Patent Publication Number: US-11655695-B2

Title: Rodless pump and multi-sealing hydraulic sub artificial lift system

Description:
BACKGROUND 
     Many oil wells are produced using rod pumps.  FIG.  1    depicts a rod pump artificial lift system, and  FIG.  2    depicts the pump action of positive displacement rod pumps. The rod pump artificial lift system includes a surface unit  1000  that drives a rod string  1001 , located inside the well&#39;s production tubing  1002 , up and down to actuate a positive displacement pump  1003 . Positive displacement pump  1003  may include both a traveling valve  2000  and a standing valve  2001 . The production tubing may be run inside production casing  1006  or in an open hole, uncased well. 
     Traveling valves are one-way check valves that move position as the valve opens and closes. Standing valves are one-way check valves that are stationary as the valve opens and closes. All existing rod pumps must have the traveling valve  2000  above the standing valve  2001  due to the need to match the traveling valve&#39;s positions with the up and down movement of the rod string  1001 . The inability to have a standing valve above the traveling valve, due to the rod string being in the way, can allow solids in the well&#39;s production tubing to be pulled by gravity down into the plunger/barrel seal, fouling the pump. On the upstroke  2100  the traveling valve is seated, lifting fluid to surface and the standing valve is open, allowing the well&#39;s produced fluid to enter the pump&#39;s production chamber  2003 . On the downstroke  2200 , the standing valve closes, while the traveling valve is open, filling the pump plunger  2004  with the fluid previously sucked into the pump&#39;s production chamber. 
     Rod pumps work satisfactorily in some vertical well applications. Less hole deviation correlates with lower levels of rod wear from friction caused by the rods rubbing against the production tubing strings. However, no well is perfectly vertical due to drilling error and rock variations, meaning that operating costs still can be lowered with a pump that is unaffected by rod wear. In a rod pump well, the well&#39;s tubing pressure is contained at surface by a stuffing box seal above the wellhead  1005 , and if this seal is worn or broken, oil can leak and contaminate the well&#39;s surrounding environment. 
     Horizontal or deviated wells have additional challenges relative to vertical or slightly deviated wells: high gas to oil ratios, surging and slug flow with multiple fluid phases, and long sideways drilling paths (step outs) above the kick off point  1004  have made rod pumps ineffective and unsuitable for these applications. The kickoff point  1004  is the point at which the well starts to turns horizontal. The portion of the well where it turns horizontal is referred to as the curve of the well  1007 .  FIG.  3    depicts a rod pump artificial lift setup and the pump traversing the curve of the well. Traditional rod pumps are not suitable to traverse through the curve of a well.  FIG.  3 A  depicts a close-up view of the continuous bend put on the rods  1001 , causing them to contact the tubing  1002  with a side force that damages both the rods and the tubing. The added costs from intermittently repairing these damages may mean that rod pumps cannot be cost effectively operated in a desirable location below the kick off point. It may be desirable to operate the pump lower in the well because the fluid above the pump can be pumped to surface. A lower pump setting depth reduces the hydrostatic pressure on the reservoir, lowers the intake pressure at the pump, and allows more hydrocarbons to be produced from the well. 
     Hydraulically powered, positive displacement pumps are an alternative to rod pumps. However, due to a number of disadvantages of existing designs, they rarely are the best solution for artificial lift and represent a small proportion of the artificial lift market share. Hydraulic pumping systems transmit power downhole by using power fluid pressurized at surface to drive a reciprocating piston pump located downhole disposed near the bottom of production tubing string. Hydraulic pumps of prior design returned the power fluid to surface mixed with the well&#39;s produced fluids (oil, gas, water). Separation of the power fluid and produced fluids is necessary for reuse of the power fluid and sale of the produced hydrocarbon fluids. 
       FIG.  4    depicts the surface apparatus of a conventional hydraulic pump setup. Hydraulic pump systems of prior design consisted of a reservoir vessel  4000  containing the cleaned power fluid  4001 , a surface pump to pressurize the power fluid  4002  and pump it down the wellhead  4003 , production tubing  4003 A to transmit the power fluid to actuate the downhole hydraulic reciprocating piston pump, and a surface separation system  4004  designed to receive the commingled return mixture  4005  of reservoir fluids and power fluid and separate the mixture into individual flow streams of power fluid and produced fluid  4006  and gas  4007 . Solids are commonly removed from the power fluid stream via a cyclonic separator  4008 , filter, or similar apparatus before returning the cleaned power fluid  4001  to the reservoir vessel  4000 . The produced fluids may further be separated out into oil  4009 , gas  4011 , and water  4010  streams via another separator. 
       FIG.  5    shows the downstroke and  FIG.  6    shows the upstroke of a double acting hydraulic pump of common use. After the power fluid is pumped down the tubing, the power fluid  5000  enters the pump&#39;s power fluid intake. The power fluid drives an engine piston  5001  from either side of the piston. The power fluid is then expelled from the pump via the engine piston power fluid exhaust port  5002  for return to surface. The engine piston is connected to a pump piston  5003  that interacts with the produced fluid from the well  5004 . The produced fluids are expelled from the produced fluids pump exhaust  5005  for return to the surface. The engine piston may only interact with the power fluid, and the production piston may only interact with produced fluids. The power fluids and production fluids are mixed after being expelled from the pump and flow up a common conduit to surface; the mixed fluid at surface must then be separated in order to recycle the power fluid and send the produced fluids to production facilities using a process similar to  FIG.  4   . In the double acting design, there are a number of small and intricate power fluid flow paths necessary to cycle the piston between the up and down strokes when pumping power fluid unidirectionally into a single-entry point into the pump. These intricate power fluid flow paths limit the stroke length of the pump due to design difficulty, expense, and flow friction associated with long, narrow power fluid flow paths. Simplification of the flow paths of the power fluid and produced fluid is highly desirable to extend pump life, reduce cost, and increase efficiency of pumping operations. 
     In existing hydraulic pump designs, there are no sealing elements directly between the power fluid chambers and the interior surface of the production tubing or interior surfaces of any subassemblies disposed on the production tubing. There is also no set of independent hydraulic connections to drive an upstroke and downstroke. The power fluid enters the pump in a singular direction, ratchets the pump piston between upstroke and downstroke, is contained within the pump as it actuates the pistons to do work, is expelled from the pump, and returns to surface commingled with the production fluid. The lack of multiple, independent power fluid chambers and the associated power fluid chamber seals is a defining feature of existing hydraulic pump design and greatly limits their use. 
     Hydraulically driven piston pumps of prior design may preferably be set near the bottom of a production tubing string in an oil and gas well.  FIG.  7    illustrates an example of a retrievable hydraulic pump setup. Power fluid  7000  is pressurized at surface and pumped down the production tubing  7001  until it reaches the pump  7002 . Hydraulic pump  7002  corresponds to the external visualization of a hydraulic pump similar in nature to the one outlined in  FIG.  5    and  FIG.  6   . The power fluid enters the pump and mixes with produced fluid  7003 , exits the pump as commingled fluid  7004  and flows up the annulus between the tubing and the casing  7005 . The power fluid flows through the pump via a top intake connected to the production tubing. There are no seals directly between the exterior of the pump and the interior of the tubing that allow power fluid to be pumped directly or independently into the piston&#39;s engine chambers. The power fluid must flow down the production tubing to enter the pump. The power fluid then exits the pump and is commingled with the produced fluids. The power fluid also flows unidirectionally. There are a number of arrangements in which the power fluid flows in a singular direction down a conduit and then actuates a hydraulic piston pump. 
     U.S. Pat. No. 4,861,239 mentions a dual power tube configuration for the resetting of a power piston that is driving a production piston with power piston and production piston connected by a solid rod, where one piston that only interacts with power fluid is connected to another piston that only interacts with produced fluid. This functional setup is a less efficient version of the analogous and commonly used hydraulic pump described in  FIGS.  5  and  7   . Similarly, U.S. Pre-Grant Publication 2005/0249613 describes a black box type hydraulic pump that utilizes multiple power fluid lines to actuate a downhole piston. The multiple power tube pump described in U.S. Pat. No. 4,861,239 (FIG. 17) has no fewer than 18 check valves, while the black box pump described in US2005/0249613 (FIG. 1) has 6 check valves. As a result, these prior art systems are ineffective at pumping, extremely complicated, and prohibitively costly to install, maintain, and service; these factors likely explain why pumps according to these designs are not in widespread commercial use today. 
