BACKGROUND OF THE INVENTION

Field of the Invention

This invention is directed to downhole surface controlled valves such as subsurface safety valves and gas vent valves for use in oil or gas wells. This type of valve typically employs a flapper, a sleeve valve, or a combination thereof valve that is held open by a flow tube held in an open position by hydraulic pressure in a control line extending from the surface. Description of Related Art

The present invention relates to operations performed and equipment utilized in a subterranean well to provide for fail safe closure of the well in emergency conditions. Surface controlled subsurface safety valve (SCSSV) and casing vent valves have been in existence in the oil and gas producing industry for a substantial period of time during which their configuration, operating pressure, valve closure mechanism and setting depth have been upgraded as the industry moves to deeper and more challenging environments.

A typical downhole valve, be it wireline retrievable or tubing mounted subsurface safety valve or casing vent valve, employs a hydraulic piston to which fluid pressure is applied via a control line externally mounted on the tubing string. This will result in the valve being moved to the open position while compressing a coiled spring which provides for valve closure when this pressure is removed. This spring device must be capable of lifting the hydrostatic head in the control line, thereby powering the piston to the closed position and allowing the valve mechanism to close. At shallow depths this presents little problem but as valves are placed deeper in the well, the configuration of the coiled spring has to change in order to provide the increased power needed to lift the deeper fluid column and allow valve closure. Larger springs and increased spring material diameter result in reduced flow through the valve until a point is reached where spring closure of the valve is no longer viable.

As setting depths have increased, different methods of valve operation have been conceived to provide fail safe operation. Electrical valves operated using solenoids by way of an externally mounted electric cable, requiring a relatively high levels of electric power have been used. Use of a second hydraulic control line to balance the hydrostatic head in the operating control line has also been used. Another approach is the use of a gas chamber in the valve charged to a predetermined pressure thus duplicating the two control line approach. Both of these involve addition of dynamic seals, thus creating possible leak paths.

All of these approaches involve substantial additional cost and bring with them reliability issues with the depth, high pressure, and temperatures of today's wells. Another approach to the design of deep set valves is needed that does not involve substantial additional costs and reduced reliability.

BRIEF SUMMARY OF SOME OF THE PREFERRED EMBODIMENTS

These and other needs in the art are addressed in one embodiment by the use of magnetic force to assist the main spring in moving the flow tube to a position which allows a flapper valve the close. As a point of reference, magnets (and the force there between) and springs (and the force of compression) work oppositely. Magnets have their strongest attraction when close, decreasing as the distance between them increases. A compression spring has its lowest force when extended and its greatest force when compressed. Therefore, when configured properly one compliments the other with respect to overcoming hydrostatic force in a downhole valve. A first magnet is embedded in the valve housing and a second magnet of opposite polarity is attached to the flow tube in proximity to the first magnet. Thus as the spring moves the flow tube and consequently the second magnet comes into closer proximity to the first magnet, the magnetic force will be increased and assist in overcoming the hydrostatic pressure in the hydraulic control line. In another embodiment of the invention, a plurality of springs are used in tandem to move the flow tube upwardly against the hydrostatic pressure in the control line. Thus, for example, if a single spring is capable of functioning property at a depth of 1500ft, two similar springs will be able to function properly at 3000ft to close the safety valve. In this way, any setting depth requirements can be accommodated by lengthening the flow tube and/or valve housing and adding more springs. While these embodiments may be used separately, they can also be combined in a single assembly valve to function together.

FIG. 1 is a cross sectional view of a safety valve according to an embodiment of the invention showing the valve in a closed position.

FIG. 2 is a cross sectional view of a safety valve according to an embodiment of the invention showing the valve in an open position.

FIG. 3 is a perspective view showing the ring magnets.

FIG. 4 is a graph showing the strength of the magnetic and spring forces as a function of the distance of travel of the flow tube. FIGs. 5A and 5B are cross sectional views of a second embodiment of the invention showing the valve in a closed position.

FIGs. 6A and 6B are cross sectional views of a second embodiment of the invention showing the valve in a closed position.

