Downhole pumps with outside pressure balancing and sand separation and isolation

Abstract

The present disclosure relates to a downhole pump designed to include a sand separation unit. In one implementation, the downhole pump comprises a barrel having a first valve for controlling fluid flow into the barrel. The first valve includes an interior cavity with a first surface. The downhole pump further includes a plunger housed within the interior cavity of the barrel. The plunger comprises a wiper-plunger having a first circumference to which one or more resilient seals are coupled. The one or more resilient seals seal a first boundary between the first circumference of the wiper- plunger and a first portion of the first surface associated with the barrel. The plunger further comprises a sand separation unit coupled to the wiper-plunger at a first side. The sand separation unit forms a balancing chamber that minimizes a pressure differential across the one or more resilient seals. The sand separation unit uses centrifugal force to separate particulate matter from fluid during a first motion of the wiper-plunger relative to the first portion of the first surface associated with the barrel. The plunger further comprises a plunger-assembly coupled to the sand separation unit at a second side. The plunger-assembly has a second valve that controls fluid flow into the plunger-assembly via a third side from the interior cavity of the barrel. Additionally, the plunger includes a second boundary between a second circumference of the plunger-assembly and a second portion of the first surface associated with the barrel. The second boundary is fillable by slippage fluid within the barrel to create a fluid seal at the second boundary.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent Application No. 62/652,364 filed on Apr. 4, 2018. The contents of the above application are hereby incorporated in its entirety by reference.

TECHNICAL FIELD

The present invention relates to subsurface, or downhole, pumps, such as are used to pump oil and other fluids and bases from oil wells.

BACKGROUND

When an oil well is first drilled and completed, the fluids (such as crude oil) may be under natural pressure that is sufficient to produce on its own. In other words, the oil rises to the surface without any assistance.

In many oil wells, and particularly those in fields that are established and aging, natural pressure has declined to the point where the oil must be artificially lifted to the surface. A subsurface pump is located down in the well below the level of the oil. A string of sucker rods extends from the pump up to the surface to a pump jack device, or beam pump unit. A prime mover, such as a gasoline, gas, or diesel engine, or an electric motor, on the surface causes the pump jack to rock back and forth, thereby moving the string of sucker rods up and down inside of the well tubing.

The string of sucker rods operates the subsurface pump. A typical pump has a plunger that is reciprocated inside of a barrel by the sucker rods. The barrel has a standing one-way valve, while the plunger has a traveling one-way valve, or in some pumps the plunger has a standing one-way valve, while the barrel has a traveling one- way valve. Reciprocation charges a compression chamber between the valves with fluid and then lifts the fluid up the tubing toward the surface.

In some wells, sand in the well fluid is a problem. The sand abrades the upper parts of the plunger and may even enter between the plunger and the barrel, thereby degrading the fluid seal between the plunger and the barrel. Pump components in a sandy well require frequent replacement.

U.S. Pat. No. 7,909,589 provides a solution to minimizing wear on pump components due to sand. A plunger has a wiper portion on top, with a fluid seal portion on the bottom. A pressure balancing chamber is provided between the wiper portion and the fluid seal portion. The pressure balancing chamber allows fluid to flow from inside the plunger to enter the chamber and balance the pressure across the wiper portion. A sand snare is provided in the pressure balancing chamber to keep the sand away from the fluid seal.

An improvement to the '589 patent has been invented.

SUMMARY

According to one innovative aspect of the subject matter described in this disclosure downhole pump including a sand separator unit is disclosed. In one implementation, the downhole pump comprises a barrel having a first valve for controlling fluid flow into the barrel. The first valve includes an interior cavity with a first surface. The downhole pump further includes a plunger housed within the interior cavity of the barrel. The plunger comprises a wiper-plunger having a first circumference to which one or more resilient seals are coupled. The one or more resilient seals seal a first boundary between the first circumference of the wiper-plunger and a first portion of the first surface associated with the barrel. The plunger further comprises a sand separation unit coupled to the wiper-plunger at a first side. The sand separation unit forms a balancing chamber that minimizes a pressure differential across the one or more resilient seals. The sand separation unit uses centrifugal force to separate particulate matter from fluid during a first motion of the wiper-plunger relative to the first portion of the first surface associated with the barrel. The plunger further comprises a plunger- assembly coupled to the sand separation unit at a second side. The plunger-assembly has a second valve that controls fluid flow into the plunger-assembly via a third side from the interior cavity of the barrel. Additionally, the plunger includes a second boundary between a second circumference of the plunger-assembly and a second portion of the first surface associated with the barrel. The second boundary is fillable by slippage fluid within the barrel to create a fluid seal at the second boundary.

