Patent Publication Number: US-9885353-B2

Title: Pressure relief mechanism for linear actuator well pump

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority to provisional application 62/021,889, filed Jul. 8, 2014. 
    
    
     FIELD OF THE DISCLOSURE 
     This disclosure relates in general to linear actuator driven reciprocating well pumps and in particular to a mechanism that relieves pressure while the piston is transitioning between completion of the up stroke and beginning of the down stroke. 
     BACKGROUND 
     A reciprocating well pump normally has a barrel secured to a string of production tubing. A piston located in the barrel strokes between a down stroke and an up stroke. A travelling valve mounted with the piston opens a bore of the piston during the down stroke to flow well fluid in the bore of the piston into the barrel above the piston. During the up stroke, the travelling valve closes to lift the well fluid from the barrel upward. A standing valve at an upper end of the barrel will be closed during the down stroke and opens on the op stroke to allow the well fluid being lifted to low up into the production tubing. 
     A string of rods may extend down the tubing for stroking the piston. Other types of stroking devices are known. For example, an electric motor may be installed below the barrel. A linear actuator coupled between the motor and the piston converts rotary motion of an output shaft of the motor into linear motion of the piston. The linear actuator may include a rotatable shaft with helical grooves engaged by a ball nut that is restrained from rotating. The rotation of the linear actuator shaft causes the ball nut to move up one set of helical grooves until reaching a crossover at the top of the linear actuator shaft, then move down a second set of helical grooves. A linking member connects the ball nut with the piston to move the piston in unison. The linear actuator shaft rotates in only one direction. 
     A dwell time occurs at or near the top of the stroke while the ball nut moves from one set of helical grooves to the other. During this dwell time, the standing valve will be open, communicating the weight of the column of well fluid in the production tubing with the well fluid in the barrel. Normally, the standing valve element is a ball that drops onto a seat due to gravity when the well fluid being pushed up by the piston stops flowing. In some instances, the well fluid pressure in the barrel is high enough to keep the standing valve element from closing, creating a stalled condition. 
     SUMMARY 
     A reciprocating well pump assembly has a barrel and a piston sub assembly reciprocally and slidably carried within the barrel between up stroke and down stroke positions. The piston sub assembly has a bore for receiving well fluid from the well during the down stroke. A travelling valve element in the piston sub assembly moves between an open position allowing the well fluid to flow up the bore into the barrel above the piston sub assembly during the down stroke to a closed position during the up stroke for lifting the well fluid located in the barrel above the piston sub assembly. A standing valve at an upper end of the barrel is movable between an open position during the up stroke of the piston sub assembly and a closed position during the down stroke of the piston sub assembly. A relief port extends from the bore of the piston sub assembly into the barrel. A relief port valve closes the relief port during the down stroke and part of the upstroke. The relief port valve opens the relief port as the piston sub assembly nears a top of the stroke to reduce fluid pressure in the barrel above the piston sub assembly and allow the standing valve to move to the closed position at the top of the stroke. 
     Preferably, the relief port extends from the bore to an annulus located between the piston sub assembly and the barrel. More specifically, the piston sub assembly has a piston that slidably engages the bore. The relief port extends from the bore to an annulus in the barrel surrounding the travelling valve element above the piston. 
     A stop is located in the barrel below the standing valve. The relief port valve engages the stop as the piston sub assembly nears the top of the stroke to cause the relief port to open. The relief port valve moves in unison with the piston sub assembly during the up stroke until reaching the stop. Continued upward movement of the piston sub assembly relative to the relief port valve after the relief port valve reaches the stop causes the relief port valve to open the relief port. Preferably, a spring urges the relief port valve toward a closed position. 
     In the embodiment shown, the relief valve comprises a valve sleeve mounted around a body of the piston sub assembly, the valve sleeve having a closed position blocking the relief port and an open position opening the relief port. The valve sleeve is in the closed position and movable in unison with the body of the piston sub assembly during the down stroke and during the up stroke until the piston sub assembly nears the top of the stroke, at which point, the body of the piston sub assembly moves upward relative to the valve sleeve, causing the valve sleeve to move to the open position. A spring urges the valve sleeve toward the closed position. 
