Patent Application
20200011327
Many hydrocarbon wells are unable to produce at commercially viable levels without assistance in lifting the formation fluids to the earth's surface. In some instances, high fluid viscosity inhibits fluid flow to the surface. More commonly, formation pressure is inadequate to drive fluids upward in the wellbore. In the case of deeper wells, extraordinary hydrostatic head acts downwardly against the formation and inhibits the unassisted flow of production fluid to the surface.
A common approach for urging production fluids to the surface uses a mechanically actuated, positive displacement pump. Reciprocal movement of a string of sucker rods induces reciprocal movement of the pump for lifting production fluid to the surface. For example, a reciprocating rod lift system 20 of the prior art is shown in
The production fluid F may not produce naturally to reach the surface so operators use the reciprocating rod lift system 20 to lift the fluid F. The system 20 has a surface pumping unit 22, a rod string 24, and a downhole rod pump 50. The surface pumping unit 22 reciprocates the rod string 24, and the reciprocating string 24 operates the downhole rod pump 50. The rod pump 50 has internal components attached to the rod string 24 and has external components positioned in a pump-seating nipple 38 near the producing zone and the perforations 15.
As shown briefly in
As the surface pumping unit 22 in
On the following downstroke, the standing valve 70 closes as the standing ball seats upon the lower seat. At the same time, the traveling valve 90 opens so fluids previously residing in the chamber 62 can pass through the valve 90 and into the interior of the plunger 80. Ultimately, the produced fluid F is delivered by positive displacement of the plunger 80, out passages in the barrel 60. The moved fluid then moves up the wellbore 10 through the tubing 30. The upstroke and down stroke cycles are repeated, causing fluids to be lifted upward through the wellbore 10 and ultimately to the earth's surface.
The conventional rod pump 50 holds pressure during a pumping cycle by using sliding mechanical seals and/or a hydrodynamic seal between the plunger's outside diameter and the barrel's inside diameter. Sand in the production fluid F and during frac flowback can damage the surfaces of the plunger 80 and barrel 60. In particular, the plunger 80 may reciprocate inside the barrel 60 utilizing a small annular clearance (approximately 0.002-in. radial) in order to form an effective hydrodynamic seal. This small clearance also allows a small amount of lubricating fluid (typically called “slippage fluid”) to pass in the annulus between the plunger 80 and barrel 60 in order to reduce friction and adhesive wear. The differential pressure across the sealing area causes fluid to migrate past the area.
When this migrating fluid contains sand or other particulates, the surfaces of the plunger 80 and barrel 60 can become abraded so the assembly eventually becomes less capable of holding pressure. Overtime, significant amounts of sand can collect between the plunger 80 and the barrel 60, causing the plunger 80 to become stuck within the barrel 60.
Production operations typically avoid using such a rod pump 50 in wellbores having sandy fluids due to the damage that can result. However, rod pumping in sandy fluids has been a goal of producers and lift equipment suppliers for some time. To prevent sand damage, inlet screens can be disposed downhole from the pump 50 to keep sand from entering the pump 50 altogether. Yet, in some applications, using an inlet screen in such a location may not be feasible, and the inlet screen and the rathole below can become fouled with sand. In other applications, it may actually be desirable to produce the sand to the surface instead of keeping it out of the pump 50.
In one technique to deal with particulate migration and to maintain the clearance with the barrel 60, the downhole pump 50 uses a soft packed plunger 80 having wiper rings that swell up in downhole fluids to tighten the plunger's fit in the barrel 60. Such wiper rings, commonly referred to as Martin-style composition rings, are currently manufactured using a combination of natural or synthetic rubber combined with a duck material. For example, cotton duck and neoprene are often used for the wiper rings. Unfortunately, these materials are limited to use in about 200-F downhole temperatures, and they are susceptible to degradation in the presence of CO2. Overtime, such conventional wiper rings degrade and fail, eliminating their effective purpose.
The subject matter of the present disclosure is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.
According to the present disclosure, a downhole pump is used for a reciprocating pump system having a rod string disposed in a tubing string. The pump comprises a barrel, a plunger, and one or more wipers. The barrel is disposed in the tubing string and has an internal surface. The plunger is coupled to the rod string and is movably disposed in the barrel. The plunger has an external surface disposed at an annular clearance relative to the internal surface. The external surface has one or more circumferential grooves defined thereabout.
