Abstract:
A stuffing box lubrication system for oilfield pumping units automatically delivers to the stuffing box, at specified time intervals, a precise volume of lubricant. The stuffing box lubrication system has a grease reservoir, a pump, a controller, a high pressure hose and grease fitting, and a stuffing box which receives the grease. In situations where the stuffing box in use is not equipped with a ported inlet for receiving the grease, the present invention may further include a stuffing box adapter, having a ported inlet, where the stuffing box adapter couples with the stuffing box.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a non-provisional application which claims priority to provisional patent application No. 61/892,337 filed on Oct. 17, 2013. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention generally relates to artificial lift systems which are utilized for production of fluids from subsurface reservoirs, including oil, water, and liquid phase hydrocarbons. More particularly, the present invention is utilized with artificial lift systems where a subsurface pump is actuated by a plurality of rods connected end-to-end, herein collectively referred to as a “rod string.” The rod string is set within a plurality of tubing joints likewise connected end-to-end, wherein the tubing joints are collectively referred to as a “tubing string.” Actuation of the subsurface pump lifts the fluid upwardly from the subsurface pump to the surface, where the fluids flow in the annular space between the rod string and the inside diameter of the tubing string as the fluid flows upwardly. 
     There are generally three different types of subsurface pumps which can be actuated by rod strings, two which are positive displacement pumps, and the third is a roto-dynamic pump. The first type of subsurface pump is a plunger/barrel pump, wherein the reciprocal motion of the rod string reciprocates the plunger within the pump barrel, such that liquids are drawn into the pump barrel and lifted upwardly through the tubing string. The reciprocating motion of the rod string is typically imparted by a pump jack. The second type is a progressive cavity pump, wherein the rotational motion of the rod string operates a rotor which turns within a stator, and fluid is transferred by means of the progress through the pump of a sequence of small fixed shape cavities as the rotor is turned. In these systems, the rod string is rotated by a motor/gear reducer combination installed at the surface. The third type of pump, the roto-dynamic pump, is a centrifugal pump in which the rod string rotates a series of impellers. This type of system utilizes a similar motor/gear reducer combination as utilized for the progressive cavity system. 
     For all of these systems, the uppermost rod in the rod string is a polish rod. The polished rod reciprocates in and out of, or rotates within, a stuffing box. The stuffing box is a close-fit assembly which cleans the polished rod, prevents debris from entering or exiting the well, and further prevents fluid from leaking from the well during operation. The stuffing box is typically mounted above a T-fitting at the top of the tubing. The stuffing box provides a dynamic seal along the length the polish rod. The stuffing box typically has a central passage through which the polish rod moves, while stuffing or packing material is compressed by an enclosing cap or fitting of the stuffing box which urges the packing material against the sides of the polish rod to create fluid seal. The packing materials are typically elastomers and other materials which are softer than the polish rod material. 
     The movement of the polish rod within the packing material generates friction, and thus heat, which breaks down and degrades the packing materials. This process reduces the integrity of the seal formed between the packing material and the polish rod. In further aggravation, the presence of solids in the produced fluid, such as sand, can accelerate this degrading of the packing material as well as adversely impact the life of the polish rod. The loss of the integrity of the seal between the polish rod and the packing material will result in the escape of fluids from the well which can result in environmental damage and the loss of valuable resources, and can result in significant clean-up expense and potential fines and penalties. Accelerated packing replacement also requires the expenditure of man-hours which might otherwise be avoided. 
     The lubrication of the polish rod and the packing material reduces the friction, and thus the heat, generated between the polish rod and packing material. This lubrication reduces the wear caused by movement of the polish rod within the packing material and extends the life of the packing and the polish rod. The typical lubricant used for this service is grease, which is typically placed in the interior of the stuffing box and carried by the polish rod into contact with the packing material. There are various proprietary lubricating greases which work particularly well for this service, where the greases may have enhanced mechanical and thermal stability, resistance to water, and corrosion resistance additives. Application of the lubricant is typically done by hand or by mechanically operated systems which continually apply a small dose of grease according to the motion of the walking beam of the pump jack, which may be connected with linkage or cable to a mechanical pump which strokes with the motion of the walking beam. While preferable to no lubrication at all, the manual lubrication requires the use of personnel, and can be overlooked and inconsistently applied. The mechanically operated systems are subject to failures in mechanical linkages, often have limited grease reservoirs, and may not deliver a consistent volume of grease into the stuffing box. 
