Abstract:
An improved plunger mechanism apparatus to increase well flow production levels in sand based wells. Efficiency of well flow is increased by the addition of radial peripheral holes extending from a hallowed out center core to outer peripheral grooves enabling a self-cleaning action which will prevent sand from accumulating on the outer surface of the plunger, allow the plunger to force fall back to the well bottom, and carry sand out of the well bottom. The self-cleaning sand plunger keeps the well clean, removes unwanted sand, self cleans and significantly reduces maintenance time in a sand based gas well.

Description:
CROSS REFERENCE APPLICATIONS  
       [0001]     This application is a non-provisional application claiming the benefits of provisional application No. 60/562,634 filed Apr. 15, 2004. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates to an improved plunger lift apparatus for the lifting of formation liquids in a hydrocarbon well. More specifically the improved plunger consists of a self-cleaning plunger apparatus that operates to increase the well efficiency in a sand-bottomed well.  
       BACKGROUND OF THE INVENTION  
       [0003]     A plunger lift is an apparatus that is used to increase the productivity of oil and gas wells. In the early stages of a well&#39;s life, liquid loading is usually not a problem. When rates are high, the well liquids are carried out of the well tubing by the high velocity gas. As the well declines, a critical velocity is reached below which the heavier liquids do not make it to the surface and start to fall back to the bottom exerting back pressure on the formation, thus loading up the well. A basic plunger system is a method of unloading gas in high ratio oil wells without interrupting production. In operation, the plunger travels to the bottom of the well where the loading fluid is picked up by the plunger and is brought to the surface removing all liquids in the tubing. The plunger also keeps the tubing free of paraffin, salt or scale build-up. A plunger lift system works by cycling a well open and closed. During the open time a plunger interfaces between a liquid slug and gas. The gas below the plunger will push the plunger and liquid to the surface. This removal of the liquid from the tubing bore allows an additional volume of gas to flow from a producing well. A plunger lift requires sufficient gas presence within the well to be functional in driving the system. Oil wells making no gas are thus not plunger lift candidates.  
         [0004]     As the flow rate and pressures decline in a well, lifting efficiency declines geometrically. Before long the well begins to “load up”. This is a condition whereby the gas being produced by the formation can no longer carry the liquid being produced to the surface. There are two reasons this occurs. First, as liquid comes in contact with the wall of the production string of tubing, friction occurs. The velocity of the liquid is slowed, and some of the liquid adheres to the tubing wall, creating a film of liquid on the tubing wall. This liquid does not reach the surface. Secondly, as the flow velocity continues to slow, the gas phase can no longer support liquid in either slug form or droplet form. This liquid along with the liquid film on the sides of the tubing begin to fall back to the bottom of the well. In a very aggravated situation there will be liquid in the bottom of the well with only a small amount of gas being produced at the surface. The produced gas must bubble through the liquid at the bottom of the well and then flow to the surface. Because of the low velocity very little liquid, if any, is carried to the surface by the gas. Thus, as explained previously, a plunger lift will act to remove the accumulated liquid.  
         [0005]     A typical installation plunger lift system  100  can be seen in  FIG. 1 . Lubricator assembly  10  is one of the most important components of plunger system  100 . Lubricator assembly  10  includes cap  1 , integral top bumper spring  2 , striking pad  3 , and extracting rod  4 . Extracting rod  4  may or may not be employed depending on the plunger type. Contained within lubricator  10  is plunger auto catching device  5  and plunger sensing device  6 . Sensing device  6  sends a signal to surface controller  15  upon plunger  200  arrival at the well top. Plunger  200  can represent the plunger of the present invention or other prior art plungers. Sensing the plunger is used as a programming input to achieve the desired well production, flow times and wellhead operating pressures. Master valve  7  should be sized correctly for the tubing  9  and plunger  200 . An incorrectly sized master valve  7  will not allow plunger  200  to pass through. Master valve  7  should incorporate a full bore opening equal to the tubing  9  size. An oversized valve will allow gas to bypass the plunger causing it to stall in the valve. If the plunger is to be used in a well with relatively high formation pressures, care must be taken to balance tubing  9  size with the casing  8  size. The bottom of a well is typically equipped with a seating nipple/tubing stop  12 . Spring standing valve/bottom hole bumper assembly  11  is located near the tubing bottom. The bumper spring is located above the standing valve and can be manufactured as an integral part of the standing valve or as a separate component of the plunger system. If present, fluid  17  would accumulate on top of plunger  200  to be carried to the well top by plunger  200 .  