The one or more wipers are disposed in the one or more circumferential grooves on the external surface of the plunger. Each of the one or more wipers comprises: an inner ring composed of a swellable material and engaged in the one or more circumferential grooves, and an outer ring composed of a second material and disposed about the inner ring. The swellable material of the inner ring energizes the outer ring across the annular clearance into slideable engagement with the internal surface of the barrel.
The swellable material can be selected from the group consisting of elastomer, ethylene propylene diene M-class rubber (EPDM), ethylene propylene copolymer (EPM) rubber, styrene butadiene rubber, natural rubber, ethylene propylene monomer rubber, ethylene vinylacetate rubber, hydrogenated acrylonitrile butadiene rubber, acrylonitrile butadiene rubber, isoprene rubber, chloroprene rubber, polynorbornene, nitrile, fluoroelastomer, fluoropolymer, and perfluoroelastomer.
The second material can be selected from the group consisting of a composite of a fiber and a binder; a composition of duck material and rubber; a composite of a para-aramid synthetic fiber and nitrile rubber; a composition of polyester and nitrile rubber; a composition of nylon and nitrile rubber; a thermoplastic; a polytetrafluoroethylene (PTFE); or a combination thereof. The second material can be comprised of a homogenous thermoplastic.
The barrel can comprise a standing valve controlling flow of fluid into a barrel chamber defined by the internal surface, and the plunger can comprise a traveling valve controlling flow of fluid into a plunger chamber inside the plunger.
The plunger can define a plunger chamber therein communicating through at least one side port of the plunger with the annular clearance. The plunger can further comprise a filter disposed on the plunger adjacent the at least one side port.
The pump can further comprise one or more unitary composition rings disposed in one or more others of the circumferential grooves on the external surface of the plunger.
The inner ring can comprise a split or full ring installed in the circumferential groove. Alternatively, the inner ring can comprise the swellable material formed in the circumferential groove. For its part, the outer ring can comprise a split of full ring installed in the circumferential groove over the inner ring.
According to the present disclosure, a plunger is used for a downhole pump of a reciprocating pump system having a rod string disposed in a tubing string. The plunger couples to the rod string and is movably disposed in a barrel of the pump. The plunger comprises an external surface disposed at an annular clearance relative to an internal surface of the barrel. The external surface has one or more circumferential grooves defined thereabout.
The plunger comprises one or more wipers disposed in the one or more circumferential grooves on the external surface of the plunger. Each of the one or more wipers comprises an inner ring composed of a swellable material and engaged in the one or more circumferential grooves, and an outer ring composed of a composite material and disposed about the inner ring. The swellable material of the inner ring energizes the outer ring across the annular clearance into slideable engagement with the internal surface of the barrel. The plunger may further comprise any of the other features discussed above.
According to the present disclosure, a method of assembling a downhole pump of a reciprocating pump system comprises: positioning one or more inner rings of a swellable material in one or more circumferential grooves defined in an external surface of a plunger of the downhole pump; positioning one or more outer rings of a second material about the one or more inner rings; and positioning the plunger inside a barrel of the downhole pump.
Positioning the one or more inner rings in the one or more circumferential grooves can comprise filling the one or more circumferential grooves with the swellable material forming the one or more inner rings; or fitting the one or more inner rings as split or full rings inside the one or more circumferential grooves.
Positioning the one or more outer rings about the one or more inner rings can comprise fitting the one or more outer rings as split or full rings about the one or more inner rings; or installing the one or more inner rings and the one or more outer rings as a unit in the one or more circumferential grooves.
The method can further comprise coupling a screen assembly on the plunger below a mandrel of the plunger having the one or more circumferential grooves; and/or coupling the plunger to a pump rod; and coupling the pump rod to a rod string of the reciprocating pump system.
The foregoing summary is not intended to summarize each potential embodiment or every aspect of the present disclosure.
