Apparatus to measure the earth's local gravity and magnetic field in conjunction with global positioning attitude determination

摘要

The present invention provides a method for determining magnetometer errors during wellbore survey operations. It is capable of determining errors on up to three axes, with or without the use of an external reference measurement of the local magnetic field, and is capable of providing an accurate result using data from a minimum number of surveys. A model is used to correct the observed data and the corrected data are transformed from the tool coordinate system to a different coordinate system referenced to the earth. The difference between the corrected transformed data and reference data in the earth coordinate system is minimized to determine the model parameters. The present invention also provides a method for determining residual uncertainty in the measurements and for quality control of the measurements. Once a survey has been obtained with reference to magnetic north, it is corrected using magnetic declination data obtained concurrently with the survey using surface GPS receivers, magnetometers and accelerometers.