Top tensioned riser adaptor

Abstract

An adaptor for a top tensioned riser that allows the riser to be tied in with wellheads beyond the normal range of the top tensioned riser. An adaptor spool attaches between the top tensioned riser and the subsea wellhead. An adaptor spool hanger may land in the adaptor spool. The adaptor spool is provided with a side penetration to which a flow line may be connected. The flow line is provided with a connector that connects to a production line from a remote location. This allows the fluid production to flow from the remote location through the existing top tensioned riser to the host facility. The tieback connector/stress joint may also be provided with a flow line prepared to accept remote field tiebacks, which are also piggable.

Description

RELATED APPLICATIONS

This application references and claims the benefit of Provisional Application Ser. No. 60/689,846 filed on Jun. 13, 2005.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention is generally related to production risers used on offshore structures and more particularly to top tensioned risers.

2. General Background

In the offshore production of oil and gas (fluids), offshore host facilities can be one of many different types, such as TLP's (tension leg platforms), Mini-TLP's, Spars, Semi-submersibles, etc. These host facilities most often bring production fluid onboard and produce the fluid for export through a pipeline. The fluid comes from subsea wells either directly to the host facility or via manifolds that commingle the production fluid from several different wells, prior to the fluids being brought onboard a host facility.

The means typically used to bring the production fluids to the host facility include steel catenary risers (SCR's), flexible flowlines, top tensioned risers (TTR's), and free standing risers.

Steel catenary risers (SCR's) are essentially a pipeline that hangs off of the host facility by way of either a hang-off porch and flex joint or pull tube and stress joint. Installation involves a lay barge, which drives up installation costs, as field welding is required to manufacture the SCR. The weight of the SCR imparts a high hang off load onto the host facility. There are also fatigue issues associated with host facility motions being transmitted into the SCR.

Flexible flowlines are a multi-layer flexible hose that hang off the host facility via a collar. The hoses hang in a catenary shape similar to an SCR but with a more dramatic sag. The flexible flowline offers the benefit of faster installation times relative to the SCR, as there are no in-field welds that must be made. Typically, the flexible flowline is reeled out during installation. The flexible flowline can also reduce the payload imparted onto the host facility, as the departure angles for flexible flowlines are smaller than SCR's, which yield a shorter free hanging catenary length, reducing the weight, which is another benefit. However, multiple layers are required to produce the flexible flowlines which typically cause the weight per foot to be higher than the SCR. Weight must be considered in a case by case basis. Flexible flowlines are expensive to manufacture relative to pipe. Not only is the manufacturing cost high, but the flexible flowlines have temperature and pressure limitations relative to steel pipe.

Another alternative is a top tensioned riser (TTR). These risers are made of steel pipe with specialty joints located at the sea floor and the keel of the host facility. These specialty joints help reduce localized high bending loads generated in these areas. The weight of the TTR is either supported by the host facility or via air cans that provide buoyancy independent of the host facility. Installation of the top tensioned riser is accomplished via a rig located on top of the host facility. The subsea wellhead that a TTR is tying back to must be located within a relatively small distance from the well slot where the TTR enters the host facility. This is one of the main restrictions of a TTR.

A free standing riser (FSR) is a combination of a TTR and a flexible riser. The FSR is a buoyancy can supported TTR that is located outside of the host facility. Another difference is that the top of the FSR's air can is located well below the mean water level, approximately five hundred feet. A flexible flowline is then attached from the top of the FSR to the host facility. This riser concept has several benefits. Host facility motions are decoupled from the riser via the flexible flowline. Another benefit is that the payload imparted on the host facility is small because only approximately one thousand feet of flexible flowline is hanging from the host facility.

It can be seen that TTR's have some disadvantages. For example, if the wells that the TTR's are producing from have their production deplete before the design life of the riser is up, the TTR cannot readily be moved to accommodate another wellhead, as described above. Because TTR's have not been designed to be tied in from wellheads beyond the normal reach of a TTR, the useful life of TTR's can be limited. This results in the need to have other types of risers, as described above, which adds to the complexity and cost of an offshore host facility.

