Abstract:
An apparatus and method for enhancing oil recovery through improved injection well performance is provided, wherein a fluid is injected into the well bore at a pressure P i , and a downhole fluid-actuated engine and pump assembly is employed as a booster in order to generate a high pressure output at pressure P h  greater than P i  and a low pressure output at pressure P l  lower than P i ; the respective output streams are directed to lower and higher permeability geological strata adjacent the well bore in order to increase production.

Description:
This application is a division of application Ser. No. 09/928,183 filed Aug. 10, 2001, now allowed. 
    
    
     BACKGROUND OF THE INVENTION 
     1 Field of the Invention 
     The present invention is broadly concerned with improved systems for enhancing oil recovery by increasing the efficiency of injection wells. More particularly, the invention is concerned with a method and corresponding apparatus for operating an injection well having a well bore extending downwardly through geographical strata with higher and lower permeabilities respectively, wherein a downhole booster pump is employed to generate higher and lower pressure output streams which are directed to the lower and higher permeability strata. 
     2. Description of the Prior Art 
     When hydrocarbon producing wells are drilled, initial hydrocarbon production is usually attained by natural drive mechanisms (water drive, solution gas, or gas cap, e.g.) which force the hydrocarbons into the producing well bores. If a hydrocarbon reservoir lacks sufficient pore pressure (as imparted by natural drive), to allow natural pressure-driven production, artificial lift methods (pump or gas lift, e.g.) are used to produce the hydrocarbon. 
     As a large part of the reservoir energy may be spent during the initial (or “primary”) production, it is frequently necessary to use secondary hydrocarbon production methods to produce the large quantities of hydrocarbons remaining in the reservoir. Water flooding is a widespread technique for recovering additional hydrocarbon and usually involves an entire oil or gas field. Water is injected through certain injection wells selected based on a desired flood pattern and on lithology and geological deposition of the pay interval. Displaced oil is then produced into producing wells in the field. 
     Advancements in secondary hydrocarbon producing technology has led to several improvements in waterflood techniques. For example, the viscosity of the injected water can be increased using certain polymer viscosifiers (such as polyacrylamides, polysaccharides, and biopolymers) to improve the “sweep efficiency” of the injected fluid. This results in greater displacement of hydrocarbons from the reservoir. 
     The ability to displace oil from all the producing intervals in a hydrocarbon reservoir is limited by the lithological stratification of the reservoir. That is, there are variations in permeability in different geological strata which allow the higher permeability zones to be swept with injected fluid first while leaving a major part of the hydrocarbon saturation in the lower permeability intervals in place. Continued injection of flooding fluid results in “breakthrough” at the producing wells at the high permeability intervals which can render continued injection of the flooding medium uneconomical. 
     A number of approaches have been used in the past to increase the efficiency of injection well practice and to avoid “breakthrough.” This has involved use of gel treatments to decrease the permeability of a higher permeability strata and thereby improve the sweep efficiency. Attempts have also been made to use polymer gels having selective penetration properties which will preferentially enter high permeability strata. However, these polymers are rare and expensive. 
     SUMMARY OF THE INVENTION 
     The present invention is broadly directed to systems for operating injection wells having a well bore extending downwardly through geological strata or zones having higher and lower fluid permeabilities, and includes the steps of injecting a fluid into the well bore at a pressure P i , and using the injected fluid to generate first and second higher and lower pressure output streams at pressures P h  and P l , respectively, whereupon such streams are directed out of the well bore and into the appropriate geological stratum. In preferred forms, the injected fluid is directed to a fluid-actuated downhole engine and pump assembly, and a first portion of the injected fluid is delivered to the engine which creates work with consequent reduction in the pressure of the first fluid portion to a level below the initial pressure P i . Some of the created work is transferred to the pump to generate the high pressure output stream. A second portion of the injected fluid is delivered to the pump and is pressurized therein, the pressurized pump output comprising at least a part of the high pressure output stream. 
     In practice, the engine and pump assembly is located within the well bore proximal to the strata to be treated, typically by placing the assembly within a tubing string. In order to permit passage of the output streams through the geological strata, the well casing is divided with appropriately located and sized output openings. 
