WO2007028982A1

WO2007028982A1 - Subsea pipeline end & drilling guide frame assembly

Info

Publication number: WO2007028982A1
Application number: PCT/GB2006/003292
Authority: WO
Inventors: Neil Alexander Keron
Original assignee: Keron Engineering Ltd
Priority date: 2005-09-07
Filing date: 2006-09-06
Publication date: 2007-03-15
Also published as: GB0518188D0; GB2429990A

Abstract

An arrangement for making the final tie-in connection between a subsea offshore oil or gas well and the associated pipeline and umbilical system without the use of divers or remotely operated vehicles and comprising a drilling guide (3), a Christmas tree (17) and an umbilical connection plate (11) to which the umbilical is connected prior to submersion of the assembly.

Description

SUBSEA PIPELINE END & DRILLING GUIDE FRAME ASSEMBLY

The present invention relates to drilling guide frame assemblies and methods of installation thereof.

The offshore oil industry frequently makes use of subsea wells which are drilled from a floating vessel (semi-submersible drilling rig or drill ship). These are usually connected to a central processing platform via one or more sub-sea pipelines installed after the well has been drilled. In addition to the pipelines, a hydraulic or electro- hydraulic umbilical is installed to control various functions on the sub-sea wellhead and Christmas tree from the central processing platform.

The first operation in drilling a new well is to lower a guide frame (Figure 1) to the seabed from the drill rig or ship. This guide frame is used as a guide through which all subsequent drilling operations are carried out. After the well has been drilled, a device comprising various valves known as the Christmas tree is installed on the wellhead by the drill rig or ship. The Christmas tree is lowered from the drill rig or ship and is connected remotely (ie without diver intervention) via a hydraulic device known as a collet connector. The collet connector is fitted to the underside of the Christmas tree. When the tree is in the vicinity of its final location on the wellhead, the collet connector is activated hydraulically from the drill rig or ship to cause it to grip a mating ring on the wellhead. As the collet connector closes on the mating ring, it pulls the Christmas tree and the wellhead tightly together to form a leak proof seal between the two items. Ideally, the installation would be timed such that the pipelines and umbilical are on site ready for connection to the Christmas tree when drilling of the well is complete. This would enable these lines to be connected to the Christmas tree prior to its lowering to the seabed. However, in practice, this approach is not possible due to the difficulty of accurately estimating when drilling of the well will be completed and the extremely high costs of renting the various vessels required to perform the various operations making it uneconomical to have either the drill rig sat on station unused awaiting arrival of the pipelines and umbilical or to have the vessel carrying the pipelines and umbilical on station awaiting completion of drilling the well. Instead, then, the drill rig or ship leaves the location with the Christmas tree connected to the wellhead once drilling of the well is completed leaving the sub-sea well ready for the ρipeline(s) and umbilical to be connected at the seabed.

The pipeline(s) and umbilical are installed either by specialised construction vessels such as laybarges or reelships or, where the pipelines are of limited length, the pipelines and umbilical can be constructed in their entirety at a convenient onshore location and towed to the desired offshore location by tug boats. The pipeline and umbilical can be towed along the seabed (bottom tow), floating just above the seabed (off-bottom tow), at mid-depth or on the surface of the ocean. The use of towed pipelines can bring significant cost savings in remote areas where the cost of mobilising specialised construction equipment is high. Alternatively the pipeline may be installed by laybarge or reel boat. The invention is applicable to all three methods.

After installation of the pipelines and umbilical it is necessary to make the final connection (or tie-in) between the pipelines and umbilical and the Christmas tree. Due to the intricacies of the interconnections between the Christmas tree and the pipelines and umbilical, it is not possible to effect those connections automatically as is done with the connections of the Christmas tree to the wellhead. Instead, the tie-ins must be carried out either by divers operating from a specialised diver support vessel (DSV) or by remotely operated vehicle (ROV) which also operates from a specialised ship. In either case, this operation is time consuming and costly, particularly in remote areas of the world where the cost of mobilising specialist vessels is high.

