GB2386623A

GB2386623A - Subsea casing deployment

Info

Publication number: GB2386623A
Application number: GB0206942A
Authority: GB
Inventors: Antony Stephen Bamford
Original assignee: Individual
Current assignee: Individual
Priority date: 2002-03-22
Filing date: 2002-03-22
Publication date: 2003-09-24
Also published as: GB0206942D0

Abstract

Casing is run from a floating vessel to the seafloor in deepwater by attaching it to an umbilical 11 suspended from the vessel in a catenary loop via upper 19 and lower 13 running tools. The lower running tool 13 provides orientation and a soft landing at the seafloor together with guidance into the wellbore. Automatic releasable attachment mechanisms, e.g inertial reel mechanisms, attach the casing to the umbilical 11 at intermediate points. On landing and correctly spacing out a casing hanger below a blowout preventer stack, the upper 19 and lower 13 running tools latch so that both can be recovered, together with the casing attachment mechanisms.

Description

Subsea Casing Deployment System This invention relates to running casing

to line the borehole for deepwater drilling operations conducted from a floating vessel.

In deepwater drilling operations it is normal to use a steel riser to connect the seafloor wellhead and the floating vessel. The riser provides a conduit for the drill string to make the hole and the casing is used to line the borehole after drilling. The internal diameter of this riser must normally allow all drilling tools and casing equipment to pass through it.

The size and weight of the riser system has a major impact on the vessel design.

Hence new methods of drilling from a floating vessel have been proposed based on small diameter, lightweight reeled riser systems with restricted internal diameters.

Running casing through this riser is not possible.

Other drilling is conducted using a conventional jointed drill string with returns to the sea floor. The new method of running casing described could also be used for this application. This invention describes in detail how casing strings can be assembled on a floating vessel attached to a single tensioned umbilical and deployed to the seafloor. It also describes how the casing string is orientated and landed at the appropriate position in the wellbore. Arrangements for cementing the casing in place and forming the annular seal are provided.

Figure 1 shows the general arrangement of one subsea drilling system to be used with this casing deployment system.

The well is established by running a suction anchor (1) on a high strength lightweight control umbilical (2), complete with a blowout preventer stack (3) already in place on the conductor casing (4) which is attached to and runs through the suction anchor (1) The entire assembly is deployed as a single unit on the tensioned umbilical.

Figure 1 shows two positions, one for drilling and the second for running casing.

When drilling has been completed to the desired depth, the drill string (5) and bottom hole assembly (6) are retracted into the lower riser or lubricator (7).

When the bit is above the level of the revolver (8), this can be rotated so that the drilling assembly can be parked in the storage receptacle (9). This exposes the wellbore ready to run casing.

The casing joints are connected to each other on the vessel in the manner illustrated in figure 2. An "A" frame (10), handling tower or similar structure is used to handle the casing joints. The advantage of an "A" frame is that it can be used to launch the casing over the side of the vessel (amidships) or over the stern. The tensioned Page 1

umbilical (11) is run over the sheave (12) which is positioned on the "A" frame. The angle of the "A" frame ( 10) may be adjusted according to operational requirements.

The lower casing running tool (13) is connected to the first joint of casing on deck.

This is in turn attached to the tensioned umbilical (11) The suspension deck (14) has provision to hang-ofthe casing while individual joints are comected. There is also a fairleader arrangement (15) to control and capture the tensioned umbilical making it much easier to connect individual joints (16) of casing to the umbilical.

The casing will be handled by a separate winch line (17) run over its sheave (18) on the "A" frame. When the requisite number of casing joints have been made up, the casing is suspended by the upper running tool (19) and connected to a flexible coiled tubing or riser (20). Provision must be made for a bend controller (21) at the attachment to the upper running tool. Alternative methods of rurming the casing include using an electric conductor cable as used in oilwell logging operations.

The flexible coiled tubing (20) together with its bend controller (21) are paid out over a "Big Wheel" injector system (22), designed to handle both diameters of pipe.

