Patent Publication Number: US-7717182-B2

Title: Artificial lift with additional gas assist

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a continuation of U.S. patent application Ser. No. 11/415,715, filed May 2, 2006 now abandoned, which is a divisional of U.S. patent application Ser. No. 10/648,814, filed Aug. 26, 2003, now U.S. Pat. No. 7,063,161, which are hereby incorporated by reference in their entireties. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   Embodiments of the present invention generally relate to the field of fluid extraction from bore holes. More particularly, the present invention relates to artificial lifting devices and methodologies for retrieving fluids, such as crude oil and other liquid hydrocarbons, from bores where the fluid does not have sufficient hydrostatic pressure to rise to the surface of the earth of its own accord. 
   2. Description of the Related Art 
   The recovery of fluids such as oil from bore holes is typically accomplished by the pumping of fluid collected in the bore hole by mechanical or fluid power means. These means are necessitated when the pressure of the fluid at the base of the bore hole does not exceed the hydrostatic head needed to cause the fluid to rise to, and over, the earths&#39; surface of its own accord. Several methodologies are known to provide this pumping action, each with its own limitations. 
   In one methodology, a rod pump repeatedly reciprocates a rod up and down in the casing lining the well at the well head. The rod extends down the well to a production zone, where a pump is located and connected, at its outlet, to production tubing. As the pump downstrokes, the rod pushes a piston in the pump, to force fluids in the piston bore outwardly therefrom and thence into the production tubing. During rod upstroke, a valve closes the connection to the production tubing, and a second valve opens the piston bore to the formation, such that well fluid is drawn into the piston bore. Thus the recovery rate of fluid from the well is dependant upon the stroke of the rod and the number of strokes of the rod per unit of time. The pumps are typically used where the amount of oil to be recovered is marginal, but is sufficient to justify the relatively low cost of this pump arrangement. 
   A second methodology for artificial lifting uses a down hole positive displacement pump, typically a progressive cavity pump. These pumps typically use an offset helix screw configuration, where the threads of the screw or “rotor” portion are not equal to those of the stationary, or stator portion over the length of the pump, to effect a positive displacement of the fluid through the pump. This requires that the rotating surface of the rotor be sealingly engaged to that of the stator. This is typically accomplished by providing at least the inner bore surface of the stator with a compliant material such as neoprene rubber. The rotor pushes against this compliant material as the rotor rotates, thereby sealing the cavity formed between it and the stator to positively displace fluid through the pump. The rotor is driven by a rod extending down the casing from the surface, and this rod is rotated at relatively low rpm to cause pump operation. One problem associated with this methodology is that these pumps have limited applicability where high temperatures are encountered. 
   An additional downhole style of pump is the rotary pump, such as a vane or turbine pump, which uses a high speed rotation of an impeller(s) to accelerate fluids and direct them up the bore. Rotation of the impeller(s) is typically accomplished by coupling the impellers(s) to an electric motor which is attached to the impeller(s) downhole. Although it would be desirable to rotate the impeller(s) by a mechanical, surface mounted means, such as a surface mounted motor having a rotateable rod extending down the well bore, this is typically not done, because the speed at which the rod would have to be turned results in “whipping” or other imbalance effects of the rod, causing the relatively long rod to strike the casing or production tubing, eventually rupturing one or both of the rod, tubing and/or casing. Additionally, the durability of the electric motor in the hostile downhole location is limited, and as a result, the motors typically fail after nine months to one year, thereby requiring pulling of the string to retrieve and replace the motor. 
   A further method of well bore fluid recovery is known as jet pumping. This methodology takes advantage of the venturi effect, whereby the passage of fluid through a venturi causes a pressure drop, and the well fluids being recovered are thereby brought into the fluid stream. To accomplish this in a well, a hollow string is suspended in the casing to the recovery level, and the jet pump is located at the end of the tubing within the production zone of the well. The jet pump includes an inlet, a reduced diameter portion and a flared outlet, thereby forming a venturi. A passage extends between this venturi and the production zone. A fluid under pressure is flowed down the string and through the passages in the pump and thence up to the surface through the annulus between the well casing and the hollow string. The passing of the high pressure fluid through the venturi causes a pressure drop in the high pressure fluid, and thus in the passage to the production zone, thereby causing the production fluids to be pulled into the stream of high pressure fluid passing through the pump and thus carried to the surface therewith. Preferably, the fluid being used for recovery is of the same species as that being recovered. Thus, excess returns of fluid are recovered, and the remaining fluid is recycled and again directed down the well. This technique suffers from limited fluid recovery rate and the need for extensive equipment, the cost of which typically exceeds the value of the oil which may be recovered, which would be acceptable if the recovery rate were greater. 
