Borehole angle control by gage corner removal effects from hydraulic fluid jet

In apparatus for drilling a borehole in earth material including a rotary drill bit, a drill string connected to the drill bit and extending into the borehole to position the drill bit in drilling contact with the earth material in the borehole, means for selectively continuously rotating the drill string and the drill bit connected thereto to drill and cut the borehole into the earth material, and an improved means for selectively controlling the advancement angle of the borehole cut by rotating said drill bit against the earth material comprising, in combination:

• a drill bit support structure;
• a cutter assembly positioned on said bit support structure, said cutter assembly comprising cutting elements arranged for cutting an axially extending cylindrical sidewall of the borehole and a drill face of the borehole extending transversely with respect to the sidewall and a gage corner of the borehole extending circumferentially from the drill face radially outward at an inclination to the sidewall;
• fluid jet emitting means connected to said drill bit structure for emitting at least one jet of pressurized fluid impinging essentially only on the gage corner material formed by said cutter assembly;
• means adapted for selectively conducting pressurized fluid through said jet emitting means during a predetermined partial interval of each one of a plurality of revolutions of said drill bit and for terminating conduction of pressurized fluid through said jet emitting means during the remaining interval of the one revolution of said drill bit,
• said means for selectively conducting pressurized fluid to said fluid emitting jet means further comprises:
• (a) energy deriving means for deriving energy from rotational movement of said drill string relative to the cylindrical sidewall of said borehole, said energy deriving means being fixed to said drill string at a predetermined position axially spaced from said connected drill bit at which gravity induced sag in said drill string causes said energy deriving means to contact the low side portion of the sidewall during an interval of one rotation of said drill string and to avoid contact with the sidewall during the remaining interval of one rotation, said energy deriving means deriving energy only during periods of contact with the sidewall of said borehole;
• and
• (b) means utilizing the energy derived for pressurizing a source of fluid and for supplying pressurized fluid to said jet emitting means during periods of contact of said energy deriving means with the sidewall of said borehole.