NO20140354A1 - Vertical valve tree and well overhaul system - Google Patents

Description

Vertical valve stem and overhaul assembly

The present invention relates to a vertical valve tree for a seabed well. In particular, a new valve tree has been provided which, due to its features, reduces the need for equipment during overhaul operations. An overhaul assembly and associated procedures are also presented.

Background

Within the field of subsea wells, a valve tree is used to control the flow of produced hydrocarbons from the well. It includes valves which are arranged to open and close for such flow.

During overhaul operations in the subsea well, the operator needs access to the well through the valve tree. In such a scenario, the valve three valves must be in open mode. Consequently, additional funds are needed to maintain well integrity. From a surface installation, a riser is typically stretched down to the well. In some cases, a string, such as a coiled pipe or cable, extends from the surface installation into the well, through the riser and the valve tree to which the riser is attached.

At the top of the well, the valve tree is arranged (at the wellhead). Between the valve tree and the lower part of the riser, there are further assemblies designed to secure the well fluids. This includes a well control package (WCP) (also sometimes referred to as the lower riser package - LRP) located at the top of the valve tree. The WCP contains two valves in the main bore that provide two barriers. These valves are either two gate valves, or one gate valve and one safety head. Both the sluice valves and safety heads are capable of cutting a string that extends through the valve / safety head. The safety head, however, exhibits better cutting properties than the sluice valve.

To make it possible to disconnect the riser from the top of the subsea well quickly, an emergency disconnect package (EDP) is arranged on top of the WCP. If a floating surface installation is used, this can drift off from the position directly above the well. The riser will then show an inclined position in relation to the vertical line directly above the well. The EDP makes it possible to disconnect the riser from the WCP even if such an inclination is present. When disconnected, the EDP will cut off any string that extends through it and seal off the lower end of the riser to prevent the fluid in the riser from flowing into the sea. The WCP will shut down the well and also cut off any string.

Accordingly, known valve trees are capable of opening and closing for a flow flowing through it. The WCP is capable of shutting off the flow path and cutting any string extending through it.

US Patent Publication US8353338 discloses a wellbore control valve comprising a housing defining a through bore adapted to receive a string. The attached Fig. 1a, Fig. 1b, and Fig. 1c show such a valve. A first lock and a second lock are arranged inside the house. The locks are movable in different directions, across the through bore, between an open bore position and a closed bore position. When moving the sluices from the open-bore position to the closed-bore position, a string arranged between the sluices can be cut. A first seal seat forms a seal with one of the sluices in the closed bore position to seal the through bore.

A typical field of application for the valve described in US8353338 is well drilling. In an emergency, a wellbore control valve, such as described in the aforementioned publication, is capable of cutting the string extending through the through bore. Such a string can, for example, be an overhaul/drill pipe or intervention tool. The valve will then close and seal the through bore, as a seal is formed between the first lock and the first sealing seat.

Providing two sluices provides an improved cutting function of the string. However, one can also imagine other types of cut-off valves that have only one sluice, which can have both a sealing and a cutting function.

One purpose of the present invention is to simplify the equipment used during overhaul operations in a seabed well.

The invention

In accordance with a first aspect of the present invention, there is provided a vertical valve tree (VXT) having a production well and two valves in the production well. Each valve comprises a valve gate which is functionally connected to an actuator which moves the valve gate bidirectionally between an open and a closed position. The production well is sealed by the valves when these are in the closed position. In accordance with the present invention, the valve lock is provided with a string cutting edge.

The valve actuators may be of any suitable type, for example comprising a hydraulic piston or a rotary stem. The string cutting edge of the valve lock is adapted to cut a string extending through the valve. Such a string can typically be a coiled pipe or a cable that extends into the subsea well below the vertical subsea valve tree.

The vertical valve tree may comprise an overhaul subsea control module (workover subsea control module) which includes an emergency disconnection package control device (EDP control means) and control device for vertical valve tree.