   An additional method of well bore fluid recovery is gas-assisted lifting, in which a gas is injected into the fluid to be recovered. The injected gas forms bubbles in the fluid. These bubbles rise to the surface and propel well fluids upwardly therewith. This technique likewise suffers from limited fluid recovery and the need for extensive equipment, the cost of which typically exceeds the value of the oil which may be recovered. 
   Therefore, there exists in the art a need to provide enhanced artificial lifting methods, techniques and apparatus, having a greater return on investment and or durability. 
   SUMMARY OF THE INVENTION 
   The present invention generally provides methods, apparatus and articles for the improved artificial lifting of fluids, using a pump having enhanced fluid lifting capability from the well bore. 
   In one embodiment, the invention provides a pumping member locatable in a production zone of a well, and a secondary lift mechanism, simultaneously present in the well bore to enhance artificial lifting of well fluids. Preferably, the secondary lift mechanism is a gas injected into a liquid, whereby the gas forms gas bubbles in the well fluid and enhances the buoyancy thereof for recovery of the fluid. 
   In a further embodiment, the invention provides a jet pump, positioned within a well bore at a fluid production location, and the fluid passing through the jet pump and thereby providing the suction of the well bore fluids into the fluid stream further includes a material dissolved therein which provides additional lift to the fluid as it is carried up the bore. Preferably, this material is a material which is inserted at the well head under pressure into a pressurized stream of pumping fluid to be passed through the jet pump, which material becomes gaseous after leaving the jet pump and thereby provides additional lifting capability to the returning stream of pumping fluid and well bore fluid. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
       FIG. 1  is a schematic view of a borehole, down hole equipment and adjacent well head peripherals used to provide the gas assisted artificial lifting of the present invention; and 
       FIG. 2  is a sectional view of a jet pump located in a producing zone of a well bore. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to  FIG. 1 , there is shown, in schematic representation, a producing oil well having a first borehole  10  extending from a well head  12  at the opening of the borehole to the surface  14 , and a lower terminus  16 , in a production zone  18 . Multiple such production zones may be traversed by the borehole. The well bore is cased, i.e., casing  20  extends along the borehole  10  to isolate the earth formation  22  around the borehole  10  from exposure to any tools or materials present in borehole  10 . 
   Extending into production zone  18 , and suspended on the end of a hollow tube  24 , is a jet pump  26 . As will be explained further herein, jet pump  26  includes an inlet section  32  extending into fluid communication with the fluids in the production zone  18 , a pumping liquid inlet  30  in fluid communication with the interior of hollow tube  24  (shown in  FIG. 2 ) and an outlet  28  in fluid communication with the cased portion of the borehole  10 . The fluid exiting the outlet  28  flows upwardly in the borehole  10  in the space or annulus  66  between the hollow tube  24  and the casing  20  in the wellbore  10 , to the earths&#39; surface. 
   Referring still to  FIG. 1 , well head  12  is positioned at the opening of the well at the surface of the earth, and generally includes at least a first portion  52  in sealing (typically welded or flange clamped) to the upper terminus  54  of casing  20 , and an upper portion  56  including valving and other apparatus as will be further described herein. First portion  52  also includes a valved return outlet  68  therein, through which material moving upwardly in the annulus  66  between the casing  20  and the hollow tube  24  can be recovered. Upper portion  56  includes a hanger  60 , from which the upper terminus  62  of hollow tube  24  is suspended, such as by being welded or clamped therein, and an upper valved inlet  64 , preferably collinear with the centerline of the hollow tube  24 , through which pumping liquid is injected into the well though hollow tube  24 . Thus, pumping fluid may be injected in a flow controlled mode, through throttling thereof by the valved inlet  64 , at a high pressure to pass through the jet pump  26  where well fluids are pulled from the production region  18  and then returned through the annulus  66  to valved return outlet  68  where the well fluid can be recovered and the pumping fluid separated therefrom and reused. 
   As also shown in  FIG. 1 , the separation of well fluids and recovery of the pumping fluid is accomplished by fluid control system  80  located generally adjacent to wellhead  12 . The fluid control system  80  is configured to enable recirculation of the fluids returned from the wellbore  10  until a desired return of wellbore fluids is achieved, and thereafter either or both of the introduced gas, as well as the recovered wellbore fluids, may be recovered from the well and distributed from the system. 
