GB2426771A

GB2426771A - Retrofit remedial subsurface safety valve (SSSV)

Info

Publication number: GB2426771A
Application number: GB0603506A
Authority: GB
Inventors: Mark Buyers; David Forsyth
Original assignee: Omega Completion Technology Ltd
Current assignee: Omega Completion Technology Ltd
Priority date: 2005-02-22
Filing date: 2006-02-22
Publication date: 2006-12-06
Anticipated expiration: 2026-02-22
Also published as: GB0603506D0; GB0503615D0; GB2426771B

Abstract

A subsurface safety valve (SSSV) unit is installed in production tubing retrospectively and comprises a means to lock 10 and seal 12 with the tubing, a valve 13 and a hydraulic valve control line 14 extending inside the tubing from the top of the SSSV unit to the surface. The retrofit SSSV can be installed within a worn or damaged SSSV as a remedial valve. The hydraulic valve control line extends to the surface through the wellhead via a wellhead insert mounted inside the Christmas tree; the wellhead insert provides connections to allow normal control of the well with slots 27 providing connection to flow lines.

Description

Retrofit Safety Valve and Welihead Insert This invention relates to a

retrofit safety valve and/or a welihead insert for use in a tubing string of a production installation for extracting sub-surface gaseous and/or liquid hydrocarbons, and to a method of installation of such components.

In the oil and gas industries where hydrocarbons are extracted from deep in the earth, wells are required to access these hydrocarbons. The wells are firstly drilled through the rock and periodically lined with a metal casing. This prevents collapse of the hole whilst it is being drilled and also serves to isolate the various rock strata, one from another. When the rock which contains the hydrocarbons is reached, pressures in excess of the normal pressure gradient may be experienced. These pressures are held in check by the column of drilling mud. The mud also serves to cool and lubricate the drill bit whilst allowing the recovery of the drill cuttings to surface. Higher pressures may be countered by adding weight to the drilling mud such that the system is in balance.

When the well drilling phase is finished, a Wellhead and Christmas tree are installed at I..

is surface combined with a tubing stnng (see figure 1). The tubing (1) is a pipe which seals at the welihead (2) on surface and penetrates almost to the boom of the well where it is also S sealed by use of a packer. The Christmas tree (3) features a number of valves which are *tS) used to control the flow of hydrocarbons from the well and hold back any pressure. There are usually two normally open Master Valves (4, 5) which can contain the pressure from the tubing. A second valve is required in the event of the first failing. Above this will be two "wings" to the Christmas tree, each with a valve. These are called the Flow Valve (6) and the Kill Valve (7). At the top of the Christmas tree is a service valve called the Swab Valve (8). This is used for introducing tools into the well and for routine maintenance. The swab valve is normally closed unless well operations are being carried out. A Tree Cap (9) above this also acts as a pressure barrier.

When the drilling mud has been removed to allow the production of hydrocarbons to begin, there will be a pressure imbalance. This may show as a surface well pressure of thousands of pounds per square inch. Control and containment of this pressure is critical as loss of control will lead to a very dangerous situation involving release of hydrocarbons and risk of fire or explosion. The well control is especially critical in the offshore environment where personnel live and work in close proximity to the wells with no easy means of escape in the event of an emergency.

All well types feature a Sub Surface Safety Valve as a contingency device in the event of a catastrophic event at surface (see figure 2). The SSSV is normally positioned hundreds of feet below the surface and is held open by application of hydraulic pressure. The pressure is conveyed to the SSSV along a " tube which is strapped to the outside of the production tubing called a control line (1). The control line attaches to the bottom of the wellhead and penetrates through a port to the outside. Maintenance of hydraulic pressure through this io control line ensures that the Safety Valve is open but removal of the pressure will close the valve.

The safety valve features a pressure bearing body (6) with a central bore (7) which houses the valve.

The hydraulic pressure acts on a piston (2) which compresses a spring (3). A central tube (4) linked to the piston holds open a flapper valve (5) whilst hydraulic pressure is maintained. The spring will return the tube to the up position when the pressure is removed allowing the flapper valve to close. The equipment is designed in this way so that a catastrophic event at surface such as an explosion will also sever the hydraulic line and close the safety valve - thus rectifying the situation.

