Abstract:
Upstream and downstream pump assemblies are mounted in a capsule having a bulkhead between the upstream and downstream pump assemblies, dividing the capsule into upstream and downstream chambers sealed from each other. In a dual operation mode, well fluid flows through the inlet of the capsule into the upstream chamber, where it is pumped to a first pressure level by the upstream pump assembly and discharged into the downstream chamber. The downstream pump assembly then pumps the well fluid to a second pressure level and discharges the well fluid out the outlet of the capsule. The assembly has also an upstream pump assembly only operational mode and a downstream pump assembly only operational mode.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to provisional application 60/802,626, filed May 23, 2006. 
     
     FIELD OF THE INVENTION 
       [0002]    This invention relates in general to an electrical submersible pump (ESP) and in particular to a downhole capsule containing two ESP modules. 
       BACKGROUND OF THE INVENTION 
       [0003]    An electrical submersible pump (“ESP”) assembly for wells typically comprises a submersible motor that drives a pump, typically a centrifugal pump. The pump assembly is usually suspended on a string of tubing within the well. The power cable to the motor is strapped alongside the tubing. Periodically, the pump assembly has to be retrieved for maintenance or repair, and this step requires pulling the tubing. Pulling the tubing requires a workover rig and is time consuming, particularly for offshore installations. 
         [0004]    In some cases a dual tandem pump assembly is used to provide more lift. Normally two pumps are connected together and driven by a single motor. The pumps thus operate in unison with each other. Repair or replacement of either pump requires pulling the tubing and the entire assembly. 
         [0005]    Often a pressure and temperature sensor will be mounted to the base of the motor for sensing the pressure and temperature of the dielectric liquid within the motor. The power to the motor fluid sensor and the signals are superimposed on the ESP power cable Another measuring tool comprises a reservoir sensor, which is an electrical device that senses various characteristics of the producing reservoir of the well on the exterior of the motor. These tools typically send signals up a dedicated communication line extending to the surface. 
       SUMMARY 
       [0006]    In this invention a capsule having an upper end for connection to a string of production tubing lowered within casing of a well. An electrical submersible pump assembly is located within and suspended by the upper end of the capsule. A bulkhead is located within the capsule below the pump assembly. An electrically powered device suspended by and below the bulkhead. A power lead extends from the electrically powered device through the bulkhead, alongside the pump assembly within the capsule and sealingly through the upper end of the capsule. The electrically powered device may be suspended below the capsule or contained within the capsule. 
         [0007]    The electrically powered device may be a sensor for sensing reservoir characteristics or it may be a second submersible pump assembly. In one embodiment having two ESP&#39;s, the bulkhead divides the capsule into upstream and downstream chambers, each chamber containing one of the pump assemblies. The power cables for each motor pass through the capsule alongside the outlet. The two submersible pump assemblies may operate simultaneously or one may operate while the other is shut down. 
         [0008]    The reservoir sensor unit may be suspended below the hanger or bulkhead. The power and signals for the reservoir sensor unit may be supplied via a dedicated sensor line to the surface, or the sensor line may only extend to the motor sensor. In the latter case, the reservoir sensor and the motor sensor may be superimposed on the ESP power cable. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIGS. 1A and 1B  comprise a vertical sectional view of a capsule containing two ESP modules in accordance with this invention. 
           [0010]      FIG. 2  is an enlarged sectional view of the lower hanger contained within the capsule of  FIG. 1 . 
           [0011]      FIG. 3  is an alternate embodiment of the lower hanger contained in the capsule of  FIG. 1 . 
           [0012]      FIG. 4  is a schematic view illustrating both ESP&#39;s of the capsule of  FIG. 1  operating. 
           [0013]      FIG. 5  is a schematic view illustrating the upper ESP of the capsule of  FIG. 1  operating and the lower ESP not operating. 
           [0014]      FIG. 6  is a schematic view illustrating the lower ESP of the capsule of  FIG. 1  operating and the upper ESP not operating. 
