Abstract:
A piston and seals for a reciprocating pump improve pumping of subterranean fluids containing fine solids to surface. The pump comprises a pump barrel and piston. The piston is suspended from a reciprocating rod string or from reciprocating production tubing. The barrel is held stationary relative to the casing of a well. A standing valve is located at the bottom of the barrel. The piston and travelling valve are located at the bottom of the piston rod for minimizing the dead-space between standing and travelling valves. Upper and lower stacks of hydraulic piston seal rings are positioned on the piston above and below the travelling valve for minimizing piston height. Each seal has radially flared lips at its leading edge. The piston has spaced grooves formed therein, corresponding to the seal ring flared lips. At least the lower seal stack is axially movable so that the flared lips alternate between being compressed against the piston during the pumping stroke and being engaged with their respective grooves on the return stroke thereby relaxing the lips, reducing seal wear and releasing pressure trapped between the upper and lower seals. A barrel wiper at the lower seal ensures sand is excluded from the lower seal. Large bore flow passages are provided in the piston rod and valves.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation-in-part of U.S. patent application Ser. No. 09/045,049 on Mar. 20, 1998 now U.S. Pat. No. 6,099,274 and U.S. Provisional application Ser. No. 60/041,028, filed Mar. 21, 1997. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to oil wells which produce a large fraction of sand and reciprocating pistons, seals and pumps capable of pumping such sand and oil on a continuous basis. 
     BACKGROUND OF THE INVENTION 
     In Southern Alberta, Canada, heavy oil is sometimes recovered from unconsolidated sandstone formations using a technique called cold production. The operator of the well aggressively perforates the well and purposefully produces formation sand along with the heavy oil. This technique pulls sand from the formation, increasing oil mobility and formation permeability for improving the flow of viscous oil to the well. Typically sand production is high upon well completion and for a period thereafter. Often a sump is used, located below the perforations for collecting the first inrush of sand. Conventional pumps such as progressive cavity pumps (PCP) or reciprocating rod pumps can be used with sand concentration less that about 20%. PCP&#39;s are more tolerant of sand than are reciprocating pumps. However, excessive sand concentrations still persist in some wells. The sump and well can sand-in and sand slugs can pump umps and halt production until an expensive and time-consuming workover clears the sand. Usually, by that time PCP failure has occurred. If a low cost reciprocating pump jack or rotary top drive is used to operate the pump, an expensive service rig must be called in to pull the pump or flush the PCP. Even more costly is to maintain a service rig at the well. 
     For removing excessive sand and for emptying a sump, prior art techniques include using a reciprocating barrel pump with a lower, sand-collecting tailpiece. This process is termed “bailing”. The pump is located above the tailpiece. The pump draws solids and liquid into the tailpiece. Solids settle and liquid continues upwardly to spill back into the annular space between the pump barrel and the wellbore. Solids collect until the tailpiece is full and it is pulled out of the well. 
     In U.S. Pat. No. 4,711,299 to Caldwell, a reciprocating barrel pump is applied to a well with solids, and more specifically a well having undesirable liquids which need to be pumped out of the well. The pump barrel is suspended from a tubing string. An upper check valve is fitted at the top of the barrel. A stationary piston having a hollow piston rod hangs from and below the barrel. A tailpiece is once again provided which hangs from the piston rod. A lower check valve is fitted at the bottom of the piston rod, adjacent or within the tailpiece. When the barrel reciprocates, sand and liquid is drawn into the tailpiece. The entrance to the piston rod is purposefully narrow to cause high velocity liquid flow. Solids are not intended to pass above the lower check valve. In some implementations a screen rejects solids. Liquid continues up through the piston rod and out of the well as required. 
     Bailers do not pump sand to the surface and must be pulled from the well to remove sand and return the conventional pump to the well. 