According to a first aspect of the present invention there is provided a drilling guide frame assembly for instaUing a drilling and production base at an undersea well location, the base comprising a drilling guide for guiding the drilling of a subsea well , at least one pipeline end connector from which, in use, extends pipeline means for transporting oil from the wellhead to a storage means and which has an end configured for connection to a conduit of a Christmas tree, and an umbilical connection plate from which, in use, extends an umbilical cord for controlling operation of the base and Christmas tree and which has an end configured for connection to an umbilical conduit of a Christmas tree, the at least one pipeline end connector and the umbilical connection plate being positioned and configured on the guide frame assembly relative to the drilling guide such that, upon engagement of a Christmas tree onto the drilling guide, the at least one pipeline end connector and the umbilical connection plate are automatically aligned with and engage with the associated conduits on the Christmas tree.

A drilling guide assembly in accordance with the invention has the advantage that the required connections of the pipeline(s) and the umbilical to the guide assembly are carried out at the surface, thereby removing the need to use divers or ROVs and hence reducing costs. Furthermore, these connections are made before installation drilling is commenced, and hence the timing of these operations can be accurately estimated, and the arrival of the various vessels required to complete the tasks timed to minimise lay- away times of the vessels.

According to another aspect of the present invention there is provided a Christmas tree valve assembly for use with a drilling guide assembly according to the invention, comprising a first collet connector which engages, in use, with a well head drilled through the driUing guide of the guide assembly, an umbilical collet connector which engages, in use, with an umbilical connection plate of the guide assembly so as to provide a coupling therewith, and at least one pipeline collet connector which, in use, engages with a pipeline end connector of the guide assembly so as to provide a coupling therewith, said umbilical and said at least one pipeline collet connectors being configured relative to the said first collet connector such that, in use, they automatically align with their associated connection means on the guide assembly when the first collet connection is engaged on the well head.

The present invention still further provides a method of installing a drilling guide frame assembly according to the invention, comprising the steps of: connecting pipeline means and umbilical means respectively to the at least one pipeline end connector and the umbilical connection plate of the guide assembly prior to submersion of the assembly; locating the assembly at the desired subsea wellhead location; drilling the well through the drilling guide of the assembly; locating a Christmas tree on the drilling guide of the assembly; and operating connection means on the Christmas tree automatically to connect wellhead, pipeline outlet and umbilical conduits provided on the Christmas tree respectively to the drilling guide, the at least one pipeline end connector and the umbilical connection plate of the drilling guide frame assembly.

According to the present invention a subsea drilling guide frame is incorporated in to a pipeline end frame which is connected whilst onshore to an onshore constructed pipeline/umbilical system and towed to the offshore subsea drilling location at the head or tail of the pipeline/umbilical system. The normal circular drilling guide is incorporated in to the overall pipeline end frame assembly in order to effect the connection of the pipeline/umbilical system to a subsequently installed Christmas tree. When the pipeline end drilling guide frame assembly has been installed at the correct offshore location, the subsea well is drilled in the normal manner through the central circular guide assembly.

The guide frame assembly preferably includes collet connector rings similar to that on the wellhead on the pipeline end connector and the umbilical connection plate. The Christmas tree is then fitted with the normal collet connector for connection to the wellhead but in addition incorporates a short pipe spool which is also fitted at its downstream end with a collet connector which matches the ring on the pipeline termination and also with a collet connector for engagement with the collet connector ring of the umbilical connection plate. The geometry of the various elements in the guide frame assembly and on the Christmas tree is carefully arranged such that when the main Christmas tree collet connector is in proximity to the mating ring on the wellhead, the piping spool collet connector is in proximity to the mating ring on the pipeline termination. As the main collet connector is activated to connect the Christmas tree to the wellhead, the pipe spool collet connector is activated to connect the piping spool to the pipeline end flange. A similar hydraulic connector is installed on the tree to connect an umbilical 'spool piece' from the Christmas tree to the umbilical termination plate. The guide frame assembly can be fitted at either the leading end or the trailing end of the pipeline/umbilical assembly.

In addition to the arrangements for making the final tie-in, the guide frame assembly- pipeline-umbilical system preferably comprises arrangements for controlling the buoyancy of the system. During tow out it is desirable to make the guide frame assembly and pipeline/umbilical system as light as possible to minimise the towing forces required. Once in its desired location, it is desirable to maximise the weight of the system to provide resistance to underwater current and wave forces. This may be achieved during pipeline tows by ensuring that the pipeline is sealed and empty before tow thereby maximising its buoyancy. Once at the desired location the pipeline can be flooded with seawater to increase the submerged weight. The seawater which is added is used to hydrotest the pipeline prior to admitting hydrocarbons. Once in service the weight of the oil inside the pipeline provides the necessary weight. However for the guide frame assembly, there are no additional contents which can provide extra weight. According to a preferable development to the present invention, the weight is controlled by constructing the framework of the guide frame assembly from hollow steel pipe. During tow the hollow pipes are kept empty which provides buoyancy. Once the guide frame assembly is at its correct location the hollow pipes are flooded with water by opening appropriate flooding and vent valves operated by hydraulic action from the tow boat via the hydraulic umbilical. If additional weight is required, instead of filling with seawater, the guide frame assembly can be filled with a cement grout pumped from the tow boat via a small diameter pipeline included in the pipeline bundle for this specific purpose. The grout which will remain in this pipeline adds weight to the pipeline-umbilical bundle which is desirable to provide extra on-bottom stability.

