US3802802A

US3802802A - Pump system

Info

Publication number: US3802802A
Application number: US00154415A
Authority: US
Inventors: F Greer
Original assignee: Individual
Current assignee: Individual
Priority date: 1971-06-18
Filing date: 1971-06-18
Publication date: 1974-04-09
Anticipated expiration: 1991-04-09
Also published as: JPS5521195B1; DE2230291A1; CA958282A; GB1352109A

Abstract

A pumping system employs the method of using an inoffensive fluid as a displacing fluid to pump an offensive fluid to be displaced. The system is illustrated in a well pumping operation and includes a pump structure for establishing a moving fluid interface between the displacing fluid and the well fluid to be displaced from the well reservoir so that the displacing fluid functions as a piston to pump well fluid to well surface. A gas elimination system and a diluent injection system may be associated with the pump structure to remove gas evolved from the well fluid and to inject a diluent into the well fluid reservoir to reduce well fluid viscosity.

Description

Apr. 9, 1974 United States Patent [1 1 Greer 1 PUMP SYSTEM Primary E.\'aminerW'il1iam L. Freeh Assistant E\'aminerLeonard Smith [22] Filed:

Attorney, Agent, or Firm-l-luebner & Worrel [57] ABSTRACT A pumping system employs the method of using an in- 417/431 [51] Int. F09b 35/02 417/92, 99, 101-103,

offensive fluid as a displacing fluid to pump an offen- [58] Field of Search................

sive fluid to be displaced. The system is illustrated in a well pumping operation and includes a pump structure for establishing a moving fluid interface between the displacing fluid and the well fluid to be displaced from References Cited the well reservoir so that the displacing fluid functions as a piston to pump well fluid to well surface. A gas elimination system and a diluent injection system may be associated with the pump structure to remove gas 417/313 X evolved from the well fluid and to inject a diluent into 4l7/92 the wellfluid reservoir to reduce well fluid viscosity. 417/92 S T m N m E m M m m S dn .i .1 T ms ow A nfimwnmm T e weo SFDHTPB D E93 O64 T265226 999999 NHHHHHH U 79947- 223349 85 33 787 9 996576 32 3 31 Claims 10 Drawing Figures PATENTEDAPR 9 1974 SHEET 5 BF 6 PUMP SYSTEM BACKGROUND OF THE INVENTION The present invention relates to pumps and pumping 5 methods and more particularly to a pump and pumping method suitable for use in downhole well pumping operations, such as oil well pumping operations, as well as in other pumping operations.

Heretofore, various types of pumps have been devised for pumping well fluids, such as crude oils. Unfortunately, the crude oil pumped is oftentimes of an extremely offensive nature containing various impurities such as sand, silt, sludge, and salt water so as to be abrasive and/or corrosive. A problem common with the design of many of these prior art pumps has been that they have included moving parts, such as plunger mechanisms, which contacted the offensive fluids being pumped. Thus, as a consequence, the offensive crude oils or well fluids have generally caused considerable wear, excessive friction, and corrosion ofthe parts, particularly the moving parts, of the prior art pumps. Considerable expense, therefore, has generally been associated with the use of these prior art pumps in such well pumping operations where an offensive well fluid is being pumped since the pumps had to be frequently shut down, removed from their downhole locations, and rebuilt or repaired to change and replace their worn and/or corroded moving parts.

Additionally, many prior art pumps constructed for well pumping operations have been designed so that the displacing well fluid is caused to 'move upward in physical contact with a reciprocating sucker rod string. Unfortunately, the contact of the well fluid which was generally of a high viscosity with the sucker rod string acted to restrict the downward movement, so called rod fall, of the sucker rod string, and thereby severely restricted the upper cycle rate at which the plunger could be driven in these pumps to pump well fluid to the well surface. Further, substantial stress was placed on the sucker rod string by the downward movement of a pumping jack to which it was connected since the upward flowing well fluid resisted the sucker rod strings downward movement. Consequently, pump outputs 1 prior to this time have been limited-since it has not been possible to exceed rod fall rates greater than approximately three strokes per minute without running the danger of breaking the sucker rod string.

Other problems common with prior art downhole well pumps have been that they have been subject to being locked up by gas locks caused by gas evolved from the pumped well fluid and by the paraffin occurring in paraffin based crude oils. Additionally, prior art pumps have been unsuitable to pump extremely high viscosity crude oil mixtures, such as sand laden crude oils, since in order to avoid excessive wear from contact with the high viscosity well fluids filtering mechanisms were employed to filter the impurities from the oil and these filters unfortunately restricted to a significant extent oil flow into the pump.

SUMMARY OF THE INVENTION movable pump parts with the offensive fluid so as to substantially reduce friction, pump wear, and pump corrosion.

It is further an object of the present invention to provide an improved pump suitable for downhole use which is operable to establish and maintain an interface between a displacing fluid and a fluid to be displaced and to displace this interface in a reciprocal motion so that the displacing fluid functions at the interface as a piston to prevent gas lock and pump the displaced fluid to a selected location.

It is, additionally, an object of the present invention to provide an improved pump for downhole use which utilizes a displacing fluid to pump well fluid to well surface and is arranged for connection with a sucker rod string isolated from the well fluid, thereby to obviate the aforementioned disadvantages inherent with the prior art pumps having well fluid pumped to well surface in contact with the sucker rod string.

It is still another object of the present invention to provide an improved method for removing crude oil from an oil well reservoir, such as an oil well reservoir containing unconsolidated reservoir sands, in which the crude oil-impurity mixture in the well reservoir is pumped to well surface without separation or filtration.

It is also an object of the present invention to provide an improved gas elimination system for use with down hole pumps which operates to remove gas evolved from the well fluid from the pump thereby to prevent gas locks.

It is another object of the present invention to provide an improved fluid injection system for use with a downhole pump which operates to inject controlled quantities of a diluent into a well fluid being pumped so as to dilute anddecrease the viscosity of the well fluid.

It is yet another object of the present invention to provide an improved method for pumping a fluid to be displaced which employs the concept of using a displacing fluid which may be miscible with the displaced fluid to pump the displaced fluid to a selected location.

