Patent Publication Number: US-2012024521-A1

Title: Hydraulic lubricator for use at a wellhead

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of the filing of U.S. Provisional Application Ser. No. 61/400,385, entitled “Hydraulic Lubricator,” filed 27 Jul. 2010, the entire disclosure of which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to a lubricator for use at oil and gas wells, and in particular to a hydraulic lubricator apparatus and system that minimizes manual manipulation of the lubricator rod. 
     BACKGROUND OF THE INVENTION 
     In many down-hole operations conducted in the oil and gas exploration and extraction industry, “lubricators” are used to manage well pressure when it becomes necessary to access the pressurized well. A lubricator may be supported in a derrick or from a crane jib. 
     Accordingly a lubricator, in this field of endeavor, essentially is a high-pressure pipe fitted to the top of a wellhead (e.g. a “Christmas tree” in the art) so that various items and down-hole tools can be inserted into a high-pressure oil or gas (or other) well. U.S. Pat. No. 7,699,099 to Bolding et al., and my co-pending U.S. patent application Ser. No. 12/930,188 filed 30 Dec. 2010, which are here incorporated by reference, offer recent disclosures regarding well head “Christmas tree” components and configurations. 
     The top of the lubricator assembly features a high-pressure section and sealing components. The tool(s) to be placed into the well are placed in the lubricator. The lubricator is temporarily installed upon the “tree” and tested. After testing, lubricator valve(s) are opened to equalize to wellbore pressure. The top valves of the “tree” are then opened to allow the tools to drop (or be pumped by hydraulic pressure) down the bore. Removal of the down-hole tool(s) is accomplished by the reverse process; the tool is pulled up the bore and into the lubricator under wellbore pressure, the tree valves are closed, and the wellbore pressure within the lubricator is bled off. After the high pressure in the lubricator is safely released, the lubricator can be opened. In short, a lubricator provides a sort of “pressure lock” via which tools may be inserted into and retrieved from a well which is under pressure. 
     A broad survey of background art for lubricators generally is provided by U.S. Pat. Nos. 6,827,147 to Dallas, 5,893,417 to Pizzolato, 4,062,406 to Akkerman et al., and 3,924,686 to Arnold, the entire disclosures of which are incorporated herein by reference. 
     SUMMARY OF THE INVENTION 
     Disclosure of the Invention 
     There is disclosed lubricator apparatus and method for use at a wellhead such as an oil or natural gas well. The lubricator has a polished rod on which an item, such as a back pressure valve, may be disposed for placement, for example to isolate the wellhead from the well pressure to permit wellhead servicing. The rod is moved by hydraulic power, rather than manually. A piston is connected to the polished rod within the lubricator barrel. Hydraulic pressure within the barrel, above or below the piston, is controlled to cause the rod to move up and down, under power, to permit the rod and items thereon to be lowered and retrieved. 
     In a preferred embodiment, the lubricator has a yoke assembly removably mountable to a wellhead, and a barrel portion, detachably engageable with the yoke assembly. The barrel portion has a barrel housing having a first end and a second end, a rod movable coaxially within the barrel housing and having a segment of the rod variably extendable from the barrel housing second end, and a piston secured to the rod and movable within the barrel housing, there being defined in the barrel housing a head space between the piston and the barrel housing first end and a barrel space between the piston and the barrel housing second end. An upper port is defined in the barrel housing for permitting a hydraulic fluid to enter or exit the head space, and a lower port is defined in the barrel housing for permitting hydraulic fluid to enter or exit the barrel space. At least one valve is provided for regulating hydraulic pressure in the head space or the barrel space, thereby controllably driving the piston to-and-fro within the barrel housing and moving the rod axially in the barrel housing. 
     This disclosure provides a means of safely and hydraulically actuating the main rod or tube of a lubricator. 
     There is provided lubricator apparatus which replaces known manually-operated lubricator rods. 
     Accordingly, there also is provided a method for rapid and safe change-out of devices used in well head equipment. 
     A primary object of the present invention is to provide a method and apparatus for hydraulically moving the polished tool rod of an oilfield lubricator. 
     A primary advantage of the present invention is that it replaces manual actuation of a lubricator rod with hydraulic actuation of the rod to provide a more secure and safe operation. 
