Alsthom

Claude Dreuilhe

Georges Obrecht

In a method of measuring azimuth for non-vertical drilling, during rotation of the drill pipe string two components of the magnetic field are measured continuously within a cylindrical section of the drill pipe string. This section is fabricated from the ferromagnetic steel usually employed for fabricating the drill pipes. The two components are measured by a magnetometer and lie along two axes perpendicular to the axis of the section and rotating with it. At the moment when the component of the acceleration due to gravity is maximum along one of these two axes, an accelerometer device commands the calculation and recording of the ratio of the two measured components of the magnetic field. On the basis of the value thus recorded, the measured inclination of the drill pipe string and the local inclination of the magnetic field, the azimuth of the drill pipe string relative to magnetic north is calculated. The method may be used for the continuous determination of the position of a drilling tool during the progress of drilling along a curve.

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Saint Ismier, France

Claude Dreuilhe