A rotary steerable drill string (16) employs a drill bit (10) selected to positively contribute to underpressure in a preselected azimuthal segment of the borehole relative to an opposing azimuthal section. Generally, a high flow velocity of drilling fluid in the selected azimuthal segment relative to in other segments will result in a more pronounced underpressure in the selected azimuthal segment. Drill bit designs which locally enhance the drilling fluid flow velocity are proposed to be employed in the present rotary steerable drill string.

A system can be used for drilling a wellbore. The system can include a steering collar, an actuation cylinder, and a radial seal. The steering collar can be positioned on a drilling tool for forming a wellbore. The actuation cylinder can be positioned on the drilling tool for abutting a steering pad for actuating the steering pad. The radial seal can be positioned on the drilling tool between the steering collar and the actuation cylinder.

A cartridge for a drill bit of a rotary directional drilling system, the cartridge comprising: a cartridge housing having an inlet end for receiving drilling fluid from a drill string and an outlet end at which drilling fluid can exit the cartridge housing; a flow diverter configured to selectively control the flow direction of drilling fluid as the drilling fluid exits the cartridge housing; and a bearing assembly for supporting the flow diverter; wherein the bearing assembly comprises at least one bearing located at the outlet end of the cartridge housing.

A new horizontal directional drilling (HDD) bit comprising a bit body is provided with illustrated embodiments including a flat bit design and a cobble bit design. Cutter teeth may be cut (e.g. formed or machined) into the base steel material of the bit body. Additionally, a broken edge profile may be generated to avoid sharp corners for better receipt of hard facing material such as laser clad beads that may be applied in higher wear regions.

Spherical projectiles may be used to form one or more holes in geologic or other material. These holes may be used for drilling, tunnel boring, excavation, and so forth.

A drill bit comprises a bit body having a longitudinal axis and a blade extending radially outward from the longitudinal axis along a face region and axially along a gauge region. A gauge region includes a cutting element located proximate to an uphole edge of the blade in the gauge region. A remainder of the gauge region is free of cutting elements mounted thereon. A method of drilling a borehole comprises rotating the bit about the longitudinal axis, engaging a formation with cutting elements mounted to the face region, and increasing a lateral force applied substantially perpendicular to the longitudinal axis such that the cutting element engages the formation and such that side cutting exhibited by the tool is initially minimal and substantially constant and subsequently increases in a substantially linear manner with increasing lateral force.

A rotary drill bit includes movable gauge elements biased to protrude radially through a circumferential engagement surface of a gauge pad. The gauge elements are retractable to protrude a lesser distance against the bias of a biasing mechanism. Fluid chambers are defined adjacent the gauge elements, and fluid is permitted to be bled into and out of the fluid chambers to delay and slow the retraction and extension of the gauge elements. During straight drilling operations, the biasing mechanisms maintain the gauge elements in an extended position providing stability to the drill bit. When a steering force is applied to the drill bit, the gauge elements retract slowly as fluid is bled from the fluid chambers. As the gauge elements rotate with the drill bit, the retracted configuration may be maintained as gauge elements disengage the geologic formation on a side of the drill bit opposite the steering direction.

A rotary steerable system including a steering section and a control section. A combined length of the steering section and the control section is less than 150 inches, preferably less than 80 inches, more preferably less than 75 inches, and most preferably less than 70 inches. A length to steering section diameter ration is less than 13, less than 12, less than 10, or less than 9. The steering section diameter is a minimum diameter of the steering section.

A rotary steerable system including a steering section having at least one piston, at least one distribution flow passage extending from a valve to one of the pistons, and two main flow passages bypassing the pistons. At least a portion of each main flow passage is closer to a central point of the steering section than an outer boundary of the distribution flow passage. At least a portion of each main flow passage may also be closer to the central point of the steering section than an inner boundary of the pistons in a retracted position. The distribution flow passages are contained within a central area, with a ratio of a central area diameter to steering section diameter being 0.5 or less, preferably 0.4 or less. The steering section may include two piston sets and two distribution flow passages each extending from the valve to a piston.

A rotary steerable system including a steering section having at least one piston configured to extend a stroke length radially outward from a default position when activated. A ratio of the stroke length to a steering section diameter is greater than about 0.06. The steering section includes two piston sets. A ratio of a length of the piston to a diameter of the piston is between 1 and 1.4.