     The preferred engine and pump assembly includes a primary block having a valve chamber, an engine piston chamber, a pump piston chamber, an injected fluid inlet, and high and low pressure fluid delivery outlet openings. The primary block also includes an elongated operator shaft extending along the length of the block from the valve chamber and through the engine and piston pump chambers. This shaft supports an engine piston slidable within the engine chamber and a pump piston slidable within the pump piston chamber. A movable valve member is also located within the valve chamber. In order to direct the incoming injected stream and deliver the desired outputs, the primary block has an injected fluid passageway system operably coupling the valve chamber and the engine piston chamber for alternate delivery of injected fluid into the engine piston chamber on opposite sides of the engine piston, in response to the location of the valve member. This injected fluid passageway system also couples the injected fluid inlet and the pump piston chamber for alternate delivery of injected fluid to the pump piston chamber on opposite sides of the pump piston. The injected fluid passageway system is in communication with the low pressure fluid delivery opening, whereas the high pressure fluid delivery opening of the block is in operative communication with the pump piston chamber. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a vertical sectional, partially fragmentary view illustrating the preferred injection well assembly of the invention positioned within a well bore adjacent geological strata of higher and lower fluid permeabilities and operable to generate high and low pressure output streams for delivery into the strata; 
     FIG. 2 is an enlarged, somewhat schematic vertical sectional view depicting the internal construction of the engine and pump assembly used in the injection well assembly, and illustrating the engine and pump assembly at the beginning of the upstroke thereof; 
     FIG. 3 is a view similar to that of FIG. 2, but illustrating the engine and pump assembly at the beginning of the downstroke thereof; 
     FIG. 4 is a block diagram schematically illustrating the injection fluid flow to the engine and pump assembly, as well as the higher and lower pressure output streams therefrom; and 
     FIG. 5 is a block diagram schematically illustrating a prior art injection and pump assembly used in production wells to assist in recovery from the production wells. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Turning now to the drawings, and particularly FIG. 1 an injection well assembly  10  is illustrated in use within a well bore  12  extending downwardly through the earth  14  and through a geological strata  16  and  18  of higher and lower permeability, respectively. Broadly speaking, the well assembly  10  includes a well casing  20 , an elongated, sectionalized tubing string  22  ending in a tubing nipple  24 , and a fluid-actuated engine and pump assembly  26  telescoped within nipple  24 . 
     In more detail, casing  20  is essentially conventional sectionalized well casing, but includes a first series of apertures  28  adjacent higher permeability strata  16 , and a second series of apertures  30  adjacent low permeability strata  18 . 
     Tubing string  22  is also conventional and is made up of a number of end-to-end interconnected tubular sections  22   a  as well as nipple  24  presenting an open outlet end  32 . As illustrated, nipple  24  is threadably secured to the next adjacent section  22   a , and has a series of circumferentially spaced outlet slots  34 . String  22  is positioned within casing  20  by means of vertically spaced apart packing rings  36 . The inner face of nipple  24  has appropriate grooves  38  and connectors  39  to insure proper positioning of assembly  26  therein. Although nipple  24  is illustrated in the drawing figures as being disposed at the lower terminal end of tubing string  22 , additional tubing sections can be coupled to the lower end of nipple  24  and extend downwardly therefrom. 
     Referring now to FIGS. 2 and 3, engine and pump assembly  26  has a primary block  40 , an upper inlet block  42 , a lower cap block  44 , and an outer tubular wall  46  coupled with cap block  44  and extending upwardly past block  42 . 
     Primary block  40  includes, from top to bottom, an injection fluid inlet  48 , a valve chamber  50 , a bore section  52 , an engine piston chamber  54 , a bore section  56 , a piston pump chamber  58 , a high pressure fluid chamber  60  and a high pressure outlet chamber  62 . Additionally, block  40  has an injected fluid passageway system broadly referred to by the numeral  64  and made up of: a passageway  66  extending from inlet  48  downwardly and communicating with an annular passageway  68  formed between the outer surface of block  40  and wall  46 ; upper and lower passageways  70  and  72  in communication with passageway  68  and extending to a point above and below chamber  58 ; a passageway  74  extending between the upper end of valve chamber  50  and communicating with the upper end of engine piston chamber  54 ; and a passageway  76  extending from valve chamber  46  to communication with engine piston chamber  54  adjacent the lower end thereof. Block  40  further has a low pressure fluid passageway system including a dogleg passageway  78  extending between valve chamber  50  and an annular passageway  80  formed between the outer surface of block  40  and wall  46 ; and a passageway  82  extending between the lower end of valve chamber  50  and communicating with passageway  80 . Finally, block  40  has high pressure fluid outlets  83  and  83   a  respectively extending from the upper and lower ends of chamber  58  and communicating with chamber  60 . 