     Other objects, advantages and novel features, and further scope of applicability of the present invention will be set forth in part in the detailed description to follow, taken in conjunction with the accompanying drawings, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated into and form a part of the specification, illustrate several embodiments of the present invention and, together with the description, serve to explain the principles of the invention. The drawings are only for the purpose of illustrating a preferred embodiment of the invention and are not to be construed as limiting the invention. In the drawings: 
         FIG. 1  is a diagrammatic side view of a type of lubricator generally in accordance with the prior art; 
         FIG. 2  is an enlarged view of a portion of the lubricator seen in  FIG. 1 , diagramming some of the components used to control pressures in the lubricator; 
         FIG. 3  is a partially exploded, partial sectional side view of a lubricator apparatus, showing the barrel portion and certain components attachable to the distal end of the polished tool rod; 
         FIG. 4  is a side view of the barrel portion of the lubricator apparatus according to the present disclosure; 
         FIG. 4A  is an enlarged view of a portion of the barrel portion of the lubricator depicted in 
         FIG. 4 ; 
         FIG. 5  is a side sectional and schematic view of the barrel portion of the lubricator apparatus according to the present disclosure; 
         FIG. 6  is a perspective illustration of the complete lubricator apparatus according to the present disclosure, suspended by a crane on a service vehicle, and showing the hydraulic cables running from the hydraulic power take-off on the vehicle to the body of the lubricator; 
         FIG. 7  is an enlarged side view of the lubricator apparatus seen in  FIG. 6 ; and 
         FIG. 8  illustrates a suitable control panel on the vehicle seen in  FIG. 6 , usable to remotely control the actuation of the polished tool rod in the lubricator. 
     
    
    
     The drawings are intended to be diagrammatic only, and are not necessarily to scale either within a particular figure or between figures. Like numerals are used to denote the same or similar components throughout the several figures. 
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Best Modes for Carrying Out the Invention 
     The present invention relates to an apparatus and method for the hydraulic operation of a lubricator. To insert down-hole tools into an oil or gas wellbore, or to perform maintenance or repair to the blowout preventer stack (BOP), it frequently is required to isolate the well&#39;s blowout BOP or “Christmas tree” from the pressure within the well. For example, it may be desired to install in the well tubing, below the tree, a back pressure valve (BPV). A properly selected and installed BPV blocks the well pressure coming up from the well during the removal of the BOP and during installation of, or repairs to, the Christmas tree. 
     Use of the hydraulic lubricator disclosed herein in a correct and controlled environment allows a trained service technician to complete safely the foregoing tasks with no strain. The hydraulic lubricator can be actuated by hydraulic pressure to allow the polished rod inside the described barrel to scope in and out, which allows assorted plugs to be set below the BOP or Christmas tree under wellbore pressure (or without pressure). 
     The normal purposes and procedural steps known in the art for installing and operating a well head lubricator tool are generally followed per known conventions, except as described in detail below. Rather, the presently disclosed apparatus offers an advantageous improvement, useable in cooperation with known lubricator devices (for example the 10,000 PSI WP Lubricator, Stock Number A1800-4V, available from G. B. International, Ltd., of Friendswood, Tex.). Among the improvements described herein, the present apparatus and system permits the polished tool rod in the lubricator to be manipulated hydraulically rather than manually. Nevertheless, standard safety precautions, and operating protocols, should otherwise be observed and followed. 
     The lubricator, with a back pressure valve (BPV) attached, is mounted on the top of the Christmas tree. In most operations, a one-way “H” Back Pressure Valve is used. However, if the BOP stack itself is being tested a two-way BPV is indicated. 
     In the present disclosure, the polished tool rod is extended down through the tree by regulated hydraulic force, allowing the threaded BPV to be screwed into the threaded top of the well&#39;s tubing hanger. The rod is then retrieved under the controlled hydraulic power. The lubricator may then be removed from the tree. After maintenance or repair has been completed, or the down-hole tool placed, the BPV must be retrieved to resume productive operation of the well. The lubricator is again connected to the tree cap, and the tool rod again hydraulically inserted down into the tree. Pressure in the tree can then again be equalized, and the BPV engaged and removed using the lubricator. 