As a surface pumping unit (such as in
On the following downstroke, the standing valve 104 closes as the standing ball 106 seats upon the lower seat 108. At the same time, the traveling valve 134 opens so fluids previously residing in the chamber 115 can pass through the valve 134 and into the interior 132 of the plunger 130. Ultimately, the produced fluid is delivered by positive displacement of the plunger 130, out passages 111 in the barrel 110. The moved fluid then moves up a wellbore through tubing (as shown in the system of
The rod pump 100 holds pressure during a pumping cycle by using a hydrodynamic seal 140 in the annular clearance between the plunger's outside diameter and the barrel's inside diameter. In the presence of sandy fluid, this annular clearance can be compromised due to damage, allowing a greater amount of slippage fluid to pass and decreasing pump efficiency. To effectively maintain this small annular clearance while operating in the presence of sandy production fluid, the downhole pump 100 can utilize a bypass port with a screen 170 on the plunger 130 to filter out sand from the slippage fluid. The screen 170 is used in conjunction with one or more wipers 160 that prevent the sand from entering the annular clearance between the working plunger 130 and the barrel 110. Due to the location of the screen 170, there is no pressure differential across the wipers 160 so they are essentially acting as wiping members and not sealing members.
These one or more wipers 160 are configured to meet the gravity of the fluids being produced and the bottom hole temperature of the well. The one or more wipers 160 also allow the plunger 130 to be used for sandy conditions in which particulates in the wellbore fluids are being produced. Details of the one or more wipers 160 are now discussed with reference to
As shown in
At its downhole end, the barrel 110 has a standing valve (not shown)—not unlike that used on the pump 100 of
The plunger 130 is reciprocally disposed in the barrel 110. As shown in the further detail of
The proximal end 132 of the plunger 130 has fluid passages 134 for fluid in the plunger 130 to exit into the barrel 110 uphole of the hydrodynamic seal 140. In turn and as shown in
As noted above and as best shown in
For example, the plunger 130 can include a wiper mandrel 150 at its upper end that couples by the coupler 132 to the rod 102. In its external surface 152, the wiper mandrel 150 has a series of circumferential grooves 156 that hold the wipers 160, which can prevent particulate from entering the annular sealing region 113 between the working plunger 130 and the barrel 110.
As noted previously with respect to claim 2, the plunger 130 in some implementations can use a screen in conjunction with the wipers 160. Therefore, as shown in
For its part, the screen assembly 170 filters out sand and other particulate from the slippage fluid communicated from inside the plunger 130 into the annular region 113 to form the hydrodynamic seal 140. As shown in
A screen filter 175 disposed in the bore 174 prevents the particulate in the produced fluid inside the plunger 130 from passing into the annular region 113. In this way, the screen filter 175 separating the interior of the plunger 130 from the annulus between the plunger 130 and the barrel 110 can filter fluid in the plunger's interior before it can pass to the annular region 113 as slippage fluid. Due to the location of the screen filter 175, there is essentially no pressure differential across the wipers 160 so that the wiper 160 act as wiping members and not sealing members.
In contrast to a conventional combination of neoprene and cotton duck used for conventional Martin-style composition rings, the present wipers 160 include an inner ring 162 composed of a first material, and include an outer ring 164 composed of a second material. The outer ring 164 withstands abrasion, while the inner ring 162 energizes the outer ring 164 against the barrel's inner bore 112 to create an essentially “zero-clearance” wiping barrier.
Turning to
The inner ring 162 is composed of a swellable material configured to swell in the presence of well fluid. As it swells, the swellable material of the inner ring 162 energizes the outer ring 164 into slideable engagement with the internal surface 112 of the barrel 110. As shown in
The swellable inner ring 162 expands or swells during use (i.e., increases in thickness T1) and pushes the outer ring 164 outward from the mandrel 150 into the annular region 113 between the mandrel 150 and the barrel's bore 112. During use, the second thickness T2 of the outer ring 164 may decrease due to abrasive effects or the like, yet the swellable inner ring 162 can continue to push the outer ring 164 across the clearance C and to keep the outer ring 164 in “zero-clearance” wiping engagement with the barrel's bore 112.