     It will be observed that annular passageway  68  and  80  are separated by an intermediate sealing ring  84 , whereas a lower sealing ring  86  defines the bottom extent of passageway  68  and an upper sealing ring  88  defines the upper boundary of passageway  80 . 
     A shiftable operator  90  is housed within block  40  and extends between upper valve chamber  50  and lower piston pump chamber  58 . Operator  90  includes an elongated shaft  92  having a continuous axial bore  94 . A pair of spaced apart recesses  96  and  98  are formed in the upper end of shaft  92  and are important for purposes to be described. Shaft  92  also supports an engine piston  100  which is slidable within chamber  54  and a pump piston  102  slidable within chamber  58 . It will be noted that a cup-like injection fluid-retaining cup member  104  is affixed to the upper surface of chamber  60  and receives the lowermost end of shaft  92 . 
     The valving system within block  40  includes a shiftable, annular valve member  106  situated within chamber  50 . Valve member  106  includes an upper, annular recess  108  formed in the outer sidewall thereof, as well as a lateral bore  110 . Valve member  106  is vertically shiftable within chamber  50 , with the lower end of valve member  106  located outboard of bore section  52 . The valving system further includes a check valve assembly  112  adjacent piston pump chamber  58 . Specifically, a pair of upper check valves  114 ,  116  are located above chamber  58  and in communication therewith. Check valve  114  also communicates with passageway  70 , while check valve  116  communicates with passageway  83 . A pair if lower check valves  118 ,  120  are adjacent the bottom of chamber  58  and communicate with the latter as well as passageways  72  and  83   a , respectively. 
     Engine and pump assembly  26  is located within nipple  24  by conventional means, including a pair of sealing rings  122 ,  124  located on opposite sides of output slots  34 . Rings  122 ,  124  are also located on opposite sides of a series of openings  126  provided through tubular wall  46 . 
     Inlet block  42  is positioned above primary block  40  and includes an elongated, a central inlet passageway  128  which communicates with inlet  48  of primary block  40 . Although not shown in FIGS. 2 and 3, it will be understood that passageway(s) are provided throughout the entire tubing string  22  so as to permit injection of fluid. 
     Lower cap block  44  includes a caged ball check valve  130  including an apertured housing  132  and a check ball  134  captively retained within housing  132 . Housing  132  is concentric with a pressurized fluid outlet port  136  formed through cap block  44 . 
     The principle operation of the preferred injection well assembly  10  can be understood from a consideration of FIG.  4 . That is, injection fluid at pressure P i  is delivered to engine and pump assembly  26 , with a first portion of the injection fluid being directed to the engine for operation thereof, whereas a second portion of the injection fluid is directed to the pump in order to pressurize the second portion. Thus, engine and pump assembly  26  produces two output streams, namely an output stream of pressure P l  (which is lower than P i ) from the engine, and an output stream of pressure P h  (which is higher than P i ) from the pump. 
     The preferred engine and pump assembly  26  is a modified version of an assembly  138  illustrated in FIG.  5 . Such prior art equipment is used in production wells (rather than injection wells) and is operated by injection fluid at pressure P i , producing a lower pressure engine output stream at pressure P o . The engine in turn operates the pump which pumps well fluid at an inlet pressure of P w  and an outlet pressure of P h (P h  being higher than P w ). In normal practice, the output streams from the engine and pump are comingled to yield a single output stream of intermediate pressure between P o  and P h . 
     The detailed operation of injection well assembly  10  is best understood from a consideration of FIGS. 2 and 3. FIG. 2 depicts engine and pump assembly  26  at its lowermost position, at the start of the upstroke, whereas FIG. 3 depicts the assembly at its uppermost position, at the beginning of the downstroke. In the ensuing discussion, it will be assumed that the assembly  26  is fully primed and is operating normally. 