   Thus, fluid control system  80  includes a high pressure system  82 , which supplies fluid under pressure to the jet pump  26 , a return system  84 , which receives fluid returning from the wellbore through return outlet  68  and selectively separated, where necessary and proper, and start up system  86  which is used, in conjunction with high pressure system  82 , to initiate pumping from the wellbore  10 . 
   Referring still to  FIG. 1 , high pressure system  82  generally includes multiphase pump  88 , a fluid inlet  90 , through which a relatively low pressure stream of a mixture of gas and liquid is conveyed into the low pressure, or entry, side of multiphase pump  88 , and a high pressure outlet line  94  extending from multiphase pump high pressure outlet to the end of hollow tube  24  extending upwardly through the wellhead  12 . Multiphase pump  88  is capable of receiving a mixture of a liquid and a gas, and simultaneously pressurizing them, such that the fluid pressure in the exit of the pump may be sufficiently high to dissolve the gas into the liquid. 
   After the high pressure fluid is passed through the hollow tube  24 , jet pump  26  and then upwardly in the annulus  66  between the casing  20  and the hollow tube  24 , it exits the return outlet  68  and enters return system  84 . Return system  84  provides separation of well fluids from the high pressure pumping fluid, as well as valving and control circuitry to determine the proper routing of the fluids returning from the well. As shown in  FIG. 1 , a separator  96  is fed returning fluid through return conduit  98 , which is selectively opened, closed or throttled by return valve  101  located in fluid communication with return outlet  68 . Separator  96  separates gas in the returning fluid from liquids, such that gas is supplied therefrom to return gas line  100 , and fluid is supplied therefrom to return liquid line  102 . Return gas line  100  extends from separator  96  to a tee or junction  104 , having a recycle gas line  106 , and a production gas outlet  108  extending therefrom. Gas entering production gas outlet  108  may be fed to a gas flowline  110 , or throttled or prevented from entering gas flowline  110 , by gas outlet valve  112 . Gas entering gas recycle line  106  will return to a pump low pressure inlet line  111  ported to the low pressure inlet of the multiphase pump  88  through fluid inlet  90 , unless throttled or restricted therefrom by gas recycle line valve  114 . Thus, to divert gas for production from the well, gas recycle line valve  114  is closed and gas outlet valve  112  is opened. Contrary settings of these valves will divert the gas recovered from separator  96  to multiphase pump inlet line  90 , for re-injection into the well. Furthermore, it is contemplated that intermediate valve settings may be used, such that some gas is recovered through flowline  110 , while some is returned to the inlet line  90  of multiphase pump for re-injection into the well. 
   Liquid separated from the returning fluid recovered from the well passes into return line  102 , and is likewise fed to a tee or junction  116 , having a production side outlet  118  which is controlled by liquid production valve  120 , and a liquid recycle line  122 , the access to which is controlled by liquid recycle valve  124 . Each of liquid recycle valve  124  and liquid production valve  120 , as well as gas outlet valve  112  and gas recycle valve  114 , are electronically controlled, such as by a microprocessor controller or computer  151 , which controls their state of open, close or throttling as will be hereinafter described. To prevent backflow of fluids in the return lines  100 ,  102  and pump inlet lines  106 ,  128 , as well as the possibility of gas flowing in a reverse direction in the liquid lines or liquid flowing in a reverse direction in the gas lines, each of at least lines  100 ,  102   106  and  128  include one way valves (not shown) therein, such as check valves, which prevent rearward flow of fluids therepast, but allow forward flow of fluids therepast. 
   Liquid which is passed through liquid recycle valve  124  and is thus directed to be re-injected into the well enters cyclone  126 , which separates solids from the liquid stream. Sand, as well as other production region solids, as well as accumulated mud or other impurities in the casing, will typically be returned from the wellbore through return outlet  68 , and should be separated from any recycled liquids before such liquids enter the multiphase pump  88 . Thus, cyclone  126  has extending therefrom recycle liquid pump return line  128 , through which recycled liquid from the borehole is returned to the low pressure inlet through inlet line  90  of multiphase pump  88 , as well as a solid return line  130 , which is configured for removal or conveyance of solids from the system, it being understood that the solids may be carried in a fluid stream upon exit from the cyclone  126 . As shown in  FIG. 1 , this solid material is shown as returning to the liquid production flowline  118  downstream of valve  120 , although other disposal regimens are specifically possible. 
