Downhole combination tool

A system for guiding and drilling a subterranean borehole to intercept a subterranean ferromagnetic body exhibiting target magnetic field comprising:

• (1) a subsurface tool comprising a non-magnetic housing, a first sensing means within said housing for continuously measuring the earth's gravity field, a second sensing means within said housing for continuously measuring the components of a magnetic field along mutually orthogonal axes simultaneously at two locations in said borehole;
• said tool further comprising means for transferring electrical current from a location inside said drill string into the earth formation being drilled, said tool being installed in a drill string proximate a collar wherein said means for transferring electrical current from an electrical supply conductor comprises:
• (a) at least one current conducting pin extending in electrically insulated relation through said drill string;
• (b) formation contactor means extending from said current conducting pin means for electrically transmitting current into the wall of the bore hole drilled;
• and
• (c) guide and latch means comprising a pair of elongated guide legs formed at a juncture with a latch pin receptacle depending downwardly from said guide leg juncture, said guide and latch means being connected to said electrical supply conductor and supported by said wireline and disposed to establish guiding and releasable latching relation with said current conducting pin means as said guide and latch means is moved downwardly by said wireline;
• said guide and latch means being of bifurcated form defining a pair of elongated depending guide legs disposed for guiding contact with current conducting pin means and an electrical contact latch receptacle receiving said current conducting pin means in electrically contacting releasable latched relation therein;
• (2) transmission and receiving means mounted in said housing and operatively connected to said first and second sensing means for transmitting said gravity and magnetic field measurements to the surface while drilling and for receiving guidance control information transmitted to said tool;
• and
• (3) surface equipment in communication with said housing transmission and receiving means comprising processing means for continuously calculating azimuth and inclination of said borehole and position of said borehole relative to said subterranean body using measurements of said first and said second sensing means.