NO340579B1

NO340579B1 - Back pressure valve for a completion string comprising sand screens

Info

Publication number: NO340579B1
Application number: NO20150590A
Authority: NO
Inventors: Christian Berven; Jon Eirik Haugneland Kvithyll; Michael Kennedy Williamson
Original assignee: Toolserv As
Priority date: 2015-05-13
Filing date: 2015-05-13
Publication date: 2017-05-15
Also published as: NO20150590A1; GB201718013D0; GB2555257A; GB2555257B; WO2016182451A1

Description

BACK PRESSURE VALVE FOR A COMPLETION STRING COMPRISING SAND SCREENS

The present invention relates to a back pressure valve for a completion string comprising sand screens, the back pressure valve comprising a valve body, a valve seat, a valve head for sealing against the valve seat, a valve stem connected to the valve head for guiding the valve head and a resilient member arranged around a portion of the valve stem.

A back pressure valve is a type of check valve designed to hold pressure from below, or downstream of the valve, at the same time as it enables fluids to be pumped from above, or upstream of, the valve. There are many fields in which back pressure valves are used. The back pressure valve of the present invention, however, is designed for use in the production of petroleum from a petroleum well, more specifically in a completion string comprising sand screens.

Wherever used herein, the words upstream/above and downstream/below refer to the relative positions of parts of the valve and/or completion string when in use in a well.

Completion of a petroleum well is the process of making the well ready for production. In that process the maximizing of recovery from the petroleum reserves is a main issue which requires management of fluid flow through the reservoir. Inflow control devices, for instance in relation with sand screens, like the Schlumberger ResFlow inflow control device are increasingly popular for this use. In order to install such an inflow control device successfully, a greater pressure must be maintained within the completion string, than in the annulus, as this will keep the inflow control device in a closed position thus preventing any fluids or debris from entering inside of the completion string during the completion phase.

One way of maintaining such higher pressure inside the completion string, is to use a heavy weight fluid, for instance a heavy weight low solids oil based mud inside of the string and a light weight fluid in the annulus, creating a hydrostatic imbalance and keeping the valves of the inflow control device closed.

After lowering and installation of the completion string, the heavy weight fluid is flushed through the back pressure valve into the annulus and returned to the surface.

One problem connected to lowering and installing a completion string with an inflow control device as mentioned above, is that prior art float valves or back pressure valves at the end of the completion string, below the sand screens, have shown not to be able to prevent the heavy weight fluid, for instance low solids oil based mud, from entering the annulus through the back pressure valve. When the heavy weight mud enters the annulus the pressures inside and outside of the completion string will be equalized and the valves of the sand screens will open at an undesirable time.

Calculations show that the back pressure valve should have an opening pressure of about 200 psi («1379 kPa), i.e. the back pressure valve should be able to withstand a pressure of about 200 psi («1379 kPa) from the heavy weight fluid inside of the string, in order to be suitable for use in a completion string comprising sand screens.

In order to overcome this problem, it is known from prior art to use an inner string which is removed after successfully lowering the completion string. However, the use of an inner string is time consuming.

There are many known back pressure valves, for instance the poppet valve of patent publication EP 0 255 269 Bl, which is a fluid activated poppet valve installed in the casing to prevent back flow of cement into the casing from the annulus if the pressure in the casing is reduced.

Another example of a prior art back pressure valve, is the plunger-type valve described on the web-site of America West Drilling Supply.

Patent publication US 5413180 A discloses method and apparatus for completing wells, especially for isolating a production interval during backwashing and sand control operations performed prior to placing the well in production. A check valve is provided wherein the check valve has an upper conical valve portion with cylindrical valve stem depending therefrom. The valve stem is slidably mounted within a valve stem guide. A spring is wound around the valve stem, said spring biasing the conical valve to a closed position.

WO 2007/014009 Al discloses a downhole non-return valve for injection of fluid, for instance water or gas, into a pressurized downhole environment. The non-return valve comprises a housing, a plug movable between an open position and a fully sealed position, and a biasing member urging the plug towards the fully sealed position but where the biasing member is selected to be insufficient to move the plug to the fully sealed position.

EP 2636840 Al discloses a bottom hole assembly for a capillary injection system comprising a plurality of injection valves connected in series. Each injection valve includes a tubular housing håving a valve seat, a valve member, and a biasing member pushing the valve member towards engagement with the valve seat.

Conventional back pressure valves for cemented liners are designed primarily to hold pressure from below hence the testing requirements do not involve verifying the valve opening pressure. For use in a completion string comprising sand screens, this is however, as mentioned above, critical. The theoretical opening pressure of a certain conventional poppet valve was calculated to be 30 psi («207 kPa), whereas tests surprisingly showed that the valve in fact opened at only 4 psi («28 kPa). The intuitive solution to this would be to simply replace the valve spring with a stronger spring, but even when replacing the spring with a spring six times stronger, the opening pressure was still found to be 4 psi («28 kPa). Thus a standard poppet valve is not suitable for providing the necessary opening pressure of 200 psi («1379 kPa) for running of the completion string with sand screens without an inner string.

