Plunger lift assembly with an improved free piston assembly

Abstract

An improved free piston assembly for use in combination with a plunger lift assembly is provided. The piston assembly includes a sleeve member, a retention sleeve, and a flow restriction member. The sleeve member has an inner surface defining an opening for the flow of formation fluids. The opening includes a first section and a second section. The retention sleeve is configured to be affixed to the first section of the opening. The flow restriction member is not latched to the sleeve member and is configured to have an interference fit with the retention sleeve. The interference fit provides a force that is sufficient to overcome the force of gravity on the flow restriction member when formation fluid forces acting on the flow restriction member are decreased or removed. The second section of the opening is configured to prevent the passage of the flow restriction member.

Claims

1. A piston assembly comprising: (a) a sleeve member having an inner surface, the inner surface providing a seat to accommodate a flow restriction member; (b) the flow restriction member without being latched to the sleeve member configured to move between a seated position and an unseated position, wherein in the seated position the flow restriction member is in physical contact with the seat and prevents the flow of fluids through the sleeve member, and wherein in the unseated position the flow restriction member permits the flow of fluids through the sleeve member; and wherein the sleeve member includes a raised lip for retaining the flow restriction member in the sleeve member, wherein the raised lip provides sufficient retention force to overcome the force of gravity on the flow restriction member when fluid forces acting on the flow restriction member are decreased or removed and the raised lip is a semi-circumferential notched lip and physically spaced apart from the flow restriction member when the flow restriction member is in the seated position.

2. The piston assembly of claim 1, wherein the sleeve member further includes a first section and a second section, wherein the raised lip is located in the first section and the second section includes an opening that is configured to prevent the passage of the flow restriction member through the opening.

3. The piston assembly of claim 2, wherein the flow restriction member is configured to move between the seated position and the unseated position in the first section.

4. The piston assembly of claim 2, wherein the raised lip retains the flow restriction member in the first section.

5. The piston assembly of claim 2, wherein the opening is configured to receive a separator rod.

6. The piston assembly of claim 2, wherein the flow restriction member is configured to seal the opening in the seated position.

7. The piston assembly of claim 1, wherein the raised lip is located on the inner surface of the sleeve member.

8. The piston assembly of claim 1, wherein the sleeve member further includes an outer contoured surface configured to create a turbulent fluid flow when the piston assembly is transported in a production tubing.

9. The piston assembly of claim 1, wherein the sleeve member is cylindrical.

10. The piston assembly of claim 1, wherein the raised lip is a discontinuous raised lip.

11. The piston assembly of claim 1, wherein the flow restriction member is a ball.

12. The piston assembly of claim 1, wherein the sleeve member is made from a material selected from the group consisting of stainless steel, chrome steel, cobalt, zirconium ceramic, tungsten carbide, silicon nitride and titanium alloys.

13. The piston assembly of claim 1, wherein the flow restriction member is made from a material selected from the group consisting of stainless steel, chrome steel, cobalt, zirconium ceramic, tungsten carbide, silicon nitride and titanium alloys.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic view of a well equipped with a plunger lift system that includes one embodiment of the improved free piston assembly of this invention, certain parts being broken away for clarity of illustration;

(2) FIG. 2 is a schematic view of the sleeve member of this invention with the retention assembly in place but without the flow restriction member.

(3) FIG. 3 is cross sectional view of the sleeve member, flow restriction member and spring loaded retention means embodiment of this invention.

(4) FIG. 4 is an exploded cross sectional view of the sleeve member, flow restriction member and spring loaded retention assembly with the flow restriction member being held in place by the spring loaded retention assembly.

(5) FIG. 5 is an exploded cross sectional view of the retention assembly of FIG. 4.

(6) FIG. 6 is a cross sectional view of the sleeve member, flow restriction member, and spring loaded retention means of this invention showing the flow restriction member seated in the sleeve member and being axially removed from the retention means.