In accomplishing these and other objects, there is pumping system suitable for pumping an offensive fluid. The term offensive fluid as'used herein refers to any fluid the contact of which with pump parts, particularly moving parts, is considered undesirable and detrimental to the pump. Examples of such offensive fluids are abrasive and erosive high viscosity fluids, corrosive acids, etc. The fluid which is of an offensive nature may be a high viscosity sand bearing crude oil. The pumping system provided is for a well pumping operation and includes a sucker rod string mounted in a fluid sealed tubing string so as to be isolated from well fluid. A pump structure is mounted on the lower end of the tubing housing of the sucker rod string. The pump structure includes a first chamber housing a plunger which is connected by a downwardly extending passage to a lower second or discharge chamber. The discharge chamber has port means through which the crude oilimpurity mixture forming the well fluid in the well reservoir may be pumped into the chamber-and then discharged to a'point isolated from the oil reservoir. The discharge point is connected in communication with well surface through a production tubing string. Means are included for supplying a controlled amount of displacing fluid of an inoffensive lubricating nature, which preferably is kerosene, to the plunger chamber so that a fluid interface region is formed between the kerosene and the crude oil in the downward extending passage.

tubing string. Since gas is oftentimes evolved from they well fluid, a gas trap may be associated with the upper end of the downward extending passage and a valve operated conduit may be connected with the gas trap to selectively conduct trapped gas to a portion of the discharge chamber where it will be pumped with the crude oil up the production tubing string. It has been found however, that the replenishment of the displacing fluid 4 FIG. 5 is a view taken along the line 5-5 of FIG. 312;

FIG. 6 is a view taken along the line 6-6 of FIG. 3b;

FIG. 7 is a view taken along the and FIG. 8 is a side elevation view of a portion of the pumping system of FIG. 1 which has been modified to include a diluent injection assembly and which is partially cut away to illustrate the internal construction of the diluent injection assembly.

line 77 of FIG. 3a;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings in more detail, there is shown in FIGS. 1-7 a well pumping system generally designated by the numeral 11 positioned in the bore or casing 13 of an oil well. The pumping system 11 has vertically extending

tubing strings

15 and 17 positioned within the well bore 13 to extend from the surface of r the well to the bottom region of the well whereat well to maintain the displacing fluid crude oil interface inherently operates to prevent the pumping system from gas locking. Additionally, a fluid injection system may be associated with the pump structure for injecting a diluent fluid into the high viscosity crude oil so as to dilute the crude oil and thereby reduce its viscosity. Thus, there is provided pumping system and method of pumping wherein limited contact is made between the offensive fluid displaced and the moving'parts of the pumping mechanism. Additionally, a pumping system is provided which is suitable for removing crude oil by the method-of pumping a crude oil-impurity mixture without separation from a well reservoir to well surface, thereby to significantly enhance oil producing rates from well reservoirs characterized by being high viscosity fluent mixtures of crude oil with impurities such as oil well reservoirs containing unconsolidated reservoir sands.

Additional objects of the present invention reside in the specific construction and method of operation of the exemplary well-pumping system hereinafter particularly described in the specification and shown in the several drawings.

BRIEF DESCRIPTION OF THE DRAWINGS ofthe downhole portion of the well pumping system of FIG. 1 taken along line 3-3 of FIG. 2 illustrating the plunger of the pumping system on its downstro-ke with FIG. 3a representing the upper half of the downhole pumping system and FIG. 3b representing the lower half of the downhole pumping system.

FIGS. 4a and 4b correspond, respectively, to FIGS. 3a and 3b but illustrate the operation of the pumping system when the plunger is on its upstroke;

fluid in the form of high viscosity crude oil-impurity 'mixture 19 is located. Such high viscosity crude oil 19 which is generally laden with sand and silt is commonly encountered in oil drilling operations in the Santa Maria, California region. Due to the sand and other impurities generally found in this crude oil 19, the oil 19 is generally of a highly offensive nature, being abrasive and erosive and sometimes containing corrosive salt water. The tubing string 15 provides a fluid sealed housing for a string of sucker rods 21 which are connected in a conventional manner to a prime mover 23, illustrated in FIG. 1 as a pumping jack, which is mounted at well surface adjacent the well bore 13. It is noted that the string of sucker rods 21 and the pumping mechanism associated with the pumping system 11 may be driven by means other than a pumping jack, such as, an appropriately adapted hydraulic engine, electric motor, gas expansion engine, etc. The tubing string 17 functions as a string of production tubing and defines means for isolating pumped crude oil from the well reservoir and conducting the crude oil 19 to the well surface, In this manner of employing

tubing strings

15 and 17, the sucker rod'string 21 is isolated from the well fluid 19 so that rod fall is not restricted thereby and rod fall cycle rates as high as ten strokes per minute may be employed for pumping well fluid to well surface. Such rod fall. rates of ten strokes per minute may develop pumping pressures as high as 6,0007,000 pounds per square inch without placing undue stress on the sucker rod string 21 which is isolated out of contact with the well fluid 19.

Mounted on the lower end of the tubing string 15 by means of a coupler 25 is a conduit section 27 having a hollow side extension portion 29. The conduit section 27 with its extension 29 defines a first cavity or chamber 31. The cavity 31 is shaped to have a cylindrical portion in line with the vertically extending string of sucker rods 21 which defines a plunger chamber. A

plunger 33 is mounted in this plunger chamber for re- .ciprocation up and down therein. The plunger 33 forms amovable wall portion of the chamber 31 and functions when moved upward by the sucker rod string 21 to decrease or contract the effective volume of the chamber 31. Conversely, downward movement of the sucker rod string 21 moves the plunger 33 downward to increase or expand the effective volume of the chamber 31. The chamber 31 which is made up of the region defining the plunger chamber and also the region enclosed by the side extension 29 is shown in FIGS. 3a and 4a. H

Connected by a coupler 35 to the lower end of the conduit section 27 is a conduit section 37 which opens on its upper end into the conduit section 27. The conduit section 37 provides the fixed housing in which the plunger mechanism or assembly 33 reciprocates up and down. A traveling valve 39 is connected to the plunger mechanism 33 to reciprocate therewith and the valve 39 which is preferably of the ball valve type operates to control the flow of a displacing fluid 41 in a manner hereinafter explained to the chamber 31. The displacing fluid 41 is of an inoffensive nature and preferably is kerosene or naptha blended with crude oil. The term inoffensive fluid" as used herein means a fluid which does not attack or unduly cause wear on pump parts on contact. The inoffensive fluid may be lubricating, as kerosene, could be filtered crude oil, could be a solvent for dissolving paraffin which has precipitated out of the displaced well fluid 19 onto pump parts, or any other suitable fluid the contact of which with pump parts is not considered undesirable. A tubular cap 43 is mounted on the lower end of the conduit section 37 by means ofa coupler 45 to collect and provide a reservoir for the displacing fluid 41. As shown in FIGS. 3a, 3b, 4a and 4b, the sucker rods 21 are formed to be hollow and the displacing fluid 41 is supplied by a fluid supply means 47 shown in FIG. 1 located at well surface adjacent the well bore 13. The fluid supply 47 operates in a conventional manner to supply the displacing fluid 41 at a controlled rate through the conduit 49 to the upper end of the hollow sucker rods 21. As indicated by the directional arrows in FIGS. 3a, 3b and 4a, 4b, the displacing fluid 41 flows down the sucker rods 21 out an exit portion 51 down the side of the conduit section 37 into the tubular cap 43 where'at it is collected. The traveling valve 39 functions to control the, flow of the displacing fluid 41 upward through a channel 53 which opens through the plunger mechanism 33 into the chamber 31. The chamber 31 is a fluid confining chamber which functions to hold and confine the movement of this displacing fluid 41.

