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BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    This application is directed to an anchor system for production tubing in a pumpjack type oil well. The anchor stabilizes the tubing during operation of the well as explained below. 
         [0003]    2. Description of Related Arts Invention 
         [0004]    A pumpjack is often used with a “rod pumping system” and is used to mechanically lift liquid out of the well if there is not enough bottom hole pressure for the liquid to flow all the way to the surface. The arrangement is commonly used for onshore wells to enhance or increase production. Pumpjacks are common in oil-rich areas. Depending on the size of the pump, it generally produces 5 to 40 liters of liquid at each stroke. Often this is an emulsion of crude oil and water. Pump size is also determined by the depth and weight of the oil to remove, with deeper extraction requiring more power to move the increased weight of the discharge column (discharge head). A pumpjack converts the rotary mechanism of a motor to a vertical reciprocating motion to drive the pump shaft, and is exhibited in the characteristic nodding motion. The engineering term for this type of mechanism is a walking beam. The prime mover of the pumpjack runs a set of pulleys to the transmission which drives a pair of cranks, generally with counterweights on them to assist the motor in lifting the heavy string rods. The cranks raise and lower one end to assist the motor in lifting the heavy string rods. The cranks raise and lower one end of an I-beam which is free to move on an A-frame. On the other end of the beam, there is a curved metal box called a horse head or donkey head. A cable made of steel or fiberglass, called a bridle, connects the horse head to a polished rod, a piston that passes through a stuffing box. The polished rod has a close fit to the stuffing box, letting it move in and out of the production tubing without fluid escaping. The bridle follows the curve of the horse head as it lowers and raise to create a nearly vertical stroke. The polished rod is connected to a long string of rods called sucker rods, which run through the tubing to the down-hole pump, usually positioned near the bottom of the well. At the bottom of the tubing is the down-hole pump comprised of two assemblies. This pump has two ball check valves: the first is a stationary valve at bottom called the standing valve. The second is in valve on the piston connected to the bottom of the sucker rods that travels up and down as the rods reciprocate, known as the travelling valve. Each of these valves permits wellbore liquids to move upward toward the surface but prohibits fluids from moving back downhole. Reservoir fluid enters from the formation into the bottom of the borehole through perforations that have been made through the casing and cement. When the rods at the pump end are traveling up, the traveling valve is closed and the standing valve is open due to the drop pressure in the pump barrel. Consequently, the pump barrel fills with the fluid from the formation as the traveling piston lift the previous contents of the barrel upwards. When the rods begin pushing down, the traveling valve opens and the standing valve closes due to an increase in pressure in the pump barrel. The traveling valve drops through the fluid in the barrel. The piston then reaches the end of its stroke and begins its path upward again, repeating the process. The number of strokes per time unit defines the maximum flow rate from the well. However each application affects the fill efficiency of this volume, which in turn, affects the actual flow rate of fluids from the well. Affecting efficiency is the elasticity of the tubing, wherein the tubing “stretches” axially in tension during down stokes and “compresses” or buckles axially during upstrokes. When “heavy oil” is produced by rod pumped wells often steam is injected in the well to reduce the viscosity of the hydrocarbons, enabling it to flow more readily into the wellbore. Cycling between steam injection periods and production periods, thermal effects cause the steel tubing to either expand lengthwise with heat or contract as the well cools, which also affects the efficiency of the well. A well-known tubing anchor that serves to stabilizing the tubing may be employed, but the thermal effects of steam injection cause very high alternating compression and tension loads on the tubing anchor also causing bucking and tension in the production tubing further decreasing pumping efficiency and often leading to premature failure of the tubing anchor. The great temperature variations imposed by steam injection prohibit use of any known tubing anchor. 
         [0005]    Consequently, there is a need for an anchoring system that prevents a wide variation of the tubing movement caused by up and down strokes of the sucher rods, and the expansion and contraction of the tubing during heating and cooling cycles both in an axial and radical direction. 
       BRIEF SUMMARY OF SOME OF THE PREFERRED EMBODIMENTS 
       [0006]    These and other needs in the art are addressed by an anchor that acts as a thermal expansion joint while it dampens the axial expansion and contraction of the production tubing during pump operation. An embodiment of the invention includes an anchor having an outer housing secured to the casing and includes an annular hydraulic chamber. A piston is attached to the production tubing and is located within the hydraulic chamber so as to retard and dampen axial forces of the tubing. The piston includes on its outer surface a tortuous flow path formed by a plurality of annular rings and or pathways. 