     Others, such as Site Oil Tools and Arrow Oil Tools have converted conventional bailers to systems which pump sand and liquid to the surface by the addition of an anchor. Conversion from liquid only bailer to pumps handling sand as well introduces several operational difficulties. The travelling valve is located at the top of the piston rod which means they can be in the order of 12 feet from the standing valve. Suction created by these arrangements is poor, resulting in loss of pumping. The small bore through the piston rod causes high pressures in the barrel when the piston and piston rod stroke downwardly. At these pressures, sand separates from the oil and pack up in the barrel, and also form wads or balls of sand which can bridge the production tubing or block elbows and valves at the surface. Further, the sand causes significant wear on the moving components of the pump. 
     Typically, bailers and bailer conversions use “V”-cup packing, such as that use in wellhead rod seals). The packing-type seals are virtually incapable of sustained use when exposed to sand. 
     Production pumps, which utilize reciprocating rods, seriously impede the flow path to the surface particularly when the rods alternately move contrary to the desired flow of sand-laden oil, cause fall out of sand, and suffer delayed rod fall. Further, the rod pumps and known reciprocating pumps generally use pistons having elastomeric seals snugly supported in individual piston grooves, subject to being rendered ineffective with sand. As shown in a prior art pump in FIG. 1, the piston can be 2-4 feet long, the travelling valve and standing valves are widely spaced and no means are provided for excluding sand. 
     Sands from the above-described wells are very fine and tend to pack up in the individual piston grooves and render the seals ineffectual. The sand may be likened to a lapping compound, causing high wear and ultimately resulting in barrel failure. 
     The problems of sanding in heavy oil wells is discussed in a 1995 paper presented at a Heavy Oil Symposium in Calgary, Alberta, “Practical Requirements for Sand Production Implementation in Heavy Oil Applications”, by Dusseault, M. B. et al., publication SPE 30259. The authors identify quick removal of bailers and the resulting suction as one of the causes of re-sanding. The authors further suggest improvements such as washing techniques, jet pump to surface techniques, and slow withdrawal of bailers with fluid replacement. 
     In this paper, the aforementioned authors acknowledge the superiority of PCP over reciprocation pumps, yet describe PCP failures and reiterate the need for effective sand removal and sand-tolerant pumps. 
     There is thus an expressed need for a pump which replaces the known bailer or bailer conversions, rod pumps and progressive cavity pumps for pumping liquids to the surface from wells having liquids associated with fine solids, particularly cold production heavy oil wells. 
     SUMMARY OF THE INVENTION 
     A sand-tolerant seal assembly is provided for use with a piston and barrel pump arrangement. In contradistinction with the known art of providing one of more continuous-sealing seal rings in individual grooves, applicant provides a stack of one or more seal rings having leading edge flares which are fitted to the piston and which move between a pair of retaining rings. The rings are fitted to a cylindrical portion of the piston which is periodically formed with grooves, the groove matching in number and profile of the seal ring flares. Between the retaining rings, the stack has a finite axial movement between positive and weakly sealing positions. Upon a pumping stroke, the stack of rings move, compressing the flares on the piston&#39;s cylindrical portion. On a return stroke, the stack of rings move, allowing the flares to engage the groove, decompressing the flares. 
     Decompression for 50% of the stroke reduces seal wear and can release trapped pressure between opposing seal assemblies on a double acting piston. More preferably the released pressure is directed from the stack of ring seals, through ports, and into bore of the piston. 
     When applied to downhole pumps, a reciprocating pump is provided for production (used with a rod string) or for pumping to surface (reciprocating tubing). The double acting piston of a downhole pump is fitted with both upper and lower seal assemblies. A bore wiper is provided for excluding sand from the lower seal area. Preferably the travelling valve forms part of the piston with upper and lower seals positioned at either end. The positioning of the seals aids in reducing the dead-space and minimizing piston length. 
