Abstract: An electromagnetic method and apparatus for directional drilling guidance of horizontal boreholes for the installation of pipelines and communication cables beneath rivers, highways and other obstacles is disclosed. A solenoid source, with horizontal axes, generates alternating electromagnetic fields which are measured in the borehole by a magnetometer with known orientation with respect to the direction of gravity near the drill bit. A preferred embodiment has a useable range of 150 meters from the source.

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: An apparatus and method for surveying the path of a borehole includes two single-axis field sensors located at a radius centered at a fixed location. Guide wires are located along the earth's surface above the prescribed borehole path and the known electromagnetic field produced by current in the guide wires are detected by the sensors. Values of X and Y vectors at multiple locations on a spherical surface at the radial distance of the sensors are calculated and compared with measured values to define the location of the sensors on the spherical surface to permit the lateral spacing between the sensors and the desired borehole path to be determined.