   Referring still to  FIG. 1 , start up system  86  generally includes a gas supply  131  selectively communicable with low pressure inlet line  111  through gas supply valve  132 , and a liquid supply  134 , selectively communicable with the low pressure pump inlet line  111 , through fluid supply valve  136 . Each of valves  132  and  136  are also preferably controlled by computer  151 . Each of gas supply  131  and liquid supply  134  preferably supply their contents under sufficient pressure to supply useable quantities thereof to the inlet  90  of multiphase pump  82 . Although supplies  131 ,  134  may be large reservoirs of liquid and or multiple tanks of gas, as the case may be, they may also be supplied by a pipe connection to sources of liquid and gas. Further, the liquid is preferably crude oil or other liquid hydrocarbon found in the well being exploited, and, where natural gas is present in the well, the gas is likewise preferably natural gas. 
   Referring now to  FIG. 2 , jet pump  26  is located on the end of hollow tube  24  and landed on packer  50 . Jet pump  26  is configured to receive a flow of high pressure fluid therein, from a remote, non-production zone source, in this embodiment the multiphase pump  88  and accompanying tubing, and pass that high pressure fluid through an expansion nozzle, thereby resulting in a reduced pressure at the restriction point of the nozzle. By allowing the relatively low fluid pressure well fluid in the production zone to be introduced to the stream of high pressure fluid flowing through the pump  26  at this restriction point, the well fluids will experience a pressure drop at that location and thus flow into the stream of high pressure fluid passing through the pump  26 . The fluid velocity and pressure exiting the pump  26  is still sufficient to lift the fluids leaving the pump to the earths&#39; surface  14 . 
   Jet pump  26  generally includes a well fluid inlet region  32 , a high pressure pumping fluid inlet  30 , a venturi section  150  into which both the high pressure pumping fluids flow, as shown by arrows  152 , and well fluids flow, as shown by arrows  154 . The combined well fluid/pumping fluid return stream then exits the pump  26  in a path shown by arrows  156 , to return to the earths&#39; surface  14  ( FIG. 1 ) by flowing out of pump exit  28  and then upwardly in annulus  66 . 
   Referring still to  FIG. 2 , well fluid inlet  32  is extended into production zone  18  of the well, at least co-terminus or extending beyond the lowermost surface of packer  50 . Fluid inlet extends inwardly of the housing or body of pump  26 , to an entry check valve  162 , having an entry fluid passage  164  therethrough selectively blockable by a ball  165  when pressure in the well fluid inlet  32  is less than that in the pump  26 . Fluid inlet then extends into a reservoir region  166 , from which fluid is pulled by venturi section  150  through an annular passage  168  extending from the reservoir  166  to the venturi section  150 . 
   Pumping fluid inlet  30  generally includes a valved fluid passage  170  extending in fluid communication between the interior of tube  24  through which high pressure pumping fluid is introduced to the pump  26 , and the venturi section  150 . Passage of fluid through valved fluid passage  170  is controllable by a spring loaded poppet valve  172 , which is spring biased in a direction to close valved fluid passage  170  in the event that the pressure in the tube  24  drops below a pre-selected pressure, to prevent well fluid from passing outwardly of the pump  26  through the valved fluid passage  170 . 
   Venturi  150  includes a tapered inlet  174 , through which the high-pressure pumping fluids enter the venturi  150  and which ends in an orifice  176 . Adjacent and preferably surrounding the orifice  176  at the exit of the orifice is an annular well fluid passage  178  in fluid communication through annulus  168  with well fluids to be pumped from the well, and a generally right cylindrical throat  180  extending co-linearly with the inlet  174  and in fluid communication with orifice  176  and annular well fluid passage  178 . Throat  180  extends to a flared outlet  181  having a generally expanding diameter as it extends from throat  180 , which then extends into outlet reservoir  182 . Outlet reservoir  182  has an outlet  184  therefrom to direct the fluid leaving the venturi  150  into a pump production annulus  186  and thence to pump outlets  28  (as shown by arrows  156 ) in fluid communication with annulus  66  to enable the fluid exiting the pump  26  to pass to the earths&#39; surface  14 . 
   As high pressure fluid is passed through the orifice  176 , and thus through the throat  180  and flared outlet  181  of the venturi  150 , a pressure drop occurs at the annular well fluid passage  178 , thus pulling well fluids existing at the passage  178  to flow into the stream of pumping fluid passing into throat  180 , and thence out of the pump and to the earth&#39;s surface  14 . Additionally, as the high pressure fluid travels to the earth&#39;s surface  14 , the gas in the fluid will form bubbles  190  as it comes out of solution, to aid in the return of the combined high pressure fluid stream to the earth&#39;s surface  14  and thus recovery of the well fluids by the control system  80 . 