     Referring first to FIG. 2, at the beginning of the upstroke, the injection fluid at pressure P i  is present in the following: inlet passageway  128 , inlet  48 , bore  94  of shaft  92 , cup member  104 , valve chamber  50  between the valve and adjacent portions of shaft  92 , the lower righthand generally L-shaped section of the valve chamber  50  located below valve member  106 , the lower lefthand region of valve chamber  50  located below valve member  106 , passageway  66 , annular passageway  68  between sealing rings  84  and  86 , lateral passageways  70  and  72 , check valve  118  and the area within chamber  58  below piston  102 , lateral valve bore  110 , passageway  76  and the region within chamber  54  below piston  100 . Low pressure fluid at pressure P l  is present in the following: passageway  74  and the region of chamber  54  above piston  100 , passageway  82  and annular passageway  80  between sealing rings  84  and  88 , dog-leg passageway  70 , openings  126 , the annular space between sealing rings  122 ,  124 , and outlet slots  34 . Finally, high pressure fluid at pressure P h  is present in the following: the region of chamber  58  above piston  102 , check valves  114 ,  116  and  120 , passageways  83  and  83   a , chambers  60  and  62 , check valve  130 , the region below the assembly  26 , and in the annular space between tubular wall  46  and nipple  24  up to the level of seal  124 . 
     As the injection fluid is delivered to engine piston chamber  54 , the piston  100  is moved upwardly, owing to the fact that the fluid above the piston  100  is at the lower pressure P l  below P i . This upward movement of the piston serves to eject the low pressure fluid through passageways  74  and  78  for ultimate delivery out through slots  34 . At the same time, because pistons  100  and  102  are coupled, piston  102  moves upwardly to eject the high pressure fluid above the piston  102  through conduit  83  to be finally outputted through check valve  130 . In this respect, the imbalance of forces created by differential pressures and/or differential areas on lower and upper pistons  102 ,  106  together with the direct coupling of the two pistons allows the high pressure fluid to be ejected in this manner. 
     At the top of the stroke, engine and pump assembly  26  assumes the position illustrated in FIG.  3 . It will be observed that in this position valve member recess  108  serves to communicate passageway  76  and passageway  78  and that bore  110  is shifted out of communication with passageway  76 . In this uppermost position, the injection fluid at pressure P i  is present in the following: inlet passageway  128 , inlet  48 , shaft bore  94  and cup member  104 , the inner free volume of the valve chamber  50  between the inner valve surfaces and shaft  92  including bore  110 , passageway  66  and annular passageway  68 , upper and lower passageways  70  and  72 , check valve  114  and the region within chamber  58  above piston  102 , passageway  74  and the region within chamber  54  above piston  100 . The lower pressure fluid at pressure P l  is present in the following: the region within chamber  54  below piston  100 , passageway  76 , recess  108 , dog-leg passageway  78 , annular passageway  80 , openings  126 , the annular region between seals  122  and  124 , and slots  34 , passageway  82  and recess  98 . The higher pressure fluid at pressure P h  is present in the following: the region within chamber  58  below piston  102 , check valves  116 ,  118  and  120 , passageways  83  and  83   a , chambers  60  and  62 , outlet port  136 , check valve  130  and the region below the assembly  126 , and the annular space around assembly  26  up to seal  124 . During the downstroke, the lower pressure fluid at pressure P l  is delivered through passageway  76 , recess  108 , dog-leg passageway  78 , openings  126  and slots  34 . At the same time, pressurized fluid at pressure P h  is delivered through passageway  83   a  for ultimate passage through the check valve  130 . 
     Cycling of the assembly  26  as described above thus creates, both during upstroke and downstroke, a low pressure P l  output delivered through slots  34  and a high pressure P h  output delivered through check valve  130 . Again referring to FIG. 1, it will be seen that these respective outputs pass through apertures  28  and  30  into strata  16  and  18 . 
     It should be understood that the system described above can be easily reconfigured to accommodate situations in which the lower permeability strata is located above the higher permeability strata. In such a scenario, the entire engine and pump assembly can simply be physically inverted or, alternatively, the flow of the injection fluid in the assembly can be re-routed so that the high pressure fluid exits at a point above the low pressure fluid. 
     The preferred forms of the invention described above are to be used as illustration only, and should not be utilized in a limiting sense in interpreting the scope of the present invention. Obvious modifications to the exemplary embodiments, as hereinabove set forth, could be readily made by those skilled in the art without departing from the spirit of the present invention. 
     The inventors hereby state their intent to rely on the Doctrine of Equivalents to determine and assess the reasonably fair scope of the present invention as pertains to any apparatus not materially departing from but outside the literal scope of the invention as set forth in the following claims.