     In the example shown, a downward facing relief valve stop shoulder is located in the barrel below the standing valve. A retainer on the body of the piston sub assembly limits upward movement of the valve sleeve relative to the body of the piston sub assembly. 
     Preferably, an electric motor having a rotatable drive shaft is coupled to a linear actuator for converting rotational motion of the drive shaft to reciprocating motion of the piston sub assembly. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the features, advantages and objects of the disclosure, as well as others which will become apparent, are attained and can be understood in more detail, more particular description of the disclosure briefly summarized above may be had by reference to the embodiment thereof which is illustrated in the appended drawings, which drawings form a part of this specification. It is to be noted, however, that the drawings illustrate only a preferred embodiment of the disclosure and is therefore not to be considered limiting of its scope as the disclosure may admit to other equally effective embodiments. 
         FIGS. 1A and 1B  comprise a side view of a pump assembly in accordance with this disclosure. 
         FIGS. 2A and 2B  comprise a sectional view of part of the pump assembly of  FIGS. 1A and 1B . 
         FIG. 3  is a sectional view of the pump of the pump assembly of  FIGS. 1A and 1B , shown during the upstroke. 
         FIG. 4  is a sectional view of the pump of  FIG. 3  near the top of the up stroke and with a sliding pressure relief valve sleeve contacting a stop. 
         FIG. 5  is a sectional view of the pump of  FIG. 3  at the top of the up stroke and illustrating the sliding pressure relief valve sleeve relieving pressure acting upward on the upper ball. 
         FIG. 6  is a sectional view of the pump of  FIG. 3  at the commencement of the down stroke. 
         FIG. 7  is a sectional view of the pump of  FIG. 3  during the down stroke. 
     
    
    
     DETAILED DESCRIPTION OF THE DISCLOSURE 
     The methods and systems of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings in which embodiments are shown. The methods and systems of the present disclosure may be in many different forms and should not be construed as limited to the illustrated embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey its scope to those skilled in the art. Like numbers refer to like elements throughout. 
     It is to be further understood that the scope of the present disclosure is not limited to the exact details of construction, operation, exact materials, or embodiments shown and described, as modifications and equivalents will be apparent to one skilled in the art. In the drawings and specification, there have been disclosed illustrative embodiments and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation. 
     Referring to  FIG. 1A , a well pump assembly  11  is illustrated suspended on a string of production tubing  13 . In this example, well pump assembly  11  includes a tubular sub  15  with inlet ports  16 . Sub  15  secures by threads to the lower end of production tubing  13 . Pump assembly  11  may be used in inclined and horizontal wells, thus the terms “upper” and “lower” are used only for convenience and not in a limiting manner. A tubular landing receptacle  17  secures to the lower end of sub  15 . 
     Referring to  FIG. 1B , landing receptacle  17  secures to the upper end of a seal or pressure equalizing section  19 . A gear reducer  21  secures to the lower end of seal section  19  in this embodiment. An electrical motor  23  secures to the lower end of gear reducer  21 . A sensing unit  25  optionally may be attached to the low end of motor  23  to provide readings of pressure, temperature, and other parameters. A power cable (not shown) will extend alongside tubing  13  from a wellhead at the top of the well to provide power to motor  23 . Seal section  19  reduces a pressure difference between dielectric lubricant in motor  23  and the hydrostatic pressure of the well fluid. 
     Referring to  FIG. 2A , pump  27  has a barrel  29 , a travelling valve  31 , a standing valve  33 , and a piston  34 , all of which are shown schematically. Standing valve  33  secures to the upper end of barrel  29 , and travelling valve  31  and piston  34  are part of a piston sub assembly that move axially within barrel  29  between an up stroke and a down stroke. Piston  34  slides sealingly on the inner diameter of barrel  29  to push fluid upward during an upstroke. An intake  35  located in barrel  29  below piston  34  admits well fluid through travelling valve  31  into barrel  29 . During the down stroke, the well fluid flows through travelling valve  31  as travelling valve  31  moves downward. During the down stroke, standing valve  33  is closed, preventing well fluid in production tubing  13  from flowing downward past standing valve  33 . During the up stroke, travelling valve  31  closes, causing the upward movement of piston  34  to push the well fluid above piston  34  upward through standing valve  33 , thereby lifting the column of well fluid in production tubing  13  an increment. At the top of the stroke, standing valve  33  closes. 