     The downhole pump comprises a pump barrel which located and is held stationary in the casing of cold production wells, a piston, (piston rod for pump to surface arrangements) and standing and travelling valves. The pump is capable not only of bailing but is also used in the steady-state production of oil to the surface. For a production pump, this dual role is achieved through a combination of: 
     providing large bore flow passages in the piston rod and valves and thus minimizing the separation of sand from oil and packing of sand at obstructions. This is preferably achieved by using a high strength material for the piston rod so that the wall thickness can be minimized and the bore diameter maximized; 
     minimizing of the dead-space between standing and travelling valves for improving pump efficiency and minimizing gas-locking by locating the travelling valve at the base of the piston rod and intermediate the upper and lower seals; and 
     a sand-tolerant seal assembly as described above. 
     In the case of reciprocating tubing string pumps, one also provides a complementary piston rod and pump barrel for enabling rotary actuation of the anchor, preferably either using a non-circular high strength piston rod and complementary barrel bushing or using a tang and recess, dog clutch like-arrangement. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 a  is cross-sectional view of a prior art reciprocating pump completing a downstroke; 
     FIG. 1 b  is cross-sectional view of the prior art pump of FIG. 1 a  completing an upstroke; 
     FIG. 2 a  is cross-sectional view of a well completed into a sand and oil producing formation having a reciprocating pump to surface pump of the present invention installed therein. The pump is completing an upstroke; 
     FIG. 2 b  is cross-sectional view of the well and pump to surface pump of FIG. 2 a  wherein the pump is on a downstroke; 
     FIG. 3 is a chart of the relative production of sand and fluid from a cold production heavy oil well such as that shown in FIG. 2 a;    
     FIGS. 4 a  and  4   b  are cross-sectional views of the first embodiment of the pump to surface pump depicting the positioning of the travelling and standing valves and the polygonal piston rod and complementary bushing, depicting the pump near the bottom of the downstroke and near the top of the upstroke respectively; 
     FIG. 5 is a cross-sectional view of the polygonal piston rod at line V—V of FIG. 4 a;    
     FIG. 6 is cross-sectional view of one of a plurality of hydraulic seal rings used in the pump to surface pump; 
     FIG. 7 a  is a simplified diagrammatic representation of a cross-section of the lower piston seal which demonstrates the pump&#39;s downstroke and the positive sealing achieved by the seal rings against both the piston and the barrel; 
     FIG. 7 b  is a simplified diagrammatic representation of the cross-section of the lower piston seal according to FIG. 7 a  which demonstrates the pump&#39;s upstroke wherein the seal rings shift axially until the seal rings inner lip engages the sleeve groove, weakening the seal against the piston and thereby avoiding a pressure trap between the upper and lower seals; 
     FIG. 8 a  is a cross-sectional view of a preferred embodiment of the pump corresponding to FIG. 7 a;    
     FIG. 8 b  is a cross-sectional view of a preferred embodiment of the pump corresponding to FIG. 8 b;    
     FIG. 9 is a cross-sectional view of the pump showing the piston near the bottom of its downstroke for illustrating the travelling valve, the standing valve and the piston; 
     FIG. 10 a  is an exploded side view of the piston, depicting the seals, retaining rings, riders and wipers; 
     FIG. 10 b  is an exploded cross-sectional view of the piston, depicting the seals, retaining rings, riders and wipers; 
     FIG. 10 c  is an exploded side view of the lower end of the piston, depicting the seals, retaining rings, and an optional large leading wiper; 
     FIGS. 11 a  and  11   b  are cross-sectional views of the second embodiment of the pump to surface pump illustrating the tension anchor-actuating dog clutch, disengaged and engaged respectively; 
     FIG. 12 is a chart depicting a comparison of the performance of a prior art converted bailer pump and a pump provided in accordance with the first embodiment and applied in Example I; and 
     FIGS. 13 a  and  13   b  are schematic views of the operation of a pump to surface pump and a production rod pump respectively. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Having reference to FIGS. 2 a  and  2   b , a well  1  is completed into an unconsolidated sandstone formation  2  bearing heavy oil. The well is over-drilled to form a cellar or sump  3 . The well is cased  4  and perforated  5 . A novel reciprocating pump  6  is installed. In FIG. 2 a  the pump shows an upstroke for pumping to surface and drawing sand and oil into the pump. In FIG. 2 b  the pump is shown at the bottom of the downstroke for cycling just prior to lifting the next charge of sand and oil. 
