A drill bit performs pilot rock-breaking using an outer annular drill bit and breaks a central rock pillar using a central drill bit mounted in the middle of the annular drill bit and located inside a drill bit body to induce unloading of a bottom hole stress. A method mixes rock debris produced by rock breaking of the central drill bit as abrasive with the drilling fluid flowing into the entire drill bit as abrasive jet liquid phase to form an abrasive jet. The method includes obtaining an annular borehole by braking, and breaking the rock pillar at the inner side of the annular borehole to induce unloading of the bottom hole stress, mixing the rock debris produced by breaking the rock pillar at the inner side of the annular borehole as abrasive with the drilling fluid entering the drill bit to form an abrasive jet.

A drill bit performs pilot rock-breaking using an outer annular drill bit and breaks a central rock pillar using a central drill bit mounted in the middle of the annular drill bit and located inside a drill bit body to induce unloading of a bottom hole stress. A method mixes rock debris produced by rock breaking of the central drill bit as abrasive with the drilling fluid flowing into the entire drill bit as abrasive jet liquid phase to form an abrasive jet. The method includes obtaining an annular borehole by braking, and breaking the rock pillar at the inner side of the annular borehole to induce unloading of the bottom hole stress, mixing the rock debris produced by breaking the rock pillar at the inner side of the annular borehole as abrasive with the drilling fluid entering the drill bit to form an abrasive jet.

A hybrid wellbore drilling bit assembly and a method for drilling a borehole with a hybrid wellbore drilling bit assembly are described. A base connects the hybrid wellbore drill bit assembly to a drill string. Blades are connected to the base, extending away from the base along the longitudinal axis and tapering toward the longitudinal axis of the hybrid wellbore drilling bit assembly base creating a tapered cavity. The blades have cutters to shear a core of the Earth that enters the cavity. The core of Earth expands in the cavity. A crusher is connected to the base and positioned within the cavity which crushes the core of Earth.

A hybrid wellbore drilling bit assembly and a method for drilling a borehole with a hybrid wellbore drilling bit assembly are described. A base connects the hybrid wellbore drill bit assembly to a drill string. Blades are connected to the base, extending away from the base along the longitudinal axis and tapering toward the longitudinal axis of the hybrid wellbore drilling bit assembly base creating a tapered cavity. The blades have cutters to shear a core of the Earth that enters the cavity. The core of Earth expands in the cavity. A crusher is connected to the base and positioned within the cavity which crushes the core of Earth.

A drill bit comprises a first and a second body received within the first body. Each of the first body and second body has a respective crown, each crown having an inner and an outer operative circumference. The outer operative circumference of the second body and the inner operative circumference of the first body can define a first volume that can receive a tubular core sample. The second body can define a break surface that breaks the tubular core sample into core pieces. The drill bit can be employed in a borehole with a reverse circulation system that pumps fluid around an outer surface of the bit, and returning fluid can carry the core pieces out of the borehole.

A drill bit comprises a first and a second body received within the first body. Each of the first body and second body has a respective crown, each crown having an inner and an outer operative circumference. The outer operative circumference of the second body and the inner operative circumference of the first body can define a first volume that can receive a tubular core sample. The second body can define a break surface that breaks the tubular core sample into core pieces. The drill bit can be employed in a borehole with a reverse circulation system that pumps fluid around an outer surface of the bit, and returning fluid can carry the core pieces out of the borehole.

A drill bit having a central axis can comprise a shank defining an inner bore and a crown having a cutting face. The crown can define an outer operative circumference. The crown can comprise a core-receiving slot in communication with the inner bore of the shank. One or more peripheral slots can be in communication with the inner bore of the shank. The crown can comprise one or more face channels that are in communication with the core-receiving slot and a respective peripheral slot. A base portion can be positioned within the core-receiving slot. The base portion can define a breaking surface. The peripheral slots can be configured to receive fluid moving in a distal direction toward the cutting face of the crown. The face channels can be configured to deliver fluid from the respective peripheral slot to the core-receiving slot.

A drill bit having a central axis can comprise a shank defining an inner bore and a crown having a cutting face. The crown can define an outer operative circumference. The crown can comprise a core-receiving slot in communication with the inner bore of the shank. One or more peripheral slots can be in communication with the inner bore of the shank. The crown can comprise one or more face channels that are in communication with the core-receiving slot and a respective peripheral slot. A base portion can be positioned within the core-receiving slot. The base portion can define a breaking surface. The peripheral slots can be configured to receive fluid moving in a distal direction toward the cutting face of the crown. The face channels can be configured to deliver fluid from the respective peripheral slot to the core-receiving slot.

A drill bit comprises a first and a second body received within the first body. Each of the first body and second body has a respective crown, each crown having an inner and an outer operative circumference. The outer operative circumference of the second body and the inner operative circumference of the first body can define a first volume that can receive a tubular core sample. The second body can define a break surface that breaks the tubular core sample into core pieces. The drill bit can be employed in a borehole with a reverse circulation system that pumps fluid around an outer surface of the bit, and returning fluid can carry the core pieces out of the borehole.

A drill bit comprises a first and a second body received within the first body. Each of the first body and second body has a respective crown, each crown having an inner and an outer operative circumference. The outer operative circumference of the second body and the inner operative circumference of the first body can define a first volume that can receive a tubular core sample. The second body can define a break surface that breaks the tubular core sample into core pieces. The drill bit can be employed in a borehole with a reverse circulation system that pumps fluid around an outer surface of the bit, and returning fluid can carry the core pieces out of the borehole.