HIGH PRESSURE RISER CONNECTION TO WELLHEAD

Abstract

A suspension head (11) is provided for connection between a high pressure riser (8) and a subsea wellhead (9), for use in drilling and completion operations in which a jack-up rig (1) is employed and a blowout preventer (7) is installed on the jack-up rather than on the wellhead. The use of the suspension head (11) offers improved safety and convenience, allowing the riser (8) to be isolated from the wellhead (9) in emergencies or for carrying out certain operations which would otherwise require the installation of a temporary plug.

Claims

1. A process for drilling or completing a subsea wellbore with subsea wellhead from a jack-up rig, the process comprising: a) installing a blow-out preventer on the jack-up rig; b) installing a riser between the blow-out preventer and the subsea wellhead; c) connecting a suspension head assembly between the riser and wellhead, wherein the assembly includes at least one ram or valve for sealing the well.

2. A process as claimed in claim 1 comprising closing in the wellbore by actuating the ram or valve.

3. A process as claimed in claim 2 wherein the ram or valve closes and seals around tubing or casing in the well.

4. A process as claimed in claim 2 wherein the said ram or valve is a shear and seal ram and wherein the process includes actuating the ram in the event of an emergency to shear drill pipe passing through the assembly and make a seal.

5. A process as claimed in claim 3 wherein, whilst the ram or valve is closed, the riser is removed in order to install subsea equipment.

6. A process as claimed in claim 1 wherein the suspension head assembly is installed on the wellhead by the jack-up rig.

7. A process as claimed in claim 6, wherein the suspension head assembly is installed over the side of the jack-up rig by an offshore rig crane on the jack-up rig.

8. A process as claimed in claim 1 wherein the suspension head assembly has a mass of between 10,000 and 100,000 kg.

9. A process as claimed in claim 8 wherein the suspension head assembly has a mass of between 20,000 and 60,000 kg.

10. A suspension head assembly for drilling or completing a well, the assembly comprising: (a) a first connector for connecting the assembly to a wellhead; (b) a second connector for connecting the assembly to a riser; (c) at least one ram or valve.

11. An assembly as claimed in claim 10, wherein the said at least one ram or valve comprises at least one ram or valve for closing and sealing around tubing or casing.

12. An assembly as claimed in claim 10, wherein the said at least one ram or valve comprises at least one shear and seal ram for emergency use.

13. An assembly as claimed in claim 10, comprising two or more rams or valves in a double ram block.

14. An assembly as claimed in claim 10, comprising a side inlet and associated valves.

15. An assembly as claimed in claim 10, wherein the second connector comprises a re-entry hub.

16. An assembly as claimed in claim 10, having a mass of between 10,000 and 100,000 kg.

17. An assembly as claimed in claim 16, having a mass of between 20,000 and 60,000 kg.

18. A system for drilling or completing a subsea wellbore, the system comprising a jack-up rig having a BOP installed on it, a riser, a subsea wellhead and a suspension head assembly for drilling or completing a well, the assembly comprising: (a) a first connector for connecting the assembly to the wellhead; (b) a second connector for connecting the assembly to the riser; (c) at least one ram or valve.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] A more complete understanding of the present invention and benefits thereof may be acquired by referring to the follow description taken in conjunction with the accompanying drawings in which:

[0022] FIG. 1 is a schematic representation of a jack up rig and high-pressure riser with subsea suspension head in accordance with the invention;

[0023] FIG. 2 is a schematic representation of a known type of subsea assembly comprising a subsea wellhead and high-pressure riser; and

[0024] FIG. 3 is a schematic representation of a subsea assembly including a suspension head in accordance with the invention.

DETAILED DESCRIPTION

[0025] Turning now to the detailed description of the preferred arrangement or arrangements of the present invention, it should be understood that the inventive features and concepts may be manifested in other arrangements and that the scope of the invention is not limited to the embodiments described or illustrated. The scope of the invention is intended only to be limited by the scope of the claims that follow.

[0026] As shown in FIG. 1, a jack-up type drilling rig 1 comprises a platform 2 supported by legs 3 which pass through the sea surface 4 and rest on the seafloor 5. A drilling rig tower 6 is located on the platform 2. All of this is conventional.

[0027] Unusually for drilling and completion of a subsea well/wellhead, a blowout preventer 7 is located on the platform 2, for the reasons explained above. Because the blow out preventer, or BOP, is located on the platform of the drilling rig rather than being mounted on the wellhead, a high-pressure riser 8 is required to connect the BOP 7 to the wellhead 9. Depending on the operation being performed, tubing or casing or drill string, or combinations of those, represented by reference numeral 10 in FIG. 1, passes down into the well through the wellhead 9.