SUMMARY OF THE INVENTION

The invention addresses the above need. What is provided is an adaptor for a top tensioned riser that allows the riser to be tied in with wellheads that are beyond the normal range of the top tensioned riser. An adaptor spool attaches between the top tensioned riser and the subsea wellhead. An adaptor spool hanger may land in the adaptor spool. The adaptor spool is provided with a side penetration to which a flow line may be connected. The side penetration is provided with a flow line connector hub that accepts a flowline connector from a remote well production line. This allows the production fluid to flow from the remote well through the existing top tensioned riser to the host. The tieback connector/stress joint may also be provided with a side penetration if the project anticipates the TTR being used for remote tiebacks in the future.

BRIEF DESCRIPTION OF THE DRAWINGS

For a further understanding of the nature and objects of the present invention reference should be made to the following description, taken in conjunction with the accompanying drawings in which like parts are given like reference numerals, and wherein:

FIG. 1 is a side sectional view of the invention that illustrates the adaptor spool hanger positioned in the adaptor spool.

FIG. 2 is a side sectional view of the invention that illustrates the invention may be produced for sizes up to the bore size of the TTR. As with FIG. 1, this configuration has a piggable bore.

FIG. 3 is a side sectional view of the invention that illustrates an arrangement that allows production from the vertically accessible well and a remote well.

FIG. 3a is a side sectional view of the invention that illustrates an arrangement with multiple flow lines to receive production fluids from multiple remote wells and the vertically accessible well.

FIG. 3b is a side sectional view of the invention that illustrates an arrangement where the flow lines are used for injection into, and production from, remote wells.

FIG. 3c is a side sectional view of the invention that illustrates an arrangement where production from a remote well and the vertically accessible well are allowed along with injection into the vertically accessible well.

FIG. 3d is a sectional view taken along lines 3d-3d in FIG. 3.

FIG. 3e is a sectional view taken along lines 3e-3e in FIG. 3a.

FIG. 3f is a sectional view taken along lines 3f-3f in FIG. 3b.

FIG. 3g is a sectional view taken along lines 3g-3g in FIG. 3c.

FIG. 4 is a side sectional view of the invention that illustrates an arrangement for injection of fluids into a remote well.

FIG. 5 is a side sectional view of the invention that illustrates an arrangement for production from the vertically accessible well and injection of fluids through the TTR annulus into a remote well.

FIG. 6 is a side sectional view of the invention that illustrates an arrangement for injection into the vertically accessible well and production from a remote well.

FIG. 7 illustrates an alternate embodiment of the invention where the original tieback connector/stress joint is designed according to the general principle of the invention.

FIG. 8 is a side section view that illustrates the remote tieback may have a bore size equal to the TTR bore.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawings, it is seen in FIG. 1 that the invention is generally indicated by the numeral 10. The adaptor 10 for the top tensioned riser is generally comprised of an adaptor spool 12 and an adaptor spool hanger 14. The arrangement of the hanger 14 is optional depending upon the situation.

Adaptor spool 12 is designed to physically lock to the upper most piece of the subsea wellhead 16 and so is provided with a connector 18 at the lower end for attachment to the wellhead 16. The upper end of adaptor spool 12 is designed to be connected to the tieback connector 20. Thus, the profile of the upper end of the adaptor spool mandrel 12 duplicates the profile of the upper most end of the subsea wellhead 16 and thereby forms a connection for attachment to the tieback connector 20. The tieback connector 20 is essentially the lower end of the riser 23.

Seals 24 are provided at the upper and lower ends of the adaptor spool 12 and are the same design and profiles originally used between the subsea wellhead 16 and tieback connector 20 since the adaptor spool provides the same internal profiles as the original connection between the subsea wellhead 16 and the tieback connector 20. The adaptor spool 12 may be designed to be attached to any tieback connector.