FIG. 7 is a cross sectional view of a further embodiment of the invention with the valve in the open position.

FIG. 8 is a cross sectional view of the further embodiment of FIG. 7 with the valve in the closed position.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. l an embodiment of safety valve 10 according an embodiment of to the invention includes a housing having an upper portion 1 1 , a middle portion 12 and a lower portion 13. Upper and lower portions 1 1 and 13 of the housing are adapted to be coupled to a tubular string or the like as is well known in the art. Middle portion 12 and lower portion 13 are threadedly connected to each other at 25 and 23.

A hydraulic control line 14 extends from a source 15 on the surface to an inlet port 51 in the valve body. A piston 16 is positioned with a hydraulic fluid chamber 34 and at a lower end is connected to a shoulder 18 formed on a flow tube 19 located within the valve housing. In this closed position, the magnetic force between the magnets is maximum and the force exerted by the springs is at a minimum. This allows for a greater setting depth.

Flow tube 19 includes a flow passage 33 which is in fluid communication with inlet passage 17 and outlet passage 31 when flapper 26 is in the open position.

A slightly compressed coil spring 22 surrounds flow tube 19 and its held captive between shoulder 18 and a shoulder 29 formed within middle housing portion 12.

Flapper 26 is pivotally supported by a biased spring 32 on an end portion 27 of middle housing portion 12 and is biased to a closed position as shown in FIG. 1.

A first ring magnet 38 is embedded in a portion 21 of the upper housing portion 1 1. A second ring magnet 37 of opposite polarity of the first ring magnet 38 is embedded in the shoulder 18 of the flow tube.

To open the flapper valve 26, fluid pressure is applied from the surface to the top of piston 16. Piston 16 moves downwardly as shown in FIG. 2 due to the fluid pressure and in so doing moves flow tube 19 to pivot flapper 26 off of valve seat 27. In this open position, the magnets exert a minimum amount of force, and the spring is compressed to exert its maximum force value. At the same time coil spring is compressed as shown in FIG. 2 and magnet 37 has moved away from magnet 38.

To close the valve, pressure in control line 14 is relieved. Compressed coil spring 22 will act on shoulder 18 to move the flow tube in an upward direction against the hydrostatic force of the fluid in control line 14. As the flow tube 19 moves upwardly the attractive force between magnets 37 and 38 increases thereby increasing the total force applied to overcome the hydrostatic pressure in control line 14.

This relationship is illustrated in FIG. 4. In the position shown in FIG. 2 the spring force is greatest and the magnet force is weakest. However, as the distance between magnets decrease as the flow tube moves upwardly, the magnet force increases and supplements the force of the spring which decreases as the flow tube moves upwardly. This allows for a lower pressure to be used and a flatter force curve due to both the magnet and spring force.

A second embodiment of the invention is illustrated in FIGs. 5A, 5B, 6A, and 6B. Safety valve 50 includes an upper housing portion 51 , a middle housing portion 52 and a lower housing portion 54. A valve body 53 is connected between middle housing portion 52 and lower housing portion 54. Valve body 53 includes a valve seat 82 and a flapper 81 pivotally connected to valve body 53 by a biased coil spring 57 as is known in the art.

Upper and lower housing portions 51 and 54 are configured to be coupled for example to a tubular string within the well and include flow passage 75 and 77 respectively.

A flow tube which is axially movable within the valve housing includes an upper tube

60 and a plurality of intermediate tube portions 61, 62, 63, and 64. Each flow tube has an enlarged shoulder 71 , 72, 73 and 74 which serve to compress springs 65, 66, 67, and 68 when the flow tube is moved in a downward direction.

The downward movement of the flow tube is accomplished by pressure in a fluid control line 84 which is directed to a hydraulic chamber 96 having a piston 56 positioned therein. Piston 56 abuts shoulder 71 and will cause the flow tube to move downward as a result of the pressure acting on piston 56.