   Referring again to  FIG. 1 , operation of the control system  80  of the present invention will be described. At start up, recoverable well fluids, preferably liquid or gaseous hydrocarbons, will be present in the production zone  18  of wellbore  10 . To initiate the pumping of these well fluids, the jet pump  26  will be initially operated in a fluid only, i.e., a non-gas injected, mode. To accomplish this, fluid, typically in the form of crude oil as exists at the production zone  18 , is continuously supplied from liquid supply  134  to the inlet  90  of the multiphase pump  82 , whereby a high pressure well pumping fluid is sent through high pressure outlet  94  and thus into hollow tube  24  where such high pressure fluid enters the inlet  30  of jet pump  26 . The high pressure fluid passes through the pump  26  as previously described, pulling some of the well fluids into the stream of high pressure pumping fluid passing through the pump, and thence the combined fluids are returned to the control system  80  through annulus  66  and associate surface piping or lines. Once the hollow tube  24  and the return annulus  66  between the casing  20  and hollow tube  24  are filled with pumping fluid, the gas supply inlet valve  132  is opened, and gas is mixed with the pumping fluid and compressed in the multiphase pump  88 , such that the gas is dissolved in the liquid when it enters the hollow tube  24  with the high pressure pumping fluid. At this time the pumping rate is increased to increase the volumetric flow of pumping fluid entering the hollow tube  24 . 
   As the high pressure well pumping fluid travels to the earth&#39;s surface  14 , carrying well fluid therewith, the pressure drop experienced by the high pressure pumping fluid as it travels to the earth&#39;s surface  14  causes the pressure in the exiting fluid to be below that at which the gas can remain in a liquid or solution phase, and the gas thus forms the bubbles  190  which will assist in the lifting of the returning combined fluid stream. When the combined stream of well pumping fluid, bubbles and well fluid reaches the separator  96 , the gaseous portion is passed therefrom to the multiphase pump  88 , routed through gas line  100 , through return valve  114 , with flowline valve  112  closed. Likewise, fluid recovered from separator  96  is returned to multiphase pump  88 , flowing through valve  124 , it being understood that valve  120  is closed, thereby preventing release of the returning fluid to the flowline. Thus the gas and well pumping fluid are both initially re-pressurized and recycled down the well. At this point, additional liquid or gas from startup system may not be required, and if this is the case, then one or both of valves  132 ,  136  may be closed, as the situation dictates. 
   The flow of fluid returning through outlet  68  is monitored by virtue of a flow meter  182 , preferably a flow meter readable by computer  150 , to determine an optimum flow rate for returned fluids as compared to injected fluids. Such optimum is a function of the diameter of the hollow tube  24  and casing  20  (and thus the size of the annulus), and the jet pump rating. Such optimum flow rate contemplates the optimal additional return fluid, i.e., well fluid added to the fluid pumped down the bore, for the sizing of the equipment and energy required to operate same, at which point fluid recovery should begin. With such information, one skilled in the art can calculate a likely optimum flow for the system. 
   Once the flow rate of return of well fluid and well pumping fluid has reached an optimum condition, the liquid return valve  124  is throttled to a restricted condition, and the liquid flowline valve  120  is opened to a throttled open condition, to allow fluid in excess of that being pumped down the well, i.e., produced fluid, to pass into flowline for supply to a pipeline or reservoir. Likewise, where natural gas is returned from the well, gas recycle valve  114  is throttled to a restricted position while gas flowline valve  112  is opened to a restricted position, to allow excess gas recovered from the well to be sent down the flowline  110  for ultimate recovery. Preferably, flow meters readable by computer  151  are also disposed in flow lines  110 ,  118 , and in recycle liquid line  128  and recycle gas line  106 , as is the flow meter on return line  98  and high pressure outlet line  94 , so that computer  151  can monitor, in real time, the flows through the various lines, and ensure that the portions of gas and liquid which are sent into flow lines  110 ,  118 , do not exceed the excess fluid volume of each component returning from the wellbore  10 . 
   The use of gas in addition to the liquid flow through the jet pump significantly increases the lifting capability of the pump, providing greater efficiency of pumping. 
   While the invention has been described with specific reference to mixing of the gas and liquid in a multiphase pump, other means, such as injection of the gas in liquid form into the high pressure stream, or injection of the gas through a tube and thus into the well bore adjacent to the pump outlet or otherwise in the inlet stream is specifically contemplated. 
   While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.