(7) FIG. 7 is the same cross sectional view as shown by FIG. 6 but with the flow restriction member being unseated and being retained in the sleeve member by spring loaded retention means.

(8) FIG. 8 is a cross sectional view of one embodiment of the free piston assembly of this invention including the sleeve member and the retention member in the form of a raised lip;

(9) FIG. 8A is a cross sectional view of a portion of the embodiment of the free piston assembly of FIG. 8 showing the sleeve member with the flow restriction device seated and the retention means spaced apart from any physical contact with the flow restriction device.

(10) FIG. 8B is a cross sectional view of one embodiment of the raised lip retention means of this invention.

(11) FIG. 8C is a schematic view of the sleeve member of this invention with the raised lip retention means embodiment of FIG. 8B.

(12) FIG. 9 is an exploded schematic view of an alternative embodiment of the retention means of this invention showing a retention sleeve as the retention means.

(13) FIG. 9A is a schematic view of the sleeve member of this invention with the retention sleeve embodiment of FIG. 9.

(14) FIG. 10 is a cross sectional view of the retention sleeve embodiment of FIG. 9 showing the flow restriction member being retained by a retention sleeve.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(15) The multipart plunger embodiments shown in commonly assigned U.S. Pat. No. 6,467,541 has proven to be quite satisfactory for a wide range of applications where gas wells produce sufficient liquid that slows down gas production and ultimately kills the well. Experience and analysis resulted in two improvements being made in the operation of a multipart plunger. These improvements are disclosed in commonly assigned U.S. Pat. No. 6,719,060 and are described with more particularity below and in the specification of the U.S. Pat. No. 6,719,060 patent.

(16) In one embodiment of the plunger lift assembly used in combination with the improved free piston assembly of this invention, the technique used to separate and hold the plunger at the surface employs moving parts to receive and cushion the impact of the plunger as it arrives at the surface but employ no moving parts to hold the plunger in the well head. A separator rod is provided which the plunger sleeve slides over, thereby dislodging the flow restriction member and causing it to fall into the well. Flow from the well passes around and/or through the separator rod and the opening to the sleeve member, also referred to as the plunger sleeve. The separator rod and plunger sleeve include cooperating sections that produce a pressure drop sufficient to hold the plunger sleeve in the well head against the force of gravity. When flow through the well head is insufficient to hold the plunger sleeve against the force of gravity, the plunger sleeve falls into the well, couples with the flow restriction member at or near the bottom of the well and then moves upwardly to produce a quantity of formation liquid thereby unloading the well. Typically, the plunger sleeve is dropped into the well in response to closing of a valve at the surface that interrupts flow thereby momentarily reducing gas flow at the surface and substantially eliminating any pressure drop across the plunger sleeve. Various aspects of the separator rod and housing for the separator rod are shown and described in U.S. Pat. No. 6,719,060, which has been previously incorporated by reference.

(17) An important advantage of the separator rod used in combination with the improved free piston assembly of this invention is the plunger sleeve is dropped by momentarily shutting a valve controlling flow from the well. This allows operation of the plunger lift without using natural gas as a power source for a holding device thereby eliminating the venting of methane to the atmosphere. It also eliminates a holding device which includes moving parts subject to malfunction or failure.

(18) Major gas producing companies that operate large numbers of gas wells have gained considerable experience in keeping older gas wells flowing. Many such companies use large numbers of plunger lifts and have devised sophisticated computer programs to determine when to drop conventional one-piece plungers into a well. It will be recollected that one-piece plungers are typically held at the surface until production falls off, whereupon the well is shut in, the plunger is released and the well remains shut in for a long enough time for the plunger to fall to the bottom of the well. The flow control valve is then opened and the well produces enough formation content to drive the plunger to the surface, producing liquid along with gas and thereby unloading the well. The computer programs used to operate conventional one-piece plunger lift systems act in response to a wide variety of input information, e.g. flowing well head pressure or flow line pressure which are either the same or very close to the same, gas volume, pressure on the casing as opposed to pressure of gas flowing in the tubing and previous plunger speed as an indication of the liquid being lifted.