     When operated, as shown in FIG. 3, the pump is expected to initially produce a significant amount of sand (dotted line) at a high sand ratios of about 15 to 40% sand-to-oil. This can also occur after a workover. Over several weeks of steady state operation, the sand ratio typically drops to about 10%. The gross fluid production (solid line) initially rises as the sand ratio drops and then slowly diminishes. 
     The pump  6  (FIGS. 2 a , 2   b ) comprises a barrel  7 , a piston  8  and a piston rod  9 . The piston rod  9  is suspended in the well  1  from production tubing  10 . A tension anchor  11  is affixed to the bottom of the barrel  7  for securing the barrel to the casing  4 . Additional tubing or a tailpiece  12  extends downwards from the pump barrel  7  and into sump  3 , below the perforations  5 . The tailpiece  12  extends the pump&#39;s suction from the barrel  7 , through the anchor  11  and down to the bottom of the tailpiece  12 . 
     Surface equipment  13  causes the production tubing  10  to reciprocate or stroke up and down. A wellhead  14  contains packing for sealing the well  1  to the reciprocating tubing  10 . The pump  6  pumps fluid and sand from the sump  3 , up the production tubing  10  to the surface, through a hose  15  and into a tank  16 . 
     The pump barrel  7  is stationary, as affixed to the casing  4  by tension anchor  11 . The piston rod  9  is axially movable within the barrel  7 . The piston  8  is located at the bottom of the piston rod  9 . A one way ball or travelling valve  20  is also located at the bottom of the piston rod  9 . A one way ball or standing valve  21  is located at the bottom of the barrel  7 . In the barrel  7 , between the standing valve  21  and the travelling valve  20  is formed a fluid chamber  7   b . Both valves  20 , 21  utilize Titanium 2¼″ balls and oversized 2⅛″ seats modified from 2″ stock valves available from Harbison-Fischer Canada Ltd, Calgary, Alberta, Canada. 
     Having reference to FIGS. 6-10 b , the longevity of the pump operation is enhanced significantly by a novel piston and sealing arrangement. As shown in FIG. 9, the piston  8  is an assembly comprising the travelling valve  20 , an upper cylindrical end or seal sleeve  22  and a lower cylindrical end or seal sleeve  23 . The sleeves  22 , 23  are substantially identical. An annulus  24  is formed between each sleeve  22 , 23  and the barrel  7 . Seals are mounted on the sleeves  22 , 23 , an upper seal  25  and a lower seal  26  respectively. Each seal  25 , 26  comprises a plurality of seal rings  27  which are installed as stacks  28  on the sleeves  22 , 23 . The sleeves  22 , 23  have a base  29  and a tip  30 . The base  29  of each sleeve  22 , 23  is connected to the respective top and bottom of the travelling valve  20 . Retainers  31   b ,  31  are secured to each sleeve&#39;s tip  30  to secure the stacks  28  on their respective sleeves  22 , 23 . Each seal ring  27  is a hydraulic seal such as those available as “Polypak” (trademark) model # 461525003250-375 from Parker Seal Group of Lexington, Ky., USA. 
     Each seal ring  27  has a leading face  32  (FIG. 6) which is oriented to maintain a pressure differential in one direction. The leading face  32  of each seal ring  27  in the upper seal  25  faces the surface and is effective to create suction in the barrel  7  as the piston rod  9  and piston  8  stroke upwardly. The leading face  32  of each seal ring  27  in the lower seal  26  faces the standing valve  21  and is effective to hold pressure in the barrel  7  as the piston rod  9  falls and forces fluid from the barrel into piston rod  9  and the production tubing  10 . 
