Abstract: A method for manufacturing NMR measurement-while-drilling tool having the mechanical strength and measurement sensitivity to perform NMR measurements of an earth formation while drilling a borehole, and a method and apparatus for monitoring the motion of the measuring tool in order to take this motion into account when processing NMR signals from the borehole. The tool has a permanent magnet with a magnetic field direction substantially perpendicular to the axis of the borehole, a steel collar of a non-magnetic material surrounding the magnet, antenna positioned outside the collar, and a soft magnetic material positioned in a predetermined relationship with the collar and the magnet that helps to shape the magnetic field of the tool. Due to the non-magnetic collar, the tool can withstand the extreme conditions in the borehole environment while the borehole is being drilled.

Abstract: A method for manufacturing NMR measurement-while-drilling tool having the mechanical strength and measurement sensitivity to perform NMR measurements of an earth formation while drilling a borehole, and a method and apparatus for monitoring the motion of the measuring tool in order to take this motion into account when processing NMR signals from the borehole. The tool has a permanent magnet with a magnetic field direction substantially perpendicular to the axis of the borehole, a steel collar of a non-magnetic material surrounding the magnet, antenna positioned outside the collar, and a soft magnetic material positioned in a predetermined relationship with the collar and the magnet that helps to shape the magnetic field of the tool. Due to the non-magnetic collar, the tool can withstand the extreme conditions in the borehole environment while the borehole is being drilled.

Abstract: A magnetic structure for producing a substantially uniform magnetic field in a region external to the structure. The field produced has a predetermined magnitude but with all of its first and second order partial derivatives with respect to spatial coordinates being equal to zero at any selected point within the uniform region. The structure includes a pair of elongated magnets which are magnetized along their longitudinal axis. The magnets are spaced from each other with their corresponding end poles facing each other. A pair of annular cylindrical magnets which are magnetized in a radial direction are mounted on the end faces of each of the elongated magnets. Another annular cylindrical magnet, also having its magnetization oriented in a radial direction is located on the midplane between the two elongated magnets. The combined effect of these magnets is to create a uniform toroidal field. This field is particularly suitable for use in NMR oil well logging applications.