The invention has for its object to remedy or to reduce at least one of the drawbacks of the prior art, or at least to provide a useful alternative to prior art.

The object is achieved through features, which are specified in the description below and in the claims that follow.

The invention is defined by the independent patent claims. The dependent claims define advantageous embodiments of the invention.

In a first aspect the invention relates more particularly to a back pressure valve for a completion string comprising sand screens, the back pressure valve comprising: - a valve body; - a valve seat; - a valve head for sealing against the valve seat;

- a valve stem connected to the valve head for guiding the valve head; and

- a resilient member arranged around a portion of the valve stem; wherein the valve stem is guided by at least two supports which are spaced apart in the longitudinal direction of the valve stem, the at least two supports being configured for allowing translation of the valve stem in its longitudinal direction only, and wherein the back pressure valve further comprises a nut for adjusting the tension of the resilient member, wherein the nut constitutes one of the supports for the valve stem.

By valve seat is meant herein a valve member which either forms part of the inner surface of the valve body or which is a separate ring or element connected to the inner surface of the valve body, where the valve seat is arranged to be able to receive the valve head such that the valve head cannot pass through the valve seat. The valve seat comprises a sealing surface arranged to seal against a corresponding sealing surface of the valve head.

The valve body may be a tubular valve body.

By "supports" is meant herein any kind of element which is suitable for guiding the valve stem and making sure to prevent "wobbling" or any sideways movement of the valve stem. The supports may therefore be for instance pins or other elements extending from the inner surface of the valve body in such a way that they support the valve stem from different sides. Further, the supports may be plates or discs partly or completely enclosing the valve stem either directly or indirectly, by supporting another element which supports the valve stem directly, for instance a housing enclosing the valve stem.

When the valve stem is only allowed to move in a longitudinal direction, the pressure required to open the valve, is more predictable. The prior art back pressure valves have that in common that the valve stem is only guided by one support, either in the end near the valve head or in the opposite end. By guiding the valve stem with at least two spaced apart supports, such that the valve stem can only move in its longitudinal direction, the valve stem will not give way sideways when a force is applied to the valve head. The at least two supports thus prevent wobbling or swinging of the valve stem, which otherwise would cause it to allow fluid to pass with much lower pressures than the calculated pressure based on the strength of the resilient member.

The back pressure valve comprises a tensioning means, for example a nut, for adjusting the tension of the resilient member which makes it possible to use the valve for different pressures without necessarily håving to change the resilient member. Said nut may be formed such that it allows for the movement of the valve stem in the longitudinal direction of the valve stem.

Furthermore, the nut constitutes one of the supports for the valve stem. It is an advantage to use the same element, in this case the nut, for providing more than one function in order to make the construction of the valve simpler. The nut itself may be

supported either directly or indirectly by the valve body.

The sealing between the valve head and the valve seat may be a metal-to-metal seal. By providing a metal-to-metal seal, the back pressure valve can hold the well pressure for the entire lifetime of the well, as opposed to a valve in which the sealing comprises polymer or another material which will only be able to hold the pressure for much shorter time periods, for example for hours or days, but not over several years. A metal-to-metal seal will provide less flexibility of the material of the valve and therefore further add to the stability and high opening pressure of the valve.

The valve head may have a planar upstream surface which will make the pressure applied to the valve head more evenly distributed over the surface than with another shape of the surface. Furthermore, the planar upstream surface will aid in giving consistent opening pressures and reduce the chance of trapping debris in the seal area.

In one possible embodiment of the invention, the resilient member may be a spring.

The back pressure valve may further comprise a housing enclosing the resilient member. This has the effect that the resilient member, for example the spring, is protected from the fluid which is pumped through the valve when it is open. Furthermore, the housing may be the indirect support of the valve stem, as mentioned above, by, in one embodiment, constituting the connection between the nut and the valve body. The nut may be threaded on the outside and fastened to the housing, while being hollow on the inside allowing for the valve stem to move in the longitudinal direction of the valve stem.

The at least two supports may further be configured for keeping the housing centred in the valve body. This gives strength to the valve assembly and makes the fluid flow more even.

One of the supports may be arranged in the annulus formed between the housing and an inner wall of the valve body, encircling the housing and making contact with the inner wall of the valve body in at least two points. One possible shape of such support may be a circular body with two or more radially extending legs.

In one embodiment one of the supports may be a dise shaped unit comprising at least one aperture, and more preferably multiple apertures. It is important for the intended use of this valve that the apertures have a size large enough to allow a heavy weight fluid, like low solids oil based mud, to pass through in large volumes. The specific gravity of the fluid may, as an example, be about 1.4. Said fluid will be pumped through the valve at a rate of for example 6 barrels per minute («0.95 m<3>/minute), which is a considerable amount and which requires the valve opening and the apertures of the dise shaped unit to be large enough to prevent clogging of the valve.

Another embodiment, similar to the above, is an embodiment wherein one of the supports is dise shaped and is in contact with the inner wall of the valve body in the entire periphery of the support.

One of the supports may be positioned in a portion upstream of the resilient member and downstream of the valve head.