         [0006]     Surface control equipment usually consists of motor valve(s)  14 , sensors  6 , pressure recorders  16 , etc., and an electronic controller  15  which opens and closes the well at the surface. Well flow ‘F’ proceeds downstream when surface controller  15  opens well head flow valves. Controllers operate on time, or pressure, to open or close the surface valves based on operator-determined requirements for production. Modern electronic controllers incorporate features that are user friendly, easy to program, addressing the shortcomings of mechanical controllers and early electronic controllers. Additional features include: battery life extension through solar panel recharging, computer memory program retention in the event of battery failure and built-in lightning protection. For complex operating conditions, controllers can be purchased that have multiple valve capability to fully automate the production process.  
         [0007]     Modern plungers are designed with various sidewall geometries and can be generally described as follows: 
        A. Shifting ring plungers for continuous contact against the tubing to produce an effective seal with wiping action to ensure that all scale, salt or paraffin is removed from the tubing wall. Some designs have by-pass valves to permit fluid to flow through during the return trip to the bumper spring with the by-pass shutting when the plunger reaches the bottom. The by-pass feature optimizes plunger travel time in high liquid wells.     B. Pad plungers have spring-loaded interlocking pads in one or more sections. The pads expand and contract to compensate for any irregularities in the tubing, thus creating a tight friction seal. Pad plungers can also have a by-pass valve as described above.     C. Brush plungers incorporate a spiral-wound, flexible nylon brush section to create a seal and allow the plunger to travel despite the presence of sand, coal fines, tubing irregularities, etc. By-pass valves may also be incorporated.     D. Solid plungers have solid sidewall rings for durability. Solid sidewall rings can be made of various materials such as steel, poly materials, Teflon®, stainless steel, etc. Once again, by-pass valves can be incorporated.     E. Snake plungers are flexible for coiled tubing and directional holes, and can be used as well in straight standard tubing.        
 
         [0013]      FIG. 2  is a side view of the various sidewall geometries existing in the prior art. All geometries described have an internal orifice, and all can be found in present industrial offerings. These sidewall geometries are described as follows: 
        A. As previously discussed solid ring  22  sidewall geometry is shown in solid plunger  20 . Solid sidewall rings  22  can be made of various materials such as steel, poly materials, Teflon®, stainless steel, etc. Inner cut groves  30  allow sidewall debris to accumulate when a plunger is rising or falling.     B. Shifting ring plunger  80  is shown with shifting ring  81  sidewall geometry. Shifting rings  81  sidewall geometry allow for continuous contact against the tubing to produce an effective seal with wiping action to ensure that all scale, salt or paraffin is removed from the tubing wall. Shifting rings  81  are all individually separated at each upper surface and lower surface by air gap  82 .     C. Pad plunger  60  has spring-loaded interlocking pads  61  in one or more sections. Interlocking pads  61  expand and contract to compensate for any irregularities in the tubing, thus creating a tight friction seal.     D. Brush plunger  70  incorporates a spiral-wound, flexible nylon brush  71  surface to create a seal and allow the plunger to travel despite the presence of sand, coal fines, tubing irregularities, etc.          
         [0018]     Recent practices toward slim-hole wells that utilize coiled tubing also lend themselves to plunger systems. Because of the small tubing diameters, a relatively small amount of liquid may cause a well to load-up, or a relatively small amount of paraffin may plug the tubing.  