(19) Although they can be made to work satisfactorily with multipart plungers, these conventional programs measure the wrong things to drop a multipart plunger sleeve into a well on an optimum basis. An ideal cycle for a multipart plunger is to lift a small quantity of liquid on each plunger trip. It is not desirable to lift no liquid because the plunger takes a beating when it enters the well head with no liquid in front of itthe piston velocity is too high and the spring assemblies in the well head take too much punishment. More importantly, if no liquid is being lifted, it is quite likely there is no liquid in the bottom of the well. When this happens, there is likely considerable damage done to the bumper assembly at the bottom of the well as may be imagined by considering the damage potential of a metal article weighing a few pounds falling at terminal velocity. When there is no liquid being lifted, the plunger should be dropped less frequently.

(20) Conversely, if the plunger is lifting too large a quantity of liquid on each cycle, the productivity of the well is being unduly restricted. If the quantity of liquid becomes too large, there is a risk that plunger will not cycle and the well will be dead. When the quantity of liquid becomes larger than a small selected value, the plunger should be dropped more frequently. Thus, there is an ideal amount of liquid to be raised on each cycle and it is surprisingly small, something on the order of to barrel, depending on the flowing bottom hole pressure of the well and the flow line pressure the well is producing against. In normal situations, a preferred amount being lifted on each cycle of the plunger is on the order of about barrel. Thus, by measuring what is important to the operation of a multipart piston of a plunger lift, improved operations result.

(21) Referring to FIGS. 1-10, a hydrocarbon well 10 comprises a production string 12 extending into the earth in communication with a subterranean hydrocarbon bearing formation 14. The production string 12 is typically a conventional tubing string made up of joints of tubing that are threaded together. Although the production string 12 may be inside a casing string (not shown), it is illustrated as cemented in the earth. The formation 14 communicates with the inside of the production string 12 through perforations 16. As will be more fully apparent hereinafter, a plunger lift assembly 18 is used to lift oil, condensate or water from the bottom of the well 10 which may be classified as either an oil well or a gas well.

(22) In a typical application of this invention, the well 10 is a gas well that produces some formation liquid. In an earlier stage of the productive life of the well 10, there is sufficient gas being produced to deliver the formation liquids to the surface. The well 10 is equipped with a conventional well head assembly 20 comprising a pair of master valves 22 and a wing valve 24 delivering produced formation products to a surface facility for separating, measuring and treating the produced products.

(23) The plunger lift 18 of this invention comprises, as major components, a free piston 26, a lower bumper assembly 28 near the producing formation 14, a catcher assembly 30 and an assembly 32 for controlling the cycle time of the piston 26. The free piston 26 is of multipart design and includes a sleeve 34 (sometimes referred to as the sleeve member) and a flow restriction member 36 which is preferably a sphere as shown in U.S. Pat. No. 6,467,541, the disclosure of which has been previously incorporated herein by reference. The free piston 26 also includes retention means 50 for retaining the flow restriction member 36 in the interior of the sleeve 34 by supplying a force sufficient to overcome the force of gravity on said flow retention member 36. For purposes of this invention, the preferred flow restriction member 36 is a sphere and therefore in some instances the terms are used interchangeably. It should, however, be understood that other embodiments of flow restriction members may be equally viable in the improved free piston assembly of this invention.