           [0015]      FIG. 7  is a vertical sectional view of an alternate embodiment of a capsule, wherein one of the ESP modules of the capsule is a downhole sensor assembly. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0016]    Referring to  FIG. 1 , a well having a casing  11  is illustrated. Casing  11  is perforated at its lower end for allowing well fluid to enter. A string of production tubing  13  is suspended within casing  11 . A capsule  15  is secured to a lower end of tubing  13 . 
         [0017]    Capsule  15  is a cylindrical member of slightly smaller outer diameter than the inner diameter of casing  11  so that it can be lowered into casing  11  on tubing  13 . Capsule  15  has an upper or downstream end with a hanger  17  that is rigidly secured to the lower end of tubing  13 . 
         [0018]    An optional upper or downstream sleeve valve  19  is secured into a downstream conduit  18  below upper hanger  17 . Upper sleeve valve  19  has an interior that is communication with the interior of tubing  13  for discharging well fluid upward. Upper sleeve valve  19  has an open position in which ports  21  on its sidewall are exposed to the interior of capsule  15 . Upper sleeve valve  19  has a closed position in which ports  21  are closed to the interior of capsule  15 . 
         [0019]    An upper or downstream ESP  23  is suspended on upper sleeve valve  19 . Upper sleeve valve  19  may be a commercially available type that closes its ports  21  to the interior of capsule  15  when downstream ESP  23  is operating. When ESP  23  is not operating, upper sleeve valve  19  automatically opens its ports  21  to the interior of capsule  15 . This type of valve, known as an annulus diverter valve, is used normally in tubing above submersible pumps in applications that are prone to significant sand production. Alternately, upper sleeve valve  19  could be hydraulically actuated or stroked between the open and closed positions by pressure supplied from the surface via a hydraulic line (not shown)that extends alongside tubing  13  and sealingly through upper hanger  17 . 
         [0020]    If upper sleeve valve  19  is not utilized, upper ESP  23  would connect directly to upper hanger  17 . Upper ESP  23  is a conventional electrical submersible pump assembly, including a centrifugal pump  25 , which is shown at the upper end of the assembly. Pump  25  has an intake  26  on its lower end and is made up of a large number of stages or impellers and diffusers. One or more seal sections  27  are connected to the lower end of pump  25 . An electrical motor  29  is connected to the lower end of the seal section or sections  27 . Motor  29  is preferably a three-phase alternating current motor. Motor  29  is filled with lubricant, and seal sections  27  equalize the interior pressure of the lubricant in motor  29  with the pressure in capsule  15 . 
         [0021]    Motor  29  has an electrical power lead  31  that extends upward alongside seal section  27  and pump  25  within capsule  15 . Motor lead  31  extends through an upper penetrator or guide  33  in upper hanger  17 . Upper penetrator  33  seals motor lead  31  in upper hanger  17 . Above capsule  15 , motor lead  31  joins a power cable (not shown) that is strapped alongside tubing  13  and extends to the surface. 
         [0022]    A lower extension pipe  35  extends from the lower end of motor  29  to a lower hanger or bulkhead  37  located within capsule  15 . Lower hanger  37  is sealed to the sidewall of capsule  15 , defining an upper or downstream chamber  36  above lower hanger  37  and a lower or upstream chamber  38  below lower hanger  37 . A downstream conduit or support tube  39  secured to the lower side of lower hanger  37  is illustrated in  FIG. 1B . An optional sliding sleeve valve  41  is connected to the lower end of support tube  39 . Sliding sleeve valve  41  has ports  43  that lead to the interior of capsule  15  and may be of the same type of valve as upper sliding sleeve valve  19 . 