These and other implementations may each optionally include one or more of the following features. The one or more resilient seals are elastomeric and include at least a fiber component. Also, the downhole pump further comprises one or more openings that ensure that a first portion of the wiper-plunger has a first pressure that is substantially equivalent to a second pressure associated with the balancing chamber to minimize wear on the one or more resilient seals.

The disclosed embodiments prolong the life span of the various components of the downhole pump. More specifically, the sand separation unit and other components of the downhole pump ensure that wear on at least the plunger, the resilient seals, etc., is significantly minimized.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a well, shown with pumping equipment.

FIG. 2 is a longitudinal cross-sectional schematic view of a prior art pump.

FIG. 3 is a longitudinal cross-sectional schematic view of a pump of the present invention, in accordance with a preferred embodiment.

FIG. 4 is a partial longitudinal cross-sectional view of the body of the sand separator unit.

FIG. 5 is a longitudinal cross-sectional view of the sand separator unit, shown with the pump plunger moving on the upstroke.

FIG. 6 is a longitudinal cross-sectional view of the sand separator unit, shown with the pump plunger moving on the downstroke.

FIG. 7 is a longitudinal cross-sectional schematic view of a pump of the present invention, in accordance with another embodiment.

FIG. 8 is a longitudinal cross-sectional schematic view of a pump of the present invention, in accordance with still another embodiment.

FIG. 9 is a detail longitudinal cross-sectional view of a plunger third portion, in accordance with still another embodiment.

DETAILED DESCRIPTION

The present invention provides a downhole pump and method of pumping with a sand separation unit (also referred to as a sand separator unit elsewhere herein) that allows the use of a plunger with resilient seal members, such as wiper cups, in conjunction with a fluid seal. Both the resilient seal members and the fluid seal form seals between the plunger and the barrel. The sand separation unit forms a balancing chamber to minimize any pressure differential across the resilient seal members. The sand separation unit uses centrifugal force to separate sand and other particulates so as to only provide fluid to the balancing chamber. In this manner, sand does not enter the fluid seal. Instead, the sand is flushed out of the plunger during reciprocation of the plunger.

The pump is an improvement over U.S. Pat. No. 7,909,589. The '589 pump relies on gravity to separate the particles from the slippage flow. Such reliance encounters some difficulty in some situations. In unconventional reservoirs, fine particles may be encountered. These particles do not have enough mass to be separated by gravity and will be easily dragged by the fluid into the balancing chamber. Also, as the pump size or the plunger clearance is increased, the slippage flow rate is increased, resulting in a lower separation efficiency.

The present invention relies on the centrifugation principle to separate solids (phase I) from liquid (phase II). Generally speaking, separating multiphase mixtures requires a differential force acting on either of the phases that will drive it way from the other. Centrifugal forces are a function of the angular velocity of the fluid, which in turn can be manipulated as desired by component design. Centrifugal forces in the pump can be several orders of magnitude higher than gravity and is thus more efficient.

Before the plunger is discussed in further detail, a brief description of a downhole well and reciprocating plunger pump will be provided.

In FIG. 1, there is shown a schematic diagram of a producing oil well 11. The well has a borehole that extends from the surface 13 into the earth, past an oil bearing formation 15.

The borehole has been completed and therefore has casing 17 which is perforated at the formation 15. A packer or other device or method (not shown) optionally isolates the formation 15 from the rest of the borehole. Tubing 19 extends inside of the casing from the formation to the surface 13.