     SUMMARY 
     Both of the above-mentioned prior art publications lack (1) a landing receptacle for the downhole pumps along with any description of mating seal arrangement between the interior of the landing receptacle for the pumps and the exterior of the pumps to couple a first hydraulic line to a first working chamber and a second hydraulic line to a second working chamber, respectively (2) two working pistons, not necessarily of the same diameter, connected via a connecting rod that seals on the exterior of the rod to provide pressure isolation between two, independent working fluid chambers with hydraulic connections to the upstroke and downstroke lines located on either side of the seal, and (3) a flow path comprising one or more check valves wherein an inner through-bore, hydraulically connected to a traveling valve and standing valve through the pumps&#39; pistons, actuated by fluid pressure changes that cause reciprocation, permitting wellbore fluid to be pumped to the surface. The combination of these features in the rodless pump disclosed herein may allow the ability to run concentric power fluid strings and the production tubing string sequentially. This design can simplify pump installation and allow for the retrieval and servicing of the rodless pump disclosed herein without the added cost and expense of retrieving three or more concentric strings of tubing. The rodless pump disclosed herein may be removed via slickline or by removing only a single tubing string depending on configuration. Even when the power fluid strings are run non-concentrically and exterior to the production tubing, the prior art designs do not allow removal of the pumps from the well independently from the power fluid strings. The rodless pump described herein may have only two valves: a traveling valve and a standing valve. This can allow for efficient actuation of a simple positive displacement pump and a minimal number of failure points. 
     The rodless pump described herein can include a connecting rod with an exterior seal or seals that allow for differently sized piston areas (and associated working chambers of different diameters) to be exposed to the power fluid in the upstroke and downstroke chamber, respectively. This configuration can reduce the power at surface necessary to actuate the pump by allowing differences between the pump&#39;s intake pressure (the well&#39;s bottom hole pressure) and output pressure (the well&#39;s production tubing pressure) of the produced fluids to be balanced out by the differently sized areas exposed to the power fluid, minimizing the force necessary to reciprocate the working pistons. 
     A downhole hydraulic pump can include a first working piston having a first surface in contact with a power fluid and a second surface in contact with a wellbore fluid, a second working piston having a first surface in contact with a power fluid and a second surface in contact with a wellbore fluid, and a connecting rod coupling the first working piston to the second piston. A first working chamber may be defined at least in part by the first surface of the first working piston, and a second working chamber may be defined at least in part by the first surface of the second working piston. The downhole hydraulic pump may further include a seal arrangement respectively coupling a first hydraulic line to the first working chamber and a second hydraulic line to the second working chamber, wherein pressure applied via at least one of the first hydraulic line and the second hydraulic line causes reciprocation of the working pistons. The downhole hydraulic pump can further include a flow path comprising one or more check valves, wherein the one or more check valves may be actuated by fluid pressure changes caused by reciprocation of the working pistons, thereby permitting wellbore fluid to be pumped to the surface. The flow path may be disposed within the connecting rod. 
     Pressure may be alternately applied via the first hydraulic line and the second hydraulic line to cause reciprocation of the working pistons. The seal arrangement may be a hydraulic sub. The first working chamber and second chamber may be pressure isolated from one another by seals disposed about the connecting rod. The downhole hydraulic pump may further include an external structure allowing surface equipment to latch onto and retrieve the pump without removing a production fluid string or the first and second hydraulic lines from a well. The external structure may be a fishing neck. The pump may be mechanically affixed to the production tubing such that retrieving the pump requires removing at least a portion of a production fluid string from a well. Retrieving the pump may further require removing at least a portion of one or both of the first and second hydraulic lines from the well. 
     The first and second hydraulic lines may be independent from an annulus of the wellbore. The first hydraulic line, second hydraulic line, and the production tubing may be non-coaxial. At least one of the first and second hydraulic lines may be concentric with and exterior to a production string. Both the first and second hydraulic lines may be concentric with and exterior to the production string. One of the first or second hydraulic lines may be defined at least in part by a casing of the well. The first hydraulic line, second hydraulic line, and the production tubing may be non-coaxial. At least one of the first and second hydraulic lines may be concentric with and exterior to a production string. Both the first and second hydraulic lines may be concentric with and exterior to the production string. 
     A method of pumping fluid from a wellbore can include delivering working fluid to a first working chamber of a downhole hydraulic pump. The first working chamber may be defined at least in part by a first working piston. Delivering working fluid to the first working chamber may actuate a piston assembly of the pump comprising the first working piston in a first direction. The method can further include delivering working fluid to a second working chamber of the downhole hydraulic pump. The second working chamber may be defined at least in part by a second working piston. Delivering working fluid to the second working chamber may actuate the piston assembly of the pump, which further includes the second working piston, in a second direction opposite the first direction. The piston assembly may further include a connecting rod coupling the first working piston and the second working piston. Reciprocation of the piston assembly may one or more check valves, thereby permitting wellbore fluid to be pumped to the surface. Wellbore fluid may be pumped to the surface through a flow path disposed within the connecting rod. The method can further include alternately delivering working fluid to the first working chamber and delivering working fluid to the second working chamber via a first hydraulic line and a second hydraulic line. The first working chamber and second working chamber may be pressure isolated from one another by seals disposed about the connecting rod. 
     A downhole hydraulic pump can include a piston assembly having first and second pistons coupled by a connecting rod. The first piston may at least partially define a first working chamber, and the second piston may at least partially define a second working chamber. The downhole hydraulic pump can further include means for causing reciprocal action of the piston assembly by alternating application of hydraulic fluid pressure from the surface to the first and second working chambers. The downhole hydraulic pump may still further include a production fluid flow path that passes through the piston assembly and further includes at least one check valve actuatable by wellbore fluid pressure changes induced by reciprocation of the piston assembly. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    depicts a rod pump artificial lift system. 
         FIG.  2    depicts the pump action of positive displacement rod pumps. 
         FIGS.  3  and  3 A  depict a rod pump artificial lift setup and a pump traversing the curve of the well. 
         FIG.  4    depicts the surface apparatus of a conventional hydraulic pump setup. 
         FIG.  5    shows the downstroke of a double acting hydraulic pump. 
         FIG.  6    shows the upstroke of a double acting hydraulic pump. 
         FIG.  7    illustrates an exemplary retrievable hydraulic pump setup. 
         FIGS.  8  and  8 A- 8 D  depict a high level view of the surface and downhole apparatus for a rodless pump system. 
         FIGS.  9 A- 9 C  show fluid conduit paths for open annulus setups without a packer. 
         FIGS.  10 A- 10 C  show fluid conduit paths for closed annulus setups. 
         FIG.  11    shows the relationship between power fluid flow rate in the upstroke working chamber  11000 , power fluid flow rate in the downstroke working chamber  11001 , and surface pump pressure  11002  over time for an exemplary pump operation. 
         FIGS.  12 DS and  12 US  illustrate a “rig-less” rodless pump in the downstroke and upstroke positions, respectively 
         FIG.  12 HS  depicts a hydraulic sub receptacle for an open annulus system without a rodless pump landed in it. 
         FIG.  12    illustrates a rodless pump landed inside an open annulus hydraulic sub disposed on the end of production tubing, with production fluids filling the outer annulus inside the production casing. 
         FIGS.  12 A- 12 D  depict the fluid flow through rig-less rodless pump landed in an open annulus hydraulic sub with independent power fluid strings. 
         FIG.  13 HS  depicts a hydraulic sub receptacle for a closed annulus, rig-less rodless pump artificial lift system run above a packer to isolate the downhole fluids below. 
         FIG.  13    illustrates a rodless pump landed inside a closed annulus hydraulic sub disposed on the end of the power fluid string, with the outer annulus serving as a downstroke power fluid conduit hydraulically contained by the production casing. 
         FIGS.  13 A- 13 D  depict the fluid flow through a rodless pump landed in a closed annulus hydraulic sub with concentric power fluid strings. 
         FIGS.  14 DS and  14 US  illustrate a rodless pump that is threaded directly on the bottom of the production tubing in the downstroke and upstroke positions, respectively 
         FIG.  14 HS  illustrates a hydraulic sub receptacle for a tubing retrievable pump run in an open annulus system. 
         FIG.  14    illustrates a tubing retrievable rodless pump landed inside an open annulus hydraulic sub. 
