Alcan International Limited

Teleco Oilfield Services Inc.

Richard D. Dipersio

Martin E. Cobern

Edmund M. Hamlin

Edmund M Hamlin

Martin E Cobern

Frederick A Stone

Richard D DiPersio

Richard D Dipersio

A method and apparatus is presented for measuring the azimuth angle of a borehole being drilled, the data for determining the azimuth angle being obtained while the drillstring is rotating.

Method and apparatus for measurement of azimuth of a borehole while

A method is presented, for use in borehole drilling, for correcting errors in azimuth determination resulting from variations in the earth's magnetic field to which a measuring instrument is exposed. The method distinguishes between variations in the earth's magnetic field caused by the drillstring and variation caused by external sources, and the method corrects only for errors caused by the drillstring. If the error is caused by the drillstring, an azimuth correction is made based on dip angle data, thereby reducing errors caused by scale factor variations since dip angle is a ratio quantity of magnetic field components.

Method for the detection and correction of magnetic interference in the

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Tehachapi, CA, United States of America

Edmund M Hamlin