A plurality of spring stops 91 , 92, and 93 are fixedly attached to intermediate housing 52 such that as the flow tube moves downwardly, the springs 65, 66, and 67 are compressed between shoulders 71 , 72, 73 and a respective spring stops 91 , 92, 93. Spring 68 is compressed between shoulder 74 and valve body 53 as shown in FIG. 6B.

In order to open the valve from the closed position of FIG. 5B to the open position of FIG. 6B, control fluid under pressure is applied to chamber 96 which forces piston 56 downward. As piston 56 moves downward, the entire flow tube is forced downward by virtue of piston 56 acting on shoulder 71. The lower portion 98 of the flow tube will push against and open flapper 81 to the open position shown in FIG. 6B.

As the flow tube moves downwardly, springs 65, 66, 67, and 68 are compressed as shown in FIGs. 6A and 6B.

To close the valve, pressure in control line 84 is relieved and compressed springs 65,

66, 67, and 68 will now move the flow tube upwardly so that lower portion 98 of the flow tube moves upward of flapper 81 to allow it to be closed by the bias of the spring pivot connection. The force available to overcome the hydrostatic pressure in control line 84 is the sum of the energy stored in all the springs.

The embodiment of FIGSs. 5A, 5B, 6A and 6B may also include a pair of oppositely polarity ring magnets 38 and 37. One would be located in upper housing portion 51 and one would be located in shoulder 71 as shown in FIG. 5A. In this manner the combined supplemented magnetic force and plural spring forces could be utilized to overcome the hydrostatic pressure within control line 84.

Additional pairs of magnets 101 , 102, 103, 104, 105 and 106 may be positioned in spring stops 91 , 92, 93 and shoulders 72, 73 and 74 as shown in FIGs. 5A and B.

This application embodies the tubing retrievable subsurface safety valve. It will become obvious to one of ordinary skill in the art that the invention can also be applied to a wireline retrievable subsurface safety valve.

FIGs. 7 and 8 depict a further embodiment of a valve 1 10 according to the invention.

This embodiment is directed to a casing gas valve 1 10 and includes a housing having an upper portion 1 1 1 , a middle portion 1 12, a lower portion 1 13, a portion 1 14 and a lower connection 1 15 having an inlet 1 16.

A piston 1 18 having an enlarged portion 125 is located within upper housing portion 1 1 1. A control line 13 1 is adapted to introduce pressurized fluid to the upper portion 1 1 1 of the housing above piston 1 18. A spring 122 is captured between enlarged piston portion 125 and a shoulder 123 formed on an interior portion of middle housing portion 1 12.

A flow sleeve 127 is attached to and is axially movable with piston 1 18. Flow sleeve 127 includes one or more ports 128 as shown in FIG. 8. Middle housing portion 1 12 includes one or more outlets 1 17. In an open position shown in FIG. 7, ports 128 of flow tube 127 are aligned with outlets 1 17. In the closed position of FIG. 8, a non-ported portion of the flow tube 127 covers outlets 1 17 so that the valve is in a closed position.

A circular magnet 124 is positioned at a top portion of housing 1 1 1 and a second circular magnet of opposite polarity is placed in enlarged portion 125 of piston 1 18. In the open position of FIG. 8, fluid pressure has been applied through control line 131 which extends to the surface. The pressure acts on the top portion 125 of the piston and forces the piston downward thereby compressing spring 122, moving magnet 125 away from magnet 124 and bringing ports 128 into registry with outlets 1 17. This allows flow through the valve 1 10 from inlet 1 16 through outlets 1 17.

In order to close the valve, fluid pressure within control line 131 is relieved. This will allow compressed spring 122 to move piston 1 18 upwardly as shown in FIG. 7. As the piston moves upwardly, magnets 125 and 124 get closer to each other and the attractive force between the magnets aids the spring in moving the piston upwardly in opposition to the hydraulic force acting on the top portion of the piston. This in turn moves flow tube 127 upwardly so that ports 128 are no longer in registry with outlets 1 17 thereby closing the valve.

Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations may be made herein without departing from the spirit and scope of the invention as defined by the appended claims.