A curved bore 26 is provided through the sidewall of the adaptor spool 12 to define a flow path. Bore 26 exits the side of adaptor spool 12. Bore 26 turns to parallel the longitudinal axis of adaptor spool 12. The turn in bore 26 has a radius that is piggable and meets the minimum pigging radii dictated by industry standards.

Flow line connector 28 is provided at bore 26 and designed to receive a flow line 30. The flow line 30 extends away from the adaptor spool 12, wellhead 16, and tieback connector 20 a sufficient distance to allow the connection of a pipeline, jumper, flexible riser, etc. thereto. A suitable connection 32 is provided on flow line 30 for this purpose.

It can be seen in FIG. 1 that adaptor spool 12 is provided with a longitudinal bore 34 therethrough to allow the flow of fluids in the normal manner from the wellhead 16 into the riser 23 when the adaptor spool hanger 14 is not used.

The purpose of the hanger 14 is to divert the tubing bore from the top tensioned riser's vertical orientation to exiting the top tensioned riser system entirely. This requires the hanger to generate a seal between its OD (outer diameter) and the ID (inner diameter) of the space that it is positioned in inside of the adaptor spool 12. Seals 36 are provided on the OD of the hanger 14 for this purpose. Fluid can then flow from a field flow line, through the external flow line 30, through the adaptor spool 12, up the tubing string, and into the surface well head.

The adaptor spool hanger 14 may be deployed either with the adaptor spool or be independently run or installed into the adaptor spool 12 via a surface run tubing string or run through the top tensioned riser on a tubing string. In the latter case, the adaptor spool hanger 14 would have to be functioned to lock it to either the adaptor spool 12 or the tieback connector 20.

FIG. 2 illustrates an arrangement where the adaptor spool hanger is not used. For bores of this size the flowline connector 28 will most likely not be used. The horizontal penetration through the adaptor 12 will be fabricated as part of the adaptor. There will not be a separate connection. Bore 26 is provided with a piggable radius in this case also. This arrangement allows the accommodation of large diameter flow lines. In this arrangement, it is seen that the diameter through the riser 23, adaptor spool 12, and flowline 30 are the same. Pipe 29 is received in bore 26. FIG. 2 illustrates a more proper piggable turn in the invention. The remaining drawings illustrate a different radius turn simply for ease of illustration but are also intended to provide a piggable radius turn.

FIG. 3 illustrates an arrangement that allows a dual completion through one top tensioned riser 23. In addition to bore 26, the adaptor spool hanger 14 is also provided with a through bore 40. Fluid line 42 extends through the bore 40 from a packer 44 in the well head 16 and up through the riser 23 for producing fluids from the well. A second fluid line 46 in fluid communication with bore 26 extends up through the riser 23 for delivering production fluids from a remote well through the top tensioned riser 23.

FIG. 3a illustrates an arrangement similar to FIG. 3 where additional flow lines 30 are provided in fluid communication with the adaptor spool hanger 14 through additional bores 26 (seen in FIG. 3e) to receive fluid production from additional remote wells.

FIG. 3b illustrates an arrangement where fluid line 46 is used to deliver gas or water to a remote well to assist in production of hydrocarbons.

FIG. 3c illustrates an arrangement where fluid line 46 is used to inject water or gas into the well and fluid line 42 is used to produce hydrocarbons from the well. Flow line 30 is used as described above to receive fluids from a remote well.

FIG. 4 illustrates an arrangement where fluid line 46 is used to deliver gas or water to a remote well to assist in driving production.

FIG. 5 illustrates an arrangement where water or gas is delivered down the annulus of the riser 23 while the vertically accessible well is still producing fluids through fluid line 42. Packer 44 causes the water or gas to be directed into flow line 30 and to a remote well.