     Each seal ring  27  and stack  28  is located in the annulus  24 . The cross-section of the seal ring  27  is substantially rectangular. As shown in FIG. 6, the leading face  32  is radially flared, having an inner radially-extending lip  33  for engaging the piston  8  and an outer radially-extending lip  34  for engaging the barrel  7 . The annulus  24  at the sleeves  22 , 23  is sized for the width of the seal ring&#39;s rectangular cross-section. Accordingly, the flared lips  33 , 34  are normally compressed into a width of the rectangle cross-section for creating an effective seal against both the piston  8  and the barrel  7  (this lip compression is conceptually depicted as small arcuate marks in each seal ring  27  on FIGS. 7 a  and  7   b .) 
     The hydraulic seal ring  27  depicted in FIG. 6 has an additional O-ring  35  located midpoint of the ring&#39;s cross-section and along the leading edge  32 . The additional radial area formed by the O-ring cavity aids in hydraulically driving the lips radially into stronger engagement with their respective sealing surfaces. Not all seal ring manufacturers utilize the additional O-ring concept but most provide the inward and outward lips  33 , 34 . 
     Having reference to FIGS. 8 a , 8   b , 9  and FIGS. 10 a - 10   c , listed consecutively from the base  29  to the tip  30  of the lower sleeve  23  are: a first retaining ring  40 , the seal stack  28 , a second retaining ring  41 , a rider ring  42 , and a wiper ring  43 . The seal stack  28  is sandwiched between the retaining rings  40 , 41 . Correspondingly, listed from base to tip, the upper sleeve  22  (FIG. 9) has a first retaining ring  40 , the seal stack  28 , and a second retaining ring  41 . The seal stack  28  is sandwiched between the retaining rings  40 , 41 . 
     The first retainer rings  40  are formed of brass and the second retaining rings  41  are formed of steel. The retainer rings  40 , 41  are spaced from the barrel  7  so as to avoid contact with the barrel  7 . The lower seal  26  is subjected to more sand and accordingly includes both a rider ring  42  formed of Teflon and, more importantly, the wiper  43 , formed of Teflon or cast iron. Wiper  43  is a split spring ring with an uncompressed diameter greater than the bore of the barrel  7  which is compressed to fit in the barrel  7 . 
     Optionally, as shown in FIG. 10 c , the wiper  43  and rider ring  42  can be combined  42 , 43  (shown in cross-section) wherein a leading portion of the ring extends axially beyond the retainer  31  to be the first contact with the barrel to piston interface. 
     Each sleeve  22 , 23  is formed with circumferential grooves  44 . The grooves  44  are spaced axially, the spacing being about the axial height of each seal ring  27 . The profile of the grooves  44  is complementary to the inner lip  33  of the seal ring  27 , i.e. triangular. The retainer rings  40 , 41  are spaced an axial distance equal to the seal stack  28  plus the height of one groove  44  and thus form a gap  45 . Accordingly, the seal stack  28  will be axially movable on their respective sleeves  22 , 23  between two positions, delimited by the base retaining rings  40  and the tip retaining ring  41 . 
     When each seal ring  27  moves axially on the sleeve  22 , 23 , the inner lip  33  is compressed against the cylindrical portion of the sleeve proper (i.e. not adjacent a groove, in FIGS. 7 a  and  8   a ) and is decompressed as the inner lip  33  projects into a groove  44  (FIGS. 7 b  and  8   b ). Decompression of the lip  33  interferes with the normally good seal and enables release of pressure past the seal ring  27 . 