     Combined reference is invited to  FIGS. 1 and 2 , diagramming generally a typical lubricator device. In this disclosure, “up” and “down,” and “upper” or lower,” shall have conventional meanings in the frame of reference provided by  FIGS. 1 and 2 , as well as by  FIGS. 3 ,  6  and  7  in the drawings, in which the apparatus is seen positioned vertically, which is the use position. The lubricator  10  has a yoke portion  20  and a barrel portion  30 . The bottom of the barrel portion  30  is securely yet detachably connectable to the top of the yoke portion  20 . A tool rod  34  (which preferably is polished) is within the barrel&#39;s interior bore or hollow, and is movable coaxially relative to the barrel housing  32 ; a distal or lower segment of the rod extends from the barrel such that a portion of the rod  34  is accessible through the access window  45  of the yoke portion  20 . 
     An eye or hook  35  ordinarily is provided upon the proximate or upper first end  63  of the barrel housing  32  to assist in lifting and manipulating the lubricator  10  into position atop a wellhead  49  for use. In a known lubricator device  10 , the tool rod  34  is moved manually by field workers relative to the barrel  30  and yoke assembly  20  to place or retrieve a BPV removably attached to the distal or lower end of the rod  34 . Such movement is accomplished manually, in which one or more operators grip the polished tool rod  34 , typically with a Parmelee wrench, where the rod  34  is accessible in the open window  45  of the yoke assembly  20 . Using the Parmelee wrench(es), the operators(s) with considerable effort manually move the rod  34  up and down within the lubricator  10 —a tiring, inefficient, and potentially dangerous activity that is obviated by the present invention. The manual gripping and up or down forced movement is manually applied to the rod  34  only where it is accessible in the yoke window  45 . 
       FIG. 3  shows that that the yoke assembly  20  according to the present disclosure has, for example, a 2-inch 1502 Union male  41 , with nut, on the adapter end, for securely yet removably connecting the yoke assembly  20  (and thus the lubricator  10 ) to the wellhead according generally to convention. Similarly, for example, a 2-inch 1502 female union  42  on the extension end of the lubricator yoke assembly  20  provides for the screwed connection of any of a variety of sizes/lengths of barrels  36 . Switching of barrel sizes permits the use of tool rods  34  of different lengths, to customize the lubricator  10  to the particular application or the heights of different BOPs or Christmas trees. Again, seen in  FIG. 3  running through the yoke assembly  20 , is the tool rod  34 , which is movable up and down. The rod  34  is used ultimately to manipulate a removably attached item, for common example a BVP  37 . In the yoke assembly  20  are two packing glands  22 ,  22 ′ (ordinarily with Chevron style packing) to retain fluid pressures within the lubricator during use. Central to the functioning of the lubricator  10  are four needle valves  24 ,  25 ,  26 , and  27 , used to equalize and bleed off pressure in the lubricator, according to known conventions. A pressure gauge  18  normally is installed in the cross portion on the lubricator manifold  33  of the yoke assembly  20 . 
     Referring to  FIG. 3 , it is seen that a polished rod adapter  38  is removably but reliably attached to the distal end of the tool rod  34 , as by means of a pin-and-channel connection. The polished rod adapter  38  permits a running and retrieving tool  39  (any of a number of running tools known in the art) to be securely but releasably connected to the distal end of the tool rod  34 . Such connections often are by means of special set screw type junctions. Running and retrieving tools include, for example, solid stringer type running tools, or sliding thread type running and retrieving tools for larger BVPs  37 . The running tool  39  in turn can have a threaded engagement with any of a number of tools, particularly for instance, a BVP  37  of selected and suitable type and specification. 
     The advantageous elements of the presently disclosed apparatus are best depicted in  FIGS. 4 and 5 . According to the invention, a specialized barrel portion  36  is provided for attachment to the female union  42  ( FIG. 3 ) of the usual yoke assembly  20 . Thus, to practice the present invention, a conventional barrel portion  30  ( FIGS. 1 and 2 ) is removed from the yoke assembly  20  and replaced by the improved barrel portion  36  ( FIGS. 4 and 5 ) of the present disclosure. It is noted that the yoke assembly  20  and its components are assembled and function generally in accordance with a known lubricator device, except especially that the rod  34  in the presently disclosed apparatus need not be forced up and down manually via the access of the yoke window  45 . Rather, the presently disclosed innovation occurs primarily in the specialized barrel portion  36  which is suited for screwed engagement with a yoke portion  20  by means of a suitable steel swage  43 . 