         [0019]     Plungers use the volume of gas stored in the casing and the formation during the shut-in time to push the liquid load and plunger to the surface. This plunger lift occurs when the motor valve opens the well to the sales line or to the atmosphere. To operate a plunger installation, only the pressure and gas volume in the tubing/casing annulus is usually considered as the source of energy for bringing the liquid load and plunger to the surface. The major forces acting on the cross-sectional area of the bottom of the plunger are: 
        The pressure of the gas in the casing pushes up on the liquid load and the plunger.     The sales line operating pressure and atmospheric pressure push down on the plunger.     The weight of the liquid and the plunger weight itself pushes down on the plunger.     Once the plunger begins moving to the surface, friction between the tubing and the liquid load acts to oppose the plunger.     In addition, friction between the gas and tubing acts to slow the expansion of the gas.        
 
         [0025]     In certain wells, the well bottom consists of a sand content.  FIG. 1A  (prior art) is a blow up schematic of a well bottom section  600  (ref.  FIG. 1 ) showing accumulated water  17  and sand  13  trapped within inner cut grooves  30 . Sand  13  tends to cake up within the inner cut grooves  30  and on the sidewall rings  22  of the plunger. Shifting ring, pad or brush plungers also tend to cake with sand, which will damper the plunger operation. Solid pad plungers tend to get sand between each sidewall ring  22 . When plungers are caked with sand, they tend to get caught within the aforementioned lubricator and will require manual intervention (maintenance). Thus, the major disadvantage of prior art plunger lifts in a sandy well is that the plunger will cake with sand and fail to fall, or fall too slowly, to the bottom of the well, thus decreasing well efficiency and/or requiring continued maintenance. Plunger drop travel time slows or limits well production. Also, fishing a plunger out of a well is a problem and sometimes requires pulling the complete tubing string. Well production increases are always critical.  
         [0026]     What is needed is a plunger lift apparatus that can function in a sand-bottom well, one that can self-clean to insure continuous efficiency during lift, drop back to the well bottom quickly and easily, and assist in increasing well production by increasing lift cycle times. What is also needed is a self-cleaning plunger system for sandy wells while being retrievable from the well. The apparatus of the present invention provides a solution to these aforementioned issues.  
       SUMMARY OF THE INVENTION  
       [0027]     The main aspect of the present invention is to provide a self-cleaning plunger apparatus that will increase well production levels in a sand-bottom well.  
         [0028]     Another aspect of the present invention is to provide a plunger apparatus that will lift sand away from a well bottom during the plunger lift from the well, self clean itself at the well top, avoid getting caught (or stuck) at the well top, and allow any accumulated sand to be blown away from its sides and taken downstream for further separation and cleanout.  
         [0029]     Another aspect of the present invention is to allow the plunger to self-clean at the top of the lift in order that it could efficiently force fall inside the tubing to the well-hole bottom with increased speed without impeding well production.  
         [0030]     Yet another aspect of the present invention is to provide a self-cleaning plunger that will keep the well clean.  
         [0031]     Another aspect of the present invention is to allow for various plunger sidewall geometries to be utilized.  
         [0032]     Other aspects of this invention will appear from the following description and appended claims, reference being made to the accompanying drawings forming a part of this specification wherein like reference characters designate corresponding parts in the several views.  
         [0033]     The present invention comprises a plunger lift consisting of solid sidewall geometries, a solid top (typically a fishing neck design), and containing a hollowed out central region along with peripheral holes extending from its hollowed central core to its outer annular groves. The self-cleaning sand plunger (SCSP), the present invention, functions to carry sand, other solids and fluids from the bottom of the well to the surface. Once at the well top the SCSP is auto-caught. It will be held in the plunger auto catcher located within the lubricator. While held in the auto catcher, well pressure will force gas up through its hollowed out central core and out through the peripheral holes, functioning to clean out any sand that is caught in the outer annular grooves, thus creating a self-cleaning function. The well control system will release it to fall back into the well when conditions are satisfied. Sand that is cleaned from the annular grooves is subsequently carried downstream by the well pressure flow and into a separating station.  
