WO1998003766A1

WO1998003766A1 - Downhole two-way check valve

Info

Publication number: WO1998003766A1
Application number: PCT/CA1997/000520
Authority: WO
Inventors: Rick Picher; Charles Huard
Original assignee: Rick Picher; Charles Huard
Priority date: 1996-07-19
Filing date: 1997-07-17
Publication date: 1998-01-29
Also published as: CA2181671A1; AU3534997A

Abstract

A check valve for use downhole in the production tubing of an oil and gas well. The check valve comprises a tubular valve body including a valve seat plate having an upper surface, a lower surface, an upflow orifice and a downflow orifice, a first valve ball contained within a ball cage which may seat on the upper surface of the valve seat plate closing the upflow orifice, a second valve ball contained within a downflow valve housing which may seat on the lower surface of the valve seat plate to close the downflow orifice. The second valve ball is biased in the closed position by a coil spring mounted within the downflow valve housing. Fluid pressure from below the check valve unseats the first valve ball allowing upward flow of fluid through the check valve and the production tubing. Fluid pressure from above the check valve will cause the first valve ball to seat and close while the second ball remains seated due to the coil spring. In that position, no downward flow of fluid is allowed. Additional pressure may be intentionally applied to partially compress the coil spring and unseat the second valve ball, allowing downward flow of fluid through the check valve and thus the production tubing. At even greater pressure, the coil spring is completely compressed, allowing the second valve ball to seat on a second valve seat opposite the valve seat plate. Again, no downward flow of fluid is permitted in this position.

Description

DOWNHOLE TWO-WAY CHECK VALVE

FIELD OF INVENTION

The present invention relates to a check valve device and in particular to such a device for downhole use in oil and gas wells.

BACKGROUND TO THE INVENTION

A typical producing oil and gas well may comprise several hundreds of meters of casing and tubing. A pump connected to the bottom of the tubing permits artificial lift of well fluids which may consist of oil, water, gas or mixtures thereof as well as abrasive solids such as sand, gyp, or scale. Typically, a progressing cavity or rotary vane pump is employed to impart this artificial lift. The pump's rotating drive element (rotor) is connected to a rod string which extends upward through the tubing and terminates at a surface drive head. The motor driven surface drive head provides rotational energy which is transmitted downward through the rod string to the pump's drive element, creating the pumping action required to move well fluids to the surface where they can be collected.

When the surface drive's rotational momentum is interrupted due to a power failure, automatic on/off cycling or is simply turned off for servicing, the column of fluid will reverse flow direction in an effort to equalize itself within the tubing. The intensity and duration of this reverse fluid flow is dependent on the natural fluid level within the formation and the viscosity of the produced fluid.

Rapid flow of fluid back down the tubing string may create several undesirable conditions. The rapid decompression within the well has a damaging effect on the elastomers used in the manufacture of the aforementioned pump types. Gases that have permeated the elastomer expand rapidly causing blistering and swelling, which leads to dramatically reduced run lifes. The most critical concern associated with this rapid flow reversal is the significant safety hazard for personnel on the surface. The rapid reversal of the fluid travelling down the tubing string enters the pump from the discharge end, transforming it into a hydraulic motor. This rotational action is then transmitted back up the rod string to the surface drive. The velocity of this reverse rotation may cause surface components such as electric motor fans and drive sheaves to exceed maximum rim velocities. If that happens, the result is an explosive disintegration of the component sending shrapnel flying hundreds of feet. The potential for personal injury or death and significant property damage is obvious. Existing anti-reverse surface braking devices offered to date have not been reliable in preventing these accidents.

Reverse flow may be prevented by a check valve located in the tubing string. However, one-way check valves that merely prevent reverse flow are not entirely desirable. It is sometimes necessary to induce downward flow through the tubing to flush restrictive particles, such as sand, gyp or scale, that have built up at the suction end of the pump. A conventional check valve, while eliminating reverse flow concerns, would not permit this flushing requirement. It would also hamper the insertion of the rotor within the stator due to pressure buildup from fluid being trapped that would otherwise be displaced.