A subsurface pump 21 is located in the tubing at or near the formation 15. A string 23 of sucker rods extends from the pump 21 up inside of the tubing to a polished rod and a stuffing box 25 on the surface 13. The sucker rod string 23 is connected to a pump jack unit, or beam pump unit, 24 which reciprocates up and down due to a prime mover 26, such as an electric motor or gasoline, gas, or diesel engine.

The present invention can be used with a variety of surface drive units besides a beam pump unit 24. For example, hydraulic pump units can be used, as well as belt type lifting units. Also, the present invention can be used with a variety of connecting members besides sucker rods 23. For example, a wire line can be used.

FIG. 2 illustrates a prior art pump 31. The pump has a barrel 33 and a plunger 35. The plunger 35 reciprocates with respect to the barrel 33. The barrel has a standing valve 37 and the plunger has a traveling valve 39. In the illustrations, the valve cage and other details are not shown.

The plunger 35 is reciprocated by the sucker rods 23. As the plunger 35 is raised on the upstroke, the traveling valve 39 is closed and the standing valve 37 is opened, wherein fluid is drawn into the compression chamber 41 between the two valves 37, 39. Thus, on the upstroke, the compression chamber 41 is charged with fluid. The fluid above the traveling valve 39 is lifted toward the surface. As the plunger 35 descends on the downstroke, the traveling valve 39 opens and the standing valve 37 closes, thereby forcing the fluid in the compression chamber 41 into the plunger.

The outside diameter of the plunger 35 is sized so as to provide a fluid seal 43 between the plunger and the barrel. The fluid seal is formed by the fluid entering a clearance between the plunger and the barrel. This clearance is typically 0.002-0.008 inches.

If the fluid contains sand 45, the plunger 35 exhibits wear. This is because on the upstroke, the plunger 35 moves up into the sand 45 that is just above the plunger. The top end 47 of the plunger 35 exhibits the most wear from the sand due to the upstroke motion and due to fluid pressure. The column of fluid in the tubing extending to the surface exerts pressure on the top end of the plunger. This fluid pressure tends to force fluid with sand between the plunger 35 and the barrel 33, independently of the movement of the plunger.

With the pump 21 of the present invention, the plunger 51 is modified so as to minimize damage and abrasion caused by the sand. FIG. 3 illustrates the pump 21 of the present invention. Like parts from one figure to another have like reference numbers. Thus, the barrel 33 and valves 37, 39 are substantially similar in the two pumps 21, 31.

The plunger-assembly 51 has several parts or portions. The plunger- assembly 51 has a first portion 53, a second portion 55 and a third portion 57. Because the pump 21 is typically oriented vertically, as shown, this orientation will be used to describe the pump. Thus, the plunger-assembly first portion 53 is above the second and third portions 55, 57. The plunger-assembly second portion 55 is interposed between the plunger first and third portions 53, 57. The pump 21 can be used in a non-vertical orientation, and can even be used in a horizontal orientation. An internal passage 59 extends along the length of the plunger, through all portions 53, 55, 57. The internal passage 59 extends from the traveling valve 39 to openings 61 in the upper end of the plunger-assembly. These openings 61 communicate with the tubing that extends to the surface.

As shown in the embodiment of FIG. 3, the plunger-assembly first portion 53 is a wiper-plunger and is equipped with seals 63 around the circumference. The seals 63 form a seal against the barrel 33 inside diameter. In the preferred embodiment, the seals are conventional and commercially available valve cups, although other types of seals can be used. For example, the seals can be of elastomeric material and have a fiber component. Because the seals 63 will be abraded and worn by the sand 45 during pumping operations, a number of seals are used. For example, in one embodiment, twelve valve cups are used, with the valve cups positioned along the length of the plunger-assembly first portion 53.

The plunger-assembly second portion 55 is the sand separation unit (and includes couplings to secure to the first and third portions). The sand separation unit 55 has an internal centrifugal solids separator and forms an exterior balancing chamber 65 with the barrel.

