Calculating directional drilling tool face offsets

Abstract

A drilling tool has a bent sub or a defined “High Side”. An instrument housing which includes a magnetometer is secured to the directional drilling tool. The magnetometer measures the magnetic field vector in the plane perpendicular to the tool axis. Prior to running the directional drilling tool and the instrument housing into the well, a magnetic source is positioned next to the instrument housing at a position near the magnetometer. The magnetic source is made and positioned such that its magnetic field at the magnetometer points to the chalk line of the high side of a bent sub. The net magnetic field generated from the source is obtained by the difference in magnetic field measurements before and while the magnetic source is applied The azimuthal angle between the net magnetic field vector and the x-axis of the magnetometer or other direction sensor reference point used for tool face calculation is obtained by a computer. This angle is the angular difference or offset angle between the sensor tool face and the high side of the bent sub (as mimicked by the magnetic source). This offset angle is recorded as a signed (±) number and is added to the sensor tool face to produce the bent sub's high side tool face during the drilling operation. No manual measurement of the offset angle and input is required.