In U.S. Patent No. 4,478,558 issued to Owen on October 23, 1984, a ball-type check valve is disclosed which enables flow of fluid in the upward direction but closes and prevents downward reverse flow. The valve may be opened if the fluid above the valve is pressurized. Such fluid pressure acts on a piston which unseats the ball valve element from its valve seat to open the valve. This valve thus suffers from the disadvantage of an additional component, the piston, which requires additional length and sealing surfaces. Furthermore, the piston reduces flow through the valve because of the increased fluid friction caused by the piston. As well, suspended solids such as sand have a detrimental effect on the piston assembly and its operation. Lastly, it is necessary to pressure test the production tubing string whenever there is a drop off in production rates at surface. This test is performed to determine if losses are due to pump failure or lack of integrity between the production tubing and the casing. Tubing leaks are common due to the corrosive environment within the tubing and wear caused by the driving rod string as it rotates within the tubing. Present practice requires the operator to have a service rig pull the rod string from the tubing. A dart is then dropped down the tubing string and is allowed to fall until it seats in a pump seating nipple (PSN) usually installed one or two joints above the pump. Pressure is then introduced by filling the tubing from the surface and pumping against the dart. If a tubing leak is detected the tubing is pulled until fluid is found in the tubing string. The ruptured joint is replaced and the string is lowered to its original position. The rig must then send a special tool (overshot) down the tubing to latch onto the dart to extract it from the PSN. The rod string is then rerun into the well and landed. This operation is expensive due to rig costs and lost production the expense is increased by limited availability of rigs during peak seasons and during spring breakup.

Accordingly, there is a need in the art for a downhole check valve which prevents the natural gravity induced fluid flow reversal within the production tubing while allowing downward flow under certain surface controlled circumstances. It is also desirable for such a check valve to permit pressure testing without the need to pull the rod string from the tubing.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a downhole two-way check valve which can be mechanically set to prevent downward fluid flow except under controlled circumstances.

In one aspect of the invention, the invention is a check valve for use in the production tubing of a well bore, comprising: (a) a valve body having a lower opening and an upper opening;

(b) a valve seat member having an upflow orifice and a downflow orifice;

(c) an upflow valve associated with the upflow orifice and having an open state allowing fluid flow through the upflow orifice and a closed state preventing said fluid flow;

(d) a downflow valve associated with the downflow orifice and having an open state for allowing fluid flow through the downflow orifice and a closed state preventing said fluid flow; and

(e) biasing means associated with the downflow valve means for maintaining the downflow valve means in the closed state, which biasing means may be overcome by artificially induced fluid pressure, switching the downflow valve to the open state.

In one embodiment of the invention, the upflow valve comprises a first valve ball and a first ball cage engaging the valve seat member around the upflow orifice for retaining the first valve ball and the downflow valve comprises a second valve ball and a second ball cage engaging the valve seat member around the downflow orifice. The biasing means tends to maintain the second valve ball against the second valve seat, i.e. in the closed position. In the preferred embodiment, the biasing means comprises a coil spring and the valve further comprises adjusting means for varying the force exerted by the spring on the second valve ball.

In another aspect of the invention, the invention is a check valve for downhole use in the production tubing of a well bore comprising:

(a) a valve body having a lower opening and an upper opening, the valve body defining a first flow passage and a second flow passage; (b) an upflow valve associated with the first flow passage and having an open state allowing fluid flow through the first flow passage and a closed state preventing said fluid flow;

(c) a downflow valve associated with the second flow passage and having an open state allowing fluid flow through the second flow passage, a closed state preventing said fluid flow and a second closed state preventing said fluid flow; and

(d) biasing means associated with the downflow valve for maintaining the downflow valve in the first closed state, which biasing means may be overcome by fluid pressure, switching the downflow valve to the open state or the second closed state.

In a preferred embodiment, the downflow valve comprises a downflow valve seat having a first downflow orifice, a tubular downflow valve body having an upper end and a lower end wherein the upper end engages the downflow valve seat around the first downflow orifice, a valve ball disposed within the downflow valve body, and a second valve seat having a second downflow orifice associated with the lower end of the downflow valve body whereby the first closed state is created by the seating of the valve ball against the downflow valve seat and the second closed state is created by the seating of the valve ball against the second valve seat.

(a) a valve body having a lower opening and an upper opening, the valve body defining a first flow passage, a second flow passage and a bypass opening;

(b) a bypass cover engaging the valve body and closing the bypass opening and disengagement means for opening the bypass opening; (c) an upflow valve associated with the first flow passage below the bypass opening and having an open state allowing fluid flow through the first flow passage and a closed state preventing said fluid flow;

(d) a downflow valve associated with the second flow passage below the bypass opening and having an open state allowing fluid flow through the second flow passage, a closed state preventing said fluid flow and a second closed state preventing said fluid flow; and

(e) biasing means associated with the downflow valve for maintaining the downflow valve in the first closed state;

wherein a fluid pressure differential created by higher pressure in the upper opening than in the lower opening causes the downflow valve to switch from the first closed state to the open state, a higher fluid pressure differential causes the downflow valve to switch from the open state to the second closed state and an even higher fluid pressure differential activates the disengagement means causing the bypass cover to disengage from the valve body thereby uncovering the bypass opening.