     In this embodiment, a landing collar  37  on the upper end of pump  27  fictionally engages the interior of production tubing  13  to resist movement of pump  27  once installed within tubing  13 . A reciprocating rod  39  strokes piston  34 . Referring to  FIG. 2B , in this example, a reversing linear actuator  41  reciprocates rod  39 . Linear actuator  41  is a ball screw mechanism that is engaged on its lower end by a rotating drive shaft  43 , which is rotated by motor  23 . Linear actuator  41  transforms the rotating movement of drive shaft  43  into reciprocating movement of rod  39 . Drive shaft  43  has a set of helical grooves on which a ball element, which is restrained from rotation, moves linearly. The ball element is linked to reciprocating rod  39  that connects with piston  34 . Other mechanisms to stroke pump  27  are feasible. 
     In this example, motor  23 , gear reducer  21 , and seal section  19  are secured to landing receptacle  17 , which in turn is secured to production tubing  13 ; thus these components are installed when production tubing  13  is run. Pump  27 , linear actuator  41 , and drive shaft  43 , are run through production tubing  13  after production tubing  13  has been installed. A stabbing guide  45  on the lower end of drive shaft  43  stabs into the drive shaft of motor  23  within landing receptacle  17 . 
     Referring to  FIG. 3 , which is a more detailed view of pump  27 , standing valve  33  has a standing valve cage or housing  47  with an axial flow passage  49  extending through it. A valve element, which is normally a ball  51 , is carried within an enlarged lower portion of flow passage  49 . Ball  51  is axially movable between a downward facing shoulder  52  in flow passage  49  and a seat  53 . When ball  51  is located on seat  53 , it blocks downward flow of well fluid in flow passage  49 . However, ball  51  does not block upward flowing well fluid while it is in the upper position shown in  FIG. 3  in contact with shoulder  52 . Standing valve housing  47  secures by threads to a connector  55 , which secures to barrel  29 . Standing valve housing  47  and connector  55  may be considered to be a part of barrel  29 . 
     Travelling valve  31  has a tubular body  57  with an axial bore  59 . A valve element, typically a ball  61 , locates within an enlarged lower portion of bore  59 . Ball  61  moves between a lower position on a seat  63  and an upper position in contact with a downward facing shoulder  64  in bore  59 . While in the lower position shown in  FIG. 3 , ball  61  blocks downward flow of well fluid through bore  59 . While in the upper position, ball  61  will not block upward flowing in bore  59 . Travelling valve body  57  has a relief port  65  extending radially from bore  59  to the exterior of body  57 . Travelling valve body  57  secures by threads to the upper end of piston  34 , which slides within barrel  29 , forming a sealing engagement. Bore  59  also extends through piston  34 . Travelling valve  31  and piston  34  form a piston sub assembly. 
     A valve sleeve  67  fits closely around travel bag valve body  57 . Valve sleeve  67  may have seals  69  to seal the inner diameter of valve sleeve  67  to the outer diameter of travelling valve body  57 . Valve sleeve  67  has a relief port  71  extending from its inner diameter to its outer diameter. Valve sleeve  67  is axially movable on travelling valve body  57 . When valve sleeve relief port  71  is misaligned with body relief port  65 , as shown in  FIG. 3 , valve sleeve  67  blocks any flow through body relief port  65 . When aligned, as shown in  FIG. 5 , flow through body relief port  65  and valve sleeve relief port  71  occurs. 
     A valve sleeve annulus  73  is defined between the outer diameter of valve sleeve  67  and the inner diameter of barrel  29 . Valve sleeve  67  has an external flange or rim  74  on its upper end that slidingly engages the inner diameter of barrel  29 , but it does not seal annulus  73 . Travelling valve body  57  has an external lip  75  on its upper end that extends radially outward over an inner portion of valve sleeve rim  74 , limiting any further upward movement of valve sleeve  67  on body  57 . 
