System for continuously guided drilling

A guided drilling system for drilling in a desired direction comprising:

• a rotatable drilling shaft driven by a motor adapted to drive said drilling shaft,
• an orientation sensor, located on said rotatable drilling shaft, constructed and arranged to detect deviation of said shaft from said desired direction during rotation of said shaft while drilling, said sensor adapted to produce control signals dependent upon said detected deviation,
• a steerable pilot bit, mounted on the end of said drilling shaft, adapted to drill in said desired direction by utilizing a mechanical cutter in conjunction with multiple fluid jets disposed to provide preferential flushing at a selected region,
• a conical reamer mounted on a stiff section of said drilling shaft at a location spaced substantially above said steerable pilot bit to provide a known pivot point for deflection that enables correction of the drilling direction by said pilot bit, said conical reamer adapted to enlarge the diameter of a hole formed by said pilot bit while providing a tight lateral constraint to said shaft, and
• fluid modulation means, responsive to said sensor, adapted to regulate said jets of fluid to achieve preferential flushing in response to said signals from said sensor to correct detected deviation of said shaft from said desired direction.

For detecting deviation from vertical of a rotating shaft, a tiltmeter mounted on said shaft and comprising:

• a mechanical oscillator carried by said rotatable shaft, said mechanical oscillator including a mass disposed in a generally neutral position when said shaft, while rotating is vertical and being caused to oscillate by gravity action when said shaft, while rotating, deviates from the vertical,
• said oscillator adapted to have its natural frequency of oscillation matched to the operating frequency of rotation of said shaft, to enable said oscillator to amplify tilt-induced oscillations,
• a transducer coupled to said oscillator adapted to sense the oscillations of said oscillator, and
• indication means responsive to said transducer for determining the phase relationship of the oscillations relative to the angular position of said shaft and producing said signals of said shaft deviation from vertical.

A method of drilling in a desired direction comprising the steps of:

• (a) providing a rotating drilling shaft driven by a motor,
• (b) providing a tight stabilizer mounted on a stiff section of said drilling shaft at a location spaced substantially above a steerable bit to provide a known pivot point for deflection that enables correction of the drilling direction by said steerable bit,
• (c) drilling in the desired direction by using said steerable bit mounted on the end of said drilling shaft, said steerable bit utilizing multiple fluid jets for providing preferential flushing at a selected region,
• (d) detecting deviation of said shaft from said desired direction during rotation of said shaft, while drilling, using an orientation sensor located on said rotating drilling shaft, said sensor producing control signals dependent upon said detected deviation, and
• (e) regulating said jets of fluid using fluid modulation means for achieving directional drilling by said preferential flushing, said fluid modulation means being responsive to said signals from said sensor detecting deviation of said shaft from said desired direction.

A method of drilling in a desired direction comprising the steps of:

• (a) providing a rotating drilling shaft driven by a motor,
• (b) drilling in said desired direction by using a steerable pilot bit mounted on the end of said drilling shaft, said steerable bit utilizing a mechanical cutter in conjunction with multiple fluid jets for providing preferential flushing at a selected region,
• (c) enlarging the diameter of a hole formed by said pilot bit using a conical reamer mounted on a stiff section of said drilling shaft at a location spaced substantially above said steerable pilot bit to provide a known pivot point for deflection that enables correction of the drilling direction by said pilot bit, said conical reamer providing a tight lateral constraint to said shaft,
• (d) detecting deviation of said shaft from said desired direction during rotation of said shaft, while drilling, using an orientation sensor located on said rotating drilling shaft, said sensor producing control signals dependent upon said detected deviation, and
• (e) regulating said jets of fluid using fluid modulation means for achieving directional drilling by said preferential flushing, said fluid modulation means being responsive to said signals from said sensor detecting deviation of said shaft from said desired direction.