Abstract:
An expansion chamber to serve ESP equipment installed on the seabed located in either a caisson or a conduit on a skid. The expansion chamber provides an external reservoir for expansion and contraction of motor oil in the ESP equipment. During operation of an ESP, the heat generated in the motor raises the temperature of the motor oil, causing it to expand. The expansion chamber is connected to the ESP equipment via oil lines that allow oil to expand into the expansion chamber when the temperature of the motor oil increases. The expansion chamber has a movable barrier therein that defines primary and secondary chamber. Oil communicates with the primary chamber. Formation fluid within the conduit surrounding the motor communicates with the secondary chamber.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to provisional application 61/221,460, filed Jun. 29, 2009. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates in general to booster pump electric motors, and in particular to accommodating the expansion and contraction of dielectric lubricant of a sea floor submersible electric pump motor via a subsea expansion chamber. 
       BACKGROUND OF THE INVENTION 
       [0003]    Electrical submersible pumps (“ESP”) are used for pumping high volumes of well fluid, particularly in wells requiring artificial lift. The ESP typically has at least one electrical motor that normally is a three-phase, AC motor. The motor drives a centrifugal pump that may contain a plurality of stages, each stage comprising an impeller and a diffuser that increases the pressure of the well fluid. The motor is filled with a dielectric lubricant or oil that provides lubrication and aids in the removal of heat from the motor during operation of the ESP. A seal section is typically located between the pump and the motor for equalizing the pressure of the lubricant contained within the motor with the hydrostatic pressure of the well fluid on the exterior. The seal section is filled with oil that communicates with the oil in the motor. 
         [0004]    The ESP is typically run within the well with a workover rig. The ESP is run on the lower end of a string of production tubing. Once in place, the ESP may be energized to begin producing well fluid that is discharged into the production string for pumping to the surface. 
         [0005]    During operation, the temperature of the oil in the motor of the ESP increases due to friction in the motor, causing the volume of the oil to also expand. The oil is vital to maintaining the motor within its rated temperature and maintain reliability. However, oil may migrate outside of the motor when it expands, resulting in less oil for protecting the motor and possible contamination of other parts of the ESP. 
         [0006]    To counteract the expansion of the oil, a bladder, bellows or labyrinth seals form an expansion chamber within a seal section of the ESP. The internal expansion chamber provides additional volume into which the oil can expand. However, this requires increasing the length of the ESP system, which can be a problem for a sea floor booster pump. In addition, the internal expansion chamber may fail and the entire ESP system would need to be replaced. This could result in costly downtime. 
         [0007]    A technique is desired to allow for expansion of the motor oil surrounding the motor that may translate to extended life and increased reliability of the motor without increased ESP length. 
       SUMMARY OF THE INVENTION 
       [0008]    In the present disclosure, an ESP is described that is part of a boosting system located on the seabed. The ESP may be horizontally mounted, inclined, or vertically mounted on a skid or within a caisson in the seafloor. The ESP has at least one motor and at least one pump, with a seal section located in between. 
         [0009]    An expansion chamber comprising a primary chamber and a secondary chamber that is located external to the ESP boosting system in a vicinity of a the sea floor and has an oil port and a formation fluid port. An oil line connects to the oil port of the expansion chamber to thereby communicate with the primary chamber and communicate with the motor. A formation fluid line connects to the formation fluid port of the expansion chamber to thereby communicate with the secondary chamber and communicate with a capsule housing the motor. As the motor oil heats up and expands during operation, the motor oil flow into the primary chamber. The primary chamber expands to equalize the pressure between the motor oil and formation fluid. Further, the primary chamber may contract when the motor oil cools down. To achieve this expansion and contraction, the primary chamber may be fabricated as metallic bellows or an elastomeric bag. 
         [0010]    The external expansion chamber arrangement thus provides an effective mechanism for dealing with expanding motor oil without the need of a longer ESP. Leaks due to expanding motor oil decrease and thereby loss of motor oil decreases as does contamination of the motor oil with formation fluid. Thus, the motor life is advantageously extended and its reliability is advantageously increased. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a sectional view of an electrical submersible pump with an expansion chamber, in accordance with an embodiment of the invention. 
           [0012]      FIG. 2  is a sectional view of an alternative embodiment of the embodiment of  FIG. 1 . 
           [0013]      FIG. 3  is a sectional view of an alternative embodiment of the embodiment of  FIG. 1  mounted on a skid. 
           [0014]      FIG. 4  is a sectional view of an electrical submersible pump within a caisson, in accordance with an embodiment of the invention. 
           [0015]      FIG. 5  is a sectional view of multiple electrical submersible pumps, each with expansion chambers, in accordance with an embodiment of the invention. 
           [0016]      FIG. 6  is a sectional view of an alternative embodiment of the embodiment of  FIG. 5 . 
           [0017]      FIG. 7  is a sectional view of a standard electrical submersible pump with an expansion chamber, in accordance with an embodiment of the invention. 
           [0018]      FIG. 8  is a sectional view of an alternative embodiment of the embodiment of  FIG. 7 . 
           [0019]      FIGS. 9 and 10  show a typical motor electrical connector and line connector arrangement, in accordance with an embodiment of the invention. 
           [0020]      FIGS. 11 and 12  show a typical electrical penetrator and line connector arrangement, in accordance with an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0021]    Referring to  FIG. 1 , an electrical submersible pump (“ESP”)  20  is illustrated in a sectional view. The ESP  20  can be part of a boosting system located on the seabed. It may be horizontally mounted, inclined, or vertically mounted with a caisson in the seafloor, also referred to as a “dummy well.” A motor  22  and pump  24  are shown with a seal section  26  located in between. The seal section  26  contains a thrust bearing and can contain a pressure equalizer to equalize the pressure of lubricant in the motor  22  with the hydrostatic pressure that allows the motor oil lubricant to thermally expand and contract. The pressure equalizer may be a bellows, a bladder or a labyrinth arrangement. Alternatively, a battery of mechanical seals can be used in the seal section  26 . 