         FIGS.  14 A- 14 D  depict the fluid flow through a rodless pump landed in an open annulus hydraulic sub. 
         FIG.  15 HS  depicts a hydraulic sub receptacle for a tubing retrievable pump run in a closed annulus system run above a packer to isolate the downhole fluids below. 
         FIG.  15    illustrates a tubing retrievable rodless pump landed inside a closed annulus hydraulic sub. 
         FIGS.  15 A- 15 D  depict the fluid flow through a rodless pump landed in a closed annulus hydraulic sub. 
         FIGS.  16 A-F  illustrate a simplified visualization of a full cycle of a rodless pump with an open annulus hydraulic sub. 
         FIGS.  17 A-F  illustrate a simplified visualization of a full cycle of a rodless pump with a closed annulus hydraulic sub. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, for purposes of explanation, numerous specific details are set forth to provide a thorough understanding of the disclosed concepts. As part of this description, some of this disclosure&#39;s drawings represent structures and devices in block diagram form for sake of simplicity. In the interest of clarity, not all features of an actual implementation are described in this disclosure. Moreover, the language used in this disclosure has been selected for readability and instructional purposes, has not been selected to delineate or circumscribe the disclosed subject matter. Rather the appended claims are intended for such purpose. 
     Various embodiments of the disclosed concepts are illustrated by way of example and not by way of limitation in the accompanying drawings in which like references indicate similar elements. For simplicity and clarity of illustration, where appropriate, reference numerals have been repeated among the different figures to indicate corresponding or analogous elements. In addition, numerous specific details are set forth in order to provide a thorough understanding of the implementations described herein. In other instances, methods, procedures and components have not been described in detail so as not to obscure the related relevant function being described. References to “an,” “one,” or “another” embodiment in this disclosure are not necessarily to the same or different embodiment, and they mean at least one. A given figure may be used to illustrate the features of more than one embodiment, or more than one species of the disclosure, and not all elements in the figure may be required for a given embodiment or species. A reference number, when provided in a given drawing, refers to the same element throughout the several drawings, though it may not be repeated in every drawing. The drawings are not to scale unless otherwise indicated, and the proportions of certain parts may be exaggerated to better illustrate details and features of the present disclosure. 
     A rodless pump may be a downhole, hydraulic, positive displacement pump that uses multiple power fluid strings run exterior to the production tubing. The production tubing may be an innermost tubing string that transports saleable hydrocarbons to surface. In hydraulic pumps of prior design, the production fluid string was sometimes used as a power fluid flow conduit. Conversely, in at least some embodiments of a rodless pump, the power fluid can actuate the rodless pump system via a separate hydraulic sub that can include a seal arrangement to hydraulically couple a first hydraulic line to the first working chamber (the upstroke chamber) and a second hydraulic line to hydraulically couple to a second working chamber (the downstroke chamber), wherein pressure applied via at least one of the first hydraulic line and the second hydraulic line causes reciprocation of the working pistons. The upstroke chamber may be defined at least in part by the first surface in contact with a power fluid of a first working piston. The downstroke chamber may be defined at least in part by the first surface in contact with a power fluid of a second working piston. The hydraulic sub&#39;s seal arrangement may be disposed near the bottom of the production tubing and may allow for transfer of power fluids from conduits external to the pump directly into the pump&#39;s upstroke and downstroke power fluid chambers for pump actuation. 
     The hydraulic sub may serve as a sealing receptacle for the exterior of the pump. Additionally, a retrievable pump may land in the hydraulic sub and seal to isolate the multiple power fluid strings from production fluids. In some embodiments of the hydraulic sub, pump seals disposed against the rodless pump power fluid chambers, bidirectional flow capabilities of the power fluid conduits, and independently sealed power fluid chambers may allow rig-less retrieval of the pump and conservation of power fluids, reducing well production costs. 
     In at least some embodiments, the rodless pump may be different from existing positive displacement pumps at least in part because its hydraulic drive forces come from the opposite side of a piston exposed to production fluid. These hydraulic drive forces may result from changing pressure applied to the more than one exposed piston areas, causing the pump to change position. This drive mechanism can allow the option of placing the traveling valve below the standing valve, which may, in turn, provide advantages in pump efficiency and gas handling because of a more fully swept pumping chamber. A standing valve placed above the traveling valve may also block solids from falling back in on the seal between the upper working piston and the upper barrel assembly, resulting in superior solids handling and pump life. 
     In some applications, it may be preferable to run the rodless pump threaded on the bottom of the production tubing. In such a tubing run application, the rodless pump may seal against a hydraulic sub that may disposed on the bottom of a concentric power fluid string. 
     In at least some embodiments, a rodless pump as described herein may lower power consumption as compared to traditional rod pumps. This reduction in power may be sufficient to allow a rodless pump to be powered by relatively low power renewable sources, such as solar or wind. 
     Additionally, the rodless pump can eliminate both the surface stuffing box seal of traditional rod pumps and the surface power fluid separation apparatus of traditional hydraulic pumps, reducing the possibility of oil leaks and reducing surface footprint. 
     The rodless pump may have at least two power fluid lines and two piston areas that an upstroke line pressure and a downstroke line pressure respectively act on. The rodless pump may have a first working piston having a first surface in contact with a power fluid and a second surface in contact with a wellbore fluid. The rodless pump may also have a second working piston having a first surface in contact with a power fluid and a second surface in contact with a wellbore fluid. The pressure of a power fluid in an upstroke line may act on the lower exposed area of an upper working piston. The pressure of the power fluid in a downstroke line may act on an upper exposed area of a lower working piston. Upstroke and downstroke pistons may be mechanically connected via a rod which may be hollow in some embodiments. The pistons themselves may be partially hollow in some embodiments to allow fluid to pass through them as well through the rod. A connecting rod may contact seals positioned between the power fluid chambers, exterior to the rod. These seals isolate the power fluid chambers from pressure communication, enabling a key feature of the rodless pump: the ability to have a differently sized areas exposed to power fluid pressures in the upstroke chamber and downstroke chambers, respectively. In some embodiments, each working piston may have a first surface exposed to power fluid, and a second surface in contact with production fluid. The pistons are moved by a force originating from the opposite side of the power fluid chamber as the production fluid. As a result, solids suspended in the production fluid are less likely to foul the seal between the piston and the barrel due to the clean power fluid lubricating the piston/barrel seal. Areas of the working pistons exposed to the power fluid and density of the multiple power fluid streams may be adjusted to alter the forces acting on the upstroke and downstroke working piston areas. The forces acting on pump can be balanced downhole to minimize required power of the surface power fluid pump as a function of the difference between hydrostatic pressure in the tubing (the pressure acting on the upper area of the upper piston) and the wellbore pump intake pressure (the pressure acting on the bottom area of the lower piston). A through bore can allow passage of production fluid through both pistons, a hollow connecting rod, and a traveling valve affixed to the dual piston and rod setup. An optimal pump and hydraulic sub system design may contain pistons with different areas as dictated by well conditions. The rodless pump and hydraulic sub allow balancing of the forces downhole, at the point where force is applied to lift wellbore fluids. This can eliminate an inefficiency of traditional rod pumps arising from their need to always keep the entire rod string in tension to avoid rod buckling, which by definition results in a pumping system that is not balanced down hole at the pump. 
     The power fluid may be transferred to the power fluid chambers via two strings run exterior to the production tubing with an open annulus. The power fluid strings may be concentric to each other and/or the production tubing, or they may be non-concentric. A nonconcentric, open annulus setup may include two tubing strings run alongside the production tubing and each power fluid string being hydraulically connected to a different power fluid chamber. A concentric open annulus setup may include three sets of tubing, with the production tubing being run on the innermost string, the first power fluid string disposed around the production tubing, and the second power fluid string disposed around the first power fluid string. A mixed concentric/nonconcentric setup with an open annulus can include one power fluid string disposed around the production tubing and a second nonconcentric power fluid string run exterior to the first power fluid string. 
     The power fluid may alternatively be transferred to the power fluid chambers via a closed annulus by using a pump set above a casing packer. In some embodiments, a closed annulus setup can have one fewer power fluid string than an open setup by utilizing the annulus above the packer seal and exterior to the first power fluid conduit and/or production tubing as the second power fluid conduit. A nonconcentric, closed annulus setup may include a single power fluid string run alongside the production tubing as the first power fluid string, with the annulus exterior to both the production tubing and the power fluid string acting as the second power fluid string. A concentric closed annulus setup may include the production tubing and a concentric power fluid string disposed around the production tubing as the first power fluid string. The second power fluid flow path in this case may be the annulus sealed at the bottom by the packer, on the interior by the first power fluid string, and on the exterior by the well&#39;s casing. 
