Wellbore position is computed from survey measurements taken by a measurement-while-drilling (MWD) tool in the bottomhole assembly (BHA). The MWD tool uses accelerometers and magnetometers to measure the Earth’s gravitational and geomagnetic fields. Knowing the direction of these two fields and using them as a frame of reference enable drillers to calculate inclination and direction (azimuth) of the wellbore. Local high-resolution in-field referencing (IFR) models have been produced for the Permian Basin that significantly improve the accuracy of MWD azimuth measurements.
Ellipse of Uncertainty (EOU)
Numerous error sources are associated with MWD-survey measurements, and each error source contributes in some form to the magnitude of uncertainty that propagates along the computed wellbore trajectory.
