A drill bit includes a shank having a threaded coupling formed at an upper end thereof; a bit body mounted to a lower end of the shank and having a plenum; a gage section forming an outer portion of the drill bit; a cutting face forming a lower end of the drill bit and including: a core receptacle formed at a center of the cutting face, operable to receive a core of earth, and including: a concave core cutter mounted to a bottom of the bit body; and a core port extending from the plenum through the bottom of the bit body and operable to discharge drilling fluid onto the core and core cutter; a plurality of blades protruding from a bottom of the bit body and extending from a periphery of the core receptacle to the gage section; and a plurality of leading cutters mounted along each blade.

A drill bit includes a bit body with high and low fluid pressure bodies. The low-pressure bit body includes a fixed cutting structure, and the high-pressure bit body includes a first high-pressure fluid channel and nozzle capable of withstanding fluid pressures greater than 40 kpsi (276 MPa). A bottomhole assembly includes a drill bit with a bit body having fixed cutter and fluid jetting portions. Low and high-pressure channels in the bit body exit in the fixed cutter and fluid jetting portions. The first high-pressure nozzle is coupled to the fluid jetting portion and the high-pressure fluid channel, and a plurality of fixed cutting elements are coupled to the fixed cutter portion. A pressure intensifier is coupled to the drill bit and is configured to increase a pressure of a fluid supplied to the high-pressure fluid channel in the bit body.

A wellbore downhole tool, comprising: a nozzle assembly, the nozzle assembly includes a nozzle including: a cylindrically-shaped tube with a substantially uniform outer diameter across substantially an entire height of the nozzle, at least one retaining body opening located in an outer wall of the nozzle; a holding body including: a conduit, the conduit sized to fit the nozzle there-through, an alignment opening extending from an outer surface of the holding body to the conduit; and a retaining body sized to fit within the alignment opening of the holding body and to contact the retaining body opening of the nozzle when the nozzle is inserted in the conduit such that the cylindrically-shaped tube of the nozzle cannot rotate or move further in or out of the conduit. A method of assembling the wellbore downhole tool is also described.

Earth-boring drill bits include a bit body, an element having an attachment feature bonded to the bit body, and a shank assembly. Methods for assembling an earth-boring rotary drill bit include bonding a threaded element to the bit body of a drill bit and engaging the shank assembly to the threaded element. A nozzle assembly for an earth-boring rotary drill bit may include a cylindrical sleeve having a threaded surface and a threaded nozzle disposed at least partially in the cylindrical sleeve and engaged therewith. Methods of forming an earth-boring drill bit include providing a nozzle assembly including a tubular sleeve and nozzle at least partially within a nozzle port of a bit body.

In accordance with some embodiments, a downhole drilling tool comprises a bit body, a blade on an exterior portion of the bit body, and a gage pad on the blade. The gage pad includes a ball retainer and a ball located in the ball retainer such that an exposed portion of the ball is positioned to contact a wellbore and rotate in response to frictional engagement with the wellbore.

In accordance with some embodiments, a downhole drilling tool comprises a bit body, a blade on an exterior portion of the bit body, and a gage pad on the blade. The gage pad includes a ball retainer and a ball located in the ball retainer such that an exposed portion of the ball is positioned to contact a wellbore and rotate in response to frictional engagement with the wellbore.

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.

Drill bits having flushing channels and surface features that cooperate to evacuate cuttings. The surface features can be provided as flutes, fins, and/or ribs defined in a body portion of the bits. Optionally, the surface features can define back-cutting edges the permit back reaming.

Drill bits having flushing channels and surface features that cooperate to evacuate cuttings. The surface features can be provided as flutes, fins, and/or ribs defined in a body portion of the bits. Optionally, the surface features can define back-cutting edges the permit back reaming.