         [0007]    The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter that form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiments disclosed may be readily utilized as a basis for modifying or designing other embodiments for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent embodiments do not depart from the spirit and scope of the invention as set forth in the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    For a detailed description of the preferred embodiments of the invention, reference will now be made to the accompanying drawings in which: 
           [0009]      FIG. 1  is a schematic of a conventional pumpjack oil well. 
           [0010]      FIG. 2  is a cross sectional view of a first embodiment of an anchoring system according to the invention. 
           [0011]      FIG. 3  is a cross sectional view of an anchor according to a second embodiment of the invention. 
           [0012]      FIG. 4  is an enlarged view taken from  FIG. 3 . 
           [0013]      FIG. 5  is a cross-sectional view of one of the ring members. 
           [0014]      FIG. 6  is a cross sectional view taken along line  6 - 6  of  FIG. 3 . 
           [0015]      FIG. 7  is a schematic showing of the anchor system of  FIGS. 3-6  in a run in position. 
           [0016]      FIG. 8  is a schematic showing of the anchor system of  FIGS. 3-6  in a fully set expanded position. 
           [0017]      FIG. 9  is a schematic showing of the anchor system of  FIGS. 3-6  in an operating expanded position. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0018]    A conventional pumpjack well  10  is shown in  FIG. 1  and includes a walking beam  11  having a horse head  12  and one or more cables  13  attached to a polished rod  20 . A mechanism for pivoting the walking beam about support  17  includes pitman arm  16 , a crank  15  and a counter weight  14 . A prime mover and transmission mechanism not shown drives crank  15  in a known manner. 
         [0019]    The well includes a stuffing box  21  through which polished rod  20  reciprocates. Polished rod passes through a tee  22  and is connected to a sucker rod or rods  28 . Conduits  23  and  24  are provided for produced gas and oil respectively. 
         [0020]    The well further includes a casing  26 , cement  25  surrounding the casing, and production tubing  27 . The lower end of the casing and cement is perforated at  31  in the production zone  34  to allow fluids to enter pump chamber  35 . 
         [0021]    A standing valve  32  is fixed at a lower portion of the tubing and a traveling valve  33  is attached to the lower end of the reciprocating sucker rod thereby forming a pump as is known in the art. 
         [0022]    According to a first embodiment of the invention as shown in  FIG. 2 , the anchor  56  for the tubing  51  includes a plurality of slips  61  which are set in the well at a desired depth. 
         [0023]    Pressure from the surface applied against the traveling valve by a ball  55  and seat  60  sets the anchor  56  to the casing  52 . 
         [0024]    A compression spring  58  is positioned between anchor  56  and a flange  62  on the production tubing to keep constant tension on the tubing thereby arresting excess axial movement of the tubing caused by the reciprocating movement of the downhole pump by asserting a compression force against the tubing anchor and the flange  62  affixed to tubing  51  at a lower end  63  of the tubing. A plurality of centralizers  53 ,  54  may also be attached to tubing  51  to stabilize the tubing within the causing  52 . 
         [0025]    A second embodiment of an anchoring system is shown in  FIGS. 3-7 . The anchor includes an outer housing having a first uphole portion  73 , and a downhole portion  83  which are fixedly connected to each other at  99 . 
         [0026]    A closure cap  72  is positioned between housing portion  73  and a first section  69  of production tubing. A dampening piston  75  is attached to the first section of tubing  69  and a second section  70  of the production tubing. Dampening piston  75  is free to float within an hydraulic chamber  79  which is filled with hydraulic fluid. Two groups of rings  76 ,  77  are positioned on the outer surface of dampening piston  75  as best shown in  FIG. 4  to form a tortuous resistance flow path for the hydraulic fluid from one side of the piston to the other as the piston shuttles in the hydraulic chamber  79 . 
         [0027]      FIG. 4  is an enlarged view of the piston  75 . Piston  75  is threadly attached to tubing  69  and  70  at  114  and  115  respectively. Annular seals  118  and  119  may be positioned between the piston and tubing  69  and  70 . A first set of three rings  76  are attached to a first end of the piston by end cap  74  which is threaded on piston  75  as shown at  116 . A passageway  110  is provided in end cap  74 . Rings  76  are spaced from housing  73  is to form a tortuous path  105 . Additionally, one or more passageways  102 ,  103 , and  104  are formed in the rings to provide additional flow paths. 
         [0028]    In similar manner, a second end cap  78  is threaded on piston  75  at a second end as shown at  117  and thereby secure a second set of rings  77  on the piston. 
