Abstract:
The present invention provides a wellhead hydraulic drive unit to operate various styles of downhole pumps, which is installed as an integral part of a wellhead thereby eliminating the need for a stuffing box. The wellhead hydraulic drive unit comprises a hollow hydraulic cylinder having a piston positioned therein, a hydraulic fluid supply means attached to the hydraulic cylinder for producing reciprocation of the piston within the hydraulic cylinder, a hollow ram means slideably received within the inner wall of the hydraulic cylinder and connected to the piston for reciprocation in response to the piston; and a production tube means inserted through the ram means for enabling well fluid to be discharged from the well.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to a drive mechanism associated with artificial lift systems used in the production of oil and other fluids contained within underground formations. More specifically, this invention relates to a wellhead hydraulic drive unit that is installed as an integral part of a wellhead.  
         BACKGROUND OF THE INVENTION  
         [0002]    Fluid production wells having insufficient pressure are unable to flow liquids to the surface by natural means. Such wells require some form of energy or lift to transfer fluids to the surface.  
           [0003]    Several artificial lift systems exist to extract the liquids from liquid-bearing reservoirs. In the case of lifting oil from wells, conventional lifting units include the beam pump and the surface hydraulic piston drive. Both of these lift units are situated at the surface of the well and lift fluid to the surface by “stroking” production tubing or rods inside production casing and/or well casing. The production tubing or rods is connected to a wellbore pump configuration, comprising a chamber and a check valve, which allows fluid to enter on the down-stroke and to be lifted to the surface on the up-stroke. These conventional lift units are supplied power from combustion engines or electric drives.  
           [0004]    Beam pumps and surface hydraulic piston drives come in many sizes and are used extensively worldwide. U.S. Pat. Nos. 3,376,826; 3,051,237 and 4,296.678 are all examples of the use of a beam drive for a sucker string actuated pump. U.S. Pat. No. 4,403,919 is an example of a surface powered hydraulic pumping unit.  
           [0005]    There are many drawbacks associated with the use of conventional beam pumps and surface hydraulic piston drives. These units are large, obtrusive and unsightly in many sensitive regions. Further, the tubing and/or rods from within the wellbore must extend outside the well through a stuffing box to connect the drive units to same. The stuffing box prevents the wellbore fluids from escaping to the surrounding surface environment, however, rarely is this 100% successful thereby resulting in hydrocarbon contamination of the ground surrounding the wellhead.  
           [0006]    Additional drawbacks to the use of conventional beam pumps and surface hydraulic piston drives are as follows. These units present a hazard to workers in the surrounding area as a result of exposure to surface moving parts. Further, beam pumps often experience alignment problems resulting in stress on the rods, undue wear and eventual failure. Finally, there are numerous dangers to personnel associated with assembly, transportation, installation, operation and maintenance due to the size of the units and their many moving parts.  
           [0007]    U.S. Pat. No. 4,745,969 provides for a hydraulic/mechanical system for pumping oil wells that has a surface unit that can be hung inside of the well casing, so that there are no mechanical working parts outside of the well casing, except for surface pipeline connections. However, the &#39;969 in-casing hydraulic jack system must be suspended from 20 to 40 feet below the surface of the ground, depending upon the required stroke. Further, the hydraulic jack unit is sealed within the well casing resulting in a casing interior space for collecting reservoir fluid above the sealing means. This could result in leakage from the casing interior space to the environment, especially when lifting the hydraulic jack from the casing.  
         SUMMARY OF INVENTION  
         [0008]    The present invention provides a wellhead hydraulic drive unit to operate various styles of downhole pumps. The drive unit is installed as an integral part of the wellhead thereby eliminating the need for a stuffing box. Thus, hydrocarbon leakage from the wellhead drive unit is eliminated. Further, alignment issues through the wellhead and stuffing box associated with beam pumps and surface hydraulic drives are also eliminated.  
           [0009]    The wellhead hydraulic drive unit of the present invention is easier and safer to assemble, transport, install, operate and maintain due to its compact size and minimal moving parts. This results in lower installation and retrieval costs. Installation can be completed using a conventional service rig or a location specific small mast unit.  
           [0010]    It is important to note that well control is maintained throughout installation. There are no moving parts at the surface or above the wellhead. Once installed, the wellhead hydraulic drive unit of the present invention will have an extremely low profile. The wellhead hydraulic drive unit of the present invention can be easily installed in slant wells as well as horizontal or vertical wells.  
           [0011]    The wellhead hydraulic drive unit can be used in a variety of production applications; for example, heavy oil wells, high viscosity and low inflow wells, light oil high production wells, gas well dewatering, steam-assisted gravity drainage (SAGD) wells, slant wells, stroking production tubing or rods, water injection applications, sand disposal applications and pulse wells to stimulate production.  