     Continued reference is made to  FIGS. 4 and 5 . In the present apparatus and method, the lower or distal second end  48  of the barrel housing  32  is secured within the female side of the swage  43  by means of a pressure gland  46  having suitable packing to contain fluid pressure within the interior of barrel housing  32 . The tool rod  34  movably extends through the gland  46  and axially through the swage  43  and on into the yoke assembly  20 . The swage  43  has a secure screwed engagement with the female union  42  ( FIG. 3 ) atop the proximate end of the yoke assembly  20 . Thus, the specialized barrel portion  36  of the present apparatus may be interchanged with conventional barrel portions  30  known in the art. (Again, the barrel portion  36  of the present disclosure is substituted for a conventional barrel portion  30  ( FIGS. 1 and 2 ) on the yoke assembly  20 .) 
     A piston  50  is secured at or near the upper or proximate end of the tool rod  34 . The outside diameter of the piston  50  approximates the inside diameter of the barrel housing  32 , such that the moveable piston has a snug sliding contact with the inside of the barrel housing. Suitable glands or O-ring packing  51  provide a pressure seal between the piston  50  and the inside wall of the barrel housing  32 , yet permit the piston to undergo reciprocal movement within the barrel housing. 
     Reciprocal movement of the tool rod  34  is provided by hydraulic pressure acting on the faces of the piston  50 . To provide for such regulated pressure changes, a proximate or upper fluid port  52  is defined through the wall of the barrel housing  32  very near its (proximate or upper) first end  63 . Upper fluid port  52  permits the flow of hydraulic fluid into or out of the head space  53  between the piston  50  and the closed, upper, first end  63  of the barrel housing  32 . Further, a lower fluid port  56  penetrates the wall of the barrel housing  32  near its distal or lower second end  48 , near the gland  46 . Lower fluid port  56  permits the flow of hydraulic fluid into or out of the barrel space  57  within the barrel housing between the piston  50  and the gland  46 . 
     Accordingly, axial to-and-fro movement of the piston  50 , and thus the tool rod  34 , can be controllably accomplished by regulated changes in relative fluid pressure between the head space  53  ( FIG. 5 ) and the barrel space  57 . Referring to  FIG. 5  and especially  FIG. 4A , a first pressure tee  59  is provided in the lower fluid port  56  for providing sealed fluid communication to both a quick-coupling connector  60  and a first aperture of a needle valve  61 , which are connected to the tee fixture  59 . The first quick-coupling connector  60  is of any suitable connector type known in the art of hydraulic systems for providing a reliable, but readily releasable, sealed fluid connection between the one leg of the tee fixture  59  and a first lower hydraulic pressure hose  65 . The first or lower hose  65  is in fluid communication with a source of regulated hydraulic pressure, preferably a conventional power-take-off of an internal combustion engine or other motor, mounted on a service truck  100  ( FIG. 6 ), by which hydraulic fluid can be driven under pressure through the lower hose  65 , through the lower fluid port  56  via the lower tee  59 , and into the barrel space  57 . 
     Referring still to  FIGS. 4A and 5  particularly, the other, second, aperture of the needle valve  61  is in fluid communication with a second, upper, pressure tee fixture  66 , which may be mounted by a bracket  71  on the exterior of the barrel housing  32 . A first leg of the upper tee fixture  66  is connected to a second or upper quick-coupling connector  68 , also a connector known in the art for providing a reliable and releasable fluid connection between the one leg of the upper tee fixture  66  and a second driving hydraulic pressure hose  70 . The upper or second driving hose  70  also is in communication with a source of regulated hydraulic pressure, so that an operator of the present apparatus can controllably direct pressurized hydraulic fluid toward the upper tee  66  via the coupling connector  68 . The second leg of the upper tee  66  is in fluid communication with a hydraulic transmission hose  72 . The upper end (remote from upper tee  66 ) of the transmission hose  72  has a sealed fluid connection to the upper fluid port  52 , so that hydraulic fluid can be conveyed from the upper tee fixture  66  into the piston head space  53 . 