In order to ensure separation of the main riser or sheath (7) that is connected to the suction anchor (1) and the tensioned umbilical (11), it will be necessary for the latter to form a catenary by moving the vessel off location. This is illustrated in figure 3.

The "A" frame can be positioned in-board slightly to provide the ideal angle for the umbilical at surface.

The separation of lines should be adequate if the main riser or sheath has been weighted near to the surface.

The angular offset should be sufficient to prevent the coiled tubing string (20) from twisting up with the umbilical (11) by having the casing hanging on the low side of the umbilical. Also differences in tension and weight in water will further promote the separation. Figure 4 shows one embodiment for attaching the casing to the umbilical Inertial reels fixtures (23) are fitted over the umbilical (11) and are lined with suitable sacrificial material that protects the umbilical from damage (24) Each inertial reel fixture is connected to a slide fitting (25) that fits into a special receptacle (26) on the casing joint. This is designed for the purpose of retaining the connection, until a direct upward force parallel to the casing is applied.

Figure S shows the operation of landing the casing into the wellbore. The details of the operation of the lower casing running tool (13) can be seen. As the casing approaches the suction anchor (1), the vessel is repositioned so that the umbilical is as vertical as possible at the anchor. The incoming lower casing running tool travailing down the umbilical (11) first makes contact with the unbilical orientation pin (2). Orientation is either by rotation of a mule shoe arrangement (27) as shown, or alternatively with a powered rotation pin powered to ensure alignment of the incoming casing with the vvellbore. Once initial orientation has been made, as the Page 2

coiled tubing running string is further slacked off, allowing the sliders (28) to move downwards. A soft landing system implemented here would prevent shock loading.

The sliders connected to the lower running tool guide tube (29) are now orientated and further downward travel brings the latter down on the revolver. Provision may be made to slot it into the revolver plate as shown in figure 6. Some lock system may be required to react the bending loads that are expected to be applied to the guide tube in a strong current. The lower running tool guide tube (29) is suspended from the casing (16) by means of a collar and shoulder arrangement (30).

As shown in figure 7, further slacking of on the coiled tubing (20) allows the casing to enter the wellbore. As each inertial reel fixture (23) comes up against the lower running tool guide tube (29), the upward force removes the slide fitting (25) from the casing allowing the inertial reel to retract. Consideration could be given to creating a longitudinal slot in the guide tube (29) to store all the incoming fixtures once they have been removed from the casing.

The upper running tool (19) is attached to a landing string (31), a tubular designed to space out the casing hanger (32) to a sealing position below the blowout preventer stack (3) between the upper and lower side outlets 35 and 36. This is illustrated in figure 8.

The final landing results in a connection made between the upper running tool (19) and the lower running tool guide tube (29). This confirms the correct space out of the casing hanger below the blowout preventer stack (3) Upper and lower cementing plugs (33) and (34) of the type used in liner hangers are shown attached to the landing string (31). These are launched by a ball and dart arrangement inserted into the coiled tubing. The casing hanger would be set by means of hydraulic pressure applied down the coiled tubing (20) After releasing the hanger and energising the seal, the casing is cemented in place conventionally. With the upper running tool (19) and the lower running tool guide tube locked together, the entire running tool assembly and the inertial reel fixtures can be recovered to surface, leaving the cemented casing in place.

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Claims

We claim:

I. All methods of running casing from a floating vessel, whether deployed on coiled tubing, or any cable with or without electrical power, where it is attached to a single umbilical forming a low side catenary to prevent twisting.
2. Mechanical electrical and hydraulically operated, automatically releasable -- connectors that slide up and down the tensioned umbilical used for attaching the casing.
3. Methods of orientating the incoming casing string with the wellbore that make use of mechanical means, for example the mule shoe arrangement, powered rotation of the "stalk" which connects to the umbilical
4. Casing running tools that allow orientation of the easing string before they are landed with a sliding arrangement which can be implemented with a soft landing system.
5. A casing running tool where the upper and lower section attached to the top and bottom of the easing respectively, lock together after the easing has been run and is correctly spaced out and landed.
6. A easing running tool where the latching of the upper and lower sections allow the recovery of the releasable connectors described in claim 2 above.

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