           [0012]    In accordance with the present invention, an in-casing wellhead hydraulic drive unit for operating a downhole production pump via pump connecting means is provided, which hydraulic drive unit comprises:  
           [0013]    a hydraulic cylinder having top and bottom ends, an inner wall and a piston positioned within the inner wall for reciprocation within the hydraulic cylinder;  
           [0014]    hydraulic fluid supply means attached to the hydraulic cylinder for producing reciprocation of the piston within the hydraulic cylinder;  
           [0015]    ram means having a top and bottom end and an annulus therethrough, slideably received within the inner wall of the hydraulic cylinder and connected to the piston for reciprocation in response to the piston; and  
           [0016]    production tube means inserted through the annulus of the ram means and connected to the hydraulic cylinder for enabling well fluid to be discharged from the well.  
           [0017]    In a preferred embodiment, the in-casing wellhead hydraulic drive unit further comprises a means for mounting the hydraulic drive unit to the wellhead, said mounting means further comprising a hanger means attached to the hydraulic cylinder for landing the hydraulic cylinder within the wellhead. The hydraulic cylinder can be landed in the wellhead such that the top end of the hydraulic cylinder is positioned below the wellhead, within the wellhead or above the wellhead. The bottom end of the hydraulic cylinder is always contained within the well casing.  
           [0018]    In another preferred embodiment, the bottom end of the ram means is threaded and the pump connecting means threadably receives the bottom end of the ram means. In the alternative, a coupling means, which couples the ram means to the pump connecting means, is used. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]    [0019]FIG. 1 is a cross-sectional view of the wellhead hydraulic drive unit in accordance with a preferred embodiment of the invention.  
         [0020]    [0020]FIG. 2 is a cross-sectional view of the top end of the wellhead hydraulic drive unit inserted in a wellhead and well casing, in accordance with the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0021]    With reference to FIG. 1, the wellhead hydraulic drive unit according to the present invention is shown designated generally by the reference numeral  1 . The various parts which make up the drive unit  1  are for the most part housed within hydraulic cylinder  2 . Hydraulic cylinder  2  is comprised of cylinder outer wall  4 , cylinder inner wall  6 , cylinder top end  8  and cylinder bottom end  10 .  
         [0022]    At cylinder top end  8  is situated top gland  12 . Hanger  14  is threaded onto cylinder top end  8  of the hydraulic cylinder  2  to retain top gland  12  to hydraulic cylinder  2 . Top gland seal  16  seals top gland  12  to cylinder inner wall  6  and hanger seal  18  seals hanger  14  to cylinder outer wall  4 .  
         [0023]    It should be noted that hanger  14  profiles vary with different wellheads and are manufactured accordingly. Where applications restrict the use of hanger  14  in the wellhead itself, a landing spool (not shown) can be used. The landing spool is bolted on to the wellhead and the hanger  14  of the wellhead hydraulic drive unit  1  will then be landed within the landing spool.  
         [0024]    The wellhead hydraulic drive unit  1  can also be directly bolted to the wellhead by means of a flange (not shown), where well control precautions are not an issue. The flange means would be directly threaded onto the wellhead hydraulic drive unit  1  and then bolted directly onto the wellhead.  
         [0025]    The wellhead hydraulic drive unit  1  is operated by hydraulic power supplied from an outside source, capable of delivering and operating from 500 psi to 4,000 psi. Hydraulic fluid  32  is delivered to the wellhead hydraulic drive unit  1  via top gland  12 . Hydraulic fluid enters in through hydraulic fluid port  34  and flows down through internal porting (not shown) in top gland  12 . The hydraulic fluid  32  is then routed through the top gland porting down through a plurality of feed tubes  36  attached to top gland  12  and out feed tube ports  38  into lower annular area  40 .  
         [0026]    Hydraulic pressure in lower annular area  40  delivers force to main piston  42  for the upstroke or retraction movement. Down stroke movement or extension is normally achieved by tubing or rod weight from below (not shown). In applications where the tubing or rod weight is insufficient, hydraulic fluid can also be delivered to the top side of the main piston  42  through another hydraulic fluid port/vent  44  to actuate downward force.  
         [0027]    A plurality of piston seals  46  provides sealing between main piston  42  and cylinder inner wall  6 . A plurality of feed tube seals  48  provides sealing between main piston  42  and feed tubes  36 . Wear rings  50  help provide main piston  42  alignment to cylinder inner wall  6  of hydraulic cylinder  2 .  
         [0028]    Main piston  42  is threaded onto cylindrical ram  52  and has a non-rotational lock ring  82 . This allows for the wellhead hydraulic drive unit to provide torque to down hole tools where applicable. The torque is applied to hydraulic cylinder  2  and transmitted out to cylindrical ram  52  via main piston  42  and feed tubes  36 . It is designed to deliver either right or left hand torque in the fully open or fully closed positions only.  
         [0029]    Cylindrical ram  52  has ram outer wall  54  and ram inner wall  66 . Cylindrical ram  52  moves up and down within hydraulic cylinder  2  relative to main piston  42 . Cylindrical ram  52  extends the length of hydraulic cylinder  2  from main piston  42  through cylinder bottom end  10  of hydraulic cylinder  2 .  