Safety valves, in common with most equipment, suffer a range of technical and reliability problems. The mechanical valve mechanism may fail, the hydraulic piston within the valve may fail or leak and the control line may rupture, leak or plug. In certain cases it is possible to remove the SSSV for replacement by using wireline techniques. In other cases it is possible to set a new SSSV inside the old failed unit but still utilise the old control line.

These remedies are of little value where the problem lies with the control line as it is impossible to replace the control line without removal of the wellhead and the production tubulars. This requires a drilling rig and will be a very expensive operation.

It would be advantageous to run a new control line to a new safety valve insert situated hundreds of feet down inside the tubing and terminate the control line at the welihead with a new feed through. Unfortunately, due to normal wellhead construction, this is not possible without the control line passing through at least two valves inside the welihead.

This renders the valves useless as pressure barriers and will prevent their closure.

Additionally, the only feasible route for the new control line is out through the top of the Christmas Tree which will involve it passing through another valve, the Swab Valve. This will again entail loss of a valve as the control line will pass through its internal bore.

Additionally, problems may be experienced by the flow eroding or dragging the control line into the flow wing of the wellhead where it may become critically damaged.

Accordingly, a need exists for a method of reliably providing hydraulic communication through a wellhead for a control line without any of the previously described disadvantages. I,

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Another application of this technology exists for secondary recovery techniques. Many gas. : wells produce quantities of water when they become old. When the wells become depleted, the gas flow may become insufficient to lift the water which will fall back and create an increasing volume at the bottom of the well. This will greatly impact the efficiency of the well and may even prevent any gas flow whatsoever. 8::: One simple remedy to assist in the removal of water from the well is to drop a "soap stick" down the well. The soap forms bubbles with the water which can easily be lifted and removed with the gas flow. The well may again produce until such time as the water build up requires another treatment with soap. Some wells are deviated at the bottom meaning that the soap may not reach the water. Other wells are remote or are not easily accessible for routine service treatments such as described. It would be advantageous to run a control line into these wells and penetrate down to where the gas is produced in order that liquid soap may be pumped directly into the water. The barriers to this technique are the same as previously described for the replacement safety valves.

According to the invention there is provided a method as defined in claim 1.

Preferred features of the invention are set out in dependent claims 2 to 8.

Description of the preferred examples of the invention with reference to Figures 3 and 4.

The invention comprises two separate assemblies. A retrofittable downhole Safety Valve and a Welihead Insert. The two are connected by control line running inside the well.

The Retrofitable Sub Surface Safety Valve (RSSSV) is a unit which may be lowered inside the tubing to be installed at a chosen depth. See Figure 4. The unit features a means (10) of locking with the well tubulars, a means (12) of sealing pressure between its body and the well tubulars and a valve means (13) which is hydraulically controlled by the control line (14) which extends from the top of the unit to surface. Unlike normal Safety Valves where the control line is routed outside of the production tubing, the hydraulic control line is positioned inside the production tubing. The well production will flow around the control line. This technique may be considered perfectly adequate for a repair technique. As with normal Safety Valves, The RSSSV features a large spring (15) which will hold open the Safety Valve (13) when hydraulic pressure from surface is maintained. In the event of an emergency, removal of the hydraulic pressure will cause the valve to close and will shut off flow and pressure from the well.

A Wellhead Insert (WI) is required to provide a means of feeding the control line through the welihead and out safely. Figure 3 shows a WI installed inside a welihead. Provision of the feedthrough removes some of the other functions of the Christmas Tree and so these must be replaced. The Wellhead Insert (WI) is packaged inside the Wellhead / Christmas Tree and serves three main functions. It provides a seal with its body and the internal bore of the wellhead, it provides a valve (22) to close off pressure from the well and it provides a means (23) of feeding hydraulic pressure from a surface source to the SSSV control line.

At the bottom, it provides a connection (24) which adapts and retains normal control line and which may be hung into the wellbore for purposes as previously described. Slotc (27) allow the how to egress troni the V I and out to the tiowli ne.