       FIGS.  8  and  8 A- 8 D  depict a high level view of the surface and downhole apparatus for such a pump system.  FIGS.  8 A and  8 B  depict the surface flows of power fluids.  FIG.  8 C  depicts an open annulus pumping setup, and  FIG.  8 D  depicts a closed annulus setup with a pump run above a packer. Power fluid  8000  may be stored in a reservoir vessel  8001  that feeds a surface hydraulic pump  8002 . The surface hydraulic pump may use multiple power fluid lines, including an upstroke line  8004  and a downstroke line  8005 , that can carry the power fluid in independent conduits through the wellhead  8003  to the open annulus hydraulic sub  8006 O, or closed annulus hydraulic sub  8006 C disposed on the production tubing. The hydraulic sub may house the landed pump. The pump may be mechanically lowered or pumped into the wellbore and landed in a hydraulic sub that connects the power fluid chambers in the pump to the surface system via power fluid lines  8004  and  8005 . Multiple seals exterior to the pump may contact their mating seal areas on the interior of the hydraulic sub to force the power fluid separately into the upstroke and downstroke power fluid chambers of the pump. 
     The wellhead  8003  may have multiple power fluid lines entering it, as well as an outlet  8007 O for produced fluids produced by the pump up the production tubing  8007 . Wellhead  8003  may also have an outlet for free gas  8008 O that flows up the annulus  8008  between the production tubing, power fluid conduits, and well casing  8014 . The closed annulus setup illustrated in FIG.  8 D does not have an outlet for free gas because the annulus between the exterior of the upstroke power fluid string  8004  and the casing  8014  is occupied as the downstroke power fluid path  8005 . The gas in the concentric setup shown in  FIG.  8 D  is produced up the production tubing  8007  along with any other production fluids such as oil or water. The power fluid lines in this embodiment may include the upstroke power fluid line  8004  and the downstroke power fluid line  8005 . A surface electronic controls system  8009  can control both the hydraulic surface pump and the valve system  8010  that direct flow to and from the well. 
     Return power fluid flow from the well may be taken through the upstroke return line  8011  and the downstroke return line  8012  and collected back in the power fluid reservoir for reuse.  FIG.  8    depicts a single power fluid reservoir, but separate power fluid reservoirs may be used if use of different power fluids for the upstroke and downstroke lines is desirable. The valve system  8010  for the upstroke line may include inlet  8004 I, outlet  8004 O, and return  8004 R flow paths. The valve system for the down stroke line may include inlet  8005 I, outlet  8005 O, and return  8005 R flow paths. On the upstroke, flow paths  8004 I,  8004 O,  8005 O, and  8005 R may be open and flow paths  8005 I and  8004 R may be closed as shown in  FIG.  8 A . On the downstroke, flow paths  8005 I,  8005 O,  8004 O, and  8004 R may be open and flow paths  8004 I and  8005 R may be closed as shown in  FIG.  8 B . With a contained, multiple line power fluid setup and an open annulus, oil and water may be produced up the well&#39;s tubing to a flow line for further separation or sale, and gas may flow up the annulus between the production tubing and the casing to be produced via a gas line, reducing or eliminating the need for power fluid/produced fluid separation on surface. In a closed annulus setup, the oil, gas, and water all flow up the production tubing to surface for separation into saleable products. 
     The system may be powered by a number of power sources  8013  including grid electricity, solar cells and batteries, diesel or natural gas powered generators, etc. The surface pump may be individually powered by an independent power source, or it may use the same power source as the electronic controls system. The surface pump may alternatively use the transmission and drive system of a converted prime mover or surface unit from a traditional rod pump system. 
       FIGS.  9 A,  9 B,  9 C, and  10 A,  10 B, and  10 C  show the fluid conduit paths for upstroke line  8004  and downstroke line  8005  as they travel from the surface downhole to the pump.  FIGS.  9 A,  9 B, and  9 C  depict open annulus setups without a packer.  FIGS.  10 A, 10 B, and  10 C  show closed annulus setups. As shown in  FIG.  9 A , upstroke line  8004  and downstroke line  8005  may be concentric to the production tubing  8007 , with an open annulus  8008  that allows for a fluid level above the pump and for free gas to flow to surface. As shown in  FIG.  9 B , the upstroke line  8004  and downstroke line  8005  may be separate and independent from the production tubing  8007 , with an open annulus  8008 . As shown in  FIG.  9 C , a hybrid design may include one concentric power fluid string  8004  and one independent power fluid string  8005 , with an open annulus  8008 . 
       FIG.  10 A  depicts a concentric, closed annulus setup with the packer seal not pictured. The first power fluid string  8004  may be a separate string of tubing run concentrically to the production tubing. The second fluid flow path may be in the annulus between the exterior of the first power fluid string  8004  and the casing  8014 . Gas bubbles  8007 G are shown mixed with fluids in the interior of the production tubing string  8007  in  FIGS.  10 A,  10 B, and  10 C . In closed annulus setups, there is not a free annulus for gas to separate out of the produced fluid and flow up the casing. The gas  8007 G may be entrained in the oil and water mixture and produced up the production tubing.  FIG.  10 B  depicts a nonconcentric closed annulus setup. One power fluid line  8004  may be run exterior to and independent of the production tubing  8007 . The second fluid flow path may be in the exterior space between the first power fluid string  8004 , the production tubing, and the casing  8014 .  FIG.  10 C  depicts an independent, dual power fluid string, closed annulus setup. Both power fluid lines  8004  and  8005  may be run exterior to and independent of the production tubing  8007 . The space inside the casing not occupied by power fluid lines or production tubing may be filled with a packer fluid  8014 PAF. 
       FIG.  11    shows the relationship between power fluid flow rate in the upstroke working chamber  11000 , power fluid flow rate in the downstroke working chamber  11001 , and surface pump pressure  11002  over time for an exemplary pump operation. Positive pump rates are defined as power fluid going into a working chamber, and negative flow rates are defined as power fluid leaving a working chamber. For the upstroke  11100  the pump starts in a down stroked position, and fluid rate is increased in the first working chamber  11000  thereby actuating a piston assembly of the pump comprising the first working piston in a first direction while a corresponding, but not necessarily equal, negative flow rate is observed in the second working chamber  11001  thereby actuating a piston assembly of the pump in a second direction opposite the first direction. The surface pump pressure  11002  increases to overcome the friction resulting from fluid movement in the power fluid lines and hydrostatic pressure acting on the pump. On the downstroke  11200 , the downstroke fluid rate increases and a corresponding, but not necessarily equal negative rate is seen leaving the first working chamber  11000 . Surface pressure again rises as a result of friction in the power fluid lines and hydrostatic forces acting on the downhole pump. 
       FIGS.  12 DS and  12 US  illustrate a rodless pump  12000  that may be retrieved without a workover rig, described herein as a “rig-less version”. The rig-less version of the pump is not threaded into the production tubing string; thus a rig is not necessary to retrieve it. Rig-less rodless pump  12000  may include a fishing neck  12005  that allows for retrieval via latching with coil tubing, slick line, wire line, or a workover tubing string. Rig-less rodless pump  12000  may be constructed the same for both closed and open annulus systems. The hydraulic sub, however, may differ between a closed annulus hydraulic sub  8006 C and open annulus hydraulic sub  8006 O systems. 
