Downhole safety valve

Abstract

 A downhole safety valve (1) for preventing blow outs in an oil or gas production well comprises a cup-shaped piston and cylinder assembly, a fluid inlet (8) connected to the interior (6) of the piston (2), a fluid outlet (10) connected to the exterior (7) of the cylinder (3) and e.g. a hydraulic system (20) for pushing the piston (2) down within the cylinder (3), wherein the piston and cylinder have perforated tubular walls and the perforations (4,5) are at least partly aligned if the piston (2) is pushed down into a lower position within the cylinder (3) , but which perforations (4,5) are unaligned such that flow of hydrocarbon fluid from the valve inlet (8) to the valve outlet (10) is interrupted if the piston (2) is pushed up within the cylinder (3) in response to an increase of the oil or gas pressure in the production tubing below the valve inlet (8).

Description

BACKGROUND OF THE INVENTION

[0001] The invention relates to a downhole safety valve for preventing blow-outs in a hydrocarbon fluid production well.

[0002] It is common practice to install hydraulically activated downhole safety valves in oil and/or gas production wells, which valves automatically close if the pressure of the hydraulic control fluid is released, such that the well is instantly closed if the hydraulic control system is damaged.

[0003] It is also known from US patent No. 4,911,199 to install a safety valve downhole in a well that closes automatically in response to an excessive fluid flow. An excessive fluid flow triggers a pressure difference across a venturi that lifts the valve stem up and pushes the disc-shaped valve body against the ring-shaped valve seat to close the valve. The known valve is designed to close a gas well at a well defined setting point and is not suitable to operate as a choke.

[0004] It is an object of the present invention to provide a downhole safety valve which is also suitable to perform as a choke which can be set at various intermediate positions in which the valve is partly open and controls the fluid flux and pressure in the production tubing downhole of the valve.

[0005] It is a further object of the present invention to provide a downhole safety valve which comprises a minimum of wear prone components and which is compact and reliable.

SUMMARY OF THE INVENTION

[0006] The downhole safety valve according to the invention comprises a cup-shaped piston and cylinder assembly, a fluid inlet connected to the interior of the piston, a fluid outlet connected to the exterior of the cylinder and means for pushing the piston down within the cylinder. The piston and cylinder have perforated tubular walls, which perforations are at least partly aligned if the piston is pushed down into a lower position within the cylinder, but which perforations are unaligned such that flow of hydrocarbon fluid from the fluid inlet to the fluid outlet is interrupted if the piston is pushed up within the cylinder in response to an increase of the pressure of the hydrocarbon fluid in the fluid inlet.

[0007] The fluid outlet may be connected to an annular space surrounding the outer surface of the tubular wall of the cylinder.

[0008] Preferably said means for pushing down the piston within the cylinder comprises a hydraulic or pneumatic fluid injection system for injecting a control fluid into the fluid chamber formed between the closed tops of the cup-shaped piston and cylinder. The pressure of the control fluid in said fluid chamber may be controlled by a pressure control system which accurately adjusts the pressure of the control fluid and limits said pressure below a pre-set value.

[0009] Suitably a spring pushes the piston up within the cylinder.

[0010] The pressure of the control fluid in said fluid chamber may be controlled by a pressure control system which limits said pressure to a pre-set value and is designed to gradually adjust the pressure of the control fluid such that the piston can be moved gradually within the cylinder into any intermediate position between said upper and lower positions, and the valve can be gradually opened and closed.

DESCRIPTION OF A PREFERRED EMBODIMENT

[0011] A preferred embodiment of the downhole safety valve according to the invention will be described in more detail and by way of example with reference to the accompanying drawings, in which

Figure 1 is a longitudinal sectional view of a downhole safety valve according to the invention; and

Figure 2 is a cross sectional view of the downhole safety valve shown in Figure 1, taken along the phantom line pointed at by arrows A-A in Figure 1.

[0012] Figure 1 depicts a downhole safety valve 1 which comprises a cup-shaped piston 2 which is movably arranged within a cup-shaped cylinder 3 and which is illustrated in a lower position thereof wherein an array of perforations 4 in the tubular wall 2A of the piston 2 is aligned with an array of perforations 5 in the tubular wall 3A of the cylinder 3 and the valve is in a fully opened position.

[0013] In the open position the aligned perforations 4 and 5 provide fluid communication between the interior 6 of the piston 2 and an annular space 7 that surrounds the tubular wall 3A of the cylinder 3.

[0014] The interior 6 of the piston 2 is in direct fluid communication with an inlet port 8, which is formed within a ring-shaped bottom part 9 of the valve 1. The annular space 7 is connected in fluid communication with an outlet 10 of the valve 1 by a series of axial outlet ports 11 that are drilled in a flange which surrounds a disk-shaped top 3B of the cylinder 3 and which secures the cylinder 3 within a tubular valve housing 13 which is screwed between a lower end ring 14 and an upper lock mandrel 15.

