Directional borehole drilling system and method

A directional borehole drilling system, comprising:

• at least one sonde for mounting within a drill string which is coupled to a controllable drill bit, said at least one sonde comprising:
• a storage medium that contains information that represents a desired drill bit trajectory,
• instrumentation that determines the present position and attitude angles of said bit when said bit is in a static position, and the bit's toolface angle when said bit is rotating, and
• a processor that receives said present position and dynamic toolface information from said instrumentation, determines the error between said present position and said desired trajectory, and provides said command signals to said controllable drill bit such that said drill bit bores in the direction necessary to reduce said error, said controllable drill bit comprising:
• a plurality of cone assemblies mounted about a central axis, each of which includes a cone which rotates about a respective axle and thereby drills a borehole when said bit is driven to rotate about said central axis, each cone assembly having a leg which is attached to a common frame and having its axle “toed out” such that the rolling cone exerts an outward radial force on the leg, and
• at least one mechanism coupled to respective ones of said cone assemblies that is actuated in response to a respective one of said command signals, said at least one mechanism arranged to force its respective cone to translate along its axle when actuated while allowing it to continue to rotate about its axle, and to allow its respective cone to be seated snugly against a thrust washer between it and said leg when not actuated while allowing it to continue to rotate about its axle,
• wherein each of said mechanisms comprises:
• a means for translating said mechanism's respective cone along said axle of said cone assembly, and
• a means for retaining said cone such that, when said cone is translated along its axle, it is restrained to a prescribed length of travel, and
• wherein said means for translating said cone comprises filling a closed cavity between said leg and the backside of said cone with pressurized hydraulic fluid when cone translation is commanded.

A directional borehole drilling system, comprising:

• a controllable drill bit, said bit comprising:
• a plurality of cone assemblies mounted about a central axis, each of which includes a cone that rotates about a respective axle and thereby drills a borehole when said bit is driven to rotate about said central axis, each cone assembly having a leg which is attached to a common frame and having its axle “toed out” such that the rolling cone exerts an outward radial force on the leg, and
• at least one mechanism coupled to respective ones of said cone assemblies that is actuated in response to a respective command signal, said at least one mechanism arranged to force its respective cone to translate longitudinally along its axle toward the center of said bit when actuated while allowing it to continue to rotate about its axle, and to allow its respective cone to be seated snugly against a thrust washer between it and said leg when not actuated while allowing it to continue to rotate about its axle,
• a drill string coupled to said controllable drill bit,
• a driving means coupled to said drill string that drives said bit to rotate about said central axis, and
• at least one sonde within said drill string that comprises:
• a storage medium that contains information that represents a desired drill bit trajectory,
• a first instrumentation package that determines the present position and attitude angles of said bit when said bit is in a static position,
• a second instrumentation package that determines the dynamic toolface angle of said bit and the positions of the cone assemblies coupled to said mechanisms when said bit is rotating about said central axis, and
• a processor that receives said present position and attitude angles and cone assembly position information from said instrumentation, determines the error between said present position and said desired trajectory, and provides said command signals to said controllable drill bit such that said drill bit bores in the direction necessary to reduce said error.

A directional borehole drilling system, comprising:

• a controllable drill bit, said bit comprising:
• a plurality of cone assemblies mounted about a central axis, each of which includes a cone that rotates about a respective axle and thereby drills a borehole when said bit is driven to rotate about said central axis, each cone assembly having a leg which is attached to a common frame and having its axle “toed out” such that the rolling cone exerts an outward radial force on the leg, and
• at least one mechanism coupled to respective ones of said cone assemblies that is actuated in response to a respective command signal, said at least one mechanism arranged to force its respective cone to translate along its axle when actuated while allowing it to continue to rotate about its axle, and to allow its respective cone to be seated snugly against a thrust washer between it and said leg when not actuated while allowing it to continue to rotate about its axle,
• a drill string coupled to said controllable drill bit,
• a driving means coupled to said drill string that drives said bit to rotate about said central axis, and
• at least one sonde within said drill string that comprises:
• a storage medium that contains information that represents a desired drill bit trajectory,
• a first instrumentation package that determines the present position and attitude angles of said bit when said bit is in a static position,
• a second instrumentation package that determines the dynamic toolface angle of said bit and the positions of the cone assemblies coupled to said mechanisms when said bit is rotating about said central axis, and
• a processor that receives said present position and attitude angles and cone assembly position information from said instrumentation, determines the error between said present position and said desired trajectory, and provides said command signals to said controllable drill bit such that said drill bit bores in the direction necessary to reduce said error,
• wherein each of said mechanisms comprises:
• a closed cavity formed between the backside of the cone of said mechanism's respective cone assembly, its leg and its axle, wherein hydraulic fluid may be injected to cause said cone to translate along said axle when actuated and to allow its respective cone to rest against its leg when not actuated,
• an electro-hydraulic valve assembly mounted in said leg,
• a hydraulic accumulator located within said leg,
• a journal bearing existent between the cone and its axle, and
• a positive displacement hydraulic pump located within a bore in the center of said axle, said pump pressurizing hydraulic fluid stored in said accumulator to lubricate said journal bearing.

A method of directional drilling in a borehole, comprising the steps of:

• providing a controllable drill bit that comprises a plurality of cone assemblies mounted about a central axis, each of which includes a cone that rotates about a respective axle and can be made to translate or remain seated against a leg which is attached to a common frame,
• determining a desired trajectory for said drill bit,
• determining the present position of said drill bit,
• determining the error between said present position and said desired trajectory,
• rotating said drill bit about said central axis, determining the dynamic toolface angle of said bit, and
• causing, based on said present position and said dynamic toolface angle, at least one of said cones to translate longitudinally along its axle toward the center of said bit such that said drill bit bores in a direction necessary to reduce said error.

A controllable drill bit comprising:

• a plurality of cone assemblies mounted about a central axis, each of which includes a cone that rotates about a respective axle as said bit is rotated about said central axis and can be made to translate or be seated against a leg which is attached to a common frame,
• a plurality of mechanisms coupled to respective ones of said cone assemblies, each of which is actuated in response to a respective command signal, each mechanism arranged to force its respective cone assembly to translate longitudinally along its axle toward the center of said bit when actuated and to allow its respective cone assembly to rest against it leg when not actuated, each of said mechanisms comprising:
• a closed cavity formed between the backside of the cone of said mechanism's respective cone assembly, its leg and its axle, wherein hydraulic fluid may be injected to cause said cone to translate along said axle when actuated and to allow its respective cone to rest against its leg when not actuated,
• an electro-hydraulic valve assembly mounted in said leg,
• a hydraulic accumulator located within said leg,
• a journal bearing existent between the cone and its axle, and
• a positive displacement hydraulic pump located within a bore in the center of said axle, said pump pressurizing hydraulic fluid stored in said accumulator to lubricate said journal bearing.