         [0034]     The SCSP will be dropped back into the well when well conditions are met with all liquid loading factors. The SCSP will thus be cleaned prior to its return to the well bottom. This self cleaning allows an efficient force fall back to the well bottom and avoids maintenance that may have been caused by it getting caught in the lubricator due to accumulated sand.  
         [0035]     The present invention assures an efficient lift due to its design. The present invention also optimizes well efficiency due to the fact that it is self-cleaning to allow it to quickly travel to the well bottom. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0036]      FIG. 1  (prior art) is an overview depiction of a typical plunger lift system installation.  
         [0037]      FIG. 1A  (prior art) is a blow up drawing of a well bottom having accumulated sand.  
         [0038]      FIG. 2  (prior art) is a side plan view of the various standard sidewall geometries.  
         [0039]      FIG. 3  is a side plan view of the preferred embodiment of the present invention showing the sand plunger with solid sidewall geometry.  
         [0040]      FIG. 4  is a longitudinal cross-sectional view of the preferred embodiment of the present invention showing the sand plunger with solid sidewall geometry.  
         [0041]      FIG. 5  is a side plan view of a sand plunger having a by-symmetrical sidewall design, an alternate embodiment of the present invention. 
     
    
       [0042]     Before explaining the disclosed embodiment of the present invention in detail, it is to be understood that the invention is not limited in its application to the details of the particular arrangement shown, since the invention is capable of other embodiments. Also, the terminology used herein is for the purpose of description and not of limitation.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0043]     Referring now to the drawings, the present invention provides a self-cleaning ‘sand’ plunger (SCSP) apparatus, see  FIGS. 3,4  item  300  that will increase well production levels for sand bottom based gas wells. SCSP  300  is a self-cleaning plunger apparatus to lift sand away from a well bottom during the plunger lift from the well, self-clean itself at the well top while contained within the aforementioned auto-catcher, and allow the accumulated sand to be blown out and taken downstream for further separation and cleanout prior to falling back to the well bottom, thus keeping the well clean and avoiding getting itself stuck within the well. When conditions are met, SCSP  300  is released from the auto-catcher within the lubricator (ref.  FIG. 1 ) and efficiently force-falls down into the well tubing to the well bottom allowing an optimization of well production.  
         [0044]     SCSP  300  can be employed with various solid plunger sidewall geometries.  FIGS. 3,4  show peripheral radial clean out holes  32  extending from its central hollowed out inner core  35  to its outer radial grooves  30 . Gas, under well pressure, enters its bottom entry  34 , passes up through center hollowed out inner core  35 , and exits out through peripheral radial clean out holes  32  while SPSP  300  is held in the aforementioned auto-catcher. This action blows any sand that is imbedded (trapped or caked) within the outer radial grooves  30  to be moved away from SCSP  300 . Sand will be then swept downstream by the well pressure in direction F (ref.  FIG. 1 ) to a separator where it is subsequently separated from liquids and gas. In this manner, not only is sand removed from the well bottom, but SCSP  300  is also cleaned for efficient and continued drops back to the well bottom, thus improving well efficiency. Sandy bottom wells typically would have sand accumulated to the outside of prior art plungers (ref.  FIG. 1A ), which would impede the plunger drop to the well bottom and/or get stuck within the auto-catcher (within the lubricator) requiring manual intervention or maintenance, thus raising cost and lessening well production.  