[0028] A suspension head 11 in accordance with the invention is mounted on the wellhead 9 and the high-pressure riser connected to the top of the suspension head 11.

[0029] The conventional arrangement for a subsea wellhead, as stated above, is to have the BOP mounted directly onto the wellhead. A conventional marine riser then connects the BOP to the drilling platform. The BOP is controlled from the drilling rig, and includes the normal safety features allowing the well to be closed in the event of an emergency, e.g. due to the pressure from the formation unexpectedly or suddenly increasing. Because the BOP is located on the wellhead, the pressure in the riser need not be high.

[0030] In the arrangement with the BOP on the jack-up drilling rig, the normal arrangement on the seafloor is shown schematically in FIG. 2. The high-pressure riser 8 is connected to the wellhead 9 via a riser connector 12. Casing, tubing, drill string or a combination of these, is shown at 10. Although this arrangement works well and avoids the need to use a specialized jack-up rig, there are some concerns as set out below.

[0031] In the arrangement shown in FIG. 2, the BOP on the rig provides the same safety functions which are normally performed by a subsurface BOP. However, in this arrangement, the riser 8 is exposed to high pressures from the formation. The use of this high-pressure riser represents a potential increased risk because the riser passes through the surface 4 of the sea (the splash zone) and therefore is exposed to potential risks from collisions with surface vessels, foreign objects (e.g. a barge), or from extreme weather conditions.

[0032] FIG. 3 shows in schematic form a subsea installation in accordance with the invention. The wellhead 9, tubing, etc., 10 and high-pressure riser 8 are shown, with the high-pressure riser 8 connected into the assembly via a riser connector 12. However, a suspension head assembly 20 is provided between the riser connector 12 and wellhead 9.

[0033] The suspension head assembly 20 comprises a heavy duty H4-profile connector 21 connected to the wellhead 9, a re-entry hub 24 connected to the riser connector 12, and a double ram block 26. The re-entry hub 24 includes a TH orientation pin 25. The functions of all these components, each of which is in itself a well-known piece of equipment, will be explained below.

[0034] The double ram block 26 comprises a shear/seal ram (or SSR) 22 which is designed, when actuated, to cut through drill pipe passing through the block 26 and then form a seal. The shear/seal ram 22 is obviously for use in emergencies, e.g. if formation pressure cannot be contained by the normal means and presents a danger. The block 26 also contains a casing ram 23 which is designed to seal around 10¾″ casing.

[0035] A side inlet 28 is provided below the SSR 22, which communicates with the well. Side inlet fail safe close valves 29 control the opening or closing of the side inlet. By closing the casing ram 23 and opening side inlet valves 29 below the SSR, fluid may be delivered to the well by an alternative route. This facilitates a more efficient installation and testing of the completion string. In addition, this allows the use of the tubing hanger running tool secondary release function. In the absence of the suspension head, a temporary plug would have to be installed requiring a day or more's rig time, with associated expense.

[0036] The re-entry hub 24 and orientation pin 25 are used when a tubing hanger is to be landed on the wellhead; the pin 25 is manipulated by an ROV to rotate the Tubing Hanger into the correct orientation.

[0037] The suspension head 20 also includes a control panel 27 for actuating the rams 22, 23 and connectors, and for actuating failsafe close valves 29 for the side inlet 28. The controls on control panel 27 may be actuated by a remotely operated subsea vehicle (not shown).

[0038] The suspension head assembly comprises some of the components normally found in a BOP (e.g. the rams), but is a considerably smaller and lighter piece of equipment than a BOP. A BOP includes, for example, several ram configurations, control pods, and an accumulator bank for enhancing the delivery of hydraulic power. Together all this sums up to the majority of the mass of a BOP. A BOP may have a mass of between 200 and 400 metric tonnes (200,000 to 400,000 kg) whereas a suspension head in accordance with the invention may have a mass of about 40 metric tonnes (40,000 kg). For this reason, a standard jack-up rig will normally have the lifting capacity to install a suspension head according to the invention, whilst the standard jack-up would be unable to install a BOP.

[0039] In closing, it should be noted that the discussion of any reference is not an admission that it is prior art to the present invention, especially any reference that may have a publication date after the priority date of this application. At the same time, each and every claim below is hereby incorporated into this detailed description or specification as a additional embodiments of the present invention.

[0040] Although the systems and processes described herein have been described in detail, it should be understood that various changes, substitutions, and alterations can be made without departing from the spirit and scope of the invention as defined by the following claims. Those skilled in the art may be able to study the preferred embodiments and identify other ways to practice the invention that are not exactly as described herein. It is the intent of the inventors that variations and equivalents of the invention are within the scope of the claims while the description, abstract and drawings are not to be used to limit the scope of the invention. The invention is specifically intended to be as broad as the claims below and their equivalents.