         [0023]    A lower or upstream ESP  45  is secured to the lower end of lower sliding sleeve valve  41 , and its weight is supported by upper hanger  17  through upper ESP  23  in this embodiment. Sleeve valve  41  also may be an annulus diverter type that automatically closes ports  43  when lower ESP  45  is operating and opens ports  43  when ESP  45  is not operating. Alternately, sleeve valve  41  could open and close ports  43  in response to hydraulic fluid pressure supplied from a line extending to the surface. If desired, lower sliding sleeve valve  41  may be operated independently of upper sleeve valve  19  by a separate hydraulic line from the hydraulic line leading to upper sleeve valve  19 . Alternatively, a single hydraulic line could control both sleeve valves  19 ,  41 . For example, if lower ESP  45  is a back up to be operated only after upper ESP  23  fails, sleeve valve  41  could be connected to the same hydraulic line as upper sleeve valve  19  and operated in reverse to upper sleeve valve  19 . That is, while only upper ESP  23  is operating, as illustrated in  FIG. 5 , the hydraulic pressure in the hydraulic line to sleeve valves  19 ,  41  keeps sleeve valve  19  closed and sleeve valve  41  open. When upper ESP  23  is shut down and lower ESP  45  started, the hydraulic pressure in the line to valves  19 ,  41  would be reversed by an operator at the surface to open upper sleeve valve  19  and close lower sleeve valve  41 , as shown in  FIG. 6 . 
         [0024]    If a lower sleeve valve  41  is not utilized, lower ESP  45  will be secured directly to support tube  39 . Lower ESP  45  may be the same type as upper ESP  23 , although it may be of a different length, if desired. Lower ESP  45  includes a centrifugal pump  47  with an intake  48 . Discharge port  50  of lower ESP  45  is in extension pipe  35  in upper chamber  36 . One or more seal sections  49  connect pump  47  to electrical motor  51 . A motor lead  53  extends from the upper end of motor  51  through a lower hanger penetrator  55  in lower hanger  37 . Penetrator  55  seals motor lead  53  within lower hanger  37 . Lower ESP motor lead  53  extends alongside upper ESP  23  and through an upper penetrator  56  located within upper hanger  17  to a power cable (not shown) extending to the surface. Capsule  15  has an inlet  59  located below the lower end of lower ESP  45 . Inlet  59  communicates well fluid in casing  11  to lower chamber  38  surrounding lower ESP  45 . Optionally inlet  59  comprises a stinger that stabs into a packer (not shown). The packer isolates the well fluid below it from the fluid within casing  11  surrounding capsule  15  and production tubing  13 . 
         [0025]      FIG. 2  illustrates a first embodiment of bulkhead or lower hanger  37 . In this embodiment, lower hanger  37  has seals  61  that seal against a polished bore  63  on the inner diameter of capsule  15 . Hanger  37 , along with seals  61 , is able to slide axially along polished bore  63  as indicated by the arrows. This axial movement of lower hanger  37  accommodates thermal growth of upper ESP  23  ( FIG. 1A ) during operation. Lower ESP  45  is able to grow thermally because its lower end is spaced above capsule inlet  59  and is free to move. The entire weight of both upper and lower ESP&#39;s  23 ,  45  is supported by upper hanger  17  in the embodiment of  FIG. 2 . 
         [0026]    In the embodiment of  FIG. 3 , capsule  65  differs from capsule  15  of the first embodiment in that it has a load shoulder  67  located on the inner diameter. Lower hanger  69  lands on load shoulder  67  so as to support the weight of lower ESP  45  ( FIG. 1B ). Lower hanger  69  has seals  71  that statically engage a seal surface on the inner diameter of capsule  65  above load shoulder  67 . 
         [0027]    To accommodate thermal growth of upper ESP  23  ( FIG. 1A ) in the embodiment of  FIG. 3 , a telescoping joint is utilized for connecting between lower hanger  69  and the assembly of ESP  23  ( FIG. 1A ). This telescoping joint includes an upward facing receptacle  73  in this example. Receptacle  73  is open at its upper end and slidingly receives a tubular mandrel  75  that is rigidly secured to the lower end of upper ESP  23  ( FIG. 1A ). Mandrel  75  has seals  77  that will slidingly engage a seal surface within receptacle  73 . Upper and lower stops  79 ,  81  limit the travel of mandrel  75  relative to receptacle  73  during installation of ESP  23  in capsule  65 . Receptacle  73  and mandrel  75  could alternately be reversed with mandrel  75  mounted to hanger  69  and receptacle  73  mounted to the lower end of upper ESP  23 . Discharge port  82  from lower ESP  45  ( FIG. 1B ) is located in mandrel  75 . 