         [0045]     SCSP  300  of the present invention basically is employed with following discrete steps: 
        1. SCSP  300  drops to the bottom of a well with liquid loading on top of the plunger and sand accumulating on the outer plunger surfaces, typically within the annular outer radial grooves  30 .     2. The well is open for flow at which time SCSP  300  rises towards the well top to carry liquids and accumulated sand out of the well bore.     3. SPSC  300  is caught within the lubricator at the well top by the plunger auto-catcher device (ref.  FIG. 1 ) Note: the extracting rod shown in  FIG. 1  would not be used with the SCSP as it has a solid top (typically a fishing neck).     4. The well flows for a set time or condition controlled by the well-head controller, at which time self-cleaning action begins.     5. While SCSP  300  is held by the auto-catcher, well pressure forces gas into its bottom entry  34 , through it&#39;s hollowed out inner core  35 , and out of its peripheral radial holes  32 . Gas pressure coming out of radial holes  32  creates a ‘venturi tube like’ effect functioning to blow sand out of the outer radial grooves  30 .     6. Sand is carried downstream in direction F (ref.  FIG. 1 ) by the well pressure to a separator.     7. The auto-catcher releases SCSP  300  after a set time or condition as controlled by the well system controller.     8. SCSP  300  force-falls to the well bottom with the accumulated sand removed, thus the fall is much more efficient.     9. The well plunger lift cycle starts again.        
 
         [0055]     The geometry of SCSP  300  acts as a sealed device during lift and functions to carry sand and fluids to the well surface. The auto-catcher at the well top holds SCSP  300  in place while well pressure passes gas through its center hollow core  35  and out its peripheral radial holes  32 . The gas flow out the holes creates a ‘venturi tube’ type effect and passes gas onto the outer grooves pushing the accumulated sand out and away from the grooves. Well pressure will force the sand to exit the well downstream where it will be caught in a separator for further processing. Prior art design plungers would get sand accumulated within the outer grooves (ref.  FIG. 1A ), which would not only affect the efficiency of the plunger fall, thus effecting the well productivity, but could also require manual intervention to retrieve a plunger that is stuck within the well or within the lubricator. The accumulated square inch cross-sectional area of the combined holes  32  as compared to the square inch cross-sectional area of the bottom centered out hollow core  35  is critical. If the ratio of the cross-sectional area of the combined holes  32  CA exceeds a critical point, it will cause lift failure and/or not self-clean. In one experiment a sixteen inch long sand plunger had a one inch bottom hole. One hundred twenty holes were made at one eighth inch diameter each. A particular liquid load could not be lifted that day.  
         [0056]     SCSP  300  is geometrically designed to have a fluid/gas dynamic type shape to allow it to quickly pass to the well bottom. SCSP  300  will return to the bottom with an efficient speed until it comes to rest on the bottom sitting or on a bumper spring.  
         [0057]     The preferred embodiment of the present invention employs a solid ribbed sidewall plunger construction as shown in  FIGS. 3,4  with a standard American Petroleum Institute (API) fishing neck  31  top, a hollow core  35  extending from its bottom entry  34  to at least the top of its outer ringed surface, multiple radial peripheral radial holes  32 , which are at a 90° angle to its length and extending from hollow core  35  to each peripheral groove  30 , and having an outside ribbed geometry. Other embodiments of the present invention can employ various amounts of peripheral radial holes, holes at various angles, locations and/or various outer surface geometries. Typical solid outside geometries include, but are not limited to, a hollow steel symmetrical shaped bullet plunger, Teflon® or poly sleeves, solid steel with under-cut grooves, solid steel with top cut grooves to hold fluid and bottom cut grooves to trap gas.  
         [0058]     SCSP  300  is designed with a hollow inner core  35  to allow gas to enter its core and then exit out its peripheral radial holes  32  to clean all of the outer grooves  30 . SCSP  300  can be designed with any of the standard aforementioned solid sidewall geometries with cleanout holes to allow it to quickly travel to the well bottom once it is released by the auto-catcher at the surface. SCSP  300  will carry unwanted sand buildup out of the well during lift, self clean once it reaches the top and prior to dropping back to the bottom. Sand cleaned away from SCSP  300  will be carried out of the well to a downstream separator.  
