compensated cross-axial magnetic field measurements;
- compute a wellbore azimuth using the compensated magnetic field measurements;
- and
- change a direction of drilling in response to the computed wellbore azimuth.
10 more elements
A method for compensated magnetic field measurements in a wellbore, the method comprising:
- deploying a downhole tool in the wellbore;
- the downhole tool including first and second cross-axial accelerometers and first and second cross-axial magnetic field sensors positioned such that the first and second cross-axial magnetic field sensors are configured to detect an intermittent source of electromagnetic (EM) interference;
- using the cross-axial accelerometers and the cross-axial magnetic field sensors to obtain cross-axial gravitational field measurements and cross-axial magnetic field measurements while the downhole tool is deployed in the wellbore;
- monitoring the intermittent source of electromagnetic interference;
- setting a compensated magnetic field measurement equal to a magnetic field measurement when the intermittent source of electromagnetic interference is inactive;
- computing an angle X from the cross-axial gravitational field measurements and the cross-axial magnetic field measurements when the intermittent source of electromagnetic interference is inactive;
- estimating a magnetic tool face value from the computed angle X and the cross-axial gravitational field measurements when the intermittent source of electromagnetic interference is active;
- extracting an interference signal from the magnetic field measurement using the measured cross-axial gravitational field measurements when the source of the electromagnetic interference is active;
- comparing the extracted interference signal with a threshold;
- setting the compensated magnetic field measurement equal to the magnetic field measurement when the interference signal is less than the threshold;
- setting the compensated magnetic field measurement equal to a previous compensated magnetic field measurement when the interference signal is greater than the threshold;
- computing a wellbore azimuth using the set compensated magnetic field measurement;
- and
- changing a direction of drilling in response to the computed wellbore azimuth.
11 more elements
Dependencies are inferred from the claim text.