When installing a normal guide frame from a drilling vessel it is necessary to level the frame once it is in place on the seabed in order to ensure that the well drilled through it is vertical. The levelling is normally effected by installing piles through subsidiary guides on the guide frame and jacking the frame against these piles in order to bring it level. Preferably, in the guide assembly of the present invention, the central guide which must be made level before drilling the well is installed in the guide frame assembly with three attachment points. One of these points allows the central guide to rotate about two orthogonal horizontal axes. The other two points are attached to hydraulic jacks mounted with their axis vertical. The hydraulic jacks are each supplied with hydraulic power via independent hoses included in the hydraulic umbilical incorporated in the towed pipeline-umbilical assembly or in a temporary umbilical piggy-backed to the tow wire. The hoses for the hydraulic jacks extend at the towed end of the pipeline-umbilical assembly to the deck of the tow tug. Once the pipeline/umbilical and guide frame assembly is installed at the correct location and the guide frame assembly has been weighted down by filling its hollow members with seawater or grout, the hydraulic jacks can be activated to bring the axis of the central circular drilling guide to a vertical position. After the central guide has been made vertical, the base of the main structural frame is filled with cement grout to strengthen the connection between the central circular drilling guide and the guide frame assembly.

The present invention thereby allows the tie-in between a subsea Christmas tree and a pipeline/umbilical system to be made in the minimum time without mobilising any specialised construction equipment such as DSVs. The present invention can also be used on a pipeline installed with a laybarge or reelsMp by attaching the guide frame assembly to the pipeline end before the pipeline end leaves the deck of the vessel. The guide frame assembly and pipeline end are then lowered to the seabed in the same way that the normal pipeline end is lowered to the seabed during normal pipelay operations.

In order that the invention may be well understood, there will now be described an embodiment thereof, give by way of example, reference being made to the accompanying drawings, in which:

Figure I shows a typical drilling guide frame 21 with its lowering (or running) tool 22 for lowering the guide frame to the seabed from the drilling vessel;

Figure 2 shows a typical wellhead 16 and Christmas tree 17 with flow loop or spool 18, tree connector 19 and flowline connector 20

Figure 3 shows a plan of the towed guide frame assembly attached to a towed pipeline/umbilical system in accordance with the present invention;

Figure 4 shows a section of the towed guide frame assembly attached to a towed pipeline/umbilical system in accordance with the present invention;

Referring first to Figure 3, there is shown a guide frame assembly of the invention comprising two large hollow steel tubes 1 connected by smaller hollow steel tubes 2, which together provide the main structural framework and buoyancy for the guide frame assembly. A central guide 3 is provided with flared entry guides 4 at its upper and lower ends. The guides permit easy entry of drill bits and conductor pipes. A typical pipeline 5 is carried on the frame, the pipeline 5 being routed around the guide frame assembly to minimise thermal stresses in operation. The pipeline is connected to the frame with clamp 6 which transmits the tow force from the guide frame to the pipeline, and is also supported at other points 24 in the guide frame as required. The guide frame is fitted with towing padeyes 7 to which towing shackles are attached for towing the assembly to the installation location or for the laydown operation from a laybarge or reelboat. The shackles can be fitted to the towing padeyes with hydraulically actuated pins to allow remote disconnection of the tow or laydown wire once the guide frame is in the correct location.

