ERROR REDUCTION IN COMPENSATION OF DRILL STRING INTERFERENCEFOR MAGNETIC SURVEY TOOLS

摘要

2105564 9216719 PCTABS00016 A method for determining the orientation of the axis of a borehole with respect to an earth-fixed reference coordinate system at a location in the borehole comprising the steps of: measuring two cross-borehole components or two-cross-borehole components and an axial component of the earth's gravity field at a location in the borehole; measuring two cross-borehole components of the earth's magnetic field; determining the inclination angle of the borehole axis from the gravity component measurements; determining the highside angle reference of the cross-borehole measured components of the earth's gravity and magnetic fields from the gravity component measurements; determining more than one individual estimate of the azimuthal orientation of the borehole axis from the inclination angle, the highside angle reference and the two measured cross-borehole components of the earth's magnetic field; determining an error indicative parameter for each individual estimate of the azimuthal orientation of the borehole axis; and determining a single estimate of the azimuthal orientation of the borehole axis based on the individual estimates of azimuthal orientation and the error indicative parameters for each estimate.