[0015] A pair of packing rings 16 is mounted in grooves in the outer surface of the valve housing 13 and the upper lock mandrel 15 which in use provide a seal against the inner wall of the production tubing (not shown) through which oil and/or gas are produced to surface.

[0016] Above the upper packing ring 16 there is a locking ring assembly 17 which retrievably locks the locking mandrel 15 and valve housing 13 to a recess in the inner wall of the production tubing.

[0017] A hydraulic conduit is arranged in the annular space surrounding the production tubing and is connected via a port opening in the wall of the production tubing to the annular space between the upper and lower packing rings 16. A channel 18 drilled through the valve housing 13 and the top 3B of the cylinder 3 provides fluid provides a supply conduit for hydraulic fluid from said annular space between the packing rings 16 into a fluid chamber 20 formed between the top 2B of the piston 2 and the top 3B of the cylinder.

[0018] In use hydraulic fluid is injected into said fluid chamber 20 at a controlled pressure. If this pressure is higher than the pressure of the produced hydrocarbon fluid in the interior 6 of the piston 2, then the piston 2 will be pushed down in the cylinder 3 to the lower position shown in Fig.1 wherein the lower end of the piston 2 rests on the ring-shaped bottom part 9 of the valve 1 and the perforations 4 and 5 in the piston 2 and cylinder 3 are aligned and the valve is in the open position and hydrocarbon fluid flows up from a lower part of the production tubing below the valve via the valve inlet 8, the interior of the piston 2 the perforation 4 and 5 , the annular space 7 and the axial ports 11 and the valve outlet 10 into an upper part of the production tubing.

[0019] If the pressure of the produced hydrocarbon fluid exceeds the pressure of the hydraulic fluid in the chamber 20 the piston 2 is pushed up inside the cylinder 3 such that the perforations 4 and 5 are unaligned and the valve is closed and no hydrocarbon fluids are able to flow from the lower part into the upper part of the production tubing.

[0020] If the pressure of the hydraulic fluid in the chamber 20 is balanced to the average pressure of the hydrocarbon fluid in the interior of the piston 2 and a the volume of hydraulic fluid within the chamber 20 is gradually adjusted, then the piston can be gradually moved between the fully open and fully closed positions into a series of intermediate positions in which the perforations 4 and 5 are only partly aligned and the valve is partly opened and performs as an adjustable downhole choke.

[0021] The valve 1 can be installed within the production tubing by lowering the valve 1 and locking mandrel 15 through the tubing by a wireline until the locking ring 17 is locked into a recess in the inner wall of the production tubing at a depth of about 100 metres below the wellhead.

[0022] If desired a spring may push the piston 2 up into the cylinder 3 in order to ensure that the valve 1 is always closed in case the hydraulic fluid supply to the chamber 20 is interrupted, even in the absence of an overpressure of the produced hydrocarbon fluids in the interior 6 of the piston 2.

[0023] The valve according to the invention comprises a minimum of wear prone components and is compact and can be easily transported and installed in and removed from a well. The valve therefore provides an adequate and efficient protection against uncontrolled flow of hydrocarbon fluid to the wellhead if any well or production equipment is damaged so that the risk of a well blow out is reduced significantly.

[0024] The additional functionality of the valve according to the invention as a controllable subsurface production choke is attractive since in many well the pressure of the produced gas has to be throttled back in a production choke at the earth surface, which then cools down the gas such that gas hydrates are formed, which may plug and disrupt the production facilities. If the gas pressure is reduced downhole then the heat present in the well tubulars, annuli and surrounding formation will reduce the cool down rate of the gas and inhibit the formation of gas hydrates.

Claims

1. A downhole safety valve for preventing blow outs in a hydrocarbon fluid production well, the valve comprising a cup-shaped piston and cylinder assembly, a fluid inlet connected to the interior of the piston, a fluid outlet connected to the exterior of the cylinder and means for pushing the piston down within the cylinder, wherein the piston and cylinder have perforated tubular walls, which perforations are at least partly aligned if the piston is pushed down into a lower position within the cylinder, but which perforations are unaligned such that flow of hydrocarbon fluid from the fluid inlet to the fluid outlet is interrupted if the piston is pushed up within the cylinder in response to an increase of the pressure of the hydrocarbon fluid in the fluid inlet.

2. The downhole safety valve of claim 1, wherein the fluid outlet is connected to an annular space surrounding the outer surface of the tubular wall of the cylinder.

3. The downhole safety valve of claim 1, wherein said means for pushing down the piston within the cylinder comprises a fluid injection system for injecting a control fluid into the fluid chamber formed between the closed tops of the cup-shaped piston and cylinder.

4. The downhole safety valve of claim 3, wherein said control fluid injection system comprises a pressure control system for limiting the pressure of the control fluid.

5. The downhole safety valve of claim 4, wherein a spring pushes the piston up within the cylinder.

6. The downhole safety valve of claim 4 or 5, wherein said pressure control system is designed to gradually adjust the pressure of the control fluid such that the piston can be moved gradually within the cylinder into any intermediate position between said upper and lower positions, and the valve can be gradually opened and closed.

Drawing