         [0028]    In a third embodiment (not shown), instead of lower hanger  37  ( FIG. 2 ) or  69  ( FIG. 3 ), the bulkhead would be a packer that is conventionally actuated to expand, grip and seal to the inner surface of capsule  15 . In that embodiment, the packer would support the weight of lower ESP  45  and would not be movable either upward or downward in capsule  15 . 
         [0029]    In operation, upper and lower ESP&#39;S  23 ,  45  are installed within capsule  15  while at the surface. The entire assembly then is lowered into the well on tubing  13 . The upper ends of motor leads  31 ,  53  are connected to power cables (not shown), which are strapped alongside tubing  13 . While being lowered, capsule  15  protects motor leads  31  and  53  against damage in the areas where they pass alongside upper seal section  27  and upper pump  25 . Because both motor leads  31  and  53  pass alongside these components, the clearance within casing  11  can be quite small. 
         [0030]    Once capsule  15  is at the desired depth, the operator has a choice of simultaneously operating both upper and lower ESP&#39;s  23 ,  45  as shown in  FIG. 4 , operating only the upper ESP  23  as shown in  FIG. 5 , or operating only the lower ESP  45  as shown in  FIG. 6 . To operate both ESP&#39;s  23 ,  45  simultaneously, the operator supplies power to both motors  29 ,  51  ( FIG. 1 ) and both upper and lower sleeve valves  19 ,  41  are closed, either automatically or by hydraulic pressure supplied from the surface. In fact, if the operator intends to always operate both ESP&#39;s  23 ,  45  simultaneously, sleeve valves  19 ,  41  are not required. 
         [0031]    In the booster mode of  FIG. 4 , well fluid flows through capsule inlet  59  into lower chamber  38  and lower pump intake  48 . Lower ESP  45  increases the pressure of the well fluid and discharges it from lower pump discharge port  50  into upper chamber  36  of capsule  15 . The higher pressure in upper chamber  36  is isolated by lower hanger  37  from the intake pressure in lower chamber  38 . The higher pressure fluid enters upper pump intake  26 , which boosts the pressure and discharges the well fluid into production tubing  13 . In this mode, ESP&#39;s  23 ,  45  operate in series. 
         [0032]    As illustrated in  FIG. 5 , in this mode, only upper ESP  23  operates. To avoid flowing well fluid through the stages of the non operating pump of lower ESP  45 , lower sleeve valve  41  is opened. Opening lower sleeve valve  41  could be done by hydraulic fluid pressure. Alternately, if automatic sleeve valves  19 ,  41  are used, merely supplying power to upper ESP  23  while not supplying power to lower ESP  45  will cause lower sleeve valve  41  to open while upper sleeve valve  19  remains closed. In this mode, the well fluid bypasses the pump of lower ESP  45 , flows from lower chamber  38  into the ports of lower sleeve valve  41  and discharges out lower pump discharge port  50  into upper chamber  36  of capsule  15 . The pressure in upper chamber  36  is substantially the same as at capsule inlet  59 . The well fluid flows into upper pump intake  26 , which discharges it at a higher pressure into tubing  13 . 
         [0033]    Referring to  FIG. 6 , in this mode, upper ESP  23  is not operating, rather only lower ESP  45 . This mode might occur after upper ESP  23  failed, in which case lower ESP  45  is energized as a back up. Upper sliding valve  19  is opened, and lower sliding valve  41  is closed, either by hydraulic fluid pressure or by automatic valves, as discussed. The well fluid flows from lower chamber  38  into lower pump intake  48  and is discharged out lower pump discharge  50  in upper chamber  36  at a higher pressure. The well fluid flows into the open ports of upper sleeve valve  19  rather than flowing through the stages of the pump of upper ESP  23 . The well fluid is discharged into tubing  13  at substantially the same pressure that it was discharged from lower ESP discharge  50 . 