The emergency disconnect package control device in the overhaul seabed control module (WOSCM) enables the operator to control an EDP landed above the VXT through the WOSCM. Consequently, the WOSCM can typically be used to control the valves of the VXT, as well as the valves of an EDP that is landed on top of the VXT. Alternatively or additionally, the WOSCM can control other functions of the EDP, such as bleed off valves, annulus isolation valve and crossover valves.

In accordance with a second aspect of the present invention, there is provided a seabed overhaul assembly arranged over a seabed well. The subsea overhaul assembly comprises a vertical valve tree (VXT) that has a production well fitted with a production valve, and a subsea wellhead, above which the vertical valve tree is landed. A riser extends downward from a surface installation and an emergency disconnect package (EDP) is provided between the riser and the vertical valve tree. Furthermore, the emergency disconnection package has a continuous emergency disconnection package bore that is equipped with an emergency disconnection package cut-off and sealing valve. Characteristic of the second aspect of the present invention is that the production valve is a cut-off and shut-off valve.

Between the emergency disconnection package cut and seal valve and the production valve there is preferably a valve-less path. In some embodiments, this valveless path may include a bore selector. However, the bore selector is not considered a valve herein. Alternatively, this feature can be expressed as the path between the emergency disconnect package, the cut-off and sealing valve and the production valve is either valve-less or has only one valve in the form of the bore selector. As will be understood by one skilled in the art, the feature reflects the fact that since the valve tree is provided with cut-off valves, there is no need to provide a cut-off valve between the emergency disconnect package and the vertical valve tree.

Furthermore, the emergency disconnect package can advantageously be landed directly on the vertical valve tree.

The emergency disconnect package may include a bore selector and the vertical valve tree may include an annulus access bore. By operating the bore selector, the operator can choose between access to the production bore or to the annulus bore of the VXT.

In an embodiment in accordance with the second aspect of the invention, the vertical valve tree comprises an overhaul control module comprising an emergency disconnection package control device. The emergency disconnection package control device can, for example, be designed to control the emergency disconnection package cut-off and sealing valve, and/or other functions of the emergency disconnection package.

In some embodiments, a wire may be connected between the vertical valve tree and the emergency disconnect package to connect the overhaul seabed control module to the emergency disconnect package. Alternatively, a stub plate (stab plate) may be provided which provides communication between the Overhaul Seabed Control Module and the Emergency Disconnect Package when the EDP is landed on the XT.

In accordance with a third aspect of the present invention, a method is provided for setting a vertical valve tree on a seabed wellhead. The method comprises the following steps: a) arranging an emergency disconnection package over a vertical valve tree in a vertical stack (stack); b) lowering the emergency disconnect package and vertical valve tree into a body of water and towards a subsea wellhead, while attached to the lower end

of a riser hanging down from a surface installation;

c) to land and to lock the vertical valve tree to the subsea wellhead.

In accordance with this aspect of the invention, step a) comprises the establishment of

a valve-less path between an emergency disconnect package cut-off and shut-off valve in a through-bore to an emergency disconnect package and the production bore in the vertical valve tree.

Step a) may advantageously include arranging a bore selector between the emergency disconnect package and the vertical valve tree.

Furthermore, step c) may comprise controlling a locking mechanism to the vertical valve tree by means of an overhaul subsea control module, by locking the vertical valve tree to the subsea wellhead.

Consequently, there is provided a seabed vertical valve tree, a seabed overhaul assembly, and a method for setting a seabed vertical valve tree, which results in simpler and less necessary equipment than in the prior art, when performing overhaul operations in a seabed well.

Example of embodiment

As the invention has been described in general terms above, a more detailed and non-limiting example of embodiment is presented in the following with reference to the drawings, in which

Fig. 1a is a cross-sectional view of a known sluice valve in an open position; Fig. 1b is a cross-sectional view of the valve in Fig. 1 in a closed position; Fig. 1c is an enlarged cross-sectional view of the valve in Fig. 1b; Fig. 2 is a schematic overview of a floating surface installation that undertakes

overhaul operation in a subsea well;

Fig. 3 is a principle sketch of an overhaul setup in accordance with the known

technique;

Fig. 4 is a principle sketch in accordance with Fig. 3, but illustrating a set-up i

conformity with the present invention; and

Fig. 5 is a principle sketch of a vertical valve tree during landing on a

seabed well.