Formed integral with the side extension 29 of the conduit section 27 is a preferably tubular vertically disposed conduit section 55. The conduit section 55 com municates with the chamber 31 and defines a downward extending passage 56 which communicates at its lower end with a second chamber 57 formed by a conduit section 59 branching off from the bottom portion of the conduit section 55 to extend upward therefrom. The

conduit sections

55 and 59 which are preferably formed as one integral unit form a generally U-shaped junction. Connected on the lower end of the conduit section 55 is a standing valve 61 which is preferably of the ball valve type and has an inlet port 63 connected to its lower end. The standing valve 61 in combination with the inlet port 63 provides an inlet port means which functions as is hereinafter explained to permit the flow of fluid, and in particular the flow of well fluid, only into but not out from the chamber 57. The valve 61 acts as a check valve to prevent fluid flow therethrough out from the chamber 57. It is noted that the term fluid, as here used, isused in a broad generic sense to encompass all types of fluent substances including slurries, such as percent crude oil-6O percent sand slurry which may make up an oil well reservoir. Connected to the upper end of the conduit section 59 is a standing valve 65 mounted in a coupler 67. The coupler 67 is connected to the lower end of the tubing string 17 and the tubing string 17 functions, as beforementioned. as a production tubing string for conducting pumped well fluid to the surface of the well while isolating the well fluid pumped from the sucker rod string and well reservoir. [t is noted that the tubing string 17 has no internal restrictions except its outer boundary. The standing valve 65 functions as an outlet port means for the chamber 57 through which pumped 'well fluid 19 is discharged at a discharge point into the production tubing string 17 and acts to check the flow of any fluid into the chamber 57 therethrough.

The conduit section 55 extends vertically slightly above the extension 29 to form a gas trap chamber 69. The upper end of the conduit section 55 has a coupler 71 with a standing valve 73, preferably of the ball valve type, mounted therein. The valve 73 functions to bleed trapped gas from the gas trap chamber 69 into an upper gas reservoir chamber 75 defined by a tubular cap 77 connected to the coupler 71. Connected to the upper end of the gas reservoir chamber 75 is a conduit 81 by means of a right angled elbow connector 79. The conduit 81 extends downward from the connector 79 to a point adjacent the upper portion of the structurally defined chamber 57 at which it is connected to a standing valve 83. The valve 83 is preferably of the ball valve type and is spring biased in a closed position. An outlet conduit 85 is connected from the ball valve assembly 83 in fluid sealing relation through one wall of the chamber 57 to direct gas therefrom into the upward extending portion of the conduit section 59. Thereby, the gas is pumped through the standing valve 65 with well fluid 19 into the string of production tubing 17. It is noted that

screen strainers

87 and 89 are mounted after and before, respectively, the

valves

73 and 83 to strain particles out of the gas flow so as to prevent the clogging of the elbow connector 79, the conduit 81, the valve assembly 83 or the conduit 85. Further, it is noted that the construction of the valve 73 is designed with its orifice relatively small so that, should gas not be evolved from the well fluid 19 being pumped, only negligible displacing fluid 41 will flow through the valve 73 and into the gas elimination system or assembly provided by the gas trap 69, the

valves

73 and 83, the reservoir chamber 75, the connector 79, and the

conduits

81 and 85.

In operation of the exemplary well pumping system shown in FIGS. 1-7, initially the lubricating fluid kerosene 41 is supplied to flood the

pump chambers

31, 57 and the passage 56. Prime mover 23 is then energized and acts to reciprocate the sucker rod string 21 up and down. Thereby, the plunger 33 is driven to move up and down and change the effectivevolume of the chamber 31 so that well fluid 19 is drawn into the chamber 57 and a fluid interface is formed in the upwardly extending channel or interface chamber formed bly 39 is opened by the pressure of displacing fluid 41 in the reservoir defined by the cap 43 so that displacing fluid 41 flows upward through the valve assembly 39 .into the cavity 31. Also during the downstroke of the plunger 33, a low pressure region is formed in the chamber 57 so that the pressure of the well fluid 19in the bottom of well bore 13 opens the standing valve 61 and the well fluid 19 to be pumped which is a crude oilimpurity fluentmixture flows into the chamber 57. This flow of fluid 19 into the chamber 57 forces the interface region 91 upward in the passage 56 and the displacing fluid kerosene 41 tends to flow into the expanding chamber 31, as indicated by the directional arrows in FIGS. 30 and 3b. Additionally, gas evolved from the oil 19 being pumped flows up the vertical path defined by the conduit section 55 into the gas trap 69 and forces the gas-displacing fluid interface 93 in a downward direction, as indicated by the directional arrows, during the downstroke of the plunger 33. It is noted that the valve assembly 73 is closed by the pressure dif' ferential thereacross during the downstroke of the plunger 33. Additionally during the plunger downstroke, the outlet port defined by the valve assembly 65 is closed since the displacing fluid interface 91 is moving upwards at this time in the passage 56.

FIGS. 40 and 4b show the upstroke of the plunger 33.

In the upstroke, the plunger 33 functions to contract placing fluid 41 defined in the cap 43, the valve assembly 39 is closed by the pressure differential thereacross. The downward movement of the displacing kerosene 41 in the conduit section 55 functions to move the interface region 91 downward in a piston-like movement in the passage 56 so that the well fluid 19 is forced downward toward Ihechamber 57. This downward movement of the displaced fluid 19 in the chamber 57 automatically closes the inlet valve means 61 and opens the outlet valve means 65 so that the crude oil 19 is channeled and pumped into the production tubing string 17 upward to the surface of the well. The upward movement of the displacing fluid 41 in the conduit sec tion 55 functionsto increase the pressure of the gas in the gas trap 69 so that the valve 73 opens and the evolved gas flows into the gas reservoir 75. The gas stored in the gas reservoir 75 is thus put under an increased pressure and flows down the conduit 81 to open the spring-biased valve 83. The opening of the spring-biased valve 83 bleeds'off the gas in the conduit 81 down to a predetermined pressure level established by the spring-biased valve 83. This bled off gas is discharged into the upward extending portion of the conduit section 59 where it is pumped with the well fluid 19 into the production tubing string 17 out of the well. It is noted that gas is normally only forced through the gas elimination assembly during the upstroke of the plunger 33 when the chamber 31 is being contracted to its smallest effective volume and at which time the displacing fluid 41 is exerting maximum pressure against gas in the gas trap 69.

Operation of the 'prime mover 23, thus, functions to pump oil or well fluid 19 up the production tubing 17 in a rapid and efficient manner since no moving parts other than the inlet and outlet ports defined by

valves

61 and 65 of the pumpassembly contact the offensive crude oil 19 being pumped. Further, the prime mover 23 may be driven at a relatively high cycle rate since the sucker rod string 21 is siolated from contact with the well fluid 19 so that even high viscosity fluids such as oil of the type recovered from Santa Maria, California, can be rapidly pumped up the production tubing 17. Also, kerosene or another light lubricating fluid is preferably maintained within the tubing 15 around the sucker rod string 21 which is operable to lubricate the sucker rod string 21 without restricting the rate of rod fall. This kerosene may be supplied from the supply means 47.