In the preferred embodiment, the valve body is cylindrical and hollow, the bypass cover is cylindrical and hollow and the bypass cover slidingly engages the valve body in a concentric manner. The disengagement means comprises a shear pin fixing the bypass cover in a position closing the bypass opening.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described with reference to the accompanying drawings in which:

Figure 1 is a pictorial view of the invention located in the tubing string of a producing oil and gas well. Figure 2 is a cross-sectional view of a preferred embodiment of the invention.

Figure 3 is a cross-section along line 3-3 in Figure 2.

Figure 4 is a cross-section along line 4-4 in Figure 2.

Figure 5 is a cross-section along line 5-5 in Figure 2.

Figure 6 is the cross-sectional view of Figure 2 demonstrating upward flow of fluid through a preferred embodiment of the invention.

Figure 7 is the cross-sectional view of Figure 2 demonstrating a preferred embodiment of the invention preventing downward flow of fluid.

Figure 8 is the cross-sectional view of Figure 2 demonstrating use of a preferred embodiment of the invention during a flushing operation.

Figure 9 is the cross-sectional view of Figure 2 demonstrating use of a preferred embodiment of the invention during a pressure testing operation.

Figure 10 is the cross-sectional view of Figure 2 demonstrating a preferred embodiment of the invention after a blow-out operation.

DETAILED DESCRIPTION

The invention is a device generally comprised of a tubular, cylindrical body containing two valve elements oriented in opposing directions. As indicated in Figure 1 , the device (10) is part of the tubing string (12), below the position of the pump (14), which is shown to be a rotating progressing cavity pump. The tubing string (12), including the pump (14) and device (10), are enclosed in the well casing (16). The rotating progressing cavity pump (14) comprises a rotor (18) and a stator (20). The rotor (18) is rotationally driven by the rod string (22) which extends upward through the tubing (12) up to the wellhead (24). The rod string (22) is driven by a drive element (not shown) which is typically located above the flowtee (26). Flowlines (28) extend from the flowtee (26) in a conventional fashion. A pressure gauge (30) is provided to monitor pressure of the well fluid within tubing string (12).

The construction of a preferred embodiment of the device (10) is shown in cross-sectional detail in Figure 2. The device (10) is comprised of the main housing (34) and the upper housing (36), both of which are cylindrical and tubular. The main and upper housings (34, 36) are in sealed connection to each other by means of conventional O-ring gaskets (38) and shear pins (40). The upper portion of the main housing (34) which overlaps the upper housing (36) defines bypass openings (42). The function of the upper housing (36), shear pins (40) and bypass openings (42) will be described in further detail below in conjunction with Figure 10.

Inserted into the main housing (34) are the upflow valve (44) and the downflow valve (46). Integral to both the upflow valve (44) and the downflow valve (46) is a valve seat plate (48) which is a circular plate defining two orifices: the upflow orifice (50) and the downflow orifice (52). Fluid passing through the main housing (34) must pass through either of these two orifices (50, 52). The valve seat (48) rests on shoulder (56) formed in the interior of the main housing (34) and is shrink-fit into place in a conventional fashion.

The upflow valve (44) comprises a ball (58) and ball cage (60) which retains the ball (58) within it but permits the ball (58) to travel up and down, on and off the valve seat (48). The ball cage (60) is cylindrical, tubular, open ended and forms flow openings (62) along its length. The upper end of the ball cage (60) abuts the tag plate (64) which is a disc-like element fitting the interior of the main housing (34) having two or more radial arms (66). As shown in Figure 3, the preferred embodiment has four radial arms (66). One of the radial arms (66) extends across the upper opening of the ball cage (60) to retain the ball (58) within the ball cage (60). The tag plate (64) rests on shoulder (68) formed in the interior of the main housing (34) and is shrink-fit into place.

The lower end of the ball cage (60) abuts the valve seat (48) around the upflow orifice (50). The valve seat (48) has a circular concave surface which surrounds the upflow orifice (50) and which mates with the ball (58) to seal off the upflow orifice (50).

