Provided, in one aspect, is a well system and a method for forming a well system. The well system, in one aspect, includes a main wellbore, the main wellbore having a main wellbore open hole section, and a lateral wellbore extending from the main wellbore, the lateral wellbore having a lateral wellbore open hole section. The well system, according to this aspect, further includes a main bore completion located within the main wellbore and a lateral bore completion located within the lateral wellbore, and a multilateral junction positioned at an intersection between the main wellbore open hole section of the main wellbore and the lateral wellbore open hole section of the lateral wellbore, the multilateral junction including a main bore leg forming a first pressure tight seal with the main bore completion and a lateral bore leg forming a second pressure tight seal with the lateral bore completion such that the main bore completion and the lateral bore completion are hydraulically isolated from one another.

A downhole tool includes a tool body and an actuator coupled to and selectively extendible relative to the tool body. The actuator has a working face that contacts a downhole formation, and which includes an upper portion and a lower portion. The lower portion has a tapered surface that is directed radially inwardly and axially downwardly relative to the first portion, with at least a portion of the tapered surface including an ultrahard material having a different coefficient of friction as compared to a first material of the upper portion.

A downhole tool includes a tool body and an actuator coupled to and selectively extendible relative to the tool body. The actuator has a working face that contacts a downhole formation, and which includes an upper portion and a lower portion. The lower portion has a tapered surface that is directed radially inwardly and axially downwardly relative to the first portion, with at least a portion of the tapered surface including an ultrahard material having a different coefficient of friction as compared to a first material of the upper portion.

A rotary valve can include a seat and a rotary actuator, each with a surface, the rotary actuator rotatably mounted to a housing. The surfaces can form a seal due to their engagement with an engagement force used to maintain the engagement. One biasing device can elevate pressure in a sealed volume in the valve at a constant level above an external pressure. The elevated pressure can produce a pressure differential across the rotary actuator, thereby producing at least a portion of the engagement force. Another biasing device can act between a splined hub and a mated splined shaft, thereby applying at least a portion of the engagement force through the shaft to the rotary actuator. Fluid flowing through a screen can create a pressure drop, thereby causing a pressure differential across the rotary actuator and applying at least a portion of the engagement force to the surfaces.

A rotary valve can include a seat and a rotary actuator, each with a surface, the rotary actuator rotatably mounted to a housing. The surfaces can form a seal due to their engagement with an engagement force used to maintain the engagement. One biasing device can elevate pressure in a sealed volume in the valve at a constant level above an external pressure. The elevated pressure can produce a pressure differential across the rotary actuator, thereby producing at least a portion of the engagement force. Another biasing device can act between a splined hub and a mated splined shaft, thereby applying at least a portion of the engagement force through the shaft to the rotary actuator. Fluid flowing through a screen can create a pressure drop, thereby causing a pressure differential across the rotary actuator and applying at least a portion of the engagement force to the surfaces.

A downhole tool control system for a drill string rotary steerable tool that includes a body having an inner chamber, a piston gallery extending between the inner chamber and a piston port, and an exhaust gallery extending between the inner chamber and an exhaust port. A spool in the inner chamber is movable into a plurality of positions to direct and control the timing and duration of the flow of drilling fluid to energize pistons of the rotary steerable tool, and to de-energize the pistons. The spool includes a first passage in fluid communication with a drilling fluid inlet port but not the exhaust port, and a second passage in fluid communication with the exhaust port but not the drilling fluid inlet port.

A downhole tool control system for a drill string rotary steerable tool that includes a body having an inner chamber, a piston gallery extending between the inner chamber and a piston port, and an exhaust gallery extending between the inner chamber and an exhaust port. A spool in the inner chamber is movable into a plurality of positions to direct and control the timing and duration of the flow of drilling fluid to energize pistons of the rotary steerable tool, and to de-energize the pistons. The spool includes a first passage in fluid communication with a drilling fluid inlet port but not the exhaust port, and a second passage in fluid communication with the exhaust port but not the drilling fluid inlet port.

A method for drilling a subterranean wellbore includes rotating a drill string in the subterranean wellbore to drill the wellbore. The drill string includes a rotary steerable tool or a steerable drill bit including at least first and second axially spaced pads configured to extend radially outward from a tool body and engage a wall of the wellbore. Radial displacements of each of the first and second axially spaced pads are measured while drilling. The measured radial displacements are processed to compute a rate of penetration of drilling.

A method for drilling a subterranean wellbore includes rotating a drill string in the subterranean wellbore to drill the wellbore. The drill string includes a rotary steerable tool or a steerable drill bit including at least first and second axially spaced pads configured to extend radially outward from a tool body and engage a wall of the wellbore. Radial displacements of each of the first and second axially spaced pads are measured while drilling. The measured radial displacements are processed to compute a rate of penetration of drilling.

A bottom hole assembly (BHA) includes a whipstock having a latch release mechanism and a milling tool having a plurality of blades and a lock mechanism. The BHA also includes a collar coupled to the whipstock and disposed about a portion of the milling tool, wherein the blades of the milling tool abut the collar. The milling tool is releasably coupled to the whipstock by the interaction of the latch release mechanism and the lock mechanism.