     SUMMARY OF THE INVENTION 
     The presently disclosed invention is an automated stuffing box lubrication system for oilfield pumping units. The invention provides a precise volume of lubricant to the stuffing box at specified time intervals as selected by the operator. The system comprises a large capacity grease reservoir which supplies grease to the stuffing box by a pump which is activated by a controller. The controller can be programmed to provide a precise volume of grease on a periodic basis. The grease is injected into the stuffing box through a high pressure hose and grease fitting. The controller, pump, pump motor, and grease reservoir may be contained within an enclosure cabinet, with the power supply and other electrical components contained within a segregated internal enclosure. The controller has user friendly controls for modifying the lubrication volume and intervals. The controller may be connected into a field wide supervisory control and data acquisition system so that status of the unit may be monitored. The grease reservoir may be equipped with level controls which annunciate a low level alarm when the reservoir is getting low. Power to the unit may be provided by solar panel or by low voltage (110 volt) alternative current sources. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a pump jack and an optional placement for embodiments of the pump and reservoir enclosure of the present invention. 
         FIG. 2  shows a close up view of stuffing box for a reciprocating rod string which has an injection fitting and line utilized in embodiments of the present invention. 
         FIG. 3  shows an embodiment of the pump, reservoir, and enclosed power supply components which may be used in the present invention. 
         FIG. 4  shows a close up view of an embodiment of a grease reservoir, pump and controller which may be utilized in embodiments of the present invention. 
         FIG. 5  shows a close-up view of the grease outlet of an embodiment of the present invention. 
         FIG. 6  shows a close-up view of a power supply which may be utilized with embodiments of the present invention, which has an input voltage of 110 VAC and a 12 VDC output voltage for powering the pump and controls for embodiments of the present invention. 
         FIG. 7  shows a wiring diagram from an embodiment of the present invention. 
         FIG. 8  shows an exterior operating switch on the enclosure of an embodiment of the present invention. 
         FIG. 9  shows an embodiment of a stuffing box adapter, in an open position, which allows use of the present system with alternative types of stuffing boxes which may be utilized on a well. 
         FIG. 10  shows the stuffing box adapter depicted in  FIG. 9  in the closed position. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Referring now to the figures,  FIG. 1  shows a known pumping unit  10  which is utilized to impart a reciprocating motion to a rod string. However, as discussed above, embodiments of the invention may also be utilized with pumping systems which utilize rotating rod strings, such as progressive cavity pumps and roto-dynamic pumps. As indicated in  FIG. 1 , various components of the lubrication system are contained within a weatherproof enclosure  20  which is located at close proximity to the pumping unit  10 . 
     As shown in  FIG. 2 , the rod string terminates at the surface with a polish rod  12 . Polish rod  12  reciprocates or rotates within stuffing box  14  which contains seal packing elements from maintaining a pressure seal around the polish rod  12 . In the present invention, a grease fitting  16  provides access into a cavity containing the packing elements inside the stuffing box  14 . A high pressure hose  18  conveys grease from the grease reservoir of the present invention through grease fitting  16  into the stuffing box  14  through ported inlet  17 . Stuffing box  14  comprises a cap  19  which seals the stuffing box  14  around the polish rod  12 . 
     The inventors herein have found that a HERCULES brand stuffing box with a ported inlet works well for this application, but other stuffing boxes may be utilized and the system may be adapted to work with different brands and types of stuffing box. As described in greater detail below,  FIGS. 9-10  depict a stuffing box adapter  114  which provides for connection of high pressure grease hose to the adapter, which is mounted adjacent to a stuffing box  14 ′ which is not equipped with a ported inlet. Stuffing box adapter  114  allows a relatively easy solution to allow use of the present system with surface pumping equipment which is not otherwise compatible with the system. 
     As shown in  FIG. 3 , enclosure  20  may contain the reservoir  22 , controller  24  and power supply  32 , which in  FIG. 3 , is contained within an internal enclosure  36 . An alternating current source, such as junction box  28  shown in  FIG. 1 , may provide alternating current to the present invention.  FIG. 3  shows a possible configuration of the reservoir  22 , controller  24 , grease discharge manifold  40  and inside enclosure  36 , which may utilized to contain power supply  32 . 
