Abstract: Apparatus and Methods are disclosed for determining the direction between a rotating magnetic field and alternating magnetic field sensors at a remote location. The curvature of a borehole drilling assembly between a rotating drill bit carrying a permanent magnet and sensors behind a drilling motor is measured to provide early indication of changes in drilling direction. A second application concerns measurement of the convergence and divergence and the skewness of two approximately parallel well bores to provide information for correcting the drilling direction to maintain parallelism. A third application measures the direction and distance to a point target to provide data for guiding drilling toward that target. The primary apparatus are an oriented, rotating permanent magnet and an oriented, three component alternating magnetic field sensor.

Abstract: Apparatus and Methods are disclosed for determining the direction between a rotating magnetic field and alternating magnetic field sensors at a remote location. The curvature of a borehole drilling assembly between a rotating drill bit carrying a permanent magnet and sensors behind a drilling motor is measured to provide early indication of changes in drilling direction. A second application concerns measurement of the convergence and divergence and the skewness of two approximately parallel well bores to provide information for correcting the drilling direction to maintain parallelism. A third application measures the direction and distance to a point target to provide data for guiding drilling toward that target. The primary apparatus are an oriented, rotating permanent magnet and an oriented, three component alternating magnetic field sensor.

Abstract: A method of electromagnetic geophysical exploration of the earth's subterranean formations wherein an array of magnetometers are deployed at reference sites to obtain a measure of horizontal components of the earth's electromagnetic field and magnetometers are simultaneously deployed at a plurality of exploratory sites within a region of interest to obtain a measure of the vertical component of the earth's electromagnetic field. Resultant correlations of the horizontal and vertical components of the electromagnetic field can provide a multidimensional representation of the earth's resistivity structure.

Abstract: A tuned borehole gravity gradiometer comprises a dipole mass system having means for selectively tuning the sensitivity of the gravity gradiometer to detect variations in the earth's gravity gradient within a borehole. The tuning means includes varying the metacentric height of the dipole mass system by selectively varying the center of gravity of the dipole mass system with respect to the metacenter of the dipole mass system.