The downflow valve (46) comprises a ball (70), downflow valve housing

(72) and biasing means (74). The downflow valve housing (72) is tubular and open at both ends. The top end of the downflow valve housing (72) abuts against the lower side of the valve seat plate (48), surrounding the downflow orifice (52). It is also attached to the interior of the main housing (34) in an offset concentric fashion, as shown in Figure 5.

In the preferred embodiment, the biasing means (74) comprises ball retainer (76), coil spring (78), adjusting screw (80), end plate (82) and lock nut (84). The ball retainer (76) attaches to the ball (70) and the upper end of coil spring (78). The lower end of coil spring (78) is attached to the upper end of the adjusting screw (80) which is threaded to engage a threaded bore through the end plate (82). As is obvious, the force which the coil spring (78) imparts to the ball (70) may be adjusted by raising or lowering the adjusting screw (80) and locking it into position with the lock nut (84). The end plate (82) has flow passages (86) to allow fluid flow through the downflow valve housing (72).

Operation of the device (10) is now described in reference to Figures 6, 7, 8, 9 and 10.

As shown in Figure 6, operation of the pump (14) results in fluid flowing upward through the device (10). The pressure differential between the outlet (88) and the inlet (90) lifts ball (58) off of the valve seat (48), opening the upflow valve (44). Fluid may then flow in the inlet (90), up through the upflow orifice (50), through the ball cage flow passages (62), through the tag plate (64) and finally up the outlet (88). The downflow valve (46) is maintained in a closed position with the downflow ball (70) biased against the downflow orifice (52) by the biasing means (74). Also, the pressure differential created by the pump (14) tends to keep the downflow valve (46) closed.

With reference to Figure 7, when the pump (14) is not operating, the pressure differential between the outlet (88) and the inlet (90) reverses, resulting in the upflow ball (58) seating against the valve seat (48), closing off the upflow orifice (50). The downflow ball (70) is still maintained in the closed position by the biasing means (74).

The device (10) permits downward flow of fluid if the pressure differential exceeds the biasing force of the coil spring (78). Such pressure differential may be intentionally applied to fluid with the tubing string (12) to flush the tubing string (12), including the pump (14) and the device (10), of sedimentary deposits which may inhibit fluid flow. Also, insertion or reinsertion of the rod string (22) and rotor (18) creates such pressure in the tubing string above the device (10). Therefore, the device (10) permits such insertion without first draining the fluid in the tubing string (12).

As shown in Figure 8, downward fluid pressure overcomes Ihe biasing force of the coil spring (78), resulting in unseating of the downflow ball from the valve seat (48). Fluid may then flow through the downflow orifice (52), through the downflow valve housing (72) and out the flow passages (86) in the end plate (82).

Figure 9 demonstrates the device (10) during a pressure testing operation. The fluid in the tubing string is pressurized to an extent that the pressure differential across the downflow valve (46) completely compresses the coil spring (78). As a result the downflow ball (70) rests against the valve seat (92) formed within the downflow valve housing (72) at its lower end to seal off the downflow valve (46). Thus, with both the upflow and downflow valves (44, 46) closed, the tubing string (12) is closed off except for any leaks that may exist in the tubing string (12).

As is readily apparent from the above description, it is important to choose the coil spring (78) to provide the appropriate resistance to fluid pressure differential between the inlet (90) and the outlet (88) of the device (10). In one embodiment, the spring (78) maintains the downflow valve (46) in the closed state against pressures of up to approximately 250 to 500 p.s.i. over static fluid head pressure. The spring (78) should also be compressed entirely at pressures of approximately 1 ,500 p.s.i. over static fluid head pressure so that pressure testing can be performed. Intermediate pressures of between approximately 750 p.s.i. and 1,500 p.s.i. over static fluid head pressure will then partially compress the spring (78), allowing the flushing operation described above.

As will be appreciated by those skilled in the art, the range of pressures where the downflow valve (46) transitions from closed to open to closed again will vary according to the particular characteristics of the well and the formation being tapped. The spring (70) must be chosen and adjusted with the adjusting screw (80) accordingly.

With reference to Figure 10, it is sometimes necessary to "blow" the drain within the tubing string (12), allowing unrestricted downward flow of fluid through the device (10). In the preferred embodiment, this function is performed by the upper housing (36), the shear pins (40) and the bypass openings (42). The lower end of the upper housing (36) and the upper end of the main housing (34) are sized such as to permit concentric sliding engagement of the two housings (34, 36).