A pipeline end fitting 8 is carried on the guide frame assembly having a first end to which the pipeline connects and a second end which is configured for connection to a collet connector 20 on the end of the subsequently installed Christmas tree spool piece 18. More particularly, the second end of the pipeline end fitting is arranged on the guide frame assembly in a predefined position and orientation such that as the Christmas tree engages on central guide and is pulled into position by the main collet connector, the appropriate connector of the Christmas tree is automatically aligned with and engages onto the pipeline end fitting 8, thereby enabling automation of the pipeline connection and removing the need to use divers and associated DSVs or ROVs for the operation. It will, of course, be understood that, although only a single pipeline is shown in the drawings, additional pipeline connectors may be provided for automatic connection of additional pipelines for the supply of additional services to the wellhead such as lift gas to the wellhead.

The guide frame assembly further includes an umbilical connection plate 11 to which connects an hydraulic or electro-hydraulic umbilical 10. The umbilical connection plate 11 is similarly configured in a predefined position and orientation relative to the main central guide such that it automatically connects with the appropriate port on the Christmas tree when the Christmas tree is properly engaged on the central guide of the guide frame assembly. A collet is also provided on the umbilical connection plate for securing the connection between the plate and the Christmas tree. In this way, it is possible to achieve automatic connection of the hydraulic and electric lines to mating lines on the Christmas tree in a similar manner to that used for the pipeline connection.

The hollow steel tubes 1 and 2 which form the structural frame of the guide frame assembly are sealed to prevent ingress of seawater during the tow but are connected together with a closed piping system (not shown) which allows a cement grout to be pumped in to all the hollow tubes from a single pipe when the guide frame assembly is at the correct location. A one way vent valve is provided at the highest point of the connected tubes to allow egress of air as the tubes fill with grout. If the guide frame assembly is at the front end of the guide frame assembly/pipeline assembly a temporary umbilical 15 is fitted between the guide frame and tow boat to allow pumping of the grout from the tow boat as soon as the guide frame is in the correct location. The temporary umbilical is fitted to the guide frame assembly onshore. During the tow the temporary umbilical is attached to a temporary surface buoy which is also towed by the tow boat. The guide frame assembly is installed and operated as follows. When the guide frame assembly is at its correct location the tow boat reverses to the temporary surface buoy and brings the upper end of the temporary umbilical on board to allow the necessary functions on the guide frame assembly to be carried out from the deck of the boat without diver intervention. If the guide frame assembly is at the trailing end of the guide frame assembly/pipeline assembly, a grout line can be added to the pipeline bundle to allow grout to be pumped from the tow boat.

The central circular drilling guide 3 is mounted on an adjustable frame 26 via three connection points 12, 13 and 14. Attachment point 12 allows the central guide 3 to rotate about two perpendicular horizontal axes. Attachment points 13 and 14 are provided with hydraulic jacks. When the guide frame assembly has been filled with grout and is in its final resting position on the seabed, the central circular drilling guide can be made vertical by means of the two hydraulic jacks mounted at attachment points 13 and 14. The jacks are activated either via hydraulic hoses included in the temporary umbilical to the tow boat or via additional hoses included in the permanent hydraulic umbilical 10. The adjustable frame is fitted with a circular spirit level 27 which can be monitored with a small remotely operated vehicle (ROV) operated from the tow boat. The pipeline loop is also supported on the adjustable frame so that the spatial relationship between the central circular guide frame 3 and the pipeline end fitting 8 is maintained during adjustment of the adjustable frame. The adjustable frame is also fitted with guide posts 25 which define the azimuth orientation of the blow out preventer (BOP) and Christmas tree. Once the central circular drilling guide 3 is vertical, the base of the main frame is filled with grout to provide a secure connection between the central circular drilling guide 3 and the main structural frame to guard against failure of any of the attachment points 12, 13 or 14 when drilling bits or conductor pipes are lowered or raised through the central guide.

When the guide frame assembly has been filled with grout, the central circular drilling guide has been made vertical and the base has been filled with grout the tow boat can disconnect from the guide frame assembly and leave the area.

The guide frame assembly is now ready for normal drilling operations through the central circular drilling guide. The central circular drilling guide is of sufficiently large diameter to allow passage of a thirty six inch drilling bit The first drilling tubular installed in the well is a thirty inch conductor pipe 30. To ensure that the well head is concentric with the drilling guide and to determine the correct height of the wellhead relative to the pipeline and umbilical end fittings, a locating sleeve 31 is fitted to the thirty inch conductor pipe. When the drilling operations are complete the Christmas tree 17 is lowered by the drilling vessel on to the wellhead 16 now installed in the central guide, the configuration of the pipe end fitting and the umbilical connection plate on the guide frame assembly ensuring that as the tree connector 19 engages with the top of the wellhead, the hydraulic flowline collet connectoφ) 20 engage with the mating pipeline end fitting(s) 8 and the umbilical collet connector on the Christmas tree engages with the umbilical connection plate without requiring, manual guidance or intervention by divers or ROVs. The tree connector and flowline connector(s) and hydraulic umbilical connector are activated via a temporary hydraulic umbilical from the drilling vessel.