Fig. 1a to Fig. 1c illustrate a known valve 10 which is suitable for well control for a subsea hydrocarbon well. Fig. 1a shows the valve in an open position. Two locks 18, 20 are arranged axially above each other. They both have an opening which in the open position is aligned with each other. A hydraulic actuator 30, 40 is connected to each lock 18, 20. The actuators can pull the locks out of their position shown in Fig. 1a and into their closed position, as illustrated in Fig. 1b. The actuators 30, 40 are also capable of pushing the gates 18, 20 back to their open position. Accordingly, by controlling the actuators, the operator is able to open and close the valve 10.

A cutting element 34, 36 with a cutting edge is arranged at an edge portion of each opening to the locks. When the actuators 38, 40 pull the locks from the open position towards the closed position (Fig. 1b), the cutting elements 34, 36 will engage with any string that extends through the valve 10. Such a string can typically be a cable or a coiled pipe that is used for overhaul operation in a seabed well below the valve 10.

Fig. 1c shows parts of the locks 18, 20 in the closed position. This drawing also shows sealing seats 22, 26 arranged on axially opposite sides of the two locks.

Those skilled in the art will recognize that other types than hydraulic actuators can be used to move the locks back and forth, for example an actuator that can be operated by rotation of a rotating rod.

Fig. 2 schematically illustrates a set-up in accordance with known technology during an overhaul operation on a seabed well. A floating installation 100 at the sea surface 101 is connected to a riser 103 that extends down towards a seabed well 105 below the seabed 107. At the seabed 107, a wellhead 109 is arranged at the upper part of the seabed well 105. To the wellhead 109, a vertical valve tree 200 (VXT).

To provide two barriers against well pressure in the well 105 during overhaul operation, a well control package 300 (WCP) is landed on top of the VXT 200. Furthermore, an emergency disconnect package 400 (EDP) is arranged between the riser 103 and the WCP 300. Fig. 3 is a schematic illustration of the setup in accordance with the known technique in Fig. 2. On top of the wellhead 109 (not shown in Fig. 3), VXT 200, WCP 300 and EDP 400 are arranged. Shown above EDP 400 is the riser 103 and an umbilical 111.

In this arrangement in accordance with the prior art, the VXT 200 includes two production valves 201 in its main bore (production bore) 203. Both production valves 201 are capable of opening and closing the production bore 203 in the VXT 200. In the VXT 200 there is also an annulus access bore 205 (annulus bore ). The annulus bore 205 is provided with annulus bore valves 207 which are also arranged to open and close.

As discussed with reference to Fig. 2, above the VXT 200 is a well control package 300 (WCP). A through WCP bore 303 extends through the WCP 300. The through WCP bore 303 is provided with one cut and seal valve 301 and one safety head 302. The cut and seal valve 301 and the safety head 302 are capable of to cut any string that is in the through-hole and to seal off the well. The safety head 302 is similar to a cutting gate valve.

As the operator needs access to both the annulus well 205 and the production well 203 of the VXT 200, a well selector 305 is provided in the WCP 300. With the well selector 305, the operator is able to select which of the wells, the production well 203 or the annulus access well 205, he enters when lowering of a tool down through the through WCP bore 303 to the WCP 300.

Reference is still made to the solution from prior art, shown in Fig. 3. An emergency disconnection package 400 (EDP) is arranged above the WCP 300. It has an EDP through bore 403 which is aligned with the WCP through bore 303. The EDP 400 also has a cut and seal valve 401, which is capable of cutting a string extending through the EDP 400 and to maintain fluid in the riser 103 above the EDP 400. These functions occur when the operator needs to disconnect the EDP 400 from the WCP 300, typically in a situation with excessive drift, bad weather conditions, or an approaching iceberg.