(24) The sleeve 34 is generally cylindrical having an opening that forms an interior flow passage 38 and a seal arrangement 40 to minimize liquid on the outside of the sleeve 34 from bypassing around the exterior of the sleeve 34. The seal arrangement 40 may be of any suitable type, such as wire brush wound around the sleeve 34 providing a multiplicity of bristles or the like or may comprise a series of simple grooves or indentations 42. The grooves 42 are functionally effective because they create a turbulent zone between the sleeve 34 and the inside of the production string 12 thereby restricting liquid flow on the outside of the sleeve 34. In certain embodiments of this invention, sleeve 34 also includes an interior surface 34A against which the flow restriction member 36 can seat when it is being retained in the interior opening to sleeve 34. During the lifting operation associated with the function of the free piston of this invention the flow restriction member 36 is maintained in its seated position because of formation pressure. If pressure to the flow restriction member is interrupted the force of gravity will unseat the flow restriction member and potentially cause it to exit from the sleeve 34. To prevent the flow restriction member from prematurely exiting the sleeve 34 the retention means 50 of this invention are used.

(25) As will be more fully apparent hereinafter, the flow restriction member 36, especially when configured as a sphere, is first dropped into the well 10, followed by the sleeve 34. The sphere 36 and sleeve 34 accordingly fall separately and independently into the well 10, usually while the well 10 is producing gas and liquid up the production string 12 and through the well head assembly 20. When the sphere 36 and sleeve 34 reach the bottom of the well, they impact the lower bumper assembly 28 in preparation for jointly moving upwardly. The lower bumper assembly 28 may be of any suitable design, one of which is illustrated in U.S. Pat. No. 6,209,637 and basically acts to cushion the impact of the sphere 36 and sleeve 34 when they arrive at the bottom of the well 10.

(26) An important feature of the plunger lift assembly is the catcher assembly 30 which has several functions, i.e. separating the sphere 36 from the sleeve 34, retaining the sleeve 34 in the assembly 30 for a period of time and then dropping the sleeve 34 into the well 10. The catcher assembly 30 is more fully described in U.S. Pat. No. 6,719,060 which has been previously incorporated by reference. The catcher assembly 30 comprises an outer housing or catch tube 44 which provides an outlet for formation products and a shoulder for stopping the upward movement of the sleeve 34.

(27) Inside the housing 44 is a separation rod assembly for cushioning the impact of the sleeve 34, and to some extent of the ball 36, when the free piston 26 reaches its upper limit of its travel. The sleeve 34 ultimately passes onto the lower end of the separator rod 70 thereby overcoming the retaining force of the retention means 50 and dislodging the ball 36 and allowing it to fall immediately back into the production string 12.

(28) An important feature of this invention is that the free piston assembly 26 includes retention means 50 to hold the flow restriction member 36 in the sleeve 34 to overcome the force of gravity placed on such flow restriction member. As has been previously described, retention means 50 can take a number of design forms, however, the preferred design is a plurality of spring loaded retractable members 80 used to retain the flow restriction device in the sleeve 34. The retractable members 80 are sometimes in the form and size of ball bearings. In this embodiment of the invention the spring loaded retractable members 80 are not in physical contact with the flow restriction device 36 when member 36 is seated on surface 34A. Such a configuration permits axial movement of the flow restriction member 36 between the seat 34A and the retention member 50. The axial movement of this embodiment is illustrated in FIGS. 6 and 7.

(29) In the spring loaded embodiment of the retention means a plurality of ball shaped retractable pressure members 80 are configured to protrude inwardly from apertures 82 communicating with the inner surface of the sleeve member 34. The inward bias or pressure is supplied by spring means 84 contacting the outer surface of each of the ball shaped retractable pressure members 80. The spring means 84 are held in place by a retaining ring 86 that is sized to fit into a groove 88 in the exterior surface of the sleeve 34. The retaining ring 86 may be made from any of a variety of well known materials for use in downhole applications, but specifically include elastomeric materials, soft metals, ceramics, plastics, rubber and other forms of polymeric material.

