Patent Publication Number: US-6904973-B2

Title: Downhole pump

Description:
BACKGROUND 
   The present invention relates generally to a downhole pump, and in one particular embodiment, to a double stroke downhole pump. 
   Typically, downhole pumps include a hollow plunger sliding up and down within a polished barrel to lift fluids, such as oil and water, to the surface. Usually, the fluid is forced through a check valve located at the bottom end of the plunger on the downstroke of the plunger. On the upstroke, the check valve on the plunger is closed and the plunger lifts the fluid upward. At the same time, more fluid is drawn into a chamber in barrel through a check valve located in the bottom of the barrel. In this operation, the pump is required to lift both the weight of the plunger, a rod string attached to the plunger and the oil. 
   In other arrangements, shown for example in U.S. Pat. No. 5,314,025 to Priestly and U.S. Pat. No. 6,368,084 to Skillman, the check valves and plunger are arranged such that fluids are pumped on the downstroke of the plunger. However, such pumps do not pump any fluid on the upstroke and are susceptible to gas lock. Moreover, the Priestly and Skillman patents disclose that the oil is forced upwardly through the plunger on the downstroke, which can reduce the capacity of the pump. In addition, Priestly further discloses that various seals are required between the plunger and/or rod string and the pump casing. 
   BRIEF SUMMARY 
   Briefly stated, in one aspect, one embodiment of a downhole pump includes a pump barrel defining a pumping chamber having a first end and a second end, a first one-way valve positioned at the first end of the pumping chamber, a second one-way valve positioned at the second end of the pumping chamber and a plunger movable disposed in the pumping chamber. The first one-way valve is operable to permit a flow of fluid out of the first end of the pumping chamber, while the second one-way valve is operable to permit a flow of fluid out of the second end of the pumping chamber. The plunger has first and second ends facing the first and second ends of said pumping chamber respectively. The pumping chamber has an inlet adapted to be in flow communication with a production zone. The plunger is movable in the pumping chamber between at least a first position and a second position. The second end of the plunger is positioned on a first side of the inlet when the plunger is in the first position such that the inlet is in flow communication with the second end of the pumping chamber. The first end of the plunger is positioned on a second side of the inlet when the plunger is in the second position such that the inlet is in flow communication with the first end of the pumping chamber. 
   In preferred embodiment, the plunger operates only in the lower portion of the barrel. In this embodiment, the plunger pumps fluid out of the pumping chamber and into the production tube on the downstroke. 
   In another aspect, an inlet member for use in a downhole pump includes a housing having an exterior side surface, a first end, a second end, an interior pumping passageway formed therein between the first and second ends, at least one fluid passageway formed therein between the first and second ends, and at least one inlet passageway communicating between the exterior side surface of the housing and the interior pumping passageway. The at least one fluid passageway is in fluid flow isolation with the interior pumping passageway and the inlet passageway. 
   In yet another aspect, a method of pumping fluid from a production zone located beneath the surface of the earth includes positioning a plunger in a first position wherein a second end of the plunger is positioned on a first side of an inlet and allowing a first volume of fluid to flow into a pumping chamber from the inlet. The method further includes moving the plunger in a second direction and thereby forcing at least a portion of the first volume of fluid from the pumping chamber through the second one-way valve positioned at the second end of the pumping chamber. The method also includes positioning the plunger in a second position wherein the first end of the plunger is positioned on a second side of the inlet and allowing a second volume of fluid to flow into the pumping chamber from the inlet. The method further includes moving the plunger in the first direction and thereby forcing at least a portion of the second volume of fluid through the first one-way valve positioned at the first end of the pumping chamber. 
   The various aspects and embodiments provide significant advantages over other downhole pumps. For example and without limitation, the weight of the rod string and plunger are sufficient to pump the fluids during the downstroke. In addition, the downstroke flushes any sand or debris that have entered the pumping chamber of the barrel to be flushed therefrom, thereby preventing unnecessary wear on the barrel. Moreover, in one embodiment, the double-stroke pump pumps fluid on both the downstroke and upstroke, thereby increasing the capacity of the pump. In addition, the configuration of the pump avoids gas lock. Moreover, the system avoids the need for various seals between the plunger/rod string and the barrel. Finally, as production of the well decreases, the pumping mechanism at the surface can be reset so that only the lower portion of the barrel, which is the most efficient, is used. 
   The foregoing paragraphs have been provided by way of general introduction, and are not intended to limit the scope of the following claims. The presently preferred embodiments, together with further advantages, will be best understood by reference to the following detailed description taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS 
       FIG. 1  is a cross-sectional side view of a downhole pump with the plunger positioned in a first position proximate the top of the stroke. 
       FIG. 2  is a cross-sectional side view of a downhole pump during the downstroke of the plunger. 
