GB2344364A

GB2344364A - Flow control device

Info

Publication number: GB2344364A
Application number: GB9825568A
Authority: GB
Inventors: Klaas Johannes Zwart
Original assignee: Petroline Wellsystems Ltd; Weatherford Lamb Inc
Current assignee: Petroline Wellsystems Ltd; Weatherford Lamb Inc
Priority date: 1998-11-20
Filing date: 1998-11-20
Publication date: 2000-06-07
Anticipated expiration: 2018-11-20
Also published as: GB9825568D0; GB2344364B

Abstract

A resealable downhole flow control device (10) comprises a tubular body (12) for mounting on a tubular string and defining a flow passage (32, including port 36 and flow area around the free end of flow sleeve 48) between the body bore (18) and the body exterior. A metal to metal seal arrangement defined by first and second sealing surfaces (38, 39) which when they are in sealing contact close the flow passage (32). The sealing surfaces (38, 39) are urged together by spring (26). Separation of the sealing surfaces (38, 39) is caused by pressure differences between the interior and exterior of the device (10). This forces fluid to flow through a tortuous restricted path (58) into volume (56) and the piston area (54), the retractable sleeve (30) then slides towards end connection (16) slowly opening the seal. The resultant flow area (A) between the sealing surfaces is larger than the smallest flow area defined by the stated flow passage.

Description

FLOW CONTROL DEVICE This invention relates to a flow control device, and in particular but not exclusively to a downhole flow control device for selectively permitting flow of fluid from a string bore into a surrounding annulus.

In drilling and production operations, such as in the exploration or production of hydrocarbons from subterranean formations, it is often desired to supply fluid to a selected interval of the bore.

The selected interval may be treated by supplying an appropriate fluid from the surface, the fluid being passed down through a hollow string, and exiting the string through flow ports positioned adjacent the selected interval. The flow ports typically form part of a pressure-activated valve assembly, commonly known as a chemical injection sub. Conventional injection subs include normally-closed metal-to-metal seal arrangements, which may be opened by differential pressure, that is when the sub internal bore pressure is a predetermined amount higher than annulus pressure. However, immediately the seal is"cracked", and fluid flows from the string and ir. to the annulus, the bore pressure falls, and there is a tendency for the faces forming the metal-to-metal seal to close again. The constant opening and closing, or "shuttling", of the seals of the valve assembly increases wear and damage and thus the likelihood of seal failure.

Also, as the valve is opening, or is just about to close, the sealing surfaces define only a relatively small flow area, resulting in high fluid velocities and substantive pressure drops across the seals, which tend to accelerate wear and erosion of the seals. In many cases, erosion of the seals will result in loss of sealing capability requiring retrieval and repair or replacement of the sub.

It is among the objectives of embodiments of the present invention to obviate or mitigate these problems.

According to the present invention there is provided a resealable downhole flow control device comprising: a tubular body for mounting on a tubular string and defining a flow passage between the body bore and the body exterior; and a seal arrangement defining first and second sealing surfaces, with the sealing surfaces in sealing contact the flow passage being closed, and on separation of the sealing surfaces, the flow area between the surfaces being larger than the smallest flow area defined by the flow passage.

According to another aspect of the present invention there is provided a method of controlling flow between a downhole tubular body and a surrounding annulus, the method comprising the steps of: mounting a tubular body on a tubular string and providing a flow passage between the body bore and the body exterior; providing a seal arrangement defining first and second sealing surfaces; positioning the sealing surfaces in sealing contact to close the flow passage; and then separating the sealing surfaces to permit flow through the passage, the flow area between the surfaces being selected to be larger than the smallest flow area defined by the flow passage.

The relatively large flow area between the sealing surfaces results in the velocity of the fluid flowing over the sealing surfaces being relatively low, and minimises any pressure drop in the fluid as it flows between the surfaces. As a result, there is minimal wear and erosion of the sealing surfaces, such that the flow passage may be resealed by bringing the sealing surfaces back into sealing contact.