FIGS. 4-6 show the sand separation unit in more detail. The sand separation unit 55 has a body 81, which is tubular, having an upper end 83 and a lower end 85. A longitudinal axis A extends from the upper end to the lower end. The internal passage 59 extends along the length of the body 81. The outside diameter of the body 81 is smaller than the inside diameter of the barrel 33, so as to form the balancing chamber 65 therebetween. The body 81 is sized so as not to contact the barrel during reciprocation.

The sand separation unit is provided with a valve in the upper end 83. The valve has a seat member 87, a cage 89, a ball valve 91, and a spacer 93. The seat member 87 has a seat 95 for receiving the ball valve, and a central passage 97 therethrough for fluid flow during the plunger downstroke. The seat member 87 also has outer passages 99 around and radially outward from the seat. These outer passages 99 form spiral pathways around the central passage 97.

Below the seat member 87 are one or more openings 101 in the body (the preferred embodiment uses three). These openings allow fluid communication between the interior passage 59 of the body and the exterior thereof, or balancing chamber 65. Each opening 101 has a tube 103 inserted therein and that extends from the opening radially inward. Each tube extends inward a distance so that its inner end 105 is located away from the inside diameter of the body 81. The inner ends of the tubes are located closer to the longitudinal axis A than to the body 81 inside diameter. The openings 101 and tubes 103 are sized large enough so that they will not become blocked or occluded by sand. Preferably, the tubes 103 do not extend out beyond the outside diameter of the body 81. If more than one opening and respective tube are provided, the openings and tubes are spaced circumferentially about the body (in the embodiment shown, three openings 101 and tubes 103 are provided).

A bottom plug 107 is provided in or near the lower end 85 of the body 81. The bottom plug 107 has spiral passages 109 therethrough. The spiral passages 109 are located about a central mandrel 111.

An optional spiral member 113 can be provided between the tubes 103 and the bottom plug 107. The spiral member 113 is tubular with a central passage 119 therethrough and spiral passages 121 about the spiral member.

All of the spiral passages 99, 121, 109 are oriented in the same direction. The spiral passages may be either clockwise or counter-clockwise, when viewed from the upper end of the body.

All of the components including the seat member 87, the bottom plug 107 and the spiral member 113, are located inside the body 81. The components are assembled into the body 81. The spacer 93 is used during assembly to distribute the loads during assembly evenly on the cage. In one embodiment, the cage 89 is made of Stellite, a cobalt-chromium alloy.

The plunger-assembly third portion 57 (see FIG. 3) is in the embodiment of FIG. 3 a plunger and is cylindrical. The outside diameter of the plunger-assembly third portion 57 is slightly smaller than the inside diameter of the barrel 33. The clearance between the plunger-assembly third portion 57 and the barrel 33 is sized so that fluid can enter and provide a fluid seal 43. This fluid seal is also known as a metal-to-metal clearance seal. In the preferred embodiment, the clearance is 0.002-0.008 inches. The larger clearances are for heavy crude or heavy particulate conditions.

As one option, the outside diameter of the plunger-assembly third portion 57 can be hardened for increased wearability and durability. For example, the plunger third portion can be sprayed with metal such as nickel-based spray powder. The outer spray metal layer is typically 0.01 inches thick on each side, or 0.020 inches in the total cross-section. The hardness is typically Rockwall C 50 or C 60. Of course, other types of hardening methods and materials can be used, as well as other thicknesses of hardening coats.

In the preferred embodiment, the plunger-assembly portions 53, 55, 57 are joined together with couplings. This allows replacement of an individual component rather than the plunger 51 as a whole.

The operation of the pump will now be described. In operation, the plunger-assembly 51 and the barrel 33 have reciprocal motion relative to one another. In a fixed barrel pump, the plunger is reciprocated. In a fixed plunger pump, the barrel is reciprocated.