         [0059]     The present invention assures removal of sand from the well, self-cleaning of any caked sand around the outer peripheral annular plunger grooves, movement of sand downstream to a separator, significantly less well maintenance, and a continuous well cleaning action.  
         [0060]      FIG. 3  is a side view of the preferred embodiment of the present invention showing SCSP  300  having solid ring sidewall geometry. Solid sidewall rings  22  are undercut to trap gas having a downward slant top surface  23 . The solid ring geometry can be made of various materials such as steel, poly materials, Teflon®, stainless steel, etc. Inner cut grooves  30  allow any sidewall debris to accumulate when a plunger is rising or falling. Peripheral radial holes  32  extend radially from the hollowed out inner core  35  (ref.  FIG. 4 ) to inner cut grooves  30 . Bottom entrance  34  is the open end of hollowed out center core  35  (ref.  FIG. 4 ). Standard American Petroleum Institute (API) fishing neck  3  at the top end of the sand plunger is a well known design in the art and allows retrieval of SCSP  300  from the well if necessary.  
         [0061]      FIG. 4  is a side cross-sectional view of the preferred embodiment of the present invention showing sand plunger  300  with solid sidewall geometry. Peripheral radial holes  32  extend radially from the hollowed out inner core  35  to each of the inner cut grooves  30 , which are located between solid sidewall rings  22  with downward slant surface  23 . Peripheral radial holes  32  are shown around the inner cut grooves  30  with a 90° spacing about the annular periphery. Inner cut grooves  30  allow sidewall debris to accumulate therein when SCSP  300  is at the well bottom and will contain any debris while SCSP  300  is rising or falling. Hollowed out center core  35  extends from bottom entrance  34  upward and past the last inner cut groove. When well pressure lifts SCSP  300  to the well top to be caught in the aforementioned auto-catcher, well pressure will force gas into bottom entrance  34 , up through center core  35  and out of each peripheral radial hole  32 , thus allowing the self-cleaning ‘venturi-like’ action to remove sand and any other accumulated debris from inner cut grooves  30 . Well pressure will then carry sand and other debris downstream to a separator for further processing.  
         [0062]      FIG. 5  is a side view of a sand plunger having a by-symmetrical design, an alternate embodiment of the present invention. The upper half of by-symmetrical SCSP  301  contains solid outer rings  22  with downward slant top surface  23 , while the bottom half of by-symmetrical SCSP  301  contains solid outer rings  22 A with an upward slant surface  24 . Mid outer ring  25  splits the upper from the bottom half symmetry. The upper half design shape acts to trap gas whereas the lower half acts to scrape the well sidewalls upon plunger lift. Gas enters hollowed out core  35 A through bottom entrance  34  and exits out radial holes  32 A at the upper half and also exits out of radial holes  33 A at the lower half, enabling the self-cleaning action once SCSP  301  is at the well top and within the aforementioned auto-catcher. It should be noted that this alternate embodiment is depicted with radial holes  32 A at about an upward 45° angle to the radial axis versus a 90° angle as previously shown in  FIGS. 3,4 . Radial holes  33 A are shown at a downward 45° angle to the radial axis. It should also be noted that radial holes  32 A,  33 A could be manufactured at various angles, including the radial angle shown in  FIGS. 3,4 , and still provide a self-cleaning action.  
         [0063]     It should also be noted that other alternate embodiments of the present invention could be easily employed by one skilled in the art to accomplish the self-cleaning aspect of the present invention. Alternate embodiments could employ various sidewall geometries, various numbers of radial peripheral holes, various locations of the holes within the outer grooves, and various angles extending from the inner core to the inner cut grooves and still accomplish the self-cleaning aspect of the present invention.  
         [0064]     Although the present invention has been described with reference to preferred embodiments, numerous modifications and variations can be made and still the result will come within the scope of the invention. No limitation with respect to the specific embodiments disclosed herein is intended or should be inferred.