     Rig-less rodless pump  1200  may include: fishing neck  12005 , upper hold down sub  12006 , hold down seals  12004 , standing check valve  12007 , traveling check valve  12008 , upper working piston  12009 , connecting rod  12010 , connecting rod seals  12010 S, lower working piston  12011 , bottom intake  12001 , and bullnose  12012 . The standing check valve and traveling check valves are illustrated as spring-loaded ball and seat arrangements, although other types of check valves may be used, such as a flapper, dart, or caged ball check valves. The traveling check valve is pictured in the upper working piston  12009 , which can minimize non-stroked volume within the pump chamber. However, the traveling check may also be placed within the lower working piston or the connecting rod. In some embodiments, a standing check may be located below the traveling valve. The upper working piston  12009  may be connected to the lower working piston  12011  by connecting rod  12010 . The connecting rod  12010  may contact the connecting rod seals  12010 S that may isolate the pressure between the upper power fluid chamber  12104  and lower power fluid chamber  12105 . The connecting rod seals  12010 S are pictured as O-ring type seals but may also be a metal-to-metal type seal. The production fluid chambers can include the production lift chamber  12101 , the pump chamber  12102 , and the reservoir/wellbore fluid chamber  12103 . The power fluid chambers can include the upstroke power fluid chamber  12104  and the downstroke power fluid chamber  12105 . The power fluid in the upstroke power fluid chamber  12104  exerts a force on the lower exposed area of the upper working piston  12009 LEA to actuate the pump up. The power fluid in the downstroke power fluid chamber  12105  exerts a force on the upper exposed area of the lower working piston  12011 UEA to actuate the pump down. The power fluid in the upstroke power fluid line  8004  may be in hydraulic communication with the upstroke power fluid chamber via a port and a multiple seal arrangement on the interior of the hydraulic sub. The power fluid in the downstroke power fluid line  8005  may be in hydraulic communication with the downstroke power fluid chamber via a port and a multiple seal arrangement on the interior of the hydraulic sub. 
       FIG.  12 HS  depicts an exemplary hydraulic sub receptacle for an open annulus, rig-less system  8006 O without a rodless pump landed therein. The hydraulic sub may be threaded on the bottom of the production tubing string  8007  and may include an assembly of parts exterior to the pump, such as the landing sub  12002 , pump chamber housing  12002 A, power fluid seal sub  12003 , and lower piston housing  12003 A. Because the seals isolating the lower power fluid chamber from the downhole production fluids are located up hole of the lower piston housing  12003 A, a standard tubing joint may function as a lower piston housing and attach to the bottom of the power fluid seal sub  12003 . Further apparatus such as sand separators, gas separators, or tubing anchors may be affixed to the bottom of the lower piston housing/production tubing joint. 
     The production tubing may have a landing sub above the pump  12002  that contacts the hold down seals on the pump  12004 . The hydraulic fluid seal sub may include upper and lower recesses  12003 U,  12003 L that may allow flow from the power fluid lines  8004 ,  8005  into the upper power fluid chamber  12104  and lower power fluid chambers  12105 , respectively. The hydraulic power fluid seal sub may also include seal areas  12003 LS,  12003 MS, and  12003 US that mate with the lower pump seals  12202 L, middle pump seals  12202 U and  12201 L, and upper pump seals  12201 U, respectively. This combination of upper and lower recesses surrounded by three sealing areas that seal above the top recess  12003 US, in between the two recesses  12003 MS, isolating the flows between the two power fluid chambers, and below the bottom recess  12003 LS, isolate the lower power fluid chamber from the wellbore fluids. This seal arrangement may allow the power fluid conduits to actuate the pump in the upstroke and downstroke directions without materially mixing power fluid and production fluid. This seal arrangement may also allow rig-less retrieval of the pump. 
       FIG.  12    illustrates a rig-less rodless pump  12000  landed inside an open annulus hydraulic sub  8006 O disposed on the end of production tubing  8007  with production fluids filling the outer annulus  8008  inside the production casing  8014 . Production tubing  8007  may be run into the well with the rodless pump  12000  already landed inside the hydraulic sub  8006 O. Alternatively, the pump  12000  may be landed at a time after the production tubing and hydraulic sub are run into the well. The exterior power fluid strings may be run into the well at the same time as the production tubing string. The pump  12000  may be landed in the hydraulic sub  8006 O that may be connected independently to both the upstroke power fluid conduit  8004  and the downstroke power fluid conduit  8005 . An upper landing sub  12006  is pictured above the upper working piston  12009  of the pump, but a similar lower landing sub below the lower working piston  12011  could be used for a bottom hold down. 
     The hydraulic sub may include hydraulic power fluid seal sub  12003 . The hydraulic power fluid seal sub and landing sub may be used to hold the rodless pump in the wellbore and to transfer the power fluid from the power fluid lines to and from the pump with minimal mixing of power fluid and production fluid. When the pump  12000  is landed in the hydraulic sub  8006 O, seals above and below both power fluid conduits may be engaged by the power fluid seal sub  12003 , thereby forcing the fluid from the upstroke conduit through the upper recess  12003 U and into the upstroke chamber  12104  and forcing fluid from the downstroke conduit through the lower recess  12003 L into the downstroke chamber  12105 . The upstroke fluid chamber seals are  12201 U and  12201 L, and the downstroke chamber seals are  12202 U and  12202 L. Seals  12201 L and  12202 U may be combined into a single seal in some embodiments. These seals contact seal areas  12003 LS,  12003 MS, and  12003 US to force upstroke power fluid from line  8004  in between seal areas  12003 MS and  12003 US into the upstroke power fluid chamber  12104  and downstroke power fluid from line  8005  in between seal areas  12003 MS and  12003 LS into the downstroke power fluid chamber. 
       FIGS.  12 A,  12 B,  12 C, and  12 D  depict fluid flows through a rodless pump with open annulus and independent power fluid lines. The arrows in  FIGS.  12 A,  12 B,  12 C, and  12 D  in the upstroke and downstroke lines show the direction of power fluid and production fluid during the upstroke and downstroke. On the downstroke, power fluid is flowing into the pump through the downstroke line and out of the pump, towards surface, in the upstroke line. On the upstroke, power fluid is flowing into the pump through the upstroke line and out of the pump, towards surface, in the downstroke line. 
       FIG.  12 A  depicts standing check valve  12007  in the closed position on the downstroke.  FIG.  12 B  depicts traveling check valve  12008  in the downstroke, unseated position allowing fluid to pass. During the downstroke, standing check valve  12007  may be seated, and traveling check  12008  may be unseated, allowing fluid to pass from wellbore fluid chamber  12101  into pump chamber  12102 . Wellbore fluid may enter into the rodless pump from bottom production fluid intake  12001  and may travel into the lower working piston  12011 , and then into the hollow connecting rod  12010 . From the connecting rod wellbore fluid may travel into the upper working piston  12010 , which can include the unseated traveling check valve  12008 . Wellbore fluid may then enter pump chamber  12102  on the downstroke. 
       FIG.  12 C  depicts the standing check valve  12007  in the upstroke, unseated position allowing fluid to pass.  FIG.  12 D  depicts the traveling check valve  12008  in the closed position on the upstroke. On the upstroke, the traveling check valve  12008  seats from the hydrostatic pressure acting on it in the production tubing  8007  and pump chamber  12105 . The pressure in the pump chamber increases until the pressure exceeds the pressure in the production tubing above the standing valve  12007 . As a result, the ball is moved off the seat of the standing valve as fluids flow to surface. 
       FIG.  13 HS  depicts hydraulic sub receptacle  8006 C for a closed annulus, rig-less rodless pump artificial lift system run above a packer  13000 P that seals against the casing  8014  to isolate the downhole fluids (oil, gas, and water)  13000 DF below. Packer  13000 P can include an inner seal bore that the bottom of the hydraulic sub  8006 C may be inserted into. The hydraulic sub may be attached to the bottom of power fluid string  8005 T. The uppermost part of the hydraulic sub may be the inner tubing seal carrier  13003 ITSC that is disposed on the bottom of the production tubing. At the end of the inner tubing seal carrier, inner tubing seals  13003 ITS may be inserted into and seal against inner tubing seal sub  13003 ITSS. 
     Similar to open annulus hydraulic sub  8006 O, closed annulus hydraulic sub  8006 C can include all parts exterior to the pump including the landing sub  13002 , pump chamber housing  13002 A, power fluid seal sub  13003 , and lower piston housing  13003 A. Because the seals isolating the lower power fluid chamber from the production fluids are located up hole of the lower piston housing  13003 A, a standard tubing joint with a seal on the bottom may function as a lower piston housing and attach to the bottom of the power fluid seal sub  13003 . The tubing can have a landing sub  13002  above the pump that contacts the hold down seals on the pump  12004 . The hydraulic fluid seal sub can include upper and lower recesses  13003 U,  13003 L to allow flow into the upper power fluid chamber  12104  and lower power fluid chambers  12105 , respectively. The hydraulic power fluid seal sub can also include seal areas  13003 LS,  13003 MS, and  13003 US that mate with the lower pump seals  12202 L, middle pump seals  12202 U and  12201 L, and upper pump seals  12201 U, respectively. This combination of upper and lower recesses surrounded by a seal arrangement that seals the area above the top recess  13003 US, in between the two recesses  13003 MS, isolating the flows between the two power fluid chambers, and below the bottom recess  13003 LS, can allow power fluid conduits to actuate a retrievable pump in the upstroke and downstroke directions without materially mixing power fluid and production fluid. 