Preferably, the sealing surfaces are of metal, such that when closed the sealing surfaces form a metal-to-metal seal. Alternatively, one or both of the sealing surfaces may be of other materials such as elastomers or plastics.

Preferably also, one of the sealing surfaces is fixed relative to the body, and the other is movable relative to the body.

Preferably also, the sealing surfaces are normally in sealing contact, and one of the surfaces may be biased towards the other by a spring or other biasing means.

Preferably also, the sealing surfaces are circular or annular, and one of the sealing surfaces may be defined by a sleeve.

Preferably also, the device includes means for restricting flow through the flow passage on initial separation of the sealing surfaces. In one embodiment, the flow passage includes a flow port and the flow restricting means extends over the port, said means being movable such that, as the sealing surfaces are spaced further apart, the degree of flow restriction provided by said means decreases. Conveniently, said means is defined by a portion of a sleeve defining one of the sealing surfaces.

Preferably, also, the seal arrangement is fluid pressure actuated, and most conveniently is operated by differential pressure, that is by a higher pressure within the body relative to the annulus, or vice versa. Most preferably, the device defines a piston area, application of elevated fluid pressure to said area tending to separate the sealing surfaces. The piston area preferably partially defines or communicates with a fluid chamber, fluid access to the chamber being via a restricted area flow path.

Accordingly, the flow rate of fluid to and from the chamber is restricted, thus damping piston movement.

Preferably also, the flow passage includes an inlet defined by a plurality of restricted dimension flow ports, such as slots, to prevent or restrict the flow of particulates through the passage.

According to a further aspect of the present invention there is provided a resealable downhole flow control device comprising : a tubular body for mounting on a tubular string and defining a flow passage between the body bore and the body exterior; a retractable flow restrictor positioned in the flow passage; and a seal arrangement defining first and second sealing surfaces, with the sealing surfaces in sealing contact the flow passage being closed, on initial separation of the sealing surfaces, the flow restrictor restricting flow through the flow passage, and on further separation of the sealing surfaces the flow restrictor being retracted to permit flow through the flow passage.

According to a still further aspect of the present invention there is provided a resealable flow control device comprising: a body defining a flow passage; and a seal arrangement defining first and second sealing surfaces, with the sealing surfaces in sealing contact the flow passage being closed, and on separation of the sealing surfaces, the flow area between the surfaces being larger than the smallest flow area defined by the flow passage.

These and other aspects of the present invention will now be described, by way of example, with reference to the accompanying drawing which is a sectional view of a downhole flow control device 10 in accordance with a preferred embodiment of the present invention, the lower half of the Figure showing the device in a sealing configuration and the upper half of the Figure showing the device in a flow configuration.

The device 10 comprises a tubular body 12 for mounting on a tubular string (not shown), and accordingly is provided with appropriate end connections'4, 16. The body 12 is tubular, defining a central through bore 18 to permit the passage of fluid therethrough. The body 12 comprises a two-part outer sleeve 20, an inner sleeve 22 and an end piece 24. Between the sleeves 20,22 the body 12 defines an annular volume 25 which accommodates a spring 25, restrained by a retainer 28 pinned to the sleeve 20, and a retractable sealing sleeve 30, as will be described.

The body 12 defines a normally closed flow passage 32 which extends through a plurality of longitudinal slots 34 in the inner sleeve 22, an upper portion 33 of the volume 25, and a plurality of inclined ports 36 in the outer sleeve 20.

The passage 32 is normally closed by the sealing sleeve 30, an annular metal seal surface 38 defined by a reduced thickness end portion of the sleeve 30 being positioned in sealing contact with a corresponding surface 39 defined by a metal seal ring 40 held against a shoulder 42 on the inner sleeve 22 by a retaining collar 44.