       FIG. 3  is a cross-sectional side view of a downhole pump with the plunger positioned in a second position proximate the bottom of the stroke. 
       FIG. 4  is a cross-sectional side view of the downhole pump during the upstroke of the plunger. 
       FIG. 5  is a perspective view of an inlet member. 
       FIG. 6  is an end view of the inlet member. 
       FIG. 7  is a cross-sectional view of the inlet member taken along line  7 — 7  of FIG.  6 . 
       FIG. 8  is a cross-sectional view of an alternative embodiment of a downhole pump during the downstroke of the plunger. 
       FIG. 9  is a cross-sectional view of the downhole pump shown in  FIG. 8  with the plunger positioned near the bottom of the stroke. 
   

   DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS 
   Referring to  FIGS. 1-4 , a dowuhole pump assembly  2  is shown positioned beneath the surface  4  of the earth in communication with a production zone  6  of fluid  30 . The term “fluid” should be broadly interpreted to mean any fluid, including oil and water. The downhole pump assembly includes a production tube  8  and a pump  10  positioned within the production tube. The pump  10  includes a barrel  12  defining a pumping chamber  14  and a plunger  16  movably disposed in the pumping chamber  14 . The barrel  12  and pumping chamber  14  each have first and second ends  18 ,  20 ,  22 ,  24 , with a first one-way valve  26  connected to the first end  18  of the barrel at the first end  22  of the pumping chamber and a second one-way valve  28  connected to the second end  20  of the barrel at the second end  24  of the pumping chamber. 
   The first and second one-way valves  26 ,  28 , shown as check valves, are arranged to permit one-way flow of fluid  30  out of the first and second ends  22 ,  24  of the pumping chamber respectively. The first one-way valve  26  preferably includes a valve seat  34  and a valve member  32  moveable relative thereto. The second one-way valve  28  includes a valve seat  38  and a valve member  36  moveable relative thereto. The second one-way valve also preferably includes a spring  40  biasing the valve member  36  toward the valve seat  38  to maintain the valve in a closed position against the force of gravity. The valve member  32  of the first one-way valve  26  is generally seated on the valve seat  34  by the force of gravity, although a spring can be used to assist in the seating thereof. Although the first and second ends are shown as “upper” and “lower” ends respectively, it should be understood that they can be arranged in other configurations relative to each other and are not limited thereby. Accordingly, the terms “first” and “second” are not limited to “upper” and “lower” respectively, but can directed in other orientations. 
   The plunger  16  has first and second ends  42 ,  44  facing the first and second ends  22 ,  24  of the pumping chamber  14  respectively. A pump rod string  46  is connected to the first end  42  of the plunger. It should be understood that a portion (or entirety) of the rod string can be integrally formed with the plunger, or that plunger and rod can be made as separate parts and connected by various conventional and known devices. 
   The barrel  12  is defined in part by a first, upper barrel member  48  and a second, lower barrel member  50  connected to a first and second end  52 ,  54  of a centrally located inlet member  56 , shown in  FIGS. 5-7 . Preferably, the barrel members  48 ,  50  are threadably engaged with interior threads formed on upper and lower portions of the inner surface of an interior passageway  58  extending longitudinally through the center of the inlet member  56 . It should be understood that the barrel members  48 ,  50  can be secured to the inlet member  56  in other ways, for example and without limitation by welding, adhesives, friction or snap-fits, and various clamping devices. 
   The first and second one-way valves  26 ,  28  are preferably secured to the first and second ends  18 ,  20  of the barrel by threadable engagement, although other securing devices as just described may also be employed. A sleeve  49 , or top barrel portion, is secured to and extends upwardly from the upper end of the valve  26  or a seating nipple. It should be understood that the barrel  12  and pumping chamber  14  include and are defined at least in part by the upper and lower barrel members  48 ,  50  as well as the portion of the inlet member  56  forming the interior passageway  58  and which is connected to the upper and lower barrel members. 
   The plunger  16  slides up and down within the pumping chamber  14  and makes close contact with the interior surface of the barrel members  48 ,  50  and with the interior surface of a central annular portion  60  of the inlet member  56 , which has an inner diameter substantially the same as the inner diameter of the barrel members  48 ,  50 . A motor or other conventional drive device (not shown) well known in the art, preferably located at the surface, reciprocally moves the rod string  46  and plunger  16  in a first and second direction  64 ,  66  respectively. 
   Referring again to  FIGS. 5-7 , the inlet member  56  is preferably formed as a cylindrical member having a plurality of inlet passageways  68  formed in the central annular portion  60  that communicate between an exterior side surface  70  of the inlet member and the central, interior pumping passageway  58 , which defines in part the pumping chamber  14 . Preferably, the inlet passageways  68  extend transverse, and substantially perpendicular to, a longitudinal axis  72  of the pumping chamber, although they can be formed at any angle and with any contour. The exterior surface  70  of the annular portion of the inlet member is in fluid flow communication with the production zone  6  of the fluid  30  as shown in  FIGS. 1-4 . 