Referring now to FIG. 8, a modified form of the pumping system of FIGS. 1 to 7 is shown therein in which a downward extending fluid injection system is included. The system 95 has a conduit 97 with a spring-biased valve assembly 99 mounted on the lower end of the conduit 97 and a connector 101 connecting the upper end of the conduit 97 to the tubing 15. A diluent injection assembly is, thus, provided in which a diluent fluid which may be kerosene is pumped down the tubing string 15 through the connector 101 and the conduit 97'and is injected into the well fluid 19 at a rate controlled by the spring-biased valve 99 through a nozzle or orifice means 103 connected to the valve 99. The flow of the diluent fluid is shown by directional arrows in FIG. 8. Thereby, the well fluid 19 is diluted to reduce its viscosity before being pumped into the chamber 57 and discharged therefrom into the production tubing 17. It is also noted that by pumping a lubricating fluid, such as kerosene, down the tubing string 15 external of the sucker string 21 that a lubricant is automatically provided for the reciprocating sucker string 21 which does not restrict rod fall. The diluent may be supplied by the fluid supply means 47 or by another conventional source.

lt is noted that the exemplary pump has been tested and may be used with or without the above-described gas elimination section connected thereto. For example, the gas elimination assembly has not been found necessary when using the exemplary pump to pump a crude oil-impurity fluent mixture having'an inherently low gas-oil ratio. Further, it is noted that means may be provided so that the pump is designed to pump both on the upstroke and the downstroke of its plunger mechanism 33 and that while the pump structure provided by the

conduits

27, 37, 55 and 59 is illustrated connected onto the ends of the tubing strings 15 and 17 in a downhole pumping operation that a pump mechanism operated on the same principle could be used in other pumping operations as well. The means for expanding and contracting the chamber 31 could take the form of other suitable arrangements or means other than a plunger and could be driven by a downhole motor instead of a surface mounted prime mover. Additionally, other equivalent type valving arrangements, such as poppet valves, could be employed in place of the ball type valves and the entire lower end of the pump structure could be made the inlet means to facilitate the pumping in of extremely high viscosity fluent mixtures into the pump structure, such as a 60 percent sand-40 percent crude oil mixture. Also, instead of using a production tubing string to conduct the pumped well fluid 19 to well surface, a seal could be placed in the .well bore 13 to seal off the discharge point of the pumps outlet port from the well reservoir so that the well bore or casing 13 could be utilized as a conduit to conduct the well fluid to well surface.

Further, it is noted that instead of pumping the displacing fluid down the sucker rods that solid, less expensive sucker rods could be used with other conventional means for conducting the displacing fluid into the chamber 31. Also, the displacing fluid 41 need be supplied to the chamber 3 1 only at a rate necessary to replace displacing fluid lost during the operation of pumping the well fluid up the production tubing 17, thereby to maintain the displacing fluid-well fluid interface established in the passage 56. In the case of using kerosene to pump oil the displacing fluid kerosene needs to be supplied, for example, at the rate of 10 percent of the pumps displacement. Additionally while kerosene is illustrated as the displacing fluid, it is noted that other suitable fluid which are of an inoffensive nature so as to not attack or cause undue wear of the pumping mechanism could be employed, such as water and various other suitable fluids. Filtered oil, for example, could be used to pump a crude oil-impurity mixture from a well reservoir. Further, it is noted that the displacing fluid kerosene is miscible with the well fluid crude oil and that by keeping a moving interface between the fluids that little displacing fluid is mixed with the crude oil pumped up the production tubing 17. While the downhole pumping system is utilized to pump crude oil it is to be understood that other fluidlike substances having high percentages of impurities and being extremely abrasive and/or corrosive could also be pumped by this pumping mechanism, such as mud, The pump could also be employed as an acid pump by employing as the displacing fluid an inoffensive fluid inert to the fluid being pumped to pump a high corrosive acid, such as, anhydrous sulfuric acid.

Although I have herein shown and described my invention in what I have conceived to be the most practical and preferred embodiment, it is recognized that departures may be made therefrom within the scope of my invention.

1 claim:

1. In a down hole well pumping system, the improvement comprising:

pump structure for positioning in a well bore down hole in contact with a well reservoir, said pump structure defining a first fluid confining chamber for receiving displacing fluid, a second fluid confin-- ing chamber for receiving well fluid and a fluid conducting passage interconnecting said fluid confining chambers in communication with each other, said second chamber having an inlet and outlet port defined therein, said inlet port being defined to communicate with the well reservoir in which said pump structure is positioned, said passage extending upwardly from its point of communication with said second chamber to define an upwardly extending channel of predetermined length in which displacing fluid and well fluid may interface, at least a portion of said first chamber defining a plunger chamber; inlet valve means mounted in said inlet port for conducting well fluid into said second chamber; outlet valve means mounted in said outlet port for discharging fluid from said second chamber; means for expanding and contracting the effective volume of said first chamber, each expansion and contraction of the effective volume of said first chamber being defined as a pump stroke, said means for expanding and contracting the effective volume of said first chamber being a plunger means mounted for reciprocal motion in said plunger chamber;

means for supplying displacing fluid to said pump structure on each stroke of said pump at a controllable rate to maintain the moving interface region between displacing fluid and well fluid within said upwardly extending channel and said second chamber, said displacing fluid supply means being operable to supply displacing fluid to said pump structure in time coincidence with the expansion of the effective volume of said first chamber;

said displacing fluid supply means comprising: reservoir means for displacing fluid defined as a continuation of said plunger chamber, said plunger means sealing said first chamber from said reservoir means whereby movement of said plunger means to contract and expand the effective volume of said first chamber, respectively, expands and contracts the volume of said reservoir means; means connected to said reservoir means for transferring displacing fluid thereto at a controlled rate; and valve means mounted in said plunger means for controlling the flow of displacing fluid between said reservoir means and said first chamber, said valve means being operated by the pressure differential developed between said first chamber and said reservoir means to open and close, respectively, during the expansion and contraction of the effective volume of said first chamber; and

means for conducting fluid pumped from said outlet valve means to well surface.

2. In a down hole well pumping system, the improvement comprising:

pump structure for positioning in a well bore down hole in contact with a well reservoir, said pump structure defining a first fluid confining chamber for receiving displacing fluid, a second fluid confining chamber for receiving well fluid and a fluid conducting passage interconnecting said fluid confining chambersin communication with each other, said second chamber having an inlet and outlet port defined therein, said inlet port being defined to communicate with the Well reservoir in which said pump structure is positioned, said passage extending upwardly from its point of communication with said second chamber to define an upwardly extending channel of predetermined length in which displacing fluid and well fluid may interface, at least a portion of said first chamber defining a vertically extending plunger chamber;

inlet valve means mounted in said inlet port for conducting well fluid into said second chamber;

outlet valve means mounted in said outlet port for discharging fluid from said second chamber;

means for expanding and contracting the effective volume of said first chamber, said means for expanding and contracting the effective volume of said first chamber is a plunger means mounted for up and down reciprocal motion in said plunger chamber;

means for supplying displacing fluid to said pump structure at a controllable rate to maintain the moving interface region between displacing fluid and well fluid within said upwardly extending chanvoir means for displacing fluid defined as a continuation of said plunger chamber, said plunger chamber being positioned above said reservoir means, said plunger means sealing said first chamber from said reservoir means whereby movement of said plunger means to contract and expand the effective volume of said first chamber, respectively, expands and contracts the volume of said reservoir means; means connected to said reservoir means for transferring displacing fluid thereto at a controlled rate; and valve means mounted in said plunger means for controlling the flow of displacing fluid between said reservoir means and said first chamber, said valve means being operated by the pressure differ ential developed betweensaid first chamber and said reservoir means to open and close, respectively, during the expansion and contraction of the effectivevolume of said first chamber; and means for conducting fluid pumped from said outlet valve means to well surface. 3. The invention defined in claim 2, including a string of suckerrods for reciprocating said plunger means up and down, said sucker rods being connected to said plunger means and extending therefrom to well surface, said sucker rods being hollow and defining a conduit for conducting displacing fluid from well surface to said plunger means, said plunger means having a fluid conducting path defined therethrough for conducting displacing fluid from said sucker rods to said reservoir means.