     As the seal stack  28  moves between retaining rings  40 , 41 , the inner lips  33  of each of the rings  27  simultaneously engage the grooves  44  (FIGS. 7 b , 8   b ) or alternately, all the inner lips  33  are compressed against the sleeve  22 , 23  proper (FIGS. 7 a , 8   a ). More particularly, the grooves  44  are axially offset towards the tip  30  of each sleeve  22 , 23  so that when the seal stack  28  is biased towards the base retaining ring  40 , the flared portion  33 , 34  of the seal rings  27  engage the cylindrical portion of the sleeve  22 , 23  and form an effective seal. Correspondingly, when the seal stack  28  is biased towards the tip&#39;s retaining ring  41 , the inner lip  33  engages the groove  44 , lessening the sealing action of the seal rings  27 . 
     In summary, seals  25 , 26  are provided at the leading and trailing end of the piston  8  to keep sand out of the metal-to-metal piston/barrel portions. The upper and lower seals  25 , 26  cooperate to alternately seal on their respective strokes while the opposing seal releases pressure build up between the seals. Additionally, leading the lower seal  26  is the wiper  43  for excluding the largest part of the sand fines from the piston area. 
     The steel retaining ring  41  of the lower seal  26  is formed with channels  46  to direct release pressure from the piston  8  and conduct it through ports  47  into the barrel  7  area. Optionally, the ports  47  can connect directly to the seal stack. During the downstroke, the ports  47  also assist in pressurizing the leading edge of stack of seal rings and driving them into the sealing position. 
     Having reference to FIGS. 9-10 b , the steel retaining ring  41  of the upper seal  25  is held in place with a retainer  31   b , threaded onto the piston rod  9 . The retainer  31   b  is axially elongate to limit the upward stroke of the piston  8 . This limit ensures the upper seal does not engage vent holes (not shown) usually located at the top of the barrel  7 . Set screws  49  lock the retainer  31   b  to the piston rod  9 . 
     The ports  47  are depicted as straight through to the bore of the piston rod  9 . Optionally, by axially staggering the ports  47  through the piston  8  from the sleeve  23  through the retainer  31 , the pressure release path is forced through one or more threads. Accordingly, should sand be present, it is unable to flow into the lower seal  28 . 
     In a first embodiment and having reference to a diagrammatic illustration of the pump in FIGS. 4 a , 4   b , the piston rod  9  has a polygonal cross-section and has a longitudinally extending bore  50 . The bore  50  has substantially the same internal diameter as that of the production tubing  10 . A bushing  51 , having a polygonal cross-section complementary to the piston rod  9 , is affixed to the top of the barrel  7 . The bushing  51  permits reciprocating action of the piston rod  9  but prevents relative rotation of the piston rod  9  and barrel  7 . Rotation of the tubing  10  at the surface causes rotation of the piston rod  9 . The rod  9  rotates the bushing  51  and barrel  7  for rotational activation of the tension anchor  11 . Counter-clockwise tubing rotation can be used to set the anchor  11  and clockwise rotation to unset it. 
     The piston rod  9  must be sufficiently strong in tension to withstand the cyclic pumping loads and sufficiently strong in torsion to set and unset the tension anchor. 
     In conventional bailers, a polygonal piston rod is also known however, as described above, the materials of construction are ordinary and the longitudinal bore is small in cross-section, which results in sand drop out, packing of sand in the barrel and troublesome sand wads which bridge flow passages. 
     In the novel piston rod  9 , the outer and internal diameters are maximized so as to minimally restrict the flow of sand-laden oil. To achieve this end, several obstacles had to be overcome. A large dimension polygonal piston rod  9  had to be prepared which has a minimal wall thickness. For 2⅞″ production tubing having an internal diameter of 2.441″, a piston rod can be provided having dimensions of 3″ across the flats of a hexagonal rod, with an internal diameter of 2½. This rod fits within a 3¾ ID barrel as is commercially obtained from Quinn&#39;s Oilfield Supply Ltd., of Red Deer, Alberta. 