   Referring to  FIGS. 1-7 , a first, upper production tube member  74  is secured to first end  52  of the inlet member  56  and includes an interior surface  78  spaced from an exterior surface  80  of the first barrel member so as to define an annular passageway  86  therebetween. A second, lower production tube member  76  is secured to the second end  54  of the inlet member and includes an interior surface  82  spaced from the exterior surface  84  of the second barrel member so as to define an annular passageway  88  therebetween. The lower production tube member  76  has a bottom wall  77  that closes off the production tube and isolates the interior thereof to the production zone. The centrally located inlet member  56  further defines in part the production tube, and includes a plurality of fluid passageways  90  that communicate with the fluid passageways  86 ,  88  defined by the production tube  8  and barrel  12 . Preferably, the fluid passageways  90  of the inlet member  56  extend longitudinally therethrough and are isolated from fluid flow communication with the inlet passageways  68  and interior passageway  58 , which defines in part the pumping chamber  14 . In one preferred embodiment, the sum of the cross-sectional areas of the inlet passageways  68  is greater than or equal to the sum of the cross-sectional areas of the fluid passageways  90  and the cross-sectional area of the smallest diameter of the interior passageway  58 , although other configurations and ratios may be suitable. 
   Preferably, the plurality of fluid passageways  90  are positioned and spaced circumferentially around the center passageway  58  and are further successively staggered or spaced between the plurality of inlet passageways  68 , as shown in FIG.  6 . Of course, it should be understood that the inlet member  56  can be integrally formed with one or both of the barrel and production tubes  48 ,  50 ,  74 ,  76 , and that those components are formed at least in part from the inlet member. It should also be understood that the inlet member can be configured with a single inlet passageway and/or a single fluid passageway, and that the six inlet passageways and six fluid passageways are meant to be exemplary. The term “plurality” as used herein means two or more. 
   The production tube  8  has a first, upper portion  92  in flow communication with the first end  22  of the pumping chamber and which receives fluid flowing through the first one-way valve  26 . The production tube  8  also has a second, lower portion  94  in flow communication with the second end  24  of the pumping chamber and which receives fluid flowing through the second one-way valve  28 . The fluid passageway  88 ,  90 ,  86  communicates between the first and second portions  92 ,  94 . In addition, an outlet  100  communicates with the first portion  92 . The fluid  30  is recovered from the outlet  100  for storage and transportation. 
   In operation, and referring to  FIG. 1 , the downhole pump  10  is shown with the plunger  16  in an initial, first, uppermost position, with the second end  44  of the plunger  16  positioned on a first side of the inlets  68 , such that the fluid  30  from the production zone  6  flows into a lower pumping chamber  96 . In this position, the fluid is in a dynamic state. The lower pumping chamber  96  is defined between the second end  44  of the plunger and the second end  24  of the pumping chamber. Accordingly, when the plunger  16  is in this position, the inlet  68  is in fluid communication with the second end  24  of the pumping chamber and the second one-way valve  28 . In particular, the plunger  16  is positioned between the inlets  68  and the first end  22  of the pumping chamber so as to prevent fluid  30  from flowing into an upper pumping chamber  98  and to the first end  22  of the pumping chamber and the first one-way valve  26 . The upper pumping chamber  98  is defined between the first end  22  of the pumping chamber and the first end  42  of the plunger. 
   As shown in  FIG. 1 , the length of the stroke, and the position of the plunger  16  can be controlled at the surface by controlling the stroke of the rod string  46 . Therefore, first end  42  of the plunger can abut the upper end  22  of the pumping chamber, or can be spaced therebelow, when in the first position at the top of the stroke, depending on the length of the stroke. 
   Referring to  FIG. 2 , the rod string  46  and plunger  16  are moved in a downward direction  66  toward the second end  24  of the pumping chamber. As the plunger  16  moves past and closes the inlets  68 , the second end  44  thereof pushes a volume of fluid collected in the lower pumping chamber  96  through the one-way valve  28  positioned at the second end  24  of the pumping chamber. During this phase, the fluid in the production zone  6  is in a static state. In certain preferred embodiments, the weight of the rod string  46  and plunger  16  have enough potential energy when in the first position to force the fluid  30  through the one-way valve  28  into the lower portion  94  of the production tube and to thereafter displace fluid in the fluid passageway  86 ,  88 ,  90  upwardly to the upper portion  92  of the production tube and eventually out of the outlet  100 . During operation, the downstroke also pushes any sand or debris that has entered the pumping chamber  14 , and in particular the lower pumping chamber  96 , out through the second one-way valve  28 . This prevents unnecessary wear on the lower half of the barrel, which is the most efficient. 
