Provided is a two part drilling and running tool, a downhole tool, a well system, and a method for forming a well system. The two part drilling and running tool, in at least one aspect, includes a smaller assembly coupled to an end of a conveyance, the smaller assembly having a spline or slot located along an entire length (L.sub.S) thereof. The two part drilling and running tool, in accordance with this aspect, further includes a larger bit assembly slidably coupled to the conveyance, the larger bit assembly including an other of the slot or spline, wherein the spline or slot in the smaller assembly and the other of the slot or spline in the larger bit assembly are configured to engage one another to rotationally fix the smaller assembly relative to the larger bit assembly as the smaller assembly and the larger bit assembly slidingly engage one another.

A method and system for directional drilling while conveying a liner, with latching parking capabilities for multiple trips, is disclosed. As the wellbore is drilled, each casing and liner is installed having upper and lower interior latch couplings. A liner to be installed below a parent casing includes an exterior latch assembly dimensioned for connection to the interior latch couplings of the parent casing. A bottom hole assembly may include upper and lower exterior inner string latch assemblies for connection to the upper and lower interior latch couplings of the liner to be installed. Such arrangement allows the liner to be conveyed and installed with the bottom hole assembly while directional drilling and for the liner to be temporarily hung from the parent casing for bottom hole assembly change-out while drilling. Float plugs dimensioned to be landed at lower liner interior latch couplings may be provided for cementing operations.

A method and system for directional drilling while conveying a liner, with latching parking capabilities for multiple trips, is disclosed. As the wellbore is drilled, each casing and liner is installed having upper and lower interior latch couplings. A liner to be installed below a parent casing includes an exterior latch assembly dimensioned for connection to the interior latch couplings of the parent casing. A bottom hole assembly may include upper and lower exterior inner string latch assemblies for connection to the upper and lower interior latch couplings of the liner to be installed. Such arrangement allows the liner to be conveyed and installed with the bottom hole assembly while directional drilling and for the liner to be temporarily hung from the parent casing for bottom hole assembly change-out while drilling. Float plugs dimensioned to be landed at lower liner interior latch couplings may be provided for cementing operations.

The drilling tool includes a circular-cylindrical casing pipe; an annular ring bit disposed at a leading end of the casing pipe so as to be coaxial with the casing pipe and rotatable around a central axis of the casing pipe; and a pilot bi inserted into the casing pipe and has a leading end disposed at an inner peripheral part of the ring bit. The ring bit is engaged with the pilot bit in a rotational direction, and thereby is rotatable integrally with the pilot bit and is locked to the leading end of the pilot bit. Drilling tips are mounted on the leading ends of the pilot bit and the ring bit, and first drilling tips at an outermost periphery of the pilot bit and second drilling tips at an innermost periphery of the ring bit overlap each other in a rotational trajectory around the central axis.

The drilling tool includes a circular-cylindrical casing pipe; an annular ring bit disposed at a leading end of the casing pipe so as to be coaxial with the casing pipe and rotatable around a central axis of the casing pipe; and a pilot bi inserted into the casing pipe and has a leading end disposed at an inner peripheral part of the ring bit. The ring bit is engaged with the pilot bit in a rotational direction, and thereby is rotatable integrally with the pilot bit and is locked to the leading end of the pilot bit. Drilling tips are mounted on the leading ends of the pilot bit and the ring bit, and first drilling tips at an outermost periphery of the pilot bit and second drilling tips at an innermost periphery of the ring bit overlap each other in a rotational trajectory around the central axis.

Provided is a two part drilling and running tool, a downhole tool, a well system, and a method for forming a well system. The two part drilling and running tool, in at least one aspect, includes a smaller assembly coupled to an end of a conveyance, the smaller assembly having a spline or slot located along an entire length (L.sub.S) thereof. The two part drilling and running tool, in accordance with this aspect, further includes a larger bit assembly slidably coupled to the conveyance, the larger bit assembly including an other of the slot or spline, wherein the spline or slot in the smaller assembly and the other of the slot or spline in the larger bit assembly are configured to engage one another to rotationally fix the smaller assembly relative to the larger bit assembly as the smaller assembly and the larger bit assembly slidingly engage one another.

Provided is a two part drilling and running tool, a downhole tool, a well system, and a method for forming a well system. The two part drilling and running tool, in at least one aspect, includes a smaller assembly coupled to an end of a conveyance, the smaller assembly having a spline or slot located along an entire length (L.sub.S) thereof. The two part drilling and running tool, in accordance with this aspect, further includes a larger bit assembly slidably coupled to the conveyance, the larger bit assembly including an other of the slot or spline, wherein the spline or slot in the smaller assembly and the other of the slot or spline in the larger bit assembly are configured to engage one another to rotationally fix the smaller assembly relative to the larger bit assembly as the smaller assembly and the larger bit assembly slidingly engage one another.

A bottom hole assembly for a casing-while-drilling operation utilizes a tethered float valve to retrieve the bottom hole assembly after the casing string has been positioned at a desired wellbore depth.

Provided is a two part drilling and running tool, a well system, and a method for forming a well system. The two part drilling and running tool, in one aspect, includes a conveyance, and a smaller assembly coupled to an end of the conveyance. The two part drilling and running tool, in accordance with this aspect, further includes a larger bit assembly slidably coupled to the conveyance, the smaller assembly and larger bit assembly configured to slidingly engage one another downhole to form a combined bit assembly.

Provided is a two part drilling and running tool, a well system, and a method for forming a well system. The two part drilling and running tool, in one aspect, includes a conveyance, and a smaller assembly coupled to an end of the conveyance. The two part drilling and running tool, in accordance with this aspect, further includes a larger bit assembly slidably coupled to the conveyance, the smaller assembly and larger bit assembly configured to slidingly engage one another downhole to form a combined bit assembly.