4. A well pumping system, comprising:

a sucker rod string;

a fluid sealed string of tubing for positioning in a well to extend from the bottom portion ofa well to well surface, said sucker rod string being mounted in said string of tubing for reciprocation up and down therein whereby said tubing functions as a housing to isolate said sucker rod string from well fluid thereby up and down reciprocal movement of said sucker rod string is not inhibited by well fluid;

pump structure mounted on the lower end of said string of tubing to depend therefrom into the reservoir of ,well fluid to be pumped, said pump structure defining a first fluid confining chamber in communication with a second fluid confining chamber through a fluid conducting passage, said first and second chambers being for holding, respectively, a displacing fluid and a well fluid, said passage extending upwardly from its point of communication with said second chamber to define an upwardly extending channel in which displacing fluid and well fluid may interface, said second chamber having inlet and outlet port means operable only to receive and discharge fluid, respectively; g

1 plunger means mounted for up and down reciprocal motion in said first chamber for expanding and contracting the effective volume of said first cham ber to displace up and down in said channel the region of interface between the displacing fluid and the well fluid whereby the displacing fluid functions as a piston to pump well fluid in said inlet port means and out said discharge, port means;

means for isolating the dischargepoint of said outlet port means of said pump structure from the well fluid reservoir and connecting said outlet port means in communication with well surface so that well fluid discharged from said outlet port means is pumped to well surface;

means for connecting said plunger means to said sucker rod string whereby said plunger means may be driven through said sucker rod string;

displacing fluid supply means connected to said first chamber for supplying displacing fluid thereto at a controllable rate to maintain the moving region of interface between the displacing fluid and the well fluid within said upwardly extending channel and said second chamber, said displacing fluid. supply means being operable to supply displacing fluid to said pump structure in time coincidence with the expansion of the effective volume of said first chamber;

said displacing fluid supply means comprising: structure defining a reservoir for displacing fluid, said displacing fluid reservoir being defined by a downwardly extending continuation of said first chamber and being in alignment with 'said plunger means; means connected to said dispiacing fluid reservoir for transferring displacing fluid thereto at a controlled rate; and valve means connecting said displacing fluid reservoir in communication with said first chamber for controlling the flow of displacing fluid between said displacing fluid reservoir and said first chamber, said valve means being 0perable to open and close, respectively, in time coincidence with the expansion and contraction of the effective volume of said first chamber, said valve means being operated by the pressure differential developed between said first chamber and said displacing fluid reservoir during the expansion and contraction of the effective volume of said first chamber;

said plunger means scaling said first chamber from said displacing fluid reservoir whereby the up and down reciprocal movement of said plunger means to contract and expand the effective volume of said first chamber, respectively, expands and contracts the volume of said reservoir means, said valve means being carried by said plunger means; and

prime mover means connected to said sucker rod string for driving said sucker rod string in up and down reciprocal motion thereby to drive said plunger means.

5. The invention defined in claim 4, wherein:

said sucker rods are hollow and define a conduit for conducting displacing fluid from well surface to said plunger means; and

said plunger means has a fluid conducting path defined therethrough for conducting displacing fluid from said sucker rods to said displacing fluid reservoir.

6. The invention defined in claim 4, wherein said means for isolating the discharge point of said outlet port means of said pump structure from the well fluid reservoir and connecting said outlet port means in communication with well surface is a string of production tubing detachably coupled to said outlet port means.

7. The invention defined in claim 4, wherein:

said sucker rod string defines a conduit for conducting displacing fluid from well surface to said plunger means; and

said plunger means has a fluid conducting path defined therethrough for conducting displacing fluid from said sucker rod string to said reservoir means.

8. The invention defined in claim 7, wherein said means for isolating the discharge point of said outlet port means of said pump structure from the well fluid reservoir and connecting said outlet port means in communication with well surface is a string of production tubing detachably coupled to said outlet port means.

9. A pump for down hole use, comprising:

structure defining a first fluid confining chamber for receiving displacing fluid, a second fluid confining chamber for receiving well fluid and a fluid conducting passage interconnecting said fluid confining chambers in communication with each other, said second chamber having an' inlet and outlet port defined therein, said inlet port being defined to communicate with a well reservoir, said passage extending upwardly from its point of communication with said second chamber to define an upwardly extending channel of predetermined length in which displacing fluid and well fluid may interface, at least a portion of said first chamber defining a plunger chamber;

inlet valve means mounted in said inlet port for conducting well fluid i nto said second chamber; outlet valve means mounted insaid outlet port for discharging'fluid from said second chamber; reservoir means defined as a continuation of said plunger chamber, said reservoir means being arranged for connection to a displacing fluid supply so that displacing fluid may be selectively supplied thereto;

plunger means mounted for reciprocal motion in said plunger chamber for expanding and contracting the effective volume of said first chamber, said plunger means sealing said first chamber from said reservoir means whereby movement of said plunger means to contract and expand the effective volume of said first chamber, respectively, expands and contracts the volume of said reservoir means;

and

valve means mounted in said plunger means for controlling the flow of displacing fluid between said reservoir means and said first chamber, said valve means being operated by the pressure differential developed between said first chamber and reservoir means to open and close, respectively, during the expansion and contraction of the effective volume of said first chamber.

10. The invention defined in claim 9, wherein:

said plunger chamber is defined to be substantially vertically extending; and

said reservoir means is defined as a downward continuation of said plunger chamber.

11. The invention defined in claim 10, wherein:

said plunger means is arranged for connection to a string of upwardly extending hollow sucker rods whereby sand plunger means may be driven up and down and displacing fluid may be conducted from well surface to said plunger means through a string of hollow sucker rods connected thereto; and said plunger means has a fluid conducting path defined therethrough for conducting displacing fluid to said reservoir means from the point of connection of a string of hollow sucker rods thereto.

12. The invention defined in claim 11, wherein said outlet port is arranged for being detachably coupled to a string of production tubing.

13. The invention defined in claim 9, wherein said outlet port is arranged for being detachably coupled to a string of production tubing.