   Referring to  FIG. 3 , the plunger  16  is shown at the bottom of the stroke, with the first end  42  of the plunger positioned on a second side of the inlets  68 . It should be understood that reference to the positioning of the plunger on a first or second side of the inlets simply means that at least a portion of the inlets  68  are in communication with the pumping chamber  14 , and that the phrase does not require that the inlets  68  be completely unobstructed by the plunger  14  or that the plunger  14  be completely on one side of the entirety of the inlet. For example, the positioning of the plunger on the second side of the inlet simply means that a least a portion of the inlets  68  has flow communication with the pumping chamber above the first end  42  of the plunger. 
   With the first end  42  of the plunger positioned on a second side of the inlets  68 , fluid  30  from the production zone  6  flows into the upper pumping chamber  98  through the inlets  68 , which are thereby in fluid communication with the first end  22  of the pumping chamber and the first one-way valve  26 . At this juncture, the fluid in the production zone is in a dynamic state. The plunger  16  is positioned between the inlets  68  and the second end  24  of the pumping chamber so as to prevent fluid from flowing to the second end of the pumping chamber and the second one-way valve  28  positioned at the second end thereof. As shown in  FIG. 3 , the second end of the plunger  44  can abut the second end  24  of the pumping chamber, or can be spaced thereabove, when in the second position at the bottom of the stroke, depending on the length of the stroke. 
   Referring to  FIG. 4 , the rod string  46  and plunger  16  are next moved in an upward direction  64  toward the first end  22  of the pumping chamber. As the plunger  16  moves past and closes the inlets  68 , such that the fluid in the production zone is in a static state, the first end  42  thereof pushes a volume of fluid collected in the upper pumping chamber  98  through the one-way valve  26  positioned at the first end  22  of the pumping chamber and into the upper portion  92  of the production tubing. The fluid discharged from the first one-way valve  26  thereafter displaces fluid in the upper portion  92  of the production tube and pushes fluid out of the outlet  100 . Typically, the fluid in the lower portion of the production tube remains in a static state during this portion of the pumping cycle. Typically, the upstroke does not have as much pumping capacity as the downstroke, since the rod  46  takes up some of the volume in the upper pumping chamber  98 . Since the downhole pump system pushes the fluid through both ends of the pumping chamber, the system avoids gas lock and the efficiency thereof is greatly improved. 
   As the plunger moves through the downstroke, as shown in  FIGS. 2 and 3 , a vacuum is created between the end  42  of the plunger and the end  18  of the barrel. As the end  42  of the plunger moves past the inlet openings  68 , the vacuum is released and the fluid fills the upper pumping chamber. This action creates a thump, or dynamic/sonic wave, that can dislodge fluids, and in particular oil, from rocks and other underground objects in the production zone. Accordingly, it provides a mechanism for further facilitating the recovery of the oil from the production zone. Likewise, as the plunger moves through the upstroke, as shown in  FIGS. 1 and 4 , a vacuum is created between the end  44  of the plunger and the end  20  of the barrel. As the end  44  of the plunger moves past the inlet openings  68 , the vacuum is released and the fluid fills the lower pumping chamber. This action creates a similar thump, or dynamic/sonic wave, as described above. 
   In one preferred embodiment, only the lower half of the pumping chamber  14 , otherwise referred to as the lower pumping chamber  96 , is used. In this embodiment, the plunger  16  never unblocks the inlets  68 , or moves to the second side thereof, on the downstroke. As such, fluid  30  is not allowed into the upper pumping chamber  98  and the motor does not have to work as hard to lift the rod string  46  and plunger  16 , since there is no fluid being carried thereby. 
   Referring to the alternative embodiment of  FIGS. 8 and 9 , the upper one-way valve is eliminated. Components similar to those of the embodiment shown in  FIGS. 1-4  are labeled with the same reference numbers. In this embodiment, the pump functions in the same way as the above-described double-stroke pump when using only the lower half thereof, i.e., when pumping fluid only on the downstroke. In this embodiment, the rod string  46  is sealed against a seating nipple  102  positioned at the top of the barrel  12 . A plunger  104  has a hollow cavity  106  formed therein, with a one-way valve  108  located at the bottom end  110  of the plunger. In one embodiment, the valve  108  has a valve member  116 , valve seat  118  and a spring  120 . A weep hole  112  communicates between the cavity  106  and the upper pumping chamber  98 . Fluid, such as oil, that accumulates above the top end  114  of the plunger drains through the weep hole  112  into the cavity  106 . The drained fluid is then drained through the one-way valve  108  into the lower portion  94  of the production tube on the upstroke of the plunger. 
   Although the present invention has been described with reference to preferred embodiments, those skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. As such, it is intended that the foregoing detailed description be regarded as illustrative rather than limiting and that it is the appended claims, including all equivalents thereof, which are intended to define the scope of the invention.