A flow sleeve 48 is mounted on the end of the sleeve 30 and normally covers an annular groove 50 in the outer sleeve 20 from which the ports 35 extend. Although there are no seals provided between the flow sleeve outer surface 52 and the adjacent surface of the outer sleeve 20, the surfaces are configured such that the extended flow sleeve 48 effectively closes the ports 36.

The sealing sleeve 30 is movable relative to the body 12 by differential fluid pressure applied across the body wall, which in use will be the difference between bore and annulus pressure. The fluid pressure acts on a piston area 54 defined on the sleeve 30 and partially defining a volume 56 between the sealing sleeve 30 and the outer sleeve 20.

Fluid entry to the volume 56 is gained via a tortuous restricted area pathway 58 extending from the slots 34, between the inner sleeve 22 and the sealing sleeve 30, between an end of the sealing sleeve 30 and an end of a spring force transfer sleeve 60, through a longitudinal bore 62 in the sealing sleeve 30, through a small diameter cross-bore 64 in the sleeve 30, and then between the sealing sleeve 30 and the outer sleeve 20.

Further, there is an additional volume 66 between the sealing sleeve 30 and outer sleeve 20 which communicates with the body exterior via a small diameter port 70 in the sleeve 20, one effect of this feature being that the sleeve 30 is maintained in the sealing position when annulus pressure is higher than bore pressure.

Accordingly, fluid may only flow into and from the volume 56 relatively slowly, effectively damping movement of the sleeve 30.

In one possible application, the device 10 is located in a tubular string and run downhole, until the device 10 is at the desired depth in the bore. The string bore pressure is then increased, such that fluid flows, at a low flow rate, from the body bore, through the pathway 58, to the volume 56 to act on the piston area 54. Movement of the sealing sleeve 30 induced by the pressure force on the piston area 54 also results in the displacement of fluid from the volume 66 and into the annulus, through the small diameter port 70. The pressure differential which will initiate movement of the sealing sleeve 30 is predetermined by the rate of the spring 26, and may be set to require a pressure differential of, for example, 1000 or 2000 psi.

As the sealing sleeve 30 is retracted, the sealing surfaces 38,39 are separated, allowing fluid to flow between the surfaces 38,39, but as the flow sleeve 48 still extends across the ports 36, initially there is little or no flow through the flow passage 32. However, with further movement of the sleeve 30, the end of the flow sleeve 48 exposes the annular groove 50, allowing fluid to flow through the ports 36, tris configuration of the device 10 being illustrated in the upper part of the Figure. It will be noted from the Figure that the flow area A between the sealing surfaces 38,39 is considerably larger than the flow area defined around the free end of the flow sleeve 48, such that the fluid velocity in the area between the surfaces 38,39 will be relatively low, and there will be little or no pressure drop as the fluid flows between the surfaces. Accordingly, it is unlikely that the flow of fluid through the flow passage 32 will result in any wear or erosion of the surfaces 38,39 which would prevent formation of a pressure-tight seal on the surfaces 38,39 coming together once more.

In most situations, the pressure differential between the body bore 18 and d the annulus will maintain the sealing sleeve 30 retracted. However, even if opening the flow passage 32 results in a decrease in differential pressure, such that the spring 26 tends to move the sleeve 30 towards the sealing position, the restricted and tortuous pathway 58 which the fluid must flow through to exit the volume 56 results in only relatively slow movement of the sleeve 30.

Further, in testing it has been found that such movement of the sleeve 30 towards the sealing configuration only tends to continue until the flow sleeve 48 closes the ports 36, at which point differential pressure rises once more and again causes the sleeve 30 to retract, relatively slowly, such that the sealing surfaces 38,39 do not come into contact.

It will be apparent to those of skill in the art that the device 10 permits selective communication between a string bore and an annulus under the control of bore pressure and utilises a seal arrangement which will not experience the erosion and wear which occur in existing arrangements, such that the device may be used on many occasions without loss of sealing capability.

