Patent ID: 8180571
Filing Date: 2012-05-15
Classification: E21B

Abstract:
1. A method for surveying a wellbore comprising: obtaining theoretical data regarding field strength and dip angle of the earth's magnetic field in the proximity of the wellbore; drilling a wellbore with a drilling string, the drill string comprising a measuring-while-drilling (MWD) tool with at least one set of magnetometers and at least one set of accelerometers; measuring data regarding the field strength and dip angle of the earth's magnetic field in the proximity of the wellbore from at least one position from within the wellbore using the at least one set of magnetometers and the at least one set of accelerometers positioned in the wellbore; determining the presence of magnetic shielding effects of mud within the wellbore based on the measured data and the theoretical data; and applying a correction to the measured data to correct readings obtained by the MWD tool for the shielding effect of the mud.