Patent EA-001224-B1 (EA)
Title: Method of qualifying a borehole survey
Inventor: HARTMANN ROBIN ADRIANUS
IPC: E21B47/022
Filed: 1996-11-20
Abstract: 1. A method of qualifying a survey of a borehole formed in an earth formation, the method comprising:  a) selecting a sensor comprising, at least, one magnetometer and, at least, one accelerometer for measuring an earth field parameter and a borehole position parameter selected from the borehole inclination and the borehole azimuth, after which determining the difference between the measured earth field parameter and a known magnitude of said earth field parameter, and determining the ratio of said difference to the theoretical measurement uncertainty of the earth field parameter; and the uncertainty of the measured position parameter. 2. The method of claim 1, wherein said sensor comprises at least three magnetometers and at least three accelerometers. 3. The method of any of claims 1-2, wherein the step of determining theoretical measurement uncertainties of said parameters comprises determining the theoretical measurement uncertainties of a group of sensors to which the selected sensor pertains. 4. The method of any of claims 1-3, wherein said theoretical measurement uncertainties are based on at least one of the sensor uncertainty and an uncertainty of the earth field parameter. 5. The method of any of claims 1-5, further comprising disqualifying the measurements if said ratio exceeds 1. 6. The method of any of claims 1-5, wherein said position parameter is selected from the borehole inclination and the borehole azimuth. 7. The method of claim 6, wherein in a first mode of operation the position parameter forms the borehole inclination, the earth field parameter forms the earth gravity field, and the theoretical uncertainties of the position parameter and the earth field parameter are based on the sensor uncertainty. 8. The method of claim 6 or 7, wherein in a second mode of operation the position parameter forms the borehole azimuth, the earth field parameter forms the earth magnetic field strength, and the theoretical uncertainties of the position parameter and the earth field parameter are based on the sensor uncertainty. 9. The method of any of claims 6-8, wherein in a third mode of operation the position parameter forms the borehole azimuth, the earth field parameter forms the earth magnetic field strength, and the theoretical uncertainties of the position parameter and the earth field parameter are based on the uncertainty of the earth magnetic field. 10. The method of any of claims 6-9, wherein in a fourth mode of operation the position parameter forms the borehole azimuth, the earth field parameter forms the dip angle of the earth magnetic field, and the theoretical uncertainties of the position parameter and the earth field parameter are based on the sensor uncertainty. 11. The method of any of claims 6-10, wherein in a fifth mode of operation the position parameter forms the borehole azimuth, the earth field parameter forms the dip angle of the earth magnetic field, and the theoretical uncertainties of the position parameter and the earth field parameter are based on the uncertainty of the earth field parameter. 12. The method of any of claims 8-11, wherein the step of determining the uncertainty of the measured position parameter comprises determining the maximum absolute value of the uncertainties of the measured position parameters determined in the second, third, fourth and fifth mode of operation.