(30) As can be more clearly seen in FIGS. 2-7, in this preferred embodiment of the invention a groove 88 is cut into the exterior surface of sleeve 34. A series of apertures 82 are cut into the lower surface of the groove such that the apertures 82 communicate directly with the interior surface of the sleeve 34. The apertures 82 are formed such that the diameter of the portion of each aperture closest to the interior of the sleeve is smaller that the diameter of the retractable ball member (see FIGS. 4 and 5), thus provide a seat 90 for the retractable pressure members 80 and prevent the pressure members 80 from falling into the interior of the sleeve member 34. The pressure members 80 are biased toward the interior of the sleeve member 34 by spring means 84, which can be spiral springs or leaf springs. The retractable ball members 80 are movable between a fully biased position in which at least a portion of the ball member 80 protrudes into the interior of the sleeve member to a retracted position in which the interior most surface of the ball member 80 is even with the interior surface of the sleeve member and does not provide a retaining force on the flow restriction member and does not prevent the flow restriction member from escaping from the sleeve member. The spring means 84 are in contact with the exterior surface of the retractable pressure members 80 such that the pressure members 80 protrude into the interior of the sleeve member in order to prevent the flow restriction member 36 from escaping the sleeve member 34 based on the force of gravity. The spring means 84 and pressure members 80 are mounted in the apertures 82 in the groove 88, and in turn are held in place by a retention member 86, typically in the form of a retention ring.

(31) In practice, the groove 88 for the retention means 50 is located on the sleeve 34 at a position such a shown in FIGS. 2-7. As can be seen, a substantial portion of the entire flow restriction member 36 is held inside the sleeve member 34 although the only requirement is that the flow restriction member 36, regardless of its shape, be maintained in the sleeve member until physically released by the separation rod or other form of mechanical releasing mechanism.

(32) In another preferred embodiment of the invention the retention means 50 are in the form of a raised lip 100 that provides sufficient retention force to overcome the force of gravity and keep the flow retention member in the sleeve unless the gravitational force is supplemented by a mechanical force in the form of separation rod 70. In this embodiment of the retention means of this invention, as shown more particularly in FIGS. 8, 8A, 8B and 8C, the raised lip 100 does not physically contact the flow restriction member 36 but in fact permits some axial movement of flow restriction member 36 prior to stopping its downward movement. Raised lip 100 may take a number of forms, including, but not limited to a semi-circumferential notched lip (see FIGS. 8, 8B, and 8C) or a different configuration such as shown in FIG. 8A. The raised lip 100 may be circumferential or partially circumferential and may be of any shape of configuration that is functionally effective to retain flow restriction member 36 by overcoming the force of gravity on member 36 when it is unseated.

(33) In yet another embodiment of this invention, as illustrated by FIGS. 9-10, a retention sleeve 200 is mounted in an interior section of sleeve 34. The actually mounting of the retention sleeve 200 in sleeve 34 can be done by conventional means that are within the knowledge and understanding of a person of ordinary skill in the art. By way of example, the retention sleeve 200 can be fixed to the interior surface 201 of sleeve 34 by an adhesive or, as illustrated by FIG. 10, by a series of protrusions 202 from sleeve 34 that protrude into the exterior surface 203 of sleeve 200 to prevent movement of sleeve 200 once it has been installed.

(34) As shown in FIG. 10, the retention sleeve 200 fits into and is mounted in a section 204 of sleeve 34, but no clear seat for flow restriction member 36 is provided. However, as can be readily appreciated, if the formation pressure moves the flow restriction member 36 in an upward axial direction, the flow restriction member 36 will seat in the opening to the second portion 205 of sleeve 34. A particular advantage of the retention sleeve 200 embodiment of retention means 50 is the ability of the flow restriction device 36 to seal the opening of sleeve 34 as soon as the flow restriction device 36 is fully inserted into the retention sleeve 200, regardless of where in sleeve 200 the flow restriction device 36 is placed. In practice, the flow restriction device 36 is held in sleeve 200 by frictional forces between the exterior surface 206 of the flow restriction device and the interior surface 207 of the retention sleeve.