     The needle valve  61  thus provides a fluid connection between the two tee fixtures  59 ,  66 , and thus a means for controlling hydraulic fluid flow between the upper fluid port  52  and the lower fluid port  56 . Closing the needle valve  61  prevents any fluid from moving directly between the ports  52 ,  56 , while an open needle valve  61  allows fluid flow, and thus pressure equalization, to occur between the barrel fluid ports  52 ,  56 . The pressure hoses  65 ,  70  deliver hydraulic fluid and pressure separately and (when the valve  61  is closed) independently to the respective tees  59 ,  66 , and thus separately to the ports  52 ,  56 . The condition or degree of separate delivery is controlled by the discretionary actuation of the valve  61 . 
     Thus the valve  61  is in fluid communication with the upper port  52  and with the lower port  56 , but also so that the lower port and the upper port are in fluid communication with the hoses  65 ,  60  which can deliver hydraulic pressure separately to each of the ports (via the respective tees) as indicated in  FIG. 5 . The valve  61  (preferably but not necessarily a needle valve) may be manipulated to control hydraulic fluid flow between the upper fluid port  52  and the lower fluid port  56 ; the valve in a closed condition prevents hydraulic fluid from moving directly between the ports, while when valve is open it allows hydraulic pressure equalization to occur between the ports. 
     From the foregoing, and with reference to  FIGS. 4 ,  4 A, and  5 , it is evident that the power provided by a source of hydraulic pressure, such a hydraulic power take-off of a truck-mounted internal combustion engine ( FIG. 6 ), can be harnessed to drive a controlled reciprocal movement of the piston  50 . With the needle valve  61  closed, hydraulic pressure can be delivered via the upper driving hose  70 , through the upper tee fixture  66 , and to the upper fluid port  52 . Fluid passing through the upper fluid port  52  and into the head space  53 , increasing the hydraulic pressure in the head space, moves the piston  50  axially downward (i.e., to the right in  FIGS. 4 and 5 ), away from the closed upper end  63  of the barrel housing  32 . Because the piston  50  is fixed to the tool rod  34 , movement of the piston induces corresponding movement of the tool rod. Likewise, hydraulic fluid can be controllably pumped through the first driving hose  65 , through the lower tee fixture  59  and into the barrel space  57  via the lower fluid port  56 . Increasing fluid pressure via the lower port  56  will increase fluid volume within the barrel space  57 , and the increased pressure within the barrel space will drive the piston  50  axially upward (i.e., to the left in  FIGS. 4 and 5 ), toward the upper first end  63  of the barrel housing  32 . The tool rod  34  moves accordingly. 
     A person skilled in the art recognizes that when the piston  50  is moving, a vent or “bleed” is required to relieve hydraulic pressure in the confined interior space (either the head space  53  or the barrel space  57 ) toward which the piston  50  moves. Such pressure relief can be and preferably is provided by employing an essentially closed hydraulic circuit. Thus, for example, when fluid is positively pumped into the head space  53  via the upper fluid port  52 , it simultaneously can be permitted to exit the barrel space  57  via the lower fluid port  56  (by active pumping action by the external source of hydraulic power via the hose  65 , or merely by the action of the moving piston  50 ), and vice-versa. 
     By regulated operation of the foregoing described hydraulic means, the axial up-and-down movement of the tool rod  34  is accomplished under regulated hydraulic driving power, rather than manually. The need for field technicians to manhandle the rod into and out of place, by gripping the rod  34  with a Parmelee wrench or other tool, is reduced or eliminated. 
     The practice of the invention can be further characterized as follows. 
     Before using the hydraulic lubricator apparatus  10 , it is recommended that a job hazard assessment be prepared and discussed with all well site personnel. The responsible operators should pre-check all equipment, including well equipment, to assure safe operation. The tools and hydraulic lubricator are inspected that everything is in good working condition. Before beginning lifting or working with any equipment, operators should assure that all lifting equipment and tools are the right lift rating and are free from damage. 