Claims

1. A drilling guide frame assembly for installing a drilling and production base at an undersea well location, the base comprising a drilling guide for guiding the drilling of a well, at least one pipeline end connector from which, in use, extends pipeline means for transporting oil from the wellhead to a storage means and which has an end configured for connection to a conduit of a Christmas tree, and an umbilical connection plate from which, in use, extends an umbilical cord for controlling operation of the base and Christmas tree and which has an end configured for connection to an umbilical conduit of a Christmas tree, the at least one pipeline end connector and the umbilical connection plate being positioned, and configured on the guide frame assembly relative to the drilling guide such that, upon engagement of a Christmas tree onto the drilling guide, the at least one pipeline end connector and the umbilical connection plate are automatically aligned with and engage with the associated conduits on the Christmas tree.

2. A drilling guide assembly according to claim 1, wherein the base comprises a plurality of pipeline end connectors, from each of which, in use, extends a separate pipeline.

3. A drilling guide assembly according to claim 1 or claim 2, wherein the drilling guide is mounted on the assembly by three attachment points arranged around the drilling guide.

4. A drilling guide assembly according to claim 3, wherein the drilling guide is pivotally attached to one of said attachment points for rotation about two orthogonal axes, and the other two attachment points vertically movable relative to the assembly, whereby the level of the drilMng guide may be adjusted.

5. A drilling guide assembly according to claim 4, where said other two attachment points are carried on hydraulic jacks.

6. A drilling guide assembly according to any of the preceding claims, further including a coupling for a temporary umbilical, by means of which operations of the assembly may be controlled during installation on the sea bed.

7. A drilling guide assembly according to any of the preceding claims, further rncluding ballast means for varying the buoyancy of the assembly.

8. A drilling guide assembly according to claim 7, wherein said ballast means is formed by the framework of the assembly which is formed from hollow pipe.

9. A drilling guide assembly according to any of the preceding claims, wherein the at least one pipeline end connector and the umbilical connection plate each include a collet connector ring, which, in use, engages with a collect connector formed on the associated coupling on the Christmas tree in order to facilitate automatic coupling to the Christmas tree.

10. A Christmas tree valve assembly for use with a drilling guide assembly according to any of the preceding claims, comprising a first collet connector which engages, in use, with a well head drilled through the drilling guide of the guide assembly, an umbilical collet connector which engages, in use, with an umbilical connection plate of the guide assembly so as to provide a coupling therewith, and at least one pipeline collet connector which, in use, engages with a pipeline end connector the guide assembly so as to provide a coupling therewith, said umbilical and said at least one pipeline collet connectors being configured relative to the said first collet connector such that, in use, they automatically align with their associated connection means on the guide assembly when the first collet connection is engaged on the well head.

11. A method of installing a drilling guide frame assembly according to any of claims 1 to 9, comprising the steps of: connecting pipeline means and umbilical means respectively to the at least one pipeline end connector and the umbilical connection plate of the guide assembly prior to submersion of the assembly; locating the assembly at the desired subsea wellhead location; drilling the well through the drilling guide of the assembly; locating a Christmas tree on the wellhead drilled through the drilling guide of the assembly; and operating connection means on the Christmas tree automatically to connect wellhead, pipeline outlet and umbilical conduits provided on the Christmas tree respectively to the wellhead drilled through the drilling guide, the at least one pipeline end connector and the umbilical connection plate of the drilling guide frame assembly.

12. A method according to claim 11, wherein the pipeline and umbilical are connected to the drilling guide assembly on shore and the guide assembly with attached pipeline and umbilical are towed to an offshore drilling location.

13. A method according to claim 11, wherein the pipeline and umbilical are connected to the drilling assembly on the deck of a pipeline laybarge or reel boat at said offshore drilling location .

14. A drilling guide assembly substantially as hereinbefore described with reference to the accompanying drawings.

15. A Christmas tree valve assembly substantially as herein described with reference to the accompanying drawings.

16. A method substantially as hereinbefore described with reference to the accompanying drawings.