(35) The retention sleeve can be manufactured from any of a well know variety of materials including elastomers, plastics, rubber, soft metals, other such materials, and combinations thereof, all of which are well known in the oil and gas exploration industry. Particular materials that will be functionally effective as components of sleeve 200 will depend on a number of factors such as the types of fluids that are encountered in the well, the temperatures encountered in the well and other well-related variables.

(36) Importantly, one of the primary differences between the prior art mechanical latching mechanisms and the retention means embodiments of this invention is the axial movement of the flow restriction member that is permitted by the retention means of this invention, whether in the form of spring loaded ball members, a raised lip, or a retention sleeve.

(37) In the preferred embodiments of this invention the retention ring is made from a number of materials that are well known to persons of ordinary skill in the art and include chrome steel, titanium, stainless steel, ceramic, tungsten carbide, silicone nitrate, plastic, and rubber or any other functionally effective elastomeric. On the other hand, the sleeve member and flow retention member are made from materials selected from the group consisting of stainless steel, chrome steel, cobalt, ceramic (zirconium), tungsten carbide, silicon nitride, and titanium alloys. In the most preferred embodiments of this invention the sleeve member and flow retention member are made from one or more of the materials list hereinabove and having a density of less than about 0.25 pounds per cubic inch and a tensile strength of at least 90,000 psi.

(38) Referring to FIG. 1, the piston sleeve 34 is dropped into the production string 12 simply by momentarily closing the wing valve 24. This may be automated by providing a motor operator 114 and controlling the operator 114 by an electrical signal delivered through a wire 116. Although any suitable controller may be used to cycle the plunger lift of this invention, a preferred technique is to measure or sense liquid delivered through a flow line 118 leading from the wellhead 20 and momentarily close the valve 24 in response to a parameter related to the amount of liquid flowing in the flow line 118.

(39) Operation of the plunger lift of this invention should now be understood. During upward movement of the piston 26 toward the well head 20, production through the wing valve 24 is mainly dry gas. As the piston 26 approaches the well head, there is often a small slug or batch of liquid that passes through the wing valve 24 which may cause the meter 120 or a detector (not shown) to detect the arrival of a liquid slug at the surface. If the amount of liquid is very small, it can be readily identified and disregarded by the controller 124. As the piston 26 nears the well head 20, it pushes a quantity of liquid above it through the well head and the wing valve 24 to be measured or sensed by the meter 120 or a detector. If the plunger lift and improved free piston assembly are working satisfactorily, the volume immediately above the piston 26 is a more-or-less solid stream of liquid, the volume or time of discharge of which is measured by the meter 120 or a detector.

(40) When the piston 26 reaches the separation rod 70, the ball 36 is dislodged from the piston 26 and falls immediately back into the production string 12. The sleeve 34 slips over the separation rod 70 and strokes the anvil. Any liquid remaining in the well head is driven through the flow line 118 by formation gas. Gas flowing upwardly in the flow paths around the separation rod 70, sleeve 34 and housing 44 creates a pressure drop across the sleeve 34 causing it to stay on the rod 70 against the effect of gravity. When the controller 124 determines that it is time to drop the sleeve 34 and initiate another plunger cycle, a signal is delivered on the wire 116 to energize the motor operator 114 and momentarily close the wing valve 24. This causes the pressure drop across the sleeve 34 to decrease, so that upward force acting on the sleeve 34 drops and the sleeve 34 falls into the production string.

(41) It can also be seen that cycling the sleeve 34 in response to the amount of liquid delivered during the surface allows a relatively small volume of liquid to be produced during each cycle of the piston 26. This prevents damage to the rod assembly 70 and to the downhole bumper assembly 28 caused by the production of no liquid and allows maximum trouble free gas production by keeping the well unloaded to as great an extent as reasonable.

(42) Although this invention has been disclosed and described in its preferred forms with a certain degree of particularity, it is understood that the present disclosure of the preferred forms is only by way of example and that numerous changes in the details of construction and operation and in the combination and arrangement of parts may be resorted to without departing from the spirit and scope of the invention as hereinafter claimed.