       FIG.  13    shows a detailed view of a rodless pump  12000  landed inside a closed annulus hydraulic sub  8006 C disposed on the end of the power fluid string  8005 T with the outer annulus comprising the downstroke power fluid conduit  8005  hydraulically contained by the production casing  8014 . A packer  13000 P may be set in the well first via slickline or tubing. The power fluid string tubing  8005 T may then be lowered into the well with the hydraulic sub  8006 C disposed on the bottom of the string. The bottom seal on the hydraulic sub  8006 C may be inserted into a packer  13000 P that seals against the casing, with production fluids  13000 DF below the packer. The pump may be landed in the hydraulic sub  8006 C that is connected independently to both the upstroke power fluid conduit  8004  and the downstroke power fluid conduit  8005 . An upper hold down sub  12006  is pictured above the upper working piston  12009  of the pump, but a similar lower landing sub below the lower working piston  12011  could be used for a bottom hold down. The hydraulic sub can include hydraulic power fluid seal sub  13003 . The hydraulic power fluid seal sub and landing sub may be used to hold the rodless pump in the wellbore and transfer the power fluid from the power fluid lines to and from the pump with minimal mixing of power fluid and production fluid. When the pump  12000  is landed in the hydraulic sub  8006 C, seals above and below both power fluid conduits may be engaged by the power fluid seal sub  13003 , forcing the fluid from the upstroke conduit  8004  through the upper recess  13003 U and into the upstroke chamber and fluid from the downstroke conduit  8005  through the lower recess  13003 L into the downstroke chamber. The upstroke fluid chamber seals are  12201 U and  12201 L, and the downstroke chamber seals are  12202 U and  12202 L. Seals  12201 L and  12202 U may be combined into a single seal in some embodiments. This seal arrangement may contact the areas  13003 LS,  13003 MS, and  13003 US to force upstroke power fluid from upstroke conduit  8004  in between seal areas  13003 MS and  13003 US into the upstroke power fluid chamber  12104  and downstroke power fluid from downstroke conduit  8005  in between seal areas  13003 MS and  13003 LS into the downstroke power fluid chamber  12105 . 
       FIGS.  13 A,  13 B,  13 C, and  13 D  depict fluid flow through a rodless pump  12000  landed in a closed annulus hydraulic sub  8006 C with concentric power fluid strings  8004  and  8005 . The arrows in  FIGS.  13 A,  13 B,  13 C, and  13 D  in the upstroke and downstroke lines show the direction of power fluid and production fluid during the upstroke and downstroke. On the downstroke, fluid is flowing into the pump through the downstroke line and out of the pump, towards surface, in the upstroke line. On the upstroke, power fluid is flowing into the pump through the upstroke line and out of the pump, towards surface, in the downstroke line. 
     During the downstroke, the standing check valve  12007  may be seated, and the traveling check  12008  may be unseated, allowing fluid to pass into the pump fluid chamber  12105 . Wellbore fluid may enter into the rodless pump from the bottom production fluid intake  12001  and may travel into the lower working piston  12011  and then into the hollow connecting rod  12010 . From the connecting rod, fluid can travel into the upper working piston  12010 , which contains the unseated traveling check valve  12008 . Fluid may then enter the pump chamber  12102  on the downstroke. 
       FIG.  13 A  depicts the standing check valve  12007  in the closed position on the downstroke.  FIG.  13 B  depicts the traveling check valve in the downstroke, unseated position allowing fluid to pass. On the upstroke, the traveling check  12008  may seat from the hydrostatic pressure acting on it in the production tubing and pump chamber  12102 . The pressure increases in the pump chamber until the pressure exceeds the pressure in the production tubing above the standing valve  12007 . The ball may then move off the seat of the standing valve as fluids flow to surface. 
       FIG.  13 C  depicts the standing check valve  12007  in the upstroke, unseated position allowing fluid to pass.  FIG.  13 D  depicts the traveling check valve  12008  in the closed position on the upstroke. 
       FIGS.  14 DS and  14 US  illustrate an embodiment of rodless pump  14000  that is threaded directly on the bottom of the production tubing  8007 . This embodiment is thus retrievable only by removing the tubing from the well. The tubing retrievable version of the pump is threaded into the production tubing string, and thus a rig is necessary to retrieve or lower it into the hole. The pump  14000  has a production tubing crossover sub  14005  that threads the pump assembly onto the production tubing string  8007 . The tubing retrievable rodless pump  14000  may be the same for both closed and open annulus systems. The pump can include: production tubing crossover sub  14005 , lower hold down sub  14006 , hold down seals  14004 , standing check valve  14007 , traveling check valve  14008 , upper working piston  14009 , connecting rod  14010 , and lower working piston  14011 , bottom intake  14001 , and bullnose  14012 . The standing check valve and traveling check valves are illustrated as spring-loaded ball and seat arrangements, although other types of checks may be used such as a flapper, dart, or caged ball check valves. The traveling check valve is pictured in the upper working piston  14009 , which minimizes non-stroked volume within the pump chamber. However, the traveling check may also be placed within the lower working piston or the connecting rod. In some embodiments, the standing valve may be located below the traveling valve. The upper working piston  14009  may be connected to the lower working piston  14011  by connecting rod  14010 . The connecting rod  14010  may contact the connecting rod seals  14010 S that may isolate the pressure between the upper power fluid chamber  14104  and lower power fluid chamber  14105 . The connecting rod seals  14010 S are pictured as O-ring type seals but may also be a metal-to-metal type seal. The production fluid chambers include the production lift chamber  14101 , the pump chamber  14102 , and the reservoir/wellbore fluid chamber  14103 . The power fluid chambers include the upstroke power fluid chamber  14104  and the downstroke power fluid chamber  14105 . The power fluid in the downstroke power fluid chamber  14105  exerts a force on the upper exposed area of the lower piston  14011 UEA to actuate the pump down. The power fluid in the upstroke power fluid chamber  14104  exerts a force on the lower exposed area of the upper piston  14009 LEA to actuate the pump up. The power fluid in the upstroke power fluid line  8004  is hydraulically in communication with the upstroke power fluid chamber  14104  via the hydraulic sub. The power fluid in the downstroke power fluid line  8005  is hydraulically in communication with the downstroke power fluid chamber  14105  via the hydraulic sub. 
       FIG.  14 HS  depicts the hydraulic sub receptacle  8006 TO for a tubing retrievable pump  14000  run in an open annulus system. The hydraulic sub may be attached to the bottom of the outer power fluid tubing string  8005 T. The uppermost part of the hydraulic sub  8006 TO is the seal sub  14003 SS, designed to mate with seals  14003 ITS. The seals  14003 ITS are disposed on the inner tubing seal carrier sub  14003 ITSC, which is disposed on the bottom of the inner power fluid string  8004 T. The annulus between the inner power fluid tubing  8004 T and the outer power fluid string  8005 T comprises the downstroke power fluid flow path  8005 . Downstroke power fluid flow path  8005  and upstroke power fluid flow path  8004  may be separated by the contact seals between  14003 SS and  14003  ITS. The power fluid seal sub  14003  may be above and threaded into the hydraulic landing sub extension  14002 A, landing sub  14002 , and lower piston housing  14003 A. Because the seals isolating the lower power fluid chamber from the production fluids are located up hole of the lower piston housing  14003 A, a standard tubing joint with a seal on the bottom may function as a lower piston housing and attach to the bottom of the hold down sub  14002 . The tubing can include a landing sub  14002  that contacts the hold down seals on the pump  14004 . The hydraulic fluid seal sub can also include specialized upper and lower recesses  14003 U,  14003 L to allow flow into the upper power fluid chamber  14104  and lower power fluid chambers  14105 , respectively; the hydraulic power fluid seal sub also contains seal areas  14003 LS,  14003 MS, and  14003 US that mate with the lower pump seals  14202 L, middle pump seals  14202 U and  14201 L, and upper pump seals  14201 U, respectively. This combination of upper and lower recesses surrounded by a seal arrangement that seals the area above the top recess  14003 US, in between the two recesses  14003 MS, isolating the flows between the two power fluid chambers, and below the bottom recess  14003 LS, allow the power fluid conduits to actuate the pump in the upstroke and downstroke directions without materially mixing power fluid and production fluid. 