On the top of the EDP 400 is shown the lower end of the riser 103, which constitutes a pipe from the EDP 400 to the floating installation 100. Also shown on the top of the EDP 400 is the lower end of the umbilical 111 which may contain power supply, control cables and hydraulic channels from the floating installation 100 and to the EDP 400.

For controlling the components of the WCP 300 and the EDP 400, such as an EDP disconnection mechanism (not shown) and the cut-off and shut-off valves 301, 401, the EDP 400 also includes an overhaul control module 409 (WOCM - workover control module ) (although in some embodiments such critical functions may be controlled directly by hydraulics). When the WCP 300 and the EDP 400 have landed on the VXT 200 for overhaul operations, the WOCM 409 typically also controls the functions of the VXT 200, in addition to the functions of the EDP 400 and the WCP 300. The VXT 200 includes a subsea control module 209, which is a component similar to the WOCM 409. The Subsea Control Module (SCM) 209 provided in the VXT 200 is used to control various components of the VXT 200 during normal production, i.e. when the EDP 400 and WCP 300 are not landed on the VXT 200.

Fig. 4 is a schematic diagram similar to the diagram in Fig. 3, but shows an embodiment in accordance with the present invention. In this embodiment, the VXT 200 provides cut-off and shut-off valves 10 in the production well 203 and in the annulus access well 205. Having such functionality in the wells of the VXT 200 makes it possible to omit the WCP 300, which is shown in the prior art layout in Fig. 3. The cutting and sealing valves 10 in the VXT 200 can for example be of the type shown and discussed with reference to Fig. 1a to Fig. 1c. Accordingly, the cutting and sealing valves 10 to VXT 200 in accordance with the invention have a cutting, sealing, opening and closing function.

Since the setup of this embodiment of the invention is without the WCP 300, the bore selector 405 is now incorporated into the EDP 400. The EDP 400 is preferably landed directly on the VXT 200.

Between the cut and seal valve 401 of the EDP 400 and the production well 203 of the VXT 200, there is a valveless path 250 when the EDP 400 is landed above the VXT 200. In particular, no valves are present between the top valve 10 in the production bore 203 of the VXT 200 and the lower valve of the EDP 400 (which is the EDP cut and seal valve 401). In this context, the term valve-less shall mean that there are no valves present in said path, perhaps apart from a possible bore selector which in some embodiments can be interpreted as a valve.

Through the valveless path 250, fluid and/or a string (not shown), such as a coiled pipe or a cable, can be passed. A tool may also be attached to such a string and may enter through the valveless path 250.

In a critical drift situation during an overhaul operation, the cut and seal valves 10 in the VXT 200 cut any string (not shown) extending through the annulus bore 205 or the production bore 203 of the VXT 200, and seal the bores 203, 205. The EDP 400 also cuts the any string and seals the through EDP bore 403 to retain fluid inside the riser 103.

In the embodiment shown in Fig. 4, only one control module is shown. While the setup in accordance with the prior art (see Fig. 3) comprised one SCM 209 and one WOCM 409, a setup in accordance with the present invention may comprise a combined overhaul control module and a seabed control module (WOSCM) 213. During normal production, The WOSCM 213 is adapted to control the functions of the VXT 200, preferably in the same way as an SCM in the prior art. However, during overhaul operations, the WOSCM 213 also controls the functions of the EDP 400 in addition to the functions of the VXT 200.

In a situation where the EDP 400 is landed on the VXT 200, a wire (Gumper) 215 can be connected between a wet coupling contact on the VXT 200 and a wet coupling contact on the EDP 400. Such a connection will typically be provided by means of a remote controlled vessel (ROV) (not shown). In this way, the WOSCM 213 can be connected to the EDP 400. In a critical situation, where the EDP 400 must be quickly disconnected from the VXT 200, the cable can simply be pulled off. However, one can also imagine an embodiment where the EDP 400 and VXT 200 are provided with a stab plate (not shown) which provides communication between the WOSCM 213 and the EDP 400 when the EDP 400 is landed on the VXT 200 In such an embodiment, the line 215 can be omitted.