By way of background, a pump with a fluid seal 43 has two types of flow during reciprocation of the plunger relative to the barrel. One type of flow is production flow, which refers to the total production of the pump in barrels per day (BPD). Production flow is zero while the plunger is moving on the upstroke in the barrel. Production flow occurs when the plunger is moving on the downstroke. The other type of flow is slippage flow, which is the small amount of flow that flows through the fluid seal 43 between the plunger and the barrel. As an example, slippage flow may be 2-5% of the production flow. The slippage flow occurs when the plunger is moving on the upstroke and is zero when the plunger is moving on the downstroke.

FIG. 5 shows the sand separation unit and fluid flow when the plunger moves in the upstroke direction. The ball valve 91 at the upper end 83 is closed and slippage fluid (shown by a solid line in FIG. 5) flows past the ball valve 91 into the spiral passages 99 around the seat member 87. The spiral passages 99 around the seat member impart a spiral flow to the slippage fluid; the spiral flow is ejected near the inside diameter of the body 81 and away from the longitudinal axis A of the body. Any sand in the slippage flow thus remains against the inside diameter of the body due to centrifugal forces applied by the spiral passages 99. The fluid with sand follows a path with less tight spirals, as shown by the dashed line in FIG. 5.

The centrifugal forces applied to the sand can be varied by the design of the spiral passages 99. Sand that is heavier, or fluid that is more viscous, require higher centrifugal forces, which can be provided by smaller passages, a tighter spiral pattern (more turns per unit length), or a combination of both.

After passing through the passages 99, the fluid in the center of the interior passage 59 is clean and free of sand. The clean fluid (shown by the solid line in FIG. 5) enters the inward ends 105 of the tubes 103 and flows into the balancing chamber 65. The clean fluid provides a slippage flow to the fluid seal 43 in the third portion 57 of the plunger. In addition, there is no pressure differential across the first portion 53 with the resilient seal members 63.

During reciprocation, the seals 63 wipe the inside surface of the barrel, wiping sand that may adhere to the barrel. Normally, in prior art pumps, the seals 63 would have a short life and would require frequent replacement. That is why most downhole pumps utilize a plunger that relies on a fluid seal as described with respect to FIG. 2. However, with the pump 21, the first portion 53 of the plunger has no pressure differential across it. The openings 61, 101 provide that the first portion upper end is at the same pressure as the balancing chamber 65 and thus the first portion lower end. This equal pressure across the plunger first portion 53 and its seals 63 greatly reduces the wear on these seals, prolonging the life thereof.

FIG. 6 shows the sand separation unit and fluid flow when the plunger moves in the downstroke direction. The valve 91 is open and fluid flows through the body. The fluid entering the body may contain sand. The sand is separated by the fluid passing through the bottom plug 107, which imparts centrifugal forces to the fluid. Fluid exiting the body passes through the valve seat member 87, with the fluid and sand near the inside diameter, being spun by the centrifugal forces applied. Thus, sand exits the sand separation unit on the downstroke.

Now that the fluid flow through the sand separation unit 55 has been described, the overall pump will be described. Using as an example a fixed barrel pump, the plunger has a seal provided by the resilient members 63 and another seal 43 provided by the fluid inside of the small clearance. Sand 45 from the tubing enters the top of the clearance between the plunger-assembly first portion 53 and the barrel 33. As the plunger-assembly 51 reciprocates, the seals 63 on the plunger first portion 53 isolate the balancing chamber 65 from the remainder of the pump. This minimizes sand from entering the balancing chamber 65 from the top of the overall plunger 51.

The plunger-assembly third portion 57 forms a fluid seal and carries the pressure differential across it, much like a conventional plunger 35.

FIG. 7 shows another embodiment. The plunger 21A has first, second and third portions 53A, 55, 57A. The seals between the plunger and the barrel are in a different arrangement from the embodiment of FIG. 3. The first portion 53A uses a metal-to-metal clearance seal or a fluid seal 43. This is the same type of seal used by the third portion 57 in the embodiment of FIG. 3. The third portion 57A of FIG. 7 can be a metal-to-metal clearance seal 43. Alternatively, as shown in FIG. 7, the third portion can have seals 63, which seals are the same as discussed above with respect to FIG. 3.