       FIG.  14    illustrates a detailed view of a tubing retrievable rodless pump  14000  landed inside an open annulus hydraulic sub  8006 TO. The hydraulic sub  8006 TO may be disposed on the end of the outer tubing string  8005 T that acts as a barrier between the concentric power fluid pathway  8005  and the well&#39;s open annulus containing downhole fluid  14000 DF. The outer power fluid string  8005 T and hydraulic sub  8006 TO may be lowered into the well first. The inner power fluid string  8004 T may then run inside of  8005 T and be landed on the upward facing seal area of seal sub  14003 SS. The annulus between outer power fluid string  8005 T and the inner power fluid string  8004 T can include the downstroke power fluid conduit  8005  that may be hydraulically connected to the downstroke power fluid chamber  14105 . The annulus between inner power fluid string  8004 T and the production tubing  8007  can include the upstroke power fluid conduit  8004  that may be hydraulically connected to the upstroke power fluid chamber  14104 . Tubing retrievable pump  14000  may be landed in the hydraulic sub  8006 TO that may be connected independently to both the upstroke power fluid conduit  8004  and the downstroke power fluid conduit  8005 . A lower hold down sub  14002  is illustrated below the lower piston  14009  of the pump, but a similar upper landing sub above the upper pump piston  14011  could be used for a top hold down. The hydraulic sub can include hydraulic power fluid seal sub  14003 . The hydraulic power fluid seal sub and landing sub may be used to hold the rodless pump in the wellbore and transfer the power fluid from the power fluid lines to and from the pump with minimal mixing of power fluid and production fluid. When the pump  14000  is landed in the hydraulic sub  8006 TO, seals above and below both power fluid chambers  14104  and  14105  may be engaged by the power fluid seal sub  14003  and may force the fluid from the upstroke conduit  8004  through the upper recess  14003 U and into the upstroke chamber  14104  and fluid from the downstroke conduit  8005  through the lower recess  14003 L into the downstroke chamber  14105 . The upstroke fluid chamber seals are  14201 U and  14201 L, and the downstroke chamber seals are  14202 U and  14202 L. Seals  14201 L and  14202 U may be combined into a single seal in some embodiments. This seal arrangement may contact the areas  14003 LS,  14003 MS, and  14003 US to force upstroke power fluid from  8004  in between seal areas  14003 MS and  14003 US into the upstroke power fluid chamber  14104  and to force downstroke power fluid from  8005  in between seal areas  14003 MS and  14003 LS into the downstroke power fluid chamber  14105 . 
       FIGS.  14 A,  14 B,  14 C, and  14 D  depict the fluid flow through a rodless pump  14000  landed in an open annulus hydraulic sub  8006 TO with concentric power fluid flow paths  8004  and  8005  and inner power fluid tubing  8004 T and outer power fluid tubing  8005 T. Arrows in  FIGS.  14 A,  14 B,  14 C, and  14 D  in the upstroke and downstroke lines show the direction of power fluid and production fluid during the upstroke and downstroke. On the downstroke, fluid is flowing into the pump through the downstroke line and out of the pump, towards surface, in the upstroke line. On the upstroke, power fluid is flowing into the pump through the upstroke line and out of the pump, towards surface, in the downstroke line. 
       FIG.  14 A  depicts the standing check valve  14007  in the closed position on the downstroke.  FIG.  14 B  depicts the traveling check valve in the downstroke, unseated position allowing fluid to pass. During the downstroke, the standing check valve  14007  may be seated, and the traveling check  14008  may be unseated, allowing fluid to pass to the pump chamber  14102 . For the bottom intake pump, wellbore fluid may enter into the rodless pump from the bottom production fluid intake  14001  and may travel into the lower piston  14011  and then into the hollow connecting rod  14010 . From the connecting rod fluid may travel into the upper working piston  14009 , which can include the unseated traveling check valve  14008 . Fluid may then enter the pump chamber  14102  on the downstroke. 
       FIG.  14 C  depicts the standing check valve  14007  in the upstroke, unseated position allowing fluid to pass.  FIG.  14 D  depicts the traveling check valve  14008  in the closed position on the upstroke. On the upstroke, the traveling check valve  14008  may seat from the hydrostatic pressure acting on it in the production tubing and pump chamber. The pressure in the pump chamber may increase until the pressure exceeds the pressure in the production tubing above the standing valve  14007 , and the ball is moved off the seat of the standing valve as fluids flow to surface. 
       FIG.  15 HS  depicts the hydraulic sub receptacle  8006 TC for a tubing retrievable pump  14000  run in a closed annulus system run above a packer  15000 P that seals against the casing  8014  to isolate the downhole fluids (oil, gas, and water)  15000 DF below. The packer  15000 P can include an inner seal bore that the bottom of the hydraulic sub  8006 TC may be inserted into. The hydraulic sub may be attached to the bottom of the power fluid tubing string  8005 T. The uppermost part of the hydraulic sub can include the power fluid seal sub  15003 , hydraulic landing sub extension  15002 A, landing sub  15002 , and lower piston housing  15003 A. Because the seals isolating the lower power fluid chamber from the production fluids are located up hole of the lower piston housing  15003 A, a standard tubing joint with a seal on the bottom may function as a lower piston housing and attach to the bottom of the hold down sub  15002 . The tubing retrievable pump can include a hold down sub  15002  that contacts the hold down seals on the pump  14004 . The hydraulic fluid seal sub can include upper and lower recesses  15003 U,  15003 L to allow flow into the upper power fluid chamber  14104  and lower power fluid chambers  14105 , respectively. The hydraulic power fluid seal sub can also include seal areas  15003 LS,  15003 MS, and  15003 US that mate with the lower pump seals  14202 L, middle pump seals  14202 U and  14201 L, and upper pump seals  14201 U, respectively. This combination of upper and lower recesses surrounded by a seal arrangement that seals the area above the top recess  15003 US, area in between the two recesses  15003 MS, isolating the flows between the two power fluid chambers, and area below the bottom recess  15003 LS, allow the power fluid conduits to actuate the pump in the upstroke and downstroke directions without materially mixing power fluid and production fluid 
       FIG.  15    illustrates a tubing retrievable rodless pump  14000  landed inside a closed annulus hydraulic sub  8006 TC. The hydraulic sub may be disposed on the end of the outer tubing string  8005 T that acts as a barrier between the concentric power fluid paths  8004  and  8005 . The outer tubing string  8005 T with attached hydraulic sub  8006 TC may be lowered first into the well. The production string  8007  with the tubing retrievable rodless pump  14000  may then run inside the outer tubing string  8005 T and landed in the hydraulic sub  8006 TC. The outermost annulus can include the downstroke power fluid conduit  8005  contained by the production casing  8014 . The bottom seal on the hydraulic sub  8006 TC may be inserted into a packer  14000 P that seals against the casing, with production fluids  15000 DF below the packer. The pump may be landed in the hydraulic sub  8006 TC that may be connected independently to both the upstroke power fluid conduit  8004  and the downstroke power fluid conduit  8005 . A lower hold down sub  15002  is pictured below the lower working piston  14009  of the pump, but a similar upper landing sub above the upper working piston  14011  could be used for a top hold down. The hydraulic sub can include hydraulic power fluid seal sub  15003 . The hydraulic power fluid seal sub and landing sub may be used to hold the rodless pump in the wellbore and transfer the power fluid from the power fluid lines to and from the pump with minimal mixing of power fluid and production fluid. When the pump  14000  is landed in the hydraulic sub  8006 TC, seals above and below both power fluid chambers  14104  and  14105  may be engaged by the power fluid seal sub  15003  and may force the fluid from the upstroke conduit  8004  through the upper recess  15003 U and into the upstroke chamber  14104  and fluid from the downstroke conduit  8005  through the lower recess  15003 L into the downstroke chamber  14105 . The upstroke fluid chamber seals are  14201 U and  14201 L, and the downstroke chamber seals are  14202 U and  14202 L. Seals  14201 L and  14202 U may be combined into a single seal in some embodiments. This seal arrangement contacts the areas  15003 LS,  15003 MS, and  15003 US to force upstroke power fluid from  8004  in between seal areas  15003 MS and  15003 US into the upstroke power fluid chamber  14104  and downstroke power fluid from  8005  in between seal areas  15003 MS and  15003 LS into the downstroke power fluid chamber  14105 . 