The number and size of the shear pins (40) is selected such that they will give way at pressures exceeding the pressure testing capacity of the device (10). Thus, if the spring (78) chosen permits pressure testing at above 1 ,500 p.s.i., the shear pins (40) may be selected to give way at approximately 3,000 p.s.i. Typical commercially available shear pins will break at approximately 750 to 900 p.s.i. each. Therefore, the illustrated preferred embodiment has 4 shear pins (40).

When the shear pins (40) give way, the upper and main housings (34, 36) partially disengage and stop on corresponding annular shoulders (92) and (94), thereby exposing the bypass openings (42). Fluid may then drain freely through the bypass openings (42) as is shown on Figure 10.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A downhole check valve comprising:

(a) a valve body having a lower opening and an upper opening;

(b) a valve seat member having an upflow orifice and a downflow orifice;

2. The valve of claim 1 wherein:

(a) the upflow valve comprises a first valve ball, a first ball cage engaging the valve seat member around the upflow orifice for retaining the first valve ball, wherein fluid flow from the upper opening of the valve body to the lower opening causes the valve ball to seat on the valve seat member closing the upflow orifice;

(b) the downflow valve means comprises a second valve ball, a second ball cage engaging the valve seat member around the downflow orifice for retaining the second valve ball wherein the biasing means tends to maintain the second valve ball in contact with the second valve seat, preventing fluid flow through the downflow orifice.

3. The valve of claim 1 or 2 wherein the biasing means compπses a coil spring having a top end and a lower end where the top end engages the second valve ball and the lower end engages the second ball cage.

4. The valve of claim 1 or 2 further comprising adjustment means for varying the force exerted by the biasing means tending to maintain the second valve ball in contact with the second valve seat.

5. The valve of claim 3 wherein second ball cage defines a threaded bore and the valve further comprises an adjustment screw which engages the threaded bore in the second ball cage and the lower end of the coil spring engages the adjustment screw such that the adjustment screw may be raised or lowered thereby compressing or relaxing the coil spring.

6. A downhole check valve comprising:

(a) a valve body having a lower opening and an upper opening, the valve body defining a first flow passage and a second flow passage;

(b) an upflow valve associated with the first flow passage and having an open state allowing fluid flow through the first flow passage and a closed state preventing said fluid flow;

(c) a downflow valve associated with the second flow passage and having an open state allowing fluid flow through the second flow passage, a closed state preventing said fluid flow and a second closed state preventing said fluid flow; and (d) biasing means associated with the downflow valve for maintaining the downflow valve in the first closed state, which biasing means may be overcome by fluid pressure, switching the downflow valve to the open state or the second closed state.

7. The valve of claim 6 wherein the downflow valve comprises a downflow valve seat having a first downflow orifice, a tubular downflow valve body having an upper end and a lower end wherein the upper end engages the downflow valve seat around the first downflow orifice, a valve ball disposed within the downflow valve body, and a second valve seat having a second downflow orifice associated with the lower end of the downflow valve body whereby the first closed state is created by the seating of the valve ball against the downflow valve seat and the second closed state is created by the seating of the valve ball against the second valve seat.

8. The valve of claim 7 wherein the downflow valve body defines a circular bore which is narrower than the diameter of the valve ball at the lower end such that the downflow valve body integrally forms the second valve seat.

9. The valve of claim 8 further comprising adjusting means for varying the force applied by the biasing means to the downflow valve to keep the downflow valve in the first closed state.

10. The valve of claim 9 wherein the biasing means comprises a coil spring having an upper end and a lower end, the upper end engaging the valve ball and the lower end engaging the adjustment means.

11. A downflow check valve comprising:

(a) a valve body having a lower opening and an upper opening, the valve body defining a first flow passage, a second flow passage and a bypass opening; (b) a bypass cover engaging the valve body and closing the bypass opening and disengagement means for opening the bypass opening;

(c) an upflow valve associated with the first flow passage below the bypass opening and having an open state allowing fluid flow through the first flow passage and a closed state preventing said fluid flow;

12. The valve of claim 11 wherein the valve body is cylindrical and hollow, the bypass cover is cylindrical and hollow and the bypass cover slidingly engages the valve body in a concentric manner.

13. The valve of claim 12 wherein the disengagement means comprises a shear pin fixing the bypass cover in a position closing the bypass opening.