Geomagnetic referencing-the real-time compass for directional drillers

Schlumberger has introduced the geomagnetic referencing service (GRS) as a cost-effective alternative to conducting gyroscopic surveys in realtime drilling applications. GRS provides accurate data on wellbore position and enables timely corrections to wellbore trajectory. Surveying engineers use a proprietary algorithm, a 3D crustal model and a time- and depth-varying geomagnetic reference to correct MWD measurements for magnetic drillstring interference, calculate tool orientation from the corrected measurements and advise the directional driller on course adjustments. Coordination between the operator, directional drilling contractor, MWD survey provider, geomagnetic observatory and survey engineer is essential for managing this survey technique. The workflow for geomagnetic referencing includes simultaneous acquisition and quality control of two data streams-MWD survey data at the rig site and real-time magnetic data at the observatory.