         [0030]    Cylindrical ram bottom  64  is threaded to allow for connecting to a downhole pump via pump connecting means (not shown). Pump connecting means such as tubing joints, continuous tubing, sucker rods and continuous rods can either threadably receive threaded cylindrical ram bottom  64  or various crossover adapter designs can be used to couple the ram bottom  64  with pump connecting means. The design and type of pump will determine crossover design of the coupling adapter.  
         [0031]    At cylinder bottom end  10 , end gland  56  is welded in place to cylinder inner wall  4 . A plurality of end gland seals  58  provides sealing between cylindrical ram  52  and end gland  56 . Wiper  60  wipes cylindrical ram  52  clean to keep contaminants from entering end gland seals  58 . Wear rings  62  help provide cylindrical ram  52  alignment inside end gland  56 .  
         [0032]    Housed within cylindrical ram  52  is production tube  68 . Production tube  68  is threaded into top gland  12  to create a positive pressure seal. Attached to production tube  68  is production tube piston  70 . A plurality of production tube seals  72  provides sealing between production tube piston  70  and ram inner wall  66 . An additional production tube seal  74  also provides sealing between production tube piston  70  and cylindrical ram  52 , but functions to further seal out hydraulic fluid only from the top side in upper annular area  76 .  
         [0033]    As production fluid  78  is pumped from the bottom of the well to surface, it enters into the inner diameter of cylindrical ram  52  as shown by the arrow. As production fluid enters into cylindrical ram  52 , it is produced up through the wellhead hydraulic drive unit  1  by means of the production tube piston  70  and through production tube  68 . Production fluid  78 , after passing through production tube  68  then enters top gland  12  and exits out to the surface via a flow line (not shown) which is connected to top gland  12  by threading into top gland thread  80 .  
         [0034]    [0034]FIG. 2 shows the wellhead hydraulic drive unit  1  installed in a well casing. The installation of the wellhead hydraulic drive unit  1  is unique in that it is installed as an integral part of the wellhead. As a result of this, the well control features associated with the wellhead are optimized.  
         [0035]    With reference now to FIG. 2, wellhead  84  is shown attached to well casing  86 . The wellhead hydraulic unit  1  is lowered into the wellhead  84  and well casing  86  until hanger  14  is landed in place in wellhead  84 . The lower portion of the well hydraulic drive unit  1  now hangs inside well casing annulus  88  leaving sufficient space between the cylinder outer wall  4  of hydraulic cylinder  2  and the casing inner wall  90  to allow venting of casing annular gas to the surface through wellhead port  92 . A build up of gas pressure inhibits the flow of production fluids from the formation. Thus it is important to have the means for alleviating gas pressure.  
         [0036]    It is further important to have sufficient space between cylinder outer wall  4  and casing inner wall  90  in order to determine fluid levels in the well bore to maximize fluid production.  
         [0037]    Hanger  14  is secured in wellhead  84  by four equally spaced lag screws  20  and sealed to the wellhead  84  by a plurality of wellhead seals  22 . Once hanger  14  is landed in the wellhead  84 , top cover flange  24  is then installed on wellhead  84  by a plurality of flange bolts  26  and secured down with flange nuts  28 . Top cover flange  24  is sealed to the wellhead  84  by API seal ring  30 . Cylinder top end  8  of hydraulic cylinder  2  is sealed to top cover flange  24  by top cover flange seal  94 .  
         [0038]    In practice, hydraulic fluid  32  is supplied at top gland  12  and fed through one or more feed tubes  36  having hydraulic fluid ports  34  at the bottom for hydraulic flow. This hydraulic fluid path provides for main piston  42  upstroke or hydraulic cylinder retraction. Hydraulic fluid can also be supplied directly through the top gland  12  to the top side of the main piston  42  via a second hydraulic fluid port/vent  44  for piston downstroke or hydraulic cylinder extension.  
         [0039]    The up and down stroking movement actuates the downhole pump allowing for production fluid  78  to surface. The production fluid  78  passes up through the downhole production tubing, through the cylindrical ram  52 , through the production tube piston  70  and production tube  68 , and finally through the top gland  12  to exit at the surface via a vent or flow line (not shown) attached to the wellhead hydraulic drive unit  1 .  
         [0040]    Hydraulic pressure to the main piston  42  is supplied from a surface pump via a control line connected to the cylinder top end  8  of the hydraulic cylinder (not shown). The power for the hydraulic pump can either be electric and/or internal combustion motor.  
         [0041]    While various embodiments in accordance with the present invention have been shown and described, it is understood that the same is not limited thereto, but is susceptible of numerous changes and modifications as known to those skilled in the art, and therefore the present invention is not to be limited to the details shown and described herein, but intend to cover all such changes and modifications as are encompassed by the scope of the appended claims.