         [0029]    Rings  77  are also spaced from housing  73  thereby forming a torturous path  106 . Also one or more passageways  102 ,  103 ,  104  may be provided in the rings to allow fluid flow through the rings. End cap  78  is also provided with a passageway  172 . A flow passage  111  is provided at one end of piston  75  and a second flow passage is provided at the second end of piston  75 . A pair of seals  118  and  119  may be positioned between tubulars  69  and  70  and piston  75  as shown in  FIG. 4 . 
         [0030]      FIG. 5  illustrates a front view of one of the ring members  76  and  77 . The inner surface  138  of ring member  76  is circular and sits on the circular outer surface of piston  75 . The outer surface of ring members  76  or  77  are circular with a tight clearance to the inside diameter of housing  73 . The outer surface may also include a channel or series of restricted flow paths. 
         [0031]    Thus a plurality of tortuous paths  106  are formed around the periphery of the rings allowing fluid to flow along piston  75  in a controlled manner. Additionally one or more flow passages  104  may be formed through the rings for control purposes. 
         [0032]    A slip housing  86  surrounds downstream anchor housing  83 . A first annular piston  88  is positioned between slip housing  86  and downhole anchor housing  83 . 
         [0033]    A second annular piston  89  is also positioned between slip housing  86  and downhole anchor housing  83  and includes an inclined surface  90  which is adapted to move slips  68  outwardly to engage the inner surface of the well&#39;s casing to thereby fixedly secure the anchor within the casing with the tubing  69 ,  70  temporally attached to the anchor via shear pins  94  between tubing section  95  which is attached to tubing  70  and portion  93  of the anchor housing. A plurality of shear pins  87  connect slip housing  86  to the second piston  89 . 
         [0034]      FIG. 6  illustrates the details of the anchoring slips  68  that are spaced around the periphery of slip housing  86  and anchor housing  83 . Annular moveable piston  89  forces slips  68  outwardly through radically spaced openings  110  in housing  86  in a known manner. 
         [0035]    In order to set the anchor within the well, the anchor with tubular sections  69 ,  70 , and  95  is lowered to the desired position within the well with the tool configured as shown in  FIG. 3 . Fluid under pressure is then pumped down through tubular  69  and enters hydraulic chamber  79  through passageway  101  and rupture disc  80  and tortuous pathway  81 . From there fluid under pressure flows through passageway  84  and enters pressure chamber  85  acting on piston  88  causing shear pins  87  to break thereby allowing first and second pistons  88  and  89  to move downhole to the right as shown in  FIG. 3 . This causes inclined surface  90  to push slips  68  outwardly to grip the inner surface of the casing not shown, thus anchoring the system to the casing. 
         [0036]    As the temperature within the well increases, tubing  69 ,  70 , and  95  will expand thereby shearing pins  94 . At this point the production tubing string  69 ,  70 , and  95  along with dampening piston  75  is free to move within the anchor subject to the dampening effect of piston  75  moving within hydraulic chamber  79 . 
         [0037]    The anchor can be retrieved from the well by pulling upward on the tubing. 
         [0038]    This will shear pins  92  which are positioned between downhole housing  93  and a lower cone member  91 . This allows slips  68  to fall back into slip housing  86  thereby releasing the slips  68  from engagement with the casing. 
         [0039]      FIGS. 7-9  schematically illustrates the functionality of an embodiment of the invention. 
         [0040]      FIG. 7  shows the tubulars  69 ,  70 , and  95  positioned within anchor housing  73  and  86  in the run in position. Anchor housing  86  includes slips  68  which anchor the system in the well casing, not shown. 
         [0041]      FIG. 8  depicts the anchor being set within the casing by slips  68  and also illustrates the thermal expansion of tubular  70 . 
         [0042]      FIG. 9  shows the dampening aspect of the invention as the tubular tends to move up and down due to the stroke of the sucher rod of the pump. At this point, the up and down movement of the tubular is dampened due to piston  75  which is attached to the tubular  70 and located within the hydraulic chamber  79  as explained above. 
         [0043]    Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations may be made herein without departing from the spirit and scope of the invention as defined by the appended claims.

Summary:
Apparatus and method for limiting the expansion and contraction of a production tubular within a pumpjack oil well includes an anchor having a hydraulic dampening chamber and an expansion joint. A piston is attached to the tubular and position within the hydraulic dampening chamber so that axial expansion and contraction of the tubular caused by thermal and loading forces is resisted by the constrained movement of the piston within the hydraulic chamber.