A blade on a downhole drilling tool includes a blade body and a blade cover. The blade cover is pre-sintered and conforming to the blade outer shape. The blade cover is attached to the blade body. The blade cover includes a seamless connection between a cover leading face and a cover outer face to reduce wear on the outer face of the blade.

A blade on a downhole drilling tool includes a blade body and a blade cover. The blade cover is pre-sintered and conforming to the blade outer shape. The blade cover is attached to the blade body. The blade cover includes a seamless connection between a cover leading face and a cover outer face to reduce wear on the outer face of the blade.

An earth-boring tool for drilling a subterranean formation includes a bit body having a central axis and a cavity extending into the bit body from an outer surface thereof. A bearing element assembly may be mounted within the cavity. The bearing element assembly comprises a lower retaining member, an upper retaining member mounted over to the lower retaining member, the upper retaining member comprising an aperture formed therethrough, and a spherical bearing element disposed over the lower retaining member and extending through the aperture formed through the upper retaining member. The spherical bearing element is rotatable about three axes of rotation within the lower retaining member and the upper retaining member.

A method for estimating and reducing high-frequency torsional oscillations (HFTO) during a downhole drilling operation includes estimating an HFTO propensity of an initial BHA configuration using a model that relates the HFTO propensity to at least a rock strength of a subterranean formation, a radius or diameter of the borehole, a drill bit body density, and a drill bit body radius or diameter. The estimated HFTO propensity is compared with an HFTO propensity threshold. The model is used to select a modified drill bit or bottom hole assembly (BHA) configuration that reduces the estimated HFTO propensity to a value below the HFTO propensity threshold. The modified drill bit or BHA configuration has an increased polar moment of inertia as compared to the initial drill bit or BHA configuration.

A method for estimating and reducing high-frequency torsional oscillations (HFTO) during a downhole drilling operation includes estimating an HFTO propensity of an initial BHA configuration using a model that relates the HFTO propensity to at least a rock strength of a subterranean formation, a radius or diameter of the borehole, a drill bit body density, and a drill bit body radius or diameter. The estimated HFTO propensity is compared with an HFTO propensity threshold. The model is used to select a modified drill bit or bottom hole assembly (BHA) configuration that reduces the estimated HFTO propensity to a value below the HFTO propensity threshold. The modified drill bit or BHA configuration has an increased polar moment of inertia as compared to the initial drill bit or BHA configuration.

In the drilling of oil and gas wells, some fluid isolation valves may be stuck in a closed position and may need to be milled out. Provided are methods and systems to dissipate heat and remove cuttings and shavings generated during milling of these fluid isolation barrier. The methods may include conveying a milling tool into a borehole, wherein the milling tool comprises a motor, a gear box coupled to the motor; a pump coupled to the gear box, and a mill bit coupled to the pump, milling a fluid isolation barrier positioned in the borehole using the milling tool, wherein heat is generated at the mill bit and by the motor during the milling of the fluid isolation barrier, and removing at least a portion of the heat by pumping fluid past the motor and the mill bit using the pump.

A PDC drill bit has a drill bit body and a blade. The blade is provided with cutting teeth. At least one cushion structure is rotatably connected to the drill bit body. The cushion structure makes contact with bottom hole rock, and the cushion structure swings in a direction opposite to the cutting of the drill bit. Alternatively, a cushioning portion on the cushion structure is eccentrically arranged. Under the action of the normal force of the bottom hole rock, the cushioning portion swings to an offset side. The cushion structure is detached from the bottom hole rock and is reset towards a free state under the action of a reset mechanism. Under complex motion conditions such as compound drilling and drilling into hard or non-uniform stratum conditions, the swing of the cushion structure absorbs an impact load and avoids impact damage to the cutting teeth.

A PDC drill bit has a drill bit body and a blade. The blade is provided with cutting teeth. At least one cushion structure is rotatably connected to the drill bit body. The cushion structure makes contact with bottom hole rock, and the cushion structure swings in a direction opposite to the cutting of the drill bit. Alternatively, a cushioning portion on the cushion structure is eccentrically arranged. Under the action of the normal force of the bottom hole rock, the cushioning portion swings to an offset side. The cushion structure is detached from the bottom hole rock and is reset towards a free state under the action of a reset mechanism. Under complex motion conditions such as compound drilling and drilling into hard or non-uniform stratum conditions, the swing of the cushion structure absorbs an impact load and avoids impact damage to the cutting teeth.

A mill for cutting a window in wellbore casing has cylindrical carbide or PDC cutters on its blades and non-cylindrical carbide cutting inserts located on the body of the mill where it first contacts the casing or has a relatively low cutter density. The mill may also include one or more elements made of softer material than the non-cylindrical carbide inserts, which are positioned on the blades, such as behind the non-cylindrical cutters on the same blade, where the window mill first contacts the casing during milling a window.