The inner and outer rings 162, 164 of the wipers 160 can be configured for various implementations, downhole conditions, and the like. Depending on the implementation, one or more wipers 160 may be used on the mandrel 150. In some implementations, several dozens of the wipers 160 may be installed on the mandrel 150, such as depicted here in
At the time of installation, both rings 162, 164 of the wiper 160 can have the same or different thicknesses T1 and T2, which may be selected for the particular slot depth D of the groove 156 and the clearance C of the region 113. Similarly, both rings 162, 164 of the wiper 160 can have the same or different width, which may be selected for the particular width W of the groove 156. The grooves 156 can have a configured spacings from one another, and they may have form circumferential slots with rectilinear sidewalls, although other shapes could be used.
The wipers 160 are configured to perform particular functions. For example, the wipers 160 can be configured to withstand temperatures above 225-F, and preferably temperatures up to approximately 350-F. The wipers 160 can also be configured to withstand the presence of CO2 in the wellbore fluid. Finally, the wipers 160 can preferably be abrasion resistant and able to swell approximately 15-20% allowing for an essentially “zero-clearance” wiping barrier.
The two rings 162, 164 are radially nested to perform the desired functions. The outer ring 164 (in sliding contact with the barrel's bore 112) has properties needed for wear resistance, temperature resistance, and chemical resistance. The inner ring 164 has swell properties (along with chemical and temperature resistance) needed for the application at hand. The inner ring 164 effectively energizes the outer ring 162, maintaining pressure against the barrel's bore 112. The outer ring 164 can be sacrificial in nature, as the inner ring 162 with its swelling properties can continue to energize the outer ring 164 into wiper engagement with the barrel's inner surface.
The inner ring 162 is composed of a suitable type of swellable material that may be expandable by about 25% or greater from its original volume. The swellable inner ring 162 can swell in the presence of an activation agent, such as water, oil, production fluid, etc. Any of the swellable materials known and used in downhole applications can be used for the inner ring 162. For example, the swellable material can be elastomer, ethylene propylene diene M-class rubber (EPDM), ethylene propylene copolymer (EPM) rubber, styrene butadiene rubber, natural rubber, ethylene propylene monomer rubber, ethylene vinylacetate rubber, hydrogenated acrylonitrile butadiene rubber, acrylonitrile butadiene rubber, isoprene rubber, chloroprene rubber, polynorbornene, nitrile, fluoroelastomer, fluoropolymer, and perfluoroelastomer. The swellable material of the inner ring 162 may or may not be encased in another expandable material that is porous or has holes. It is even contemplated that the inner ring 162 can be a composition of duck material and swellable material.
The second material of the outer ring 164 can include: a composition of a fiber and a binder; a composition of a duck material and a rubber; a composition of a para-aramid synthetic fiber and nitrile rubber; a composition of polyester and nitrile rubber; a composition of nylon and nitrile rubber; a thermoplastic; a homogenous thermoplastic; a polytetrafluoroethylene (PTFE); or any other material or combination thereof suitable as an effective wiping member.
As shown in
The outer ring 164 can be a split ring that is opened to fit in the circumferential groove (156) over the inner ring 162, or it too can be a solid ring—flexible enough to allow for its insertion in the groove (156). The splits in the two rings 162, 164 can be aligned or offset from one another.
Instead of separate installation of the inner ring 162 followed by the outer ring 164 into the groove (156), the two rings 162, 164 can be formed and assembled together for installation as a single unit into the groove (156). The two rings 162, 164 may also be bonded together as a single unitary piece to allow for easier assembly. These and other assembly and installation steps can be used. In fact, the rings 162, 164 can be mounted on a thinner cylindrical mandrel 150 and a plurality of spacer rings can be disposed between the wipers 160 to form the separated grooves 156 of the assembly.
The foregoing description of preferred and other embodiments is not intended to limit or restrict the scope or applicability of the inventive concepts conceived of by the Applicants. It will be appreciated with the benefit of the present disclosure that features described above in accordance with any embodiment or aspect of the disclosed subject matter can be utilized, either alone or in combination, with any other described feature, in any other embodiment or aspect of the disclosed subject matter.
In exchange for disclosing the inventive concepts contained herein, the Applicants desire all patent rights afforded by the appended claims. Therefore, it is intended that the appended claims include all modifications and alterations to the full extent that they come within the scope of the following claims or the equivalents thereof.