14. A pump for downhole use to pump well fluid from a well, said pump comprising:

structure defining a first fluid confining chamber in communication with a second fluid confining chamber through a fluid conducting passage, said first and second chambers being for holding, respectively, a displacing fluid and a well fluid, said passage extending upwardly from its point of communication with said second chamber to define an upwardly extending channel in which displacing fluid and well fluid may interface, said second chamber having inlet and outlet port means operable only to receive and discharge fluid, respectively, said pump structure having a gas trap defined therein above and in communication with the upper end of said channel to trap gas evolved from 1 the well fluid, and including valve controlled conduit means connected for conducting trapped gas from said gas trap to a point in said second chamber adjacent said outlet port means so that the gas is pumped out of said second chamber with well fluid, said valve controlled conduit means being operable to control the flow of gas therethrough as a function of the pressure level of gas being conducted therethrough and the pressure levels within said gas trap and said second chamber;

means for injecting displacing fluid at a controlled rate into said first chamber, said means arranged for connection to a source of displacing fluid;

means for expanding and contracting the effective volume of said first chamber to displace up and down in said'channel the region of interface between the displacing fluid and the well fluid whereby the displacing fluid functions as a piston to pump well fluid in said inlet port means andout said discharge port means, said means being constructed for connection with a prime mover; and

means for conducting. fluid pumped from said outlet port means to well surface.

15. The invention recited in claim 14, wherein said inlet port means includes a check valve operative to prevent fluid flow therethrough out from said second chamber and said 'outlet port means includes a check valve operative to prevent fluid flow therethrough into said second chamber.

16. The invention recited in claim 14, including means for supplying displacing fluid, said displacing fluid supply means being connected to said fluid injecting means to maintain the region of interface between the displacing fluid and the displaced fluid within said channel and second chamber.

17. The invention recited in claim 14, wherein said means for expanding and contracting the effective volume of said first chamber is a plunger means mounted therein for up and down reciprocal motion, said plunger means being adapted for connection through a string of sucker rods to a prime mover.

18. The invention recited in claim 14, including fluid injection means associated with said structure to extend into well fluid being pumped for injecting controlled quantities of a diluent fluid into the well fluid to be pumped whereby to dilute and thereby reduce the viscosity of the well fluid.

19. The invention recited in claim 14, wherein said means for expanding and contracting the effective volume of said first chamber is a plunger means mounted therein for reciprocal motion.

20. The invention recited in claim 19, including prime mover means connected to said plunger means for driving said plunger means in its reciprocal path of motion. I

21. A well pumping system, comprising:

a sucker rod string;

a fluid sealed string of tubing for positioning in a well to extend from the bottom portion of a well to well surface, said sucker rod string being mounted in said string of tubing for reciprocation up and down therein whereby said tubing functions as a housing to isolate said sucker rod string from well fluid thereby up and down reciprocal movement of said sucker rod string is not inhibited by well fluid;

pump structure mounted on the lower end of said string of tubing to depend therefrom into the reservoir of well fluid to be pumped, said pump structure defining a first fluid confining chamber in communication with a second fluid confining chamber through a fluid conducting passage, said first and second chambers being for holding, respectively, a displacing fluid and a well fluid, said passageextending upwardly from its point of communication with said second chamber to define an upwardly extendingchannel in which displacing fluid and well fluid may interface, said second chamber having inlet and outlet port means operable only to receive and discharge fluid, respectively, said pump structure having a gas trap defined therein above and in communication with the upper end of said channel to trap gas evolved from the 'well fluid, and including valve controlled conduit means connected for conducting trapped gas from said gas trap to a point in said second chamber adjacent said outlet-port means so that the gas is pumped out of said second chamber with well fluid, said valve controlled conduit means being operable to control the flow of gas therethrough as 7 a function of the pressure level of gas being conducted therethrough and the pressure levels within said gas trap and said second chamber;

plunger means mounted for up and down reciprocal motion in said first chamber for expanding and contracting the effective volume of said first chamher to displace up and down in said channel the region of interface between the displacing fluid and the well fluid whereby the displacing fluid functions as a piston to pump well fluid in said inlet port means and out said outlet port means;

means for isolating the discharge point of said outlet port means of said pump structure from the well fluid reservoir and connecting said outlet port means in communication with well surface so that well fluid discharged from said outlet port means is pumped to well surface;

means for connecting said plunger means to said sucker rod string whereby said plunger means may be driven through said sucker rod string; displacing fluid supply means connected to said first chamber for supplying displacing fluid thereto at a controllable rate to'maintain the moving region of interface'between the displacing fluid and the well fluid within said upwardly extending channel and said second chamber; and prime mover means connected to said sucker rod string for driving said sucker rod string in up and down reciprocal motion thereby to drive said plunger means.

22. The invention recited in claim 21, wherein the well fluid is of an offensive nature and the displacing fluid is of an inoffensive nature.

23. The invention defined in claim 21, including lubricating fluid within said fluid sealed string of tubing to provide a lubricated path through which said sucker rod string may reciprocate with minimum wear and substantially free fall velocity.

crude oil being pumped for injecting controlled quanti- I ties of a'diluent fluid into the high viscosity crude oil wherebyto dilute the crude oil and reduce its viscosity.

25. The invention recited in claim 24, wherein the diluent fluid is kerosene.

26. The invention defined in claim 21, wherein said means for isolating the discharge point of said outlet port means from thewell fluid reservoir and connecting said outlet port means in communication with well surface is a fluid sealed string of production tubing.

27. The invention defined in claim 26, wherein said string of production tubing is detachably coupled to said pump structure.

28. The invention defined in claim 21, wherein said displacing fluid supply means is operable to supply displacing fluid to said pump structure in time coincidence with the expansion of the effective volume of said first chamber.

29. The invention defined in claim 28, wherein said displacing fluid supply means comprises:

structuredefining a reservoir for displacing fluid;

means connected to said displacing fluid reservoir for transferring displacing fluid thereto at a controlled rate; and I valve means connecting said displacing fluid reservoir in communication with said first chamber for controlling the flow of displacing fluid between said displacing fluid reservoir and said first chamber, said valve means being operable to open and close, respectively, in time coincidence with the expansion and contraction of the effective volume of said first chamber. a

30. The invention defined in claim 29, wherein said valve means is operated by the pressure differential developed between said first chamber and said displacing fluid reservoir during the expansion and contraction of the effective volume of said first chamber.

31. The invention defined in claim 30, wherein:

said displacing fluid reservoir is defined by a downwardly extending continuation of said first cham- 17 a 18 her, said displacing fluid reservoir being in aligncontract and expand the effective volume of said ment with said plunger means; and first chamber, respectively, expands and contracts said plunger means seals said first chamber from said the volume of said reservoir means; and

displacing fluid reservoir whereby the up and down said valve means is carried by said plunger means. reciprocal movement of said plunger means to