FIG. 6 illustrates an arrangement where the adaptor spool hanger 14 is provided with a longitudinal bore 48. This allows the injection of water or gas through the annulus of the riser 23 and into the vertically accessible well while still receiving production fluids from a remote well through flow line 30 and line 46.

FIG. 7 illustrates an arrangement where the original tieback connector/stress joint has been designed with the side penetration for remote well tiebacks. Therefore, the tieback connector/stress joint may be used as it typically is until the vertically accessible well is depleted, at which time a remote well may be tied back without inserting an adaptor spool. A flowline 30 is either preinstalled onto the tieback connector/stress joint or installed via ROV at a later date. The same type of multiple line arrangements seen in FIG. 3-6 may also be used in this arrangement with the tieback connector/stress joint. FIG. 8 illustrates the large bore piggable radius and an arrangement where the adaptor spool hanger is not used. As with all Figures included herein this arrangemtn can be made with a piggable bore.

During installation, the adaptor spool 12 may be deployed from the surface during the initial top tensioned riser installation, while rerunning of an existing top tensioned riser, or retrofitted into a top tensioned riser that has already been deployed. If the spool is being deployed into an existing top tensioned riser, the adaptor spool is lowered on a down line, the tieback connector 20 is unlocked, the top tensioned riser is picked up, the adaptor spool is landed and locked to the subsea wellhead 16, with assistance provided by an ROV (remotely operated vehicle), and the top tensioned riser is then landed and locked to the adaptor spool 12. This makes the adaptor spool 12 part of the external barrier to the environment for the top tensioned riser.

The adaptor spool 12 is manufactured in order to meet or exceed all the design requirements of the top tensioned riser, i.e. material selection, drift diameter, load requirements, etc. The adaptor spool 12 will generate a sealed bore from the upper most piece of subsea wellhead equipment through to the tieback connector 20 on the top tensioned riser. This is accomplished by utilizing the same interface design and interface profiles originally between the top tensioned riser and the subsea wellhead, as indicated above.

The connector on the adaptor spool 12 is rated to meet or exceed all global loading, fatigue requirements, internal pressures, external pressures, etc.

The invention provides a number of advantages.

Existing top tensioned risers can have their life extended if the wells that the risers are producing from have their production deplete before the design life of the riser is up. Installation of the adaptor spool 12 and adaptor spool hanger 14 allows production from remote trees through the existing top tensioned riser. This allows the operator to produce remote wells in a series or parallel through the same top tensioned riser.

If the top tensioned riser is tensioned from an air can, which is independent of the host facility, the host facility may take on additional tiebacks with no additional payload implications. Otherwise, additional slots would either have to be available or planned into the original design.

If a top tensioned riser is still producing, but at a low rate, the operator can plug the bore of the riser just below the mudline using a plug 38 (seen in FIG. 2), run an adaptor spool 12 and adaptor spool hanger 14, and bring a high producing satellite well on line. The vertically accessible well can be brought back on line at a later date.

Fewer or no steel catenary risers (SCR's) could be designed into the host facility production system, thereby reducing the design criteria for the entire host facility. The numbers of SCR's and top tensioned risers could be optimized on a per project basis. This is especially beneficial to top tensioned risers that are tensioned by buoyancy cans.

Large diameter flow lines can be accommodated if the vertically accessible well is plugged after the tubing is removed from the top tensioned riser. In this case, the diameter through the riser pipe, adaptor spool 12, and flow line to a manifold would be the same. There would be no adaptor spool hanger 14 in this case.

A dual completion can be had through one top tensioned riser. The vertically accessible well can continue to produce while a second tubing string exits the adaptor spool 12 and adaptor spool hanger 14. In this instance, the adaptor spool hanger 14 will have both a longitudinal through bore and a radial bore that exits into the adaptor spool 12 as seen in FIG. 3.

Both a production line and gas lift can go out to satellite wells through the adaptor spool 12 and adaptor spool hanger 14.