     The height of the Christmas tree must be determined, since the overall stroke distance of the hydraulic lubricator  10  must exceed the height of the tree. The appropriate size and type of the BPV is determined, and the BPV selected, based on the wellhead equipment type and conditions. The appropriate running and retrieval tool  39  is obtained to install the BPV  37  on the well tubing hanger. The yoke portion  20  of the lubricator itself preferably is pressure-tested (and repaired, if needed) according to known procedures. 
     A service truck  100  equipped with a small crane lift ( FIG. 6 ) and a power take-off (PTO) for driving an auxiliary hydraulic system is brought to the well head. A spotter assists the person that is operating the truck  100 , to assure safe backing and proper placement of the truck. The parking brake and wheel chocks are applied to secure the vehicle from movement. 
     With the installation of a PTO on the transmission on the truck  100 , a control valve can actuate up-and-down the tool rod  34  of the lubricator  10 . Two-fifty-foot hydraulic hoses  65 ,  70  run from the lubricator to the control valve. In front of the truck&#39;s work bed is a tank (not shown) holding 140 gallons of water, and in the center of the bed is a tank containing for example about 40 gallons of hydraulic oil. The hoist  102  which is mounted at the bed of the truck  100  preferably can extend out up to approximately 15.5 feet and be capable of lifting about 3,200 pounds at 75 degrees—more than capable of rigging up the hydraulic lubricator on any wellhead equipment up to about nine feet tall. 
     The running and retrieval tool  39  is attached to the tool rod  34  as indicated in  FIG. 3 . The BPV  37  is screwed or otherwise appropriately attached onto the running and retrieval tool  39 , also as suggested in  FIG. 3 . 
     The Christmas tree itself (not shown, but according to ordinary norms and configurations) is managed according to known protocols for use of conventional lubricators. Succinctly, the wing valve (or valves) must be closed to stop the flow from the well in the tree. Any equipment above the swab valve that will not be needed to complete the task is removed. The master valve(s) and swab valve are opened to essentially open the “run” of the tree, after which the pressure at the top of the tree is checked and double-checked. The swab valve is closed, pressure bled off, and the tree cap connector disconnected. 
     Reference is made to  FIGS. 6 and 7 . The hoist or crane  102  is attached to the top end (e.g. by eye bolt  35 ) of the lubricator  10 , and the crane actuated to bring the lubricator  10  to an upward position, as seen in  FIGS. 6 and 7 . Taglines may be attached to the eye bolt  35  on the top of, and also near the bottom (bottom tagline  105  in  FIG. 7 ) of the lubricator  10 , to facilitate safely guiding the lubricator to the top of the Christmas tree. Preferably, a work spool and B2P adapter, using a flow tee with a 2-inch ball valve connected on the side, are fastened atop of the Christmas tree. 
     The main lubricator hydraulic hoses, i.e., driving hoses  65  and  70  are run to the lubricator  10  from the hydraulic pressure sources at the truck  100 . The first driving hose  65  is connected to the lower fluid port  56  of the lubricator barrel  32  by means of the first quick-coupling connector  60 , and the second driving hose  70  is connected to the second, upper fluid port  52  by means of the upper quick-coupling connector  68 . The power take-off (from truck  100 ) that actuates the hydraulic pump may then be actuated. The hydraulic lubricator  10  is raised with the hoist  102  to a height sufficient to permit the distal end of the tool rod  34  to be extended from below, out the bottom flange of the yoke assembly  20 , permitting attachment of the running and retrieval tool  39  to the rod adapter  38  on the distal end of the rod  34 . The lubricator  10  is raised above the wellhead, and its distal end is placed in registration with the top of the Christmas tree (not shown, but according to convention), using taglines to guide the lubricator into position. The operators then tighten the connector bolts to secure the bottom of the lubricator onto the B2P adapter flange (on the tree). 
     Once the lubricator  10  is secured to the top of the tree, the operator opens needle valve  26  and needle valve  27  on the lubricator yoke assembly  20 ; the operators listen for pressure from below the Christmas tree master valve when the opening of the master valve is begun. (If there is no sign of pressure on yoke valve  27 , but there is on yoke valve  26 , the lubricator&#39;s equalizing tube might be shut or have an obstruction.) The operator then begins opening slowly the master valve on the Christmas tree. 