       FIGS.  15 A,  15 B,  15 C, and  15 D  depict the fluid flow through a rodless pump  14000  landed in a closed annulus hydraulic sub  8006 TC with concentric power fluid paths  8004  and  8005  and power fluid tubing string  8005 T. Arrows in  FIGS.  15 A,  15 B,  15 C, and  15 D  in the upstroke and downstroke lines show the direction of power fluid and production fluid during the upstroke and downstroke. On the downstroke, fluid is flowing into the pump through the downstroke line and out of the pump, towards surface, in the upstroke line. On the upstroke, power fluid is flowing into the pump through the upstroke line and out of the pump, towards surface, in the downstroke line. 
       FIG.  15 A  depicts the standing check valve  14007  in the closed position on the downstroke.  FIG.  15 B  depicts the traveling check valve in the downstroke, unseated position allowing fluid to pass. During the downstroke, the standing check valve  14007  may be seated, and the traveling check  14008  may be unseated, allowing fluid to pass to the pump chamber  14102 . For the bottom intake pump, wellbore fluid may enter into the rodless pump from the bottom production fluid intake  14001  and may travel into the lower working piston  14011  and then into the hollow connecting rod  14010 ). From the connecting rod fluid may travel into the upper working piston  14009 , which includes the unseated traveling check valve  14008 . Fluid may then enters the pump chamber  14102  on the downstroke. 
       FIG.  15 C  depicts the standing check valve  14007  in the upstroke, unseated position allowing fluid to pass.  FIG.  15 D  depicts the traveling check valve  14008  in the closed position on the upstroke. On the upstroke, the traveling check  14008  may seat from the hydrostatic pressure acting on it in the production tubing and pump chamber. The pressure in the pump chamber may increase until the pressure exceeds the pressure in the production tubing above the standing valve  14007 , and the ball is moved off the seat of the standing valve as fluids flow to surface. 
     Seals  12201 U,  12202 L,  12202 U,  12202 L,  14201 U,  14201 L,  14202 U, and  14202 L may take the form of chevron of vee packing seals that can be arranged to provide a bidirectional or unidirectional seal, and may be energized by radial compression between seal carrier and the hydraulic sub. Although there are advantages associated with the chevron seal design, they may require a substantial force to engage when used in a static energizing design (as currently depicted). It is possible to replace the chevron seal with one or more other seal designs, such as an O-ring or multiple O-rings, as well as other seal cross-sections that perform in a similar manner. Additionally, a bonded seal arrangement could be implemented to reduce leak paths through a chevron seal design and potentially improve the reliability of the seal over time. The bonded seal arrangement could take the form of being bonded directly to the seal carrier, or bonded to a small ring of material that is then placed in the assembly. In the latter implementation another seal (such as an O-ring) would typically be used to seal the ring of material to seal carrier. Furthermore, a bonded seal arrangement could be configured where the seal is combined with another component such as the seal spacer or bottom landing sub. Another implementation would be a lip seal arrangement that is energized by the hydraulic pressure applied by the primary power source. One potential advantage of such an arrangement is lower insertion pressure, which eases landing of the pump and also protects the seal during landing. 
       FIGS.  16 A-F  illustrate a simplified visualization of a full cycle of a rodless pump with an open annulus hydraulic sub from downstroke to upstroke back to downstroke. Certain features of the pump are represented in simplified manner for viewing clarity to show an improved picture of the power fluid and production fluid, including production hydrocarbons, flows simultaneously. Previously described standing valve  12007  (shown as a flapper check instead of a ball and spring check), traveling valve  12008  (shown as a ball sitting on the top of the upper piston), upper working piston  12009 , piston rod  12010 , lower working piston  12011 , wellbore fluid chamber  12103 , pump chamber  12102 , and produced fluid chamber  12101  are depicted. The upstroke power fluid line  8004 , downstroke power fluid line  8005 , upstroke power fluid chamber  12104 , and downstroke power fluid chambers  12105  are also shown. The seal detail between the pump and tubing are simplified in this illustration. 
     In  FIG.  16 A , the working pistons sit near the bottom position as the upstroke starts. The upstroke power fluid pressure increases and power fluid flows into the upstroke power fluid chamber, while the down stroke power fluid flows back up the downstroke power fluid line. The traveling valve seats, and the standing valve opens to the tubing, allowing fluid (oil, gas, and water) to flow through. 
     In  FIG.  16 B , the pump at surface continues to apply pressure to the upstroke power fluid, overcoming the force of the hydrostatic pushing against the top surface of the top piston. The pistons move upward in reaction to the force applied to the exposed area on the bottom of the upper working piston, pressurizing the pump chamber and pushing fluid to surface. 
     In  FIG.  16 C , the working pistons have almost reached the top of the stroke as upstroke power fluid continues to fill the upstroke power fluid chamber. The wellbore fluid flows into the wellbore fluid chamber below the bottom working piston of the pump. 
     In  FIG.  16 D , the surface pump switches from applying pressure to the upstroke power fluid to the downstroke power fluid, forcing the pistons down as the downstroke chamber gains fluid volume. A vacuum is created in the pump chamber and the ball sitting on top of the traveling valve comes off seat, drawing more fluid into the pump chamber and closing the top check valve. 
     In  FIG.  16 E , the pistons continue down with the standing valve check closed, bringing upstroke power fluid back to surface and bringing more wellbore fluid into the production fluid chamber. 
     In  FIG.  16 F , the working pistons have reached the bottom of the downstroke. The pump stops applying pressure to the downstroke power fluid and switches back over to the upstroke power fluid to restart the upstroke cycle. 
       FIGS.  17 A-F  shows a simplified visualization of a full cycle of a rodless pump with a closed annulus hydraulic sub from downstroke to upstroke back to downstroke. Certain features of the pump are represented in simplified manner for viewing clarity to show an improved picture of the power fluid and production fluid, including production hydrocarbons  13000 DF, flows simultaneously. Previously described standing valve  12007  (shown as a flapper check instead of a ball and spring check), upper working piston  12009 , piston rod  12010 , lower working piston  12011 , pump chamber  12102 , produced fluid chamber  12101 , packer  13000 P, and casing  8014  are depicted. The upstroke power fluid line  8004 , downstroke power fluid line  8005 , upstroke power fluid chamber  12104 , and downstroke power fluid chambers  12105  are also shown. The seal detail between the pump and tubing are simplified in this visualization. 
     In  FIG.  17 A , the pistons sit near the bottom at of the stroke as the pump starts the upstroke. The upstroke power fluid pressure increases and power fluid flows into the upstroke power fluid chamber, while the down stroke power fluid flows back up the downstroke power fluid line. The traveling valve seats, and the standing valve opens to the tubing, allowing wellbore fluid (oil, gas, and water) to flow through. 
     In  FIG.  17 B , the pump at surface continues to apply pressure to the upstroke power fluid, overcoming the force of the hydrostatic pushing against the top surface of the top piston; the pistons move upward in response to the force acting on the lower exposed area of the upper working piston, pressurizing the pump chamber and pushing fluid to surface. 
     In  FIG.  17 C , the pistons have almost reached the top of the stroke as upstroke power fluid continues to fill the upstroke power chamber. 
     In  FIG.  17 D , the surface pump switches from applying pressure to the upstroke power fluid to the downstroke power fluid, forcing the pistons down as the downstroke chamber gains fluid volume. A vacuum is created in the pump chamber and the ball sitting in the traveling check valve comes off seat, drawing more fluid into the pump chamber and closing the standing check valve. 
     In  FIG.  17 E , the working pistons continues down with the standing valve check closed, bringing upstroke power fluid back to surface and bringing more wellbore fluid into the pump fluid chamber. 
     In  FIG.  17 F , the working pistons have reached the bottom of the downstroke. The pump stops applying pressure to the downstroke power fluid and switches back over to the upstroke power fluid to restart the upstroke cycle. The foregoing describes exemplary embodiments of a rodless downhole hydraulic pump. Although numerous specific features and various embodiments have been described, it is to be understood that, unless otherwise noted as being mutually exclusive, the various features and embodiments may be combined various permutations in a particular implementation. Thus, the various embodiments described above are provided by way of illustration only and should not be constructed to limit the scope of the disclosure. Various modifications and changes can be made to the principles and embodiments herein without departing from the scope of the disclosure and without departing from the scope of the claims.