     Reservoir  22  and controller  24  may come as an integrated unit such as the BRAVO pump packaged as manufactured by DROPSA or the G3 ELECTRIC LUBRICATION PUMP manufactured by GRACO. These units are not otherwise known to be used for lubrication of oilfield pumping unit stuffing boxes. The reservoir  22  may have a variable capacity ranging from approximately 70 ounces to 540 ounces of grease. Controller  24  may be programmed to dispense practically any volume of grease over a particular time frame, with a typical application ranging from 0.5 to 2.0 ounces of grease per day. The larger reservoir and relatively small volumes of injected grease thus have the capability of providing an extended grease supply before the reservoir requires refilling. The grease utilized with the device may be a variety of different greases and containing various additives, such as corrosion inhibitor. A grease manufactured by CHEMTOOL INCORPORATED known as ALPHA 2000, has been found to provide good service for this application. Controller  24  allows the lubrication cycle to be set up on a daily basis or other periodic basis, with a timer typically controlling the grease injection events. The actual pump time for the grease injection is usually quite brief, with a small volume of grease injected in each cycle. The controller  24  can provide a readout of the grease injection cycles over a particular period of time. The controller  24  can be connected to a field wide network, such as a supervisory control and data acquisition system (SCADA) system for providing reports of the amount grease injected over a period of time. The system may also provide an alarm upon the detection of critical operating conditions, such as when the grease level is low or when the grease injection system is not operating. 
     An integrated reservoir  22 —controller  24  is shown in  FIG. 4 . Controller  24  comprises a user interface, a pump and a motor. As shown in the Figure, the controller  24  has a user interface having a digital display  26  which is controlled by key programmable controls  28 . Controller  24  may be equipped with a data management system allows a user to download, via a USB port, performance history for the lubrication system, such as cycle detection and run times, so the effectiveness of the lubrication system may be monitored. 
       FIG. 5  shows a close up view of the grease discharge manifold  40  of the device. The discharge manifold has a delivery conduit  42  which delivers grease to the high pressure hose  18  shown in  FIG. 2 . The grease discharge manifold  40  may comprise a grease bypass valve  44 . In the event the discharge pressure reaches a pre-set maximum, bypass valve  44  recirculates the grease back to the integrated reservoir  22 —controller  24  through bypass line  46  to protect the stuffing box from being over pressured. Typical operating discharge pressures may be 500 psi, with a bypass valve set to open at a preset pressure, such as 1500 psi. 
       FIG. 6  shows an acceptable power supply  32  for providing power to the controller  24  and its pump and motor.  FIG. 7  shows a simple schematic for power supply  32 , showing the alternative current line in, the power supply connect to the grease pump  50 , which will typically run on relatively low direct current voltage, and the connection to various alarms. These alarms may indicate when the grease level is low or show a malfunction in system, such as the operation of grease bypass valve  44  because of a high pressure situation. The circuit includes annunciator light  30  which shows when the controller  24  is in operation. 
     As indicated in  FIGS. 1 and 3 , power supply  32  may be stored within its own enclosure  36  to separate it from the grease reservoir  22  and controller  24 . The device may be operated by a manual override control switch  38  which may be located on the exterior of enclosure  20  for easy access by maintenance personnel. Annunciator light  30  may also be located on the exterior of enclosure  20 . 
       FIGS. 9-10  depict a stuffing box adapter  114  which provides for connection of high pressure grease hose to the adapter, which is mounted adjacent to a stuffing box  14 ′ which is not equipped with a ported inlet. Stuffing box adapter  114  may contain packing elements  116  which seal around the polish rod  12 . Similar to the installation utilized with stuffing box  14 , stuffing box adapter  114  will have high pressure hose  18  which conveys grease from the grease reservoir of the present invention through a grease fitting inserted in a ported inlet  117 . Grease will then be carried into the stuffing box  14 ′ by the reciprocation of the polish rod. 
     While the above is a description of various embodiments of the present invention, further modifications may be employed without departing from the spirit and scope of the present invention. Thus the scope of the invention should not be limited according to these factors, but according to the following appended claims.