In a second aspect the invention relates more particularly to a completion string comprising a back pressure valve according to the first aspect of the invention.

Furthermore, the invention concerns a method for lowering the completion string comprising the back pressure valve described herein. When using a back pressure valve as described above, able to withstand pressures up to 200 psi («1379 kPa), the completion string may be lowered without håving to use an inner string, which saves time. With the use of a prior art valve, opening at much lower pressure, an inner string has to be used in order to prevent the heavy weight fluid from entering into the annulus.

In the following is described an example of a preferred embodiment illustrated in the accompanying drawings, wherein: Fig. 1 is a planar end view of a back pressure valve according to the invention; Fig. 2 is a plane view of a cross section of a back pressure valve, indicated as A-A in Figure 1;

Fig. 3 is a perspective view of the cross section shown in Figure 2; and

Fig. 4 is a principle drawing of a completion string with a back pressure valve.

Reference is first made to Figure 1 showing a back pressure valve 1 seen from below, or downstream, in working position. A valve body 2 is provided with an opening 3 through which it is possible to see a valve stem 4 enclosed by a tensioning means 5, here shown as a nut 5, which again is enclosed by a housing 6.

In Figure 2, the valve body 2 is shown to have a tubular body part 21 and a lid 22. The inner surface of the tubular body part 21 forms a constriction or narrowing of the passage, the walls of sa id constriction being arranged to receive a valve seat 7 in an upstream portion of the tubular body part 21. The valve seat 7 has inclined surfaces forming sealing surfaces against a valve head 8 when the back pressure valve 1 is in a closed position. The valve head 8 is fixedly connected to a first, upstream, end of the valve stem 4. The valve stem 4 is provided with a coilar 41 for engaging with a resilient member 9, here shown as a spring 9, which encloses the valve stem 4 downstream of the coilar 41. The resilient member 9 and the part of the valve stem 4 encircled by said resilient member 9 are held in the housing 6. In its second, downstream, end the valve stem 4 is connected to the nut 5, which is used for adjusting the tension of the spring 9. In this particular embodiment the upper part of the valve stem 4 is guided, via the housing 6, by a first support 13, here in the form of a dise 14, and by a second support 15, here represented by the nut 5. The two supports 13, 15 are arranged such that the valve stem 4 is only movable in its longitudinal direction.

When a force directed downstream is applied to an upstream surface 81 of the valve head 8, it will, once it overcomes the tension of the spring 9, force the back pressure valve 1 to open. The valve head 8 is pushed such that both the valve head 8 and the valve stem 4 are moved in a longitudinal direction causing the sealing surfaces of the valve seat 7 and of the valve head 8 to separate from each other. The compression of the spring 9 causes the valve head 8 to again form a sealing connection with the valve seat 7 as soon as the downstream directed force is removed or drops to a level where it can no longer overcome the spring force.

In the perspective view of Figure 3, it is more clearly shown how the housing 6 enclosing the spring 9 in one embodiment can be made in one piece with the circular dise 14 constituting the first support 13. In this particular embodiment the dise 14 is shown with circular apertures 16.

Figure 4 shows a principle drawing of a completion string 10 in a well. The completion string 10 comprises sand screens 101 with inflow control devices 102. Further, the completion string comprises a float valve or back pressure valve 1 below the screens 101. Heavy weight fluid, like low solids oil based mud, is kept inside the string 10 and light weight fluid is in the annulus between the string 10 and the wall of the well. The resulting hydrostatic imbalance between the inside and the outside of the string 10, will keep the inflow control devices 102 in their closed position. The back pressure valve 1 will prevent the heavy weight fluid from escaping out into the annulus.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb "comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements.

The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

1. Back pressure valve (1) for a completion string (10) comprising sand screens (101), the back pressure valve (1) comprising: - a valve body (2); - a valve seat (7); - a valve head (8) for sealing against the valve seat (7); - a valve stem (4) connected to the valve head (8) for guiding the valve head (8); and - a resilient member (9) arranged around a portion of the valve stem (4);characterized in that: - the valve stem (4) is guided by at least two supports (13, 15) which are spaced apart in the longitudinal direction of the valve stem (4), the at least two supports (13, 15) being configured for allowing translation of the valve stem (4) in its longitudinal direction only; and in that - the back pressure valve (1) further comprises a nut (5) for adjusting the tension of the resilient member (9), wherein the nut (5) constitutes one of the supports (13, 15) for the valve stem (4).

2. Back pressure valve (1) according to claim 1, wherein the valve head (8) forms a metal-to-metal seal against the valve seat (7).

3. Back pressure valve (1) according to claim 1 or 2, wherein the valve head (8) has a planar upstream surface (81).

4. Back pressure valve (1) according to any of the preceding claims, wherein the resilient member (9) is a spring.

5. Back pressure valve (1) according to any of the preceding claims, further comprising a housing (6) enclosing the resilient member (9).

6. Back pressure valve (1) according to claim 5, wherein the at least two supports (13, 15) are further configured for keeping the housing (6) centred in the valve body (2).

7. Completion string (10) comprising a back pressure valve (1) according to any of the preceding claims.