     It is necessary to calculate the number of incremental strokes of the tool rod  34  needed to move the BPV  37  (attached to the distal end of the rod) the proper distance through the tree for seating into the threads at the top of the tubing hanger. To do so, the depth to the tree&#39;s master valve and tubing plug is measured. (The measurement is taken from the bottom of the wing of lubricator to the middle of the lockdown pin gland nut.) Referring for example to  FIG. 3 , the length of the segment of the tool rod  34  that is exposed in the window of the yoke assembly  20  (between the gland nuts  44  of the packing glands  22 ,  22 ′) is measured. The distance between the gland nuts  44  is then divided by the length of the depth distance to the plug. The rod  34  is marked at the top gland nut  44 , and the rod  34  is then stroked slowly down (manually if necessary) until the mark is immediately adjacent the bottom gland nut  44 ′. This process is repeated to calculate the number of incremental strokes needed to move the tool rod through the accurate full rod stroke distance, to seat the BPV  37  at the plug (i.e., the distance the tool rod will need to be moved to reach the tubing hanger). 
     The lubricator  10 , installed atop the wellhead&#39;s tree, is then operated. First, needle valve  26  and needle valve  27  on the yoke assembly  20  are closed, and needle valve  24  and needle valve  25  are opened, which equalizes pressure within the lubricator  10  (that is, throughout the yoke assembly  20 , according to known lubricator functions). The resulting equalization of pressure allows the tool rod  34  to shift relatively freely up and down. 
     The swab valve on the Christmas tree is then slowly opened, the operators taking care to observe whether the lubricator  10  is holding the well pressure. The swab valve is shut immediately if it is evident that the lubricator will not contain the pressure; in the event leaks are discovered, the swab valve is closed again, the lubricator repaired, and swab valve reopened. 
     With the lubricator  10  under equalized pressure (the well working pressure), the operators use a control panel  110  ( FIG. 8 ) on the field vehicle  100  to regulate hydraulic pressure in the drive hoses  65 ,  70  leading from the hydraulic power take-off to the lubricator  10 . The control panel  110  seen in  FIG. 8  is exemplary only, and is configured according to principles known in the art of vehicle-mounted hydraulic equipment systems. The control panel  110  may have a prime hydraulic pump on-off switch  112 , as well as a valving switch  114  used to regulate both the speed and direction of the movement of the piston  50  within the barrel housing  32 . 
     The tool rod  34  is lowered from the lubricator  10  and through the Christmas tree toward the tubing hanger by hydraulics. Having reference to  FIGS. 4-7 , the needle valve  61  is closed. The operator, using the control panel  110 , controllably pumps fluid through the upper driving hose  70  to the upper fluid port  52  in the barrel housing  32 . The resulting fluid movement is through the upper tee  66  and transmission tube  72  to the upper port  52 . Fluid enters the head space  53  between the piston  50  and the closed upper or first end  63  of the barrel housing  32 , thus pressurizing the head space and driving the piston, and thus the tool rod  34 , downward. Valved regulation (via regulator  114 ) of the hydraulic system (according to known conventions) permits the operator to control the rate of descent of the tool rod  34 . Fluid concurrently exits the lower fluid port  56 , so that hydraulic pressure is not increased unduly in the barrel space  57  due to movement of the piston  50 . 
     The tool rod  34  is pushed down hydraulically until it stops when the BPV  37  contacts the tubing hanger. The operators preferably monitor the distance the rod  34  has travelled, to see that it travels approximately the complete stroke distance (calculated as described above) before stopping, to prevent under- or over-extension of the rod. For example, if movement of the tool rod  34  stops before it has moved the calculated approximate distance, the operators check to assure that all the valves in the well head tree are completely open to permit passage there-through of the rod and BPV  37 . In any event, care is taken to assure that the BPV  37  or other tool at the distal end of the rod  34  is not forcibly jammed into the tubing hanger by excessive hydraulic force. Attentive regulation of the hydraulic driving action on the piston  50  prevents over-extension of the rod  34 . 
