System and method for casing drilling with a subsea casing drive

Abstract

A system and method for casing drilling with a subsea casing drive adapted to engage at the outer circumference of the casing string, to impart a linear force and/or torque to the casing string, and such a subsea casing drive per se are disclosed. During drilling, the subsea casing drive is provided in a subsea unit further comprising a blowout preventer, a pressure control device and a mud pump with an outlet to a mud hose connectable to a surface vessel. The wellbore is drilled by driving the bottom hold assembly, BHA, and the casing string into the wellbore by the subsea casing drive, while discharging mud and cuttings via the mud hose and supplying mud to the BHA from the mud circulation system on the vessel via the landing string and casing string.

Claims

1. A method for casing drilling a deepwater subsea slim hole wellbore wherein use is made of a surface vessel and of a subsea unit, the subsea unit comprising: a subsea blowout preventer; a subsea pressure control device; a subsea mud pump with an outlet to a mud hose connectable to the surface vessel; and a subsea casing drive, adapted to engage at the outer circumference of the casing string, to impart a linear force and/or torque to the casing string, the method comprising the steps of: installing the subsea unit onto a wellhead; providing a bottom hole assembly, BHA, with a drill bit at a lower end of a casing joint; assembling multiple casing joints to form a casing string while suspending the casing string from the vessel; connecting a swivel to a top end of the casing string; connecting a landing string to the swivel, the swivel allowing rotation of the casing string with respect to the landing string; lowering the interconnected BHA and casing string into the subsea unit; and drilling the wellbore, wherein the drill bit of the BHA is rotated and wherein the casing string is driven by the subsea casing drive, while discharging mud and cuttings via the mud hose and supplying mud to the BHA from a mud circulation system on the vessel via the landing string and casing string.

2. The method according to claim 1, wherein the BHA comprises a mud motor, and wherein the step of driving the BHA is performed by supplying mud to the mud motor of the BHA.

3. The method according to claim 1, wherein the landing string is embodied as coiled tubing, and wherein the vessel is provided with a heave compensated coiled tubing injector to provide heave compensation during drilling.

Description

(1) The invention is further explained in relation to the drawings, in which:

(2) FIG. 1 depicts a schematic side view of the casing drilling system of the first aspect of the invention.

(3) In FIG. 1 a casing drilling system 1 is shown, according to a first aspect of the invention, for a deepwater subsea slim hole wellbore 2. The wellbore 2 comprises a surface termination, called a wellhead 4 at the bottom of the sea, indicated with reference numeral 14. This is also referred to as the mudline.

(4) The casing drilling system 1 comprises a surface vessel 3, provided on the water surface. The waterline is indicated with reference numeral 13. The vessel is a relatively small vessel, as it does not have any riser-related equipment. The surface vessel does comprise a casing string assembly installation, not shown, to assemble casing joints together to form a casing string 12. Furthermore, according to the first aspect of the invention, a bottom hole assembly (BHA) 11 is to be connected to a lower end of the casing string, and a swivel 15 to an upper end of the casing string. A landing string 16 is connected to the swivel, and the vessel 3 comprises a hoist system 17 suitable to lower and suspend the weight of these interconnected BHA 11, casing string 12, swivel 15 and landing string 16.

(5) In the shown embodiment, the landing string 16 is embodied as coiled tubing. The hoist system 16 of the vessel is embodied as a heave compensated coiled tubing injector 17, to provide heave compensation to the interconnected BHA, casing string, swivel and landing string during drilling. Alternative hoist systems are also conceivable. It is also conceivable that the heave compensation of the interconnected elements is provided differently, e.g. via the swivel or the landing string.

(6) Furthermore, the casing drilling system 1 comprises a subsea unit 5, installed on top of the wellhead 4. The subsea unit comprises a blowout preventer (BOP) 6, provided directly above the wellhead 4. Thereabove a pressure control device (PCD) 7 is provided. It is conceivable that this is a rotating control device (RCD). In the casing drilling system of the invention, a mud pump 8 is provided in the vicinity of the PCD, to provide a discharge of mud and drilling fluids and cuttings from the subsea unit 5 directly to the surface vessel 3, via mud hose 9.

(7) In the casing drilling method according to the first aspect of the invention, the interconnected BHA 11, casing string 12, swivel 15 and landing string 16 are lowered into the water 19. Advantageously, in the shown embodiment, the subsea unit 5 is provided with a guide funnel 18, to lower the interconnected BHA and casing string into the subsea unit 5.

(8) Then, the wellbore 2 is being drilled by driving the BHA and the casing string into the wellbore by the subsea casing drive 10, engaging at the outer circumference, i.e. the exterior of the casing string 12. Mud is supplied to the BHA from a mud circulation system 20 on the vessel via the landing string 16 (through the swivel 15) and casing string 12. The mud is a drilling fluid used to aid the drilling process. The BHA is optionally provided with a mud motor 11a, in which case the mud is used to drive the mud motor. Another function of the mud is to provide hydrostatic pressure.