In another situation, the VXT 200 and the EDP 400 can be installed simultaneously on the riser 103. The line 215 can then be connected between the VXT 200 and the EDP 400 before they are lowered into the sea, unless they are provided with a plug plate which discussed above.

Fig. 5 schematically illustrates a situation where the VXT 200 is about to be landed on a subsea wellhead 109. The VXT 200 is arranged to the EDP 400 and they are both lowered onto a riser 103.

Claims (11)

1. A vertical seabed valve tree (200) with a production well (203) and two valves (10) in the production well (203), whereby each valve (10) comprises a valve lock (18, 20) which is functionally connected to an actuator (38, 40) which moves the valve lock bidirectionally between an open position and a closed position, whereby the production bore (203) is sealed with the valves (10) in the closed position, characterized in that the valve lock (18, 20) is provided with a string cutting edge (34). 2. A vertical seabed valve tree (200) in accordance with patent claim 1, characterized in that it comprises an overhaul seabed control module (213) comprising emergency disconnection package control means and vertical valve tree control means. 3. A vertical seabed valve tree (200) in accordance with patent claim 1 or 2, characterized in that it comprises an annulus access bore (205) which is provided with two valves (10), which valves are sluice valves which have a valve sluice (18, 20) which is provided with a string cutting edge (34). 4. A seabed overhaul assembly arranged above a seabed well, where the seabed overhaul assembly comprises - a vertical valve tree (200) with a production well (203) which is provided with a production valve (10); - a subsea wellhead (109) above which the vertical valve tree (200) is landed; - a riser (103) extending down from a surface installation (100); - an emergency disconnection package (400) arranged between the riser (103) and the vertical valve tree (200), whereby the emergency disconnection package (400) has a continuous emergency disconnection package bore (403) which is provided with an emergency disconnection package cutting and sealing valve (401); characterized in that the production valve (10) is a cut-off and sealing valve. 5. A seabed overhaul assembly in accordance with patent claim 4, characterized in that between the emergency disconnection package cut and seal valve (401) and the production valve (10) there exists a valve-less path (250). 6. A seabed overhaul assembly in accordance with claim 4 or 5, characterized in that the emergency disconnect package (400) is landed directly on the vertical valve tree (200). 7. A seabed overhaul assembly in accordance with one of claims 4 to 6, characterized in that the emergency disconnect package (400) comprises a bore selector (405) and that the vertical valve tree (200) comprises an annulus access bore (205). 8. A seabed overhaul assembly in accordance with one of claims 4 to 7, characterized in that the vertical valve tree (200) comprises an overhaul seabed control module (213) which comprises an emergency disconnection package control device. 9. Method for setting a vertical valve tree (200) on a subsea wellhead (109), which method comprises the following steps: a) arranging an emergency disconnect package (400) over a vertical valve tree (200) in a vertical stack; b) lowering the emergency disconnect package (400) and the vertical valve tree (200) into a body of water and towards a subsea wellhead (109), while attached to the lower end of a riser (103) hanging down from a surface installation (100 ); c) landing and locking the vertical valve tree (200) to the subsea wellhead (109); characterized in that step a) comprises establishing a valve-less path (250) between an emergency disconnection package cutting and sealing valve (401) in a continuous emergency disconnection package borehole (403) and a production borehole (203) in the vertical valve tree (200). 10. Method in accordance with patent claim 9, characterized in that step a) comprises arranging a bore selector between the emergency disconnection package (400) and the vertical valve tree (200). 11. Method in accordance with patent claim 9 or 10, characterized in that step c) comprises controlling a locking mechanism to the vertical valve tree (200) by means of an overhaul seabed control module (213), by locking the vertical valve tree (200) to the seabed the wellhead (109).