Shielding of Directional Magnetic Sensor Readings in a Measurement While Drilling Tool for Oil Well Positioning

Abstract

Magnetic materials in the drilling fluid used for drilling a petroleum well can significantly shield the Earth’s magnetic field as measured by magnetic sensors inside the drilling pipe. This has been shown to sometimes cause significant errors in the accuracy of borehole positioning using magnetic surveying. In this paper we present a physical approach for correcting the measured magnetic fields for such shielding. An explicit solution of the shielding problem is derived for the simplest case of a magnetic sensor on the axis of the borehole.