METHOD FOR MAGNETIC SURVEY CALIBRATION AND ESTIMATION OF UNCERTAINTY

摘要

The present inventionprovides a method for determiningmagnetometer errors duringwellbore survey operations. It iscapable of determining errors onup to three axes, with or withoutthe use of an external referencemeasurement of the local magneticfield, and is capable of providingan accurate result using data froma minimum number of surveys.A model is used to correct theobserved data and the correcteddata are transformed from the toolcoordinate system to a differentcoordinate system referenced tothe earth. The difference betweenthe corrected transformed dataand reference data in the earthcoordinate system is minimized todetermine the model parameters.The present invention also providesa method for determining residualuncertainty in the measurementsand for quality control of themeasurements. By making theobservations over a period of time,any deterioration of the sensorsmay be identified.