     The materials of construction of the polygonal piston rod are improved to 4140 heat treated and stress relieved steel bar stock. The 12 foot long bar stock must be bored with sufficient accuracy to minimize runout and avoid weakening of the rod. Preferably, trepanning is practiced for forming the bore, preferably in combination with careful quality control to ensure the rod&#39;s wall thickness does not become too thin locally. 
     The piston  8 , is located at the bottom of the piston rod  9 . Piston seals  25 , 26  extend across the annulus  24  to seal against the inside of the barrel  7 . The piston  8  comprises a cylinder within which is located the travelling valve  20 , sandwiched between upper and lower seals  25 ,  26 . By positioning of the travelling valve  20  between the upper and lower seals, the minimum dead-space is achieved therebetween. The greater the dead-space, the less effective is the pumping suction capability and the greater is the opportunity for gas-locking. 
     In operation, when the piston  8  falls, the standing valve  21  closes and fluid and sand, in the fluid chamber  7   b , flow through the travelling valve  20  and into the piston rod  9 . When the piston  8  rises, the travelling valve  20  closes and the fluid and sand contained therein is lifted on its incremental lift to the surface. Also, as the piston  8  rises, more fluid and sand is drawn past the standing valve  21  and into the barrel  7  and fluid chamber  7   b , for the next pumping cycle. 
     In summary, the novel pump  6  maximizes flow therethrough and thus retains the sand in a suspended state. Flow maximization is achieved in part by standing and travelling valves which have a minimum dead-space between them at the bottom of the piston rod&#39;s downstroke, and a high strength piston rod formed with minimum wall thickness and having an internal diameter substantially that of the production tubing diameter. 
     In a second embodiment (FIGS. 11 a , 11   b ), the polygonal piston rod  9  and bushing  52  is replaced with a dog clutch. Without the need for a polygonal exterior, the piston rod  9  is simply formed from a length of production tubing  10  (i.e. standard 2⅞″ tubing having a 2.441″ bore), modified to accept the piston  8 . Without the polygonal rod and bushing, a rotational lock or dog clutch is provided. 
     Referring to FIGS. 11 a , 11   b , the clutch comprises an upper clutch half  60 , and a lower clutch half  61 . The clutch halves  60 ,  61  are formed of cylindrical sleeves which reside within the annulus  24  formed between the piston rod  9  and the barrel  7 . The clutch halves  60 , 61  meet axially and incorporate complementary axially extending and mating tangs  62  and recesses  63 . More particularly, the lower clutch half  61  is integrated with the top of the piston, between the piston  8  and the piston rod  9  and comprises a cylindrical sleeve which extends axially and partly up the lower part of the outside of the piston rod  9 . The lower clutch half  61  has an outer diameter smaller than the bore of the barrel  7 . Two diametrically opposed tangs  62  extend axially upwardly from the lower clutch half  61 . 
     The upper clutch half  60  is also located inside the barrel  7  and is integrated into the top of the barrel  7 . The upper clutch half  60  comprises a sleeve extending axially and partly down from the top of the barrel  7 . The inside diameter of the upper clutch half  60  is larger than the piston rod  9 . Two diametrically opposed axially-upwardly extending recesses  63  are formed in the upper clutch half  60 . The recesses  63  and tangs  62  are complementary and suited for axial mating or engagement. Accordingly, when the piston rod  9  is lifted, the tangs  62  of the lower clutch half  61  rise to the top of the pump barrel  7  and engage the recesses  63  of the upper clutch half  62 . Once the engaged, rotation of the production tubing  10  at the surface causes the barrel  7  to rotate also, operating the tension anchor  11 . 
     Having reference to FIG. 13 a  and FIG. 13 b  it is apparent that the operation of a pump to surface tool (FIG. 13 a ) requires anchoring of the barrel in the well and operation of a sucker rod pump (or often times called a production pump) does not. As shown in FIG. 13 a , the barrel of a pump to surface pump is anchored in the well and fluids flow prom the piston, up the piston rod and up the reciprocating tubing string. In a rod pump, per FIG. 13 b , the barrel is held by a stationary tubing string. A reciprocating string of rods stroke the piston and fluids flow up from the piston and up the tubing string. Accordingly, a production pump need not incorporate an anchor. 