It will also be apparent to those of skill in the art that the above-described embodiment is merely exemplary of the present invention and that numerous modifications and improvements may be made thereto without departing from the scope of the present invention. For example, other devices in accordance with the invention may provide selective communication from the annulus into the bore, and the basic principle of the invention, that of a sealing arrangement having seals defining an area which when open provides low velocity and a low pressure differential across the seals, may be utilised in a wide range of devices, and is not limited to the application described above.

Claims

CLAIMS 1. A resealable downhole flow control device comprising: a tubular body for mounting on a tubular string and defining a flow passage between the body bore and the body exterior; and a seal arrangement defining first and second sealing surfaces, with the sealing surfaces in sealing contact the flow passage being closed, and on separation of the sealing surfaces, the flow area between the surfaces being larger than the smallest flow area defined by the flow passage.
2. The device of claim 1, wherein the sealing surfaces are of metal, such that when closed the sealing surfaces form a metal-to-metal seal.
3. The device of claim 1 or 2, wherein one of the sealing surfaces is fixed relative to the body, and the other is movable relative to the body.
4. The device of claim 1,2 or 3, wherein the sealing surfaces are normally in sealing contact.
5. The device of any of the preceding claims, wherein one of the surfaces is biased towards the other.
6. The device of any of the preceding claims, wherein the sealing surfaces are circular or annular.
7. The device of any of the preceding claims, wherein one of the sealing surfaces is defined by a sleeve.
8. The device of any of the preceding claims, wherein the device includes means for restricting flow through the flow passage on initial separation of the sealing surfaces.
9. The device of claim 8, wherein the flow passage includes a flow port and the flow restricting means extends over the. port, said means being movable such that, as the sealing surfaces are spaced further apart, the degree of flow restriction provided by said means decreases.
10. The device of claim 9, wherein said means is defined by a portion of a sleeve defining one of the sealing surfaces.
11. The device of any of the preceding claims, wherein the seal arrangement is fluid pressure actuated.
12. The device of claim 11, wherein the seal arrangement is operated by differential pressure between the body and the surrounding annulus.
13. The device of any of the preceding claims, wherein the device defines a piston area, application of elevated fluid pressure to said area tending to separate the sealing surfaces.
14. The device of claim 13, wherein the piston area partially defines or communicates with a fluid chamber, fluid access to the chamber being via a restricted area flow path.
15. The device of any of the preceding claims, wherein the flow passage includes an inlet defined by a plurality of restricted dimension flow ports, to prevent or restrict the flow of particulates through the passage.
16. A method of controlling flow between a downhole tubular body and a surrounding annulus, the method comprising the steps of: mounting a tubular body on a tubular string and providing a flow passage between the body bore and the body exterior; providing a seal arrangement defining first and second sealing surfaces; positioning the sealing surfaces in sealing contact to close the flow passage; and then separating the sealing surfaces to permit flow through the passage, the flow area between the surfaces being selected to be larger than the smallest flow area defined by the flow passage.
17. A resealable downhole flow control device comprising: a tubular body for mounting on a tubular string and defining a flow passage between the body bore and the body exterior; a retractable flow restrictor positioned in the flow passage; and a seal arrangement defining first and second sealing surfaces, with the sealing surfaces in sealing contact the flow passage being closed, on initial separation of the sealing surfaces, the flow restrictor restricting flow through the flow passage, and on further separation of the sealing surfaces the flow restrictor being retracted to permit flow through the flow passage.
18. A resealable flow control device comprising: a body defining a flow passage; and a seal arrangement defining first and second sealing surfaces, with the sealing surfaces in sealing contact the flow passage being closed, and on separation of the sealing surfaces, the flow area between the surfaces being larger than the smallest flow area defined by the flow passage.
19. A resealable downhole flow control device substantially as described herein and as illustrated in the accompanying drawings.