The balancing chamber 65 in FIG. 7 equalizes the pressure across the fluid seal 43. This minimizes pressure driving sand into the upper end of the fluid seal 43. The seals 63 on the plunger third portion 57A wipe the inside of the barrel free of sand on each stroke, extending the useful life of the fluid seal 43.

The embodiment of FIG. 7, where the fluid seal 43 is above or uphole relative to the resilient seals 63 is also useful where the traveling valve 39 is located at or near the upper end of the plunger 51A. In this case, the balancing chamber 65 equalizes pressure across the resilient seals 63.

The present invention splits the function of the plunger into one portion, which provides a seal suitable for sand, and another portion, which provides a seal suitable for fluid. By providing components that are specialized to their function, the life of the overall plunger is prolonged in sandy wells.

FIG. 8 shows another embodiment of the pump. The plunger 51B has first, second and third portions 53B, 55, 57B. The first portion 53B and the third portion 57B have resilient seals 63. Providing resilient seals on both the upper and lower plunger portions 53B, 57B eliminates slippage. Slippage occurs in a fluid seal 43; the fluid slips through the clearance between the barrel and the plunger for lubrication purposes. Slippage also allows the entry of sand into the clearance between the barrel and the plunger. The sand causes wear. Resilient seals have no slippage and consequently allow no sand into the clearance between the plunger and the barrel. There is hardly any wear on either the first or the third plunger portions 53B, 57B.

FIG. 9 shows a plunger-assembly third portion 57C, in accordance with another embodiment. The plunger third portion 57C has two types of seals. One type is resilient seals 63. The resilient seals are located at one end of the third portion 57C and prevent the entry of sand into the clearance between the plunger and the barrel. The other type of seal is a fluid seal 43, which is located along the remainder of the length of the plunger third portion 57C. The outside diameter of the third portion changes to accommodate the types of seals. Thus, the outside diameter of the plunger is smaller at the resilient seals 63 than at the fluid seal 43.

Thus, a combination of resilient seals and fluid seals can be used. Resilient seals prevent the entry of sand into the clearance between the plunger and barrel. Providing a balancing chamber reduces the pressure differential across the resilient seals. Fluid seals are better suited to wear when subjected to pressure differentials but exhibit wear due to sand.

The invention can be utilized on insert-type pumps and tubing-type pumps. The invention can be used on stationary barrel-type pumps, regardless of whether the barrel is top anchored or bottom anchored. The invention can also be used on traveling barrel-type pumps.

The foregoing disclosure and showings made in the drawings are merely illustrative of the principles of this invention and are not to be interpreted in a limiting sense.

Claims

1. A downhole pump comprising:

a barrel having a first valve for controlling fluid flow into the barrel, the barrel including an interior cavity with a first surface;

a plunger housed within the interior cavity of the barrel, the plunger comprising: a wiper-plunger having a first circumference to which one or more resilient seals are coupled, the one or more resilient seals sealing a first boundary between the first circumference of the wiper-plunger and a first portion of the first surface associated with the barrel; a sand separation unit coupled to the wiper-plunger at a first side, the sand separation unit forming a balancing chamber that minimizes a pressure differential across the one or more resilient seals, the sand separation unit using centrifugal force to separate particulate matter from fluid during a first motion of the wiper-plunger relative to the first portion of the first surface associated with the barrel; a plunger-assembly coupled to the sand separation unit at a second side, the plunger-assembly having a second valve controlling fluid flow into the plunger-assembly via a third side from the interior cavity of the barrel; a second boundary between a second circumference of the plunger- assembly and a second portion of the first surface associated with the barrel, the second boundary being fillable by slippage fluid within the barrel to create a fluid seal at the second boundary.

2. The downhole pump of claim 1, wherein the one or more resilient seals are elastomeric and include at least a fiber component.

3. The downhole pump of claim 1, further comprising one or more openings that ensure that a first portion of the wiper-plunger has a first pressure that is substantially equivalent to a second pressure associated with the balancing chamber to minimize wear on the one or more resilient seals.