Claims

1. In a down hole well pumping system, the improvement comprising: pump structure for positioning in a well bore down hole in contact with a well reservoir, said pump structure defining a first fluid confining chamber for receiving displacing fluid, a second fluid confining chamber for receiving well fluid and a fluid conducting passage interconnecting said fluid confining chambers in communication with each other, said second chamber having an inlet and outlet port defined therein, said inlet port being defined to communicate with the well reservoir in which said pump structure is positioned, said passage extending upwardly from its point of communication with said second chamber to define an upwardly extending channel of predetermined length in which displacing fluid and well fluid may interface, at least a portion of said first cHamber defining a plunger chamber; inlet valve means mounted in said inlet port for conducting well fluid into said second chamber; outlet valve means mounted in said outlet port for discharging fluid from said second chamber; means for expanding and contracting the effective volume of said first chamber, each expansion and contraction of the effective volume of said first chamber being defined as a pump stroke, said means for expanding and contracting the effective volume of said first chamber being a plunger means mounted for reciprocal motion in said plunger chamber; means for supplying displacing fluid to said pump structure on each stroke of said pump at a controllable rate to maintain the moving interface region between displacing fluid and well fluid within said upwardly extending channel and said second chamber, said displacing fluid supply means being operable to supply displacing fluid to said pump structure in time coincidence with the expansion of the effective volume of said first chamber; said displacing fluid supply means comprising: reservoir means for displacing fluid defined as a continuation of said plunger chamber, said plunger means sealing said first chamber from said reservoir means whereby movement of said plunger means to contract and expand the effective volume of said first chamber, respectively, expands and contracts the volume of said reservoir means; means connected to said reservoir means for transferring displacing fluid thereto at a controlled rate; and valve means mounted in said plunger means for controlling the flow of displacing fluid between said reservoir means and said first chamber, said valve means being operated by the pressure differential developed between said first chamber and said reservoir means to open and close, respectively, during the expansion and contraction of the effective volume of said first chamber; and means for conducting fluid pumped from said outlet valve means to well surface.

2. In a down hole well pumping system, the improvement comprising: pump structure for positioning in a well bore down hole in contact with a well reservoir, said pump structure defining a first fluid confining chamber for receiving displacing fluid, a second fluid confining chamber for receiving well fluid and a fluid conducting passage interconnecting said fluid confining chambers in communication with each other, said second chamber having an inlet and outlet port defined therein, said inlet port being defined to communicate with the well reservoir in which said pump structure is positioned, said passage extending upwardly from its point of communication with said second chamber to define an upwardly extending channel of predetermined length in which displacing fluid and well fluid may interface, at least a portion of said first chamber defining a vertically extending plunger chamber; inlet valve means mounted in said inlet port for conducting well fluid into said second chamber; outlet valve means mounted in said outlet port for discharging fluid from said second chamber; means for expanding and contracting the effective volume of said first chamber, said means for expanding and contracting the effective volume of said first chamber is a plunger means mounted for up and down reciprocal motion in said plunger chamber; means for supplying displacing fluid to said pump structure at a controllable rate to maintain the moving interface region between displacing fluid and well fluid within said upwardly extending channel and said second chamber, said displacing fluid supply means being operable to supply displacing fluid to said pump structure in time coincidence with the expansion of the effective volume of said first chamber; said displacing fluid supply means comprising: reservoir means for displacing fluid defined as a continuation of said plunger chamber, said plunger chamber being positioned above said reservoir means, said plunger means sealing said first chamber from said reservoir means whereby movement of said plunger means to contract and expand the effective volume of said first chamber, respectively, expands and contracts the volume of said reservoir means; means connected to said reservoir means for transferring displacing fluid thereto at a controlled rate; and valve means mounted in said plunger means for controlling the flow of displacing fluid between said reservoir means and said first chamber, said valve means being operated by the pressure differential developed between said first chamber and said reservoir means to open and close, respectively, during the expansion and contraction of the effective volume of said first chamber; and means for conducting fluid pumped from said outlet valve means to well surface.

3. The invention defined in claim 2, including a string of sucker rods for reciprocating said plunger means up and down, said sucker rods being connected to said plunger means and extending therefrom to well surface, said sucker rods being hollow and defining a conduit for conducting displacing fluid from well surface to said plunger means, said plunger means having a fluid conducting path defined therethrough for conducting displacing fluid from said sucker rods to said reservoir means.

4. A well pumping system, comprising: a sucker rod string; a fluid sealed string of tubing for positioning in a well to extend from the bottom portion of a well to well surface, said sucker rod string being mounted in said string of tubing for reciprocation up and down therein whereby said tubing functions as a housing to isolate said sucker rod string from well fluid thereby up and down reciprocal movement of said sucker rod string is not inhibited by well fluid; pump structure mounted on the lower end of said string of tubing to depend therefrom into the reservoir of well fluid to be pumped, said pump structure defining a first fluid confining chamber in communication with a second fluid confining chamber through a fluid conducting passage, said first and second chambers being for holding, respectively, a displacing fluid and a well fluid, said passage extending upwardly from its point of communication with said second chamber to define an upwardly extending channel in which displacing fluid and well fluid may interface, said second chamber having inlet and outlet port means operable only to receive and discharge fluid, respectively; plunger means mounted for up and down reciprocal motion in said first chamber for expanding and contracting the effective volume of said first chamber to displace up and down in said channel the region of interface between the displacing fluid and the well fluid whereby the displacing fluid functions as a piston to pump well fluid in said inlet port means and out said discharge port means; means for isolating the discharge point of said outlet port means of said pump structure from the well fluid reservoir and connecting said outlet port means in communication with well surface so that well fluid discharged from said outlet port means is pumped to well surface; means for connecting said plunger means to said sucker rod string whereby said plunger means may be driven through said sucker rod string; displacing fluid supply means connected to said first chamber for supplying displacing fluid thereto at a controllable rate to maintain the moving region of interface between the displacing fluid and the well fluid within said upwardly extending channel and said second chamber, said displacing fluid supply means being operable to supply displacing fluid to said pump structure in time coincidence with the expansion of the effective volume of said first chamber; said displacing fluid supply means comprising: structure defining a reservoir for displacing fluid, said displacing fluid reservoir being defined by a downwardly extending continuation of said first chamber and being in alignment with said plunger means; means connected to said displacing fluid reservoir for Transferring displacing fluid thereto at a controlled rate; and valve means connecting said displacing fluid reservoir in communication with said first chamber for controlling the flow of displacing fluid between said displacing fluid reservoir and said first chamber, said valve means being operable to open and close, respectively, in time coincidence with the expansion and contraction of the effective volume of said first chamber, said valve means being operated by the pressure differential developed between said first chamber and said displacing fluid reservoir during the expansion and contraction of the effective volume of said first chamber; said plunger means sealing said first chamber from said displacing fluid reservoir whereby the up and down reciprocal movement of said plunger means to contract and expand the effective volume of said first chamber, respectively, expands and contracts the volume of said reservoir means, said valve means being carried by said plunger means; and prime mover means connected to said sucker rod string for driving said sucker rod string in up and down reciprocal motion thereby to drive said plunger means.

5. The invention defined in claim 4, wherein: said sucker rods are hollow and define a conduit for conducting displacing fluid from well surface to said plunger means; and said plunger means has a fluid conducting path defined therethrough for conducting displacing fluid from said sucker rods to said displacing fluid reservoir.

7. The invention defined in claim 4, wherein: said sucker rod string defines a conduit for conducting displacing fluid from well surface to said plunger means; and said plunger means has a fluid conducting path defined therethrough for conducting displacing fluid from said sucker rod string to said reservoir means.