The WI interfaces with the Wellhead / Xmas tree at its lowest point by way of an external seal (2 I) and at the top either with a Spool piece (26) or through a specially drilled hydraulic port. The spool is not part of the Xmas Tree and must be fitted. The Spool resembles a short tubular section with flanges top and bottom. It is inserted and bolted between the bottom of the Swab Valve (8) and the body of the Christmas Tree (see Fig. 1).

The Spool internal detail features a profile for location of the insert, a communication port for the RSSSV control line and a second hydraulic take off port for the WI Master Valve.

The spool also features a means (25) for locking the insert to the Wellhead / Christmas tree to prevent it being pushed upwards by the well pressure. The Swab Valve is bolted to the top of the spool once fitted and will serve the same function as previously.

It will not be possible to retrofit the specially drilled hydraulic port in many instances as the welihead will not provide a location for this to be machined. Where this is possible, an alternative locating and sealing means, similar to that provided on the RSSSV will be. :.

required. As it is desirable to position this equipment below the Master Valve, normal:: :* operation of the Christmas Tree may be retained. I..

The WI valve (replacement Master Valve) is required to replace the functionality which has been lost due to the fitment of the WI sleeve. This is hydraulically controlled via the * :: second hydraulic take off port on the spool. The new Master Valve is of the normally closed type and will require the maintenance of hydraulic pressure to hold it open. This is a normal safety provision which allows for fast and reliable operation in the event of an emergency.

Additional applications are envisaged in new wells where the facility of a retrievable Safety Valve and control line may be attractive. This might be the case where a history of failed control lines dictates a different approach from the conventional. Also, the ability to install a valve in a well at some depth from surface may be desirable for a multitude of reasons and applications.

I he foIIovng illustrations demonstrate various aspects of the invention. -s

Figure I shows a Wellhead and Christmas Tree with a section of tubing suspended below.

A variety of spools and casing equipment at the base have been omitted for clarity.

Figure 2 shows a cutaway section of a Sub Surfitce Saibty Valve.

Figure 3 shows the wellhead and Christmas Tree of figure I but fitted with a prefent'd example of wellhead insert according to the invention.

Figure 4 shows a prefened example of a retrofittable sub surthec safety vaLve according to the invention inside a joint of tubing. * .

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Claims

Claims: 1. A method of installing a retrofit safety valve in a tubing

string of a production installation for extracting sub-surface gaseous and/or liquid hydrocarbons having a wellhead and tubing string, in which a safety valve unit is lowered inside the tubing to a required depth, and said unit comprising: means (10) for locking with the well tubulars; means (12) for sealing pressure between the body of the unit and the well tubulars; a valve means (13) which is hydraulically controlled by a control line (14) extending from the top of the unit to surface; and said hydraulic control line being positioned inside the production tubing.
2. A method according to claim 1, in which the safety valve unit incorporates a large spring (15) which holds the valve means (13) open when hydraulic pressure from surface is maintained.
3. A method according to claim 1 or 2, in which a welihead insert is mounted at the welihead and serves to provide a means of feeding the control line through the welihead for: connection with the safety valve unit.
4. A method according to claim 3, in which the wellhead insert (Wi) is mounted inside the wellbhead (Christmas Tree) and serves three main functions, namely: the insert provides a seal with its body and the internal bore of the wellhead; 411 P it provides a valve (22) to close off pressure from the well; and it provides a means (23) of feeding hydraulic pressure from a surface source to the control line leading to the safety valve unit.
5. A method according to claim 4, in which the wellhead insert provides a connection (24) which adapts and retains normal control line, and slots (27) are provided to allow flow to egress from the insert and out to the flow line.
6. A method according to anyone of claims 3 to 5, in which the wellhead insert interfaces with the welihead at its lowest point by way of an external seal (21) and at the top either via a spool piece (26) or through a specially drilled hydraulic port.
7. A retrofit sub surface safety valve unit (RSSSV) for use in the method according to claim 1.
8. A wellhead insert (Wl) for use in a method according to anyone of claims Ito 7.