     Connector  55  has a downward facing shoulder or stop  77  within barrel  29 . The inner diameter of stop  77  is greater than the outer diameter of travelling valve body lip  75 . As travelling valve body  57  and valve sleeve  67  move upward in unison, lip  75  will move into the inner diameter of stop  77  past stop  77 , but valve sleeve rim  74  will abut stop  77 . Travelling valve body  57  continues to move upward at that point while valve sleeve  67  remains stationary. A spring  79  at the lower end of valve sleeve  67  urges valve sleeve  67  toward the upper position with rim  74  bearing against lip  75 . Spring  79  is illustrated as a coil spring having a lower end on an upward facing shoulder of piston  34 . 
     In operation, motor  23  rotates stab  45 , which in turn causes linear actuator  43  ( FIG. 2B ) to rotate. The rotation of linear actuator shaft  43  causes the linear actuator ball nut to move reciprocating rod  39  upward. Daring this upstroke movement of  FIG. 3 , travelling valve ball  61  is in the closed position and standing valve ball  51  in the open position. Upward movement of piston  34  pushes well fluid located above piston  34  past standing valve ball  51  into passage  49 , lifting the column of well fluid in production tubing  13 . Valve sleeve  67  will be moving in unison with travelling valve body  57  at this point. Relief ports  65 ,  71  are misaligned, blocking any fluid communication between annulus  73  and bore  59 . At this point, the pressure in annulus  73  is substantially the same as in standing valve flow passage  49 , which is higher than the pressure in travelling valve bore  59  below seat  63 . That lower pressure below seat  63  would be approximately the hydrostatic well fluid pressure at pump intake  35  ( FIG. 2A ), which may be referred to as a bottom hole pressure. 
     Referring to  FIG. 4 , valve sleeve rim  74  contacts stop  77  as travelling valve  31  approaches the top of the stroke. Travelling valve body  57  continues upward movement, as illustrated in  FIG. 5 , while valve sleeve  67  remains stationary. At or near the top of the stroke, shown in  FIG. 5 , travelling valve body relief ports  65  align with valve sleeve relief ports  71 . The alignment establishes fluid communication between annulus  73  and travelling valve body bore  59  below seat  63 . The higher pressure well fluid in barrel  29  between standing valve ball  51  and piston  34  flows from annulus  73  through relief ports  65 ,  71  into bore  59 , thus reducing the higher pressure in barrel  29  that might otherwise tend to keep standing valve ball  51  above its seat  53 . Standing valve ball  51  is thus free to drop by gravity onto seat  53 , which blocks downward flow of well fluid in flow passage  49 . A dwell exists while piston  34  changes from upward movement to downward movements, and during the dwell, the alignment of relief ports  65 ,  71  prevents standing valve ball  51  from stalling in the upper unseated position. 
       FIG. 6  illustrates a post dwell position, with piston  34  moving downward relative to valve sleeve  67  as a result of the ball nut of linear actuator  41  ( FIG. 2B ) beginning to move downward on the linear actuator shaft. Spring  79  initially keeps valve sleeve rim  74  in abutment with stop  77 . Relief ports  65 ,  71  again become misaligned, blocking any further fluid communication between annulus  73  and bore  59 . As piston  34  moves downward, well fluid flows into the lower end of bore  59  and past travelling valve ball  61 , which is now open. Well fluid within bore  59  and above piston  34  will be at the lower bottom hole pressure. The pressure on the upper side of closed standing valve ball  51  will be equal to hydrostatic pressure of the column of well fluid in production tubing  13 , much higher than the bottom hole pressure. 
     The down stroke continues, as shown in  FIG. 7 , causing lip  75  to engage valve sleeve rim  74 , which disengages from stop  77 . Valve sleeve  67  then moves downward in unison with travelling valve body  57 . At the bottom of the stroke, which is not shown, travelling valve ball  61  closes. Then upward movement of piston  34  causes well fluid to open standing valve ball  51 , as shown in  FIG. 3 . 
     While the disclosure has been described in only a few of its forms, it should be apparent to those skilled in the art that various changes may be made. For example, the standing and travelling valves may have a variety of configurations.