         [0034]    In another embodiment, which isn&#39;t shown, the lower end of capsule  15  terminates at lower hanger  37 . Lower ESP  45  is not located within capsule  15 , but is suspended by lower hanger  37 . Lower ESP  45  may have a tail pipe or stinger in that instance that would sting into a packer (not shown). 
         [0035]    Referring to  FIG. 7 , an alternate embodiment is shown wherein only one ESP is utilized. In this embodiment, capsule  83  is suspended on a string of production tubing  85  within casing  87 . ESP  89  is supported by an upper hanger  88 , which in turn is connected to tubing  85 . A motor lead  91  extends sealingly through a penetrator  93  in upper hanger  88  and down to the motor of ESP  89 . ESP  89  has a pump intake  95 , which is in capsule  83 . A hanger or bulkhead  97  is located at the lower end of ESP  89 . Hanger  97  may be constructed as in either the first embodiment of  FIG. 2  or the second embodiment of  FIG. 3 , or it could be a packer. 
         [0036]    In this embodiment, the lower end of capsule  83  terminates at lower hanger  97 . In this example, a downhole sensor  99  is suspended on a tubular member or stinger  100  that is mounted to lower hanger  97 . Sensor  99  is a conventional electrical device that senses various characteristics of the reservoir, such as pressure and water/oil contact, and will be referred to herein as a reservoir sensor. Tubular member  100  has a length selected to place reservoir sensor  99  close to perforations  102  of the reservoir. The well fluid flows upward through tubular member  100  into the interior of capsule  83  and into pump intake  95 . Tubular member  100  could sting into a packer, if desired. 
         [0037]    Optionally ESP  89  also has a conventional ESP motor sensor  103  mounted at its base. ESP sensor  103  measures parameters of the well fluid inside capsule  83 , such as intake and discharge pressure, motor temperature and vibration. ESP sensor  103  is connected electrically to the motor of ESP  89 , and the signal of ESP sensor  103  may be sent via ESP motor lead  91  and power cable to the surface. At the surface, circuitry separates the signal of ESP sensor  103  from the electrical power and provides a display. 
         [0038]    If such an ESP sensor  103  is utilized, preferably a sensor lead  101  leads from reservoir sensor  99  alongside conduit  100  and sealingly through lower hanger  97  to ESP sensor  103 . In that way, the signal from reservoir sensor  99  is also superimposed on motor lead  91  and the power cable for reception at the surface. Alternately, reservoir sensor lead  101  could extend through upper hanger  88  and alongside tubing  85  to the surface, and ESP sensor  103  could transmit its signals in a conventional manner on the power cable. If an ESP sensor  103  is not utilized, the signals for reservoir sensor  99  would preferably be communicated through reservoir sensor lead  101  to the surface. 
         [0039]    Although not shown, a dual ESP system could be employed in which the lower ESP is not located within a capsule, but is suspended below the capsule containing the upper ESP. This system could particularly be employed when a packer is not required. In addition, the capsule could be located within a subsea flowline rather than within a well, in which case the ESP or ESP&#39;s would be oriented approximately horizontal. 
         [0040]    The invention has significant advantages. In the dual ESP environment, the operator can use one ESP until it breaks down, then operate with the second ESP. This substitution extends the time before the tubing must be pulled. The capsule supports the weight of the lower ESP or a downhole reservoir sensor, rather than imposing a load on the upper ESP. If desired, the dedicated line normally used for a downhole reservoir sensor could be eliminated and signals superimposed on the ESP power cable. 
         [0041]    While the invention has been shown in only a few of its forms, it should be apparent to those skilled in the art that it is not so limited but is susceptible to various changes without departing from the scope of the invention.