     Once the BPV  37  has contacted the threaded top of the tubing hanger, the tool rod  34  is rotated (i.e., counterclockwise) according to convention to threadably engage the BPV into the tubing hanger plug. (This rotation conventionally is done manually with a Parmelee wrench gripped about the portion of the rod  34  exposed in the yoke portion  20 .) The needle valve  61  remains open during this process, so that the effort to screw the BPV  37  is not impeded by the pressure in the barrel space  57 . The pressure increase in the barrel space  57  otherwise resulting in the further downward movement of the tool rod  34  is relieved through the needle valve  61 , which (when open) permits ready pressure equalization between the barrel space  57  and the head space  53 . The number of rod rotations is counted to assure that the BPV  37  is properly and fully screwed into place. After the tool rod  34  is rotated two or three times, the operators preferably attempt manually to lift the tool rod to test whether the BPV  37  is secured to the tubing hanger. If the rod  34  is easily pulled up, the need is indicated to move it lower and re-align the BPV  37  with the tubing hanger orifice. Depending on the type of running and retrieval tool  39  being used, there are known modes for determining whether and when the BPV  37  is fully engaged into the tubing hanger. 
     Methods known in the art are then employed to disengage the running and retrieval tool  39  from the BPV  37 , leaving the latter engaged into the tubing hanger. The proper mode of disengagement depends upon the type of running and retrieval tool  39  being utilized, but is known to those skilled in the art. Whether disengagement has occurred may be tested, checking whether the rod  34  can be manually lifted slightly. 
     The tool rod  34  also may be raised hydraulically. First, the needle valve  24  and the needle valve  25  on the yoke  20  are closed. The operators then carefully open the needle valve  26  a small amount to slowly bleed off lubricator pressure. 
     The tool rod  34  is raised from within the wellhead equipment or tree by reversing the previously described hydraulic operations. The needle valve  61  is closed. The operator re-engages the hydraulic system to pressurize the barrel space  57  via fluid movement into the barrel space. Fluid transmission occurs through the first driving hose  65  to the first quick-coupling connector  60 , the lower pressure tee  59 , and on through the lower fluid port  56 . The increasing pressure in the barrel space  57  pushes against the piston  50  driving it axially upward within the barrel housing  32 , pulling the tool rod  34  upward with it. Pressure in the head space  53  is correspondingly reduced, and pressure relieved by fluid exiting outward through the upper fluid port  52  and into the transmission tube  72 . The tool rod  34  is hydraulically raised the distance required to extract the running and retrieval tool  39  an adequately from the wellhead tree. 
     After the tool rod  34  is completely raised, it may be removed. The swab valve on the tree is closed securely, and valves  26  and  27  on the lubricator manifold are carefully opened to bleed off all the pressure in the lubricator  10 . Once all the pressure is safely bled off from the lubricator  10  according to known protocols, the operators may begin to remove the bolts from the work spool on top of the tree&#39;s master valve. Using the vehicle-mounted hoist or crane  102 , the lubricator  10  and work spool are raised, and the lubricator moved carefully away from wellhead and lowered to ground level. The lubricator may then be dissembled as appropriate and stowed on the vehicle  100  for transport. The necessary equipment is installed or re-installed on the wellhead, and tested as needed. 
     The system allows a service person to set a tubing hanger with a back pressure valve under pressure, and to retrieve that same tubing hanger in a controlled environment. The system may include a service truck to be able to perform a hydro test and operate the hydraulic lubricator. A hydraulic lubricator according to this disclosure can pull up to about 7,830 pounds of upward force and push up to about 9,800 pounds of downward force. 
     It is seen, therefore, that a hydraulic lubricator is provided which eliminates the need to move the tool rod  34  up and down manually during well maintenance. While the proper seating and screwing of a BPV  37  may require manual rotation of the rod according to known procedures, the technician no longer must lift and lower the rod  34  through its full stroke by gripping the rod with a wrench, and forcing it up or down incrementally—often while in an awkward bodily position or at a potentially hazardous location many feet above the ground. Rather, the tool rod  34  is lifted and lowered within the lubricator  10  by means of hydraulic power, controlled at a control panel  110  safely and conveniently located upon the service vehicle  100 , such as a diesel engine truck. 
     Although the invention has been described in detail with particular reference to these preferred embodiments, other embodiments can achieve the same results. Variations and modifications of the present invention will be obvious to those skilled in the art and it is intended to cover all such modifications and equivalents. The entire disclosures of all applications and patents cited above are hereby incorporated by reference.