9. A pump for down hole use, comprising: structure defining a first fluid confining chamber for receiving displacing fluid, a second fluid confining chamber for receiving well fluid and a fluid conducting passage interconnecting said fluid confining chambers in communication with each other, said second chamber having an inlet and outlet port defined therein, said inlet port being defined to communicate with a well reservoir, said passage extending upwardly from its point of communication with said second chamber to define an upwardly extending channel of predetermined length in which displacing fluid and well fluid may interface, at least a portion of said first chamber defining a plunger chamber; inlet valve means mounted in said inlet port for conducting well fluid into said second chamber; outlet valve means mounted in said outlet port for discharging fluid from said second chamber; reservoir means defined as a continuation of said plunger chamber, said reservoir means being arranged for connection to a displacing fluid supply so that displacing fluid may be selectively supplied thereto; plunger means mounted for reciprocal motion in said plunger chamber for expanding and contracting the effective volume of said first chamber, said plunger means sealing said first chamber from said reservoir means whereby movement of said plunger means to contract and expand the effective volume of said first chamber, respectively, expands and contracts the volume of said reservoir means; and valve means moUnted in said plunger means for controlling the flow of displacing fluid between said reservoir means and said first chamber, said valve means being operated by the pressure differential developed between said first chamber and reservoir means to open and close, respectively, during the expansion and contraction of the effective volume of said first chamber.

10. The invention defined in claim 9, wherein: said plunger chamber is defined to be substantially vertically extending; and said reservoir means is defined as a downward continuation of said plunger chamber.

11. The invention defined in claim 10, wherein: said plunger means is arranged for connection to a string of upwardly extending hollow sucker rods whereby sand plunger means may be driven up and down and displacing fluid may be conducted from well surface to said plunger means through a string of hollow sucker rods connected thereto; and said plunger means has a fluid conducting path defined therethrough for conducting displacing fluid to said reservoir means from the point of connection of a string of hollow sucker rods thereto.

14. A pump for downhole use to pump well fluid from a well, said pump comprising: structure defining a first fluid confining chamber in communication with a second fluid confining chamber through a fluid conducting passage, said first and second chambers being for holding, respectively, a displacing fluid and a well fluid, said passage extending upwardly from its point of communication with said second chamber to define an upwardly extending channel in which displacing fluid and well fluid may interface, said second chamber having inlet and outlet port means operable only to receive and discharge fluid, respectively, said pump structure having a gas trap defined therein above and in communication with the upper end of said channel to trap gas evolved from the well fluid, and including valve controlled conduit means connected for conducting trapped gas from said gas trap to a point in said second chamber adjacent said outlet port means so that the gas is pumped out of said second chamber with well fluid, said valve controlled conduit means being operable to control the flow of gas therethrough as a function of the pressure level of gas being conducted therethrough and the pressure levels within said gas trap and said second chamber; means for injecting displacing fluid at a controlled rate into said first chamber, said means arranged for connection to a source of displacing fluid; means for expanding and contracting the effective volume of said first chamber to displace up and down in said channel the region of interface between the displacing fluid and the well fluid whereby the displacing fluid functions as a piston to pump well fluid in said inlet port means and out said discharge port means, said means being constructed for connection with a prime mover; and means for conducting fluid pumped from said outlet port means to well surface.

15. The invention recited in claim 14, wherein said inlet port means includes a check valve operative to prevent fluid flow therethrough out from said second chamber and said outlet port means includes a check valve operative to prevent fluid flow therethrough into said second chamber.

20. The invention recited in claim 19, including prime mover means connected to said plunger means for driving said plunger means in its reciprocal path of motion.

21. A well pumping system, comprising: a sucker rod string; a fluid sealed string of tubing for positioning in a well to extend from the bottom portion of a well to well surface, said sucker rod string being mounted in said string of tubing for reciprocation up and down therein whereby said tubing functions as a housing to isolate said sucker rod string from well fluid thereby up and down reciprocal movement of said sucker rod string is not inhibited by well fluid; pump structure mounted on the lower end of said string of tubing to depend therefrom into the reservoir of well fluid to be pumped, said pump structure defining a first fluid confining chamber in communication with a second fluid confining chamber through a fluid conducting passage, said first and second chambers being for holding, respectively, a displacing fluid and a well fluid, said passage extending upwardly from its point of communication with said second chamber to define an upwardly extending channel in which displacing fluid and well fluid may interface, said second chamber having inlet and outlet port means operable only to receive and discharge fluid, respectively, said pump structure having a gas trap defined therein above and in communication with the upper end of said channel to trap gas evolved from the well fluid, and including valve controlled conduit means connected for conducting trapped gas from said gas trap to a point in said second chamber adjacent said outlet port means so that the gas is pumped out of said second chamber with well fluid, said valve controlled conduit means being operable to control the flow of gas therethrough as a function of the pressure level of gas being conducted therethrough and the pressure levels within said gas trap and said second chamber; plunger means mounted for up and down reciprocal motion in said first chamber for expanding and contracting the effective volume of said first chamber to displace up and down in said channel the region of interface between the displacing fluid and the well fluid whereby the displacing fluid functions as a piston to pump well fluid in said inlet port means and out said outlet port means; means for isolating the discharge point of said outlet port means of said pump structure from the well fluid reservoir and connecting said outlet port means in communication with well surface so that well fluid discharged from said outlet port means is pumped to well surface; means for connecting said plunger means to said sucker rod string whereby said plunger means may be driven through said sucker rod string; displacing fluid supply means connected to said first chamber for supplying displacing fluid thereto at a controllable rate to maintain the moving region of interface between the displacing fluid and the well fluid within said upwardly extending channel and said second chamber; and prime mover means connected to said sucker rod string for driving said sucker rod string in up and down reciprocal motion thereby to drive said plunger means.

24. The invention recited in claim 21, wherein the well fluid is a high viscosity crude oil, the displacing fluid is kerosene, and including fluid injection means associated with said pump structure to extend into the crude oil being pumped for injecting controlled quantities of a diluent fluid into the high viscosity crude oil whereby to dilute the crude oil and reduce its viscosity.

25. The invention recited in claim 24, wherein the diluent fluid is kerosene.

26. The invention defined in claim 21, wherein said means for isolating the discharge point of said outlet port means from the well fluid reservoir and connecting said outlet port means in communication with well surface is a fluid sealed string of production tubing.

29. The invention defined in claim 28, wherein said displacing fluid supply means comprises: structure defining a reservoir for displacing fluid; means connected to said displacing fluid reservoir for transferring displacing fluid thereto at a controlled rate; and valve means connecting said displacing fluid reservoir in communication with said first chamber for controlling the flow of displacing fluid between said displacing fluid reservoir and said first chamber, said valve means being operable to open and close, respectively, in time coincidence with the expansion and contraction of the effective volume of said first chamber.

31. The invention defined in claim 30, wherein: said displacing fluid reservoir is defined by a downwardly extending continuation of said first chamber, said displacing fluid reservoir being in alignment with said plunger means; and said plunger means seals said first chamber from said displacing fluid reservoir whereby the up and down reciprocal movement of said plunger means to contract and expand the effective volume of said first chamber, respectively, expands and contracts the volume of said reservoir means; and said valve means is carried by said plunger means.