     EXAMPLE I 
     Having reference to FIG. 12 a well in Southern Alberta was run first with a competitor&#39;s commercial pump (a bailer conversion) and secondly with a pump constructed in accordance with the invention. The well was perforated at about 773 m. 
     As shown at A, the competitor&#39;s pump was run for only 30 hours before it sanded off. In other words, it was not removing the sand which was flowing into the well. As service rig was called in to change pumps. Upon post-operation inspection, the competitor&#39;s pump barrel and seals exhibited extreme damage. 
     The novel pump, according to the first embodiment, was installed. The pump was fitted to string of 3½″ tubing having a 3″ inside diameter. Five lengths or about 45 m of 3½″ tailpipe were installed. A flapper valve was used at the bottom of the tailpipe. The piston rod was reciprocated with 3 m stroke at about 1½ to 2 strokes per minute. 
     As shown at B, initial oil and sand production was about 14.5 m3/d at 70% sand. The fraction of sand dropped steadily over the next 21 days to stabilize at about 17%. Correspondingly, the oil production (less sand) rose to about 82%. Over this 21 day period, about 470 m3 of oil were produced for an average of 22 m3/d. A failure of the tension anchor interrupted production. Subsequently, a further 17 days of operation were achieved (not shown), some of which were achieved with a 1¼″ piece of shale wedged in the travelling valve with continued marginal production at 14 m3/d. 
     The pump was disassembled and inspected after the run. As stated, a 1¼ piece of shale was found wedged in the travelling valve. The barrel and piston were inspected. There were no signs of wear or seal damage from the sand. 
     EXAMPLE II 
     Two heavy oil wells, Wa and Wb were completed in Western Canada. The wells had a high gas-oil-ratio (GOR). Pumps were landed at about 800 m. Casing pressures were 713 psi and 382 respectively. Tubing pressures were 220 psi and 200 psi respectively. Well Wa had perforations at about 910 meters with a 20 degree deviation and crude gravity around 16 API. The second well Wb was a vertical well with perforations at a depth of about 880 meters, also at 16 API. 
     The wells were plagued with periodic sand slugs along with a combination of free water slugs. The operator could not keep well Wa pumping for more than a few days and the second well Wb for more than two weeks. Numerous bailing jobs and pump to surface jobs were performed to try and clean the sand from the wells. A progressive cavity pump was tried with no success. 
     An embodiment of the present invention was applied in a production pump implementation to attempt to achieve more than a few days of trouble free operation. A piston and seal assembly was provided according to FIG.  10 . 
     First, well Wa was bailed, a pump to surface job was done to remove excess accumulated sand, and the well was put on production with a pump fitted with a short 24″ tall piston and seals of the present invention. A 3¾″ outside diameter by 3¼ inside diameter pump was provided, having with a 90″ stroke at 3.5 strokes per minute—driven via a rod string suspended from an hydraulic pump jack. Well Wb was simply bailed and the novel pump was run with an 86″ stroke and at 3 spm. 
     The low friction performance of the seals and large bore through the piston virtually eliminated rod fall problems. At the time of writing, the wells were still running continuously and trouble free after 54 days, and production was increased to as much as 40 m3 per day on well Wa and to 44 m3 per day on well Wb. 
     Before implementing a pump utilizing the present invention, a considerable amount of money was spent on flushing, bailing, pump to surface, and pump changes to no avail. After running the novel pump the operator has had no workover costs and production has increased. The average combined oil production on these two wells was about 50 m3/day. At about 80 USD per m3, the revenue was about 4,000 USD per day or 120,000 USD per month. This revenue figure does not include the savings obtained due to the elimination of several pump changes and flushing.