Multiple completion tubing strings, gas lift lines, and/or water injection lines can be run through the same top tensioned riser. The adaptor spool 12 and adaptor spool hanger 14 will require multiple outlets in this instance.

The production arrangement can be used for water injection. This reverses the normal flow path, sending water down the riser and out to a water injection well. Water injection can be sent straight through the tubing, which exits the adaptor spool 12. Water injection can be sent down a top tensioned riser annulus while the vertically accessible well is still producing through the tubing. In this case, the tubing will exit the bottom of the adaptor spool hanger 14 and the top tensioned riser annulus will feed out the penetration into the adaptor spool. Water injection can be sent down the annulus of the top tensioned riser into the vertically accessible well while production comes through the adaptor spool 12 and adaptor spool hanger 14 from a satellite well.

Both dual and single barrier top tensioned risers can be accommodated by the invention.

Because many varying and differing embodiments may be made within the scope of the inventive concept herein taught and because many modifications may be made in the embodiment herein detailed in accordance with the descriptive requirement of the law, it is to be understood that the details herein are to be interpreted as illustrative and not in a limiting sense.

Claims

1. In an offshore production arrangement where a top tensioned riser is connected to a subsea wellhead by a tieback connector having a longitudinal bore in fluid communication with the subsea wellhead and the top tensioned riser, an adaptor for the top tensioned riser, said adaptor comprising:

a. an adaptor spool with a longitudinal bore therethrough; and

b. a an adaptor spool hanger received in the longitudinal bore through said adaptor spool.

2. The adaptor of claim 1, wherein said adaptor spool is received between the riser and the wellhead so as to be in fluid communication with the riser and wellhead.

3. The adaptor of claim 1, wherein said adaptor spool hanger includes a bore therethrough that exits the side of said adaptor spool hanger and said adaptor spool and is in fluid communication with the riser.

4. The adaptor of claim 3, wherein the bore through said adaptor spool hanger is piggable.

5. The adaptor of claim 1, wherein said adaptor spool hanger includes a bore therethrough that exits the side of said adaptor spool hanger and said adaptor spool and is in fluid communication with the riser and a longitudinal bore therethrough in fluid communication with the wellhead and riser.

6. In an offshore production arrangement where a top tensioned riser is connected to a subsea wellhead by a tieback connector having a longitudinal bore in fluid communication with the subsea wellhead and the top tensioned riser, an adaptor for the top tensioned riser, said adaptor comprising:

a. an adaptor spool received between the wellhead and riser, said adaptor spool having a longitudinal bore therethrough in fluid communication with the riser and wellhead; and

b. a an adaptor spool hanger received in the longitudinal bore through said adaptor spool, said adaptor spool hanger having a piggable bore therethrough that exits the side of said adaptor spool hanger and said adaptor spool and is in fluid communication with the riser.

7. The adaptor of claim 6, further comprising said adaptor spool having a longitudinal bore therethrough in fluid communication with the riser and wellhead.

8. In an offshore production arrangement where a top tensioned riser is connected to a subsea wellhead by a tieback connector having a longitudinal bore in fluid communication with the subsea wellhead and the top tensioned riser, an adaptor for the top tensioned riser, said adaptor comprising:

a. an adaptor spool received between the wellhead and riser, said adaptor spool having a bore that exits the side of said adaptor spool and is in fluid communication with the riser; and

b. a separate fluid line received in said adaptor spool, the riser, and the well for producing fluids from the wellhead.

9. In an offshore production arrangement where a top tensioned riser is connected to a subsea wellhead by a tieback connector having a longitudinal bore in fluid communication with the subsea wellhead and the top tensioned riser, an adaptor for the top tensioned riser, said adaptor comprising an adaptor spool received between the wellhead and riser, said adaptor spool having a bore that exits the side of said adaptor spool and is in fluid communication with the riser.