         [0022]    A capsule  30  houses the ESP  20  and has a cap or barrier  32  at one end and a discharge port  36  at the other end. Capsule  30  in this example is located on the sea floor and is horizontal or inclined on a skid  60  ( FIG. 3 ). Capsule  30  may be part of a flowline jumper. The cap  32  can have various types of ports and connections depending on the configuration of the ESP within the capsule  30 . In this example, the motor  22  and pump  24  are in the inverted position such that the base of the motor  22  faces the end of the capsule  30  with the cap  32 . A standard subsea connector  31  that passes through the cap  32  can thus be used to connect with the base of the motor  22  as shown in  FIGS. 9 and 10 . Alternatively, three independent phase connectors could be utilized to provide power to the motor. A power umbilical (not shown) can then provide electrical power to the motor  22  via the subsea connector  31 . 
         [0023]    In this example, a port  33  passes through the cap  32  to allow production fluid to flow into the capsule  30 . Port  33  can connect to a flow line coming directly from a well or from other subsea equipment. The fluid is discharged by the pump  24  through port  36 . The discharge end of the pump  24  has a seal assembly  34  that seals the discharge end from the capsule  30 . In this example, port  36  can connect to a production flow line or to a production riser that can move production fluid to, for example, a floating production storage and offloading unit, a tension leg platform, a fixed platform, or a land facility. A connection can also be made to other subsea equipment, such as a manifold, prior to routing production fluid to the surface. 
         [0024]    During operation of the ESP  20 , the temperature of the motor oil inside the motor  22  and circulating through the seal section  26  rises, causing the oil to expand. Due to expansion, the oil could damage the motor and seal section, resulting in less oil for protecting the motor, contamination of the motor, and possible contamination of other parts of the ESP  20 . Further, a leak caused by the expanded oil can result in formation fluid contaminating the motor oil, which is not designed to maintain the differential pressure. Contraction of the oil as it cools when the ESP  20  is not in operation is also a problem because a vacuum can form within the motor  22  and seal section  26  that can result in failure. Compensating for the expansion and contraction of motor oil due to thermal variations can thus prevent these problems. 
         [0025]    To address these problems, seal section  26  may have an expansion chamber (not shown) that allows the motor oil to expand as it heats up during operation of the ESP and equalizes the pressure of oil in the motor  22  with the hydrostatic pressure of the formation fluid. The terms “formation fluid” and “production fluid” are used interchangeably throughout. However, providing an expansion chamber within the seal section  26  significantly adds to the length of the ESP  20 , which can impact assembly and handling of the ESP at the rig or installation vessel, and during running operations or subsea hardware installations. In addition, the reliability of seal section  26  and thus that of the ESP  20  is compromised if the internal expansion chamber fails. Typically, the seal section  26  fails because it exceeds its oil expansion capacity. The expansion chamber within the capsule has a maximum oil expansion capacity limited by the space available within the capsule. An expansion chamber on the seabed, however, can be designed for larger oil expansion capacity because there are no space limitations. Thus, by locating an expansion chamber  50  on the seabed externally to the capsule  30 , or on a skid that supports capsule  30 , the length of the ESP  20  could advantageously be reduced and the reliability of the ESP  20  could advantageously be increased. 
         [0026]    Continuing to refer to  FIG. 1 , an oil line  42  passes through a connector  43  that passes through the cap  32  to allow the oil line  42  to communicate with the base of the motor  22 . The oil line  42  allows hot motor oil from the base of the motor  22  to expand out into a bellows  54  inside the expansion chamber  50 , which defines a first chamber. The bellows  54  can be made out of metal or rubber that can flex and tolerate temperature variations. Alternatively, a bladder or piston chamber, can be used instead of bellows. A capsule line  48  passes through a connector  45  that passes through the cap  32  to allow the capsule line  48  to communicate with the interior of the capsule  30  exposed to the formation fluid. The capsule line  48  allows formation fluid in the capsule  30  to travel up to a second chamber within the expansion chamber  50  defined by the expansion chamber housing  52  and the external surface of the bellows  54 . 
         [0027]    Housing  52  is sealed from hydrostatic pressure. Prior to deployment of the ESP  20  and the expansion chamber  50 , they are prefilled with oil. The bellows  54  section has a check valve  49  with a preset pressure setting that allows oil to flow from the bellows  54  to the second chamber of the expansion chamber  50 . The check valve  49  will provide communication to the motor oil fluid to the external part of the bellows  54  in case the maximum oil expansion is exceeded. The check valve  49  prevents formation fluid outside the bellows  54  to communicate with the internal portion of the bellows  54 . This overexpansion of oil is normal in the first start up of the system, until operational stability is achieved. The oil inside the bellows  54  does not communicate with the formation fluid held in the expansion chamber  50  although the formation fluid can communicate with oil external to the bellows  54 . Neither the formation fluid or oil communicate with seawater. 
         [0028]    During operation, the hot oil inside causes the bellows  54  to expand while the formation fluid in the expansion chamber  50  simultaneously exerts external pressure on the bellows  54 , thereby equalizing the pressure of oil in the motor  22  with the pressure of the formation fluid in the capsule  30  surrounding ESP  20 . Oil from bellows  54  flows back through oil line  42  into motor  22 . Further, when the ESP  20  is shut down, the motor oil cools and contracts. Without a provision for contraction, the contraction can create a vacuum within the ESP system that can lead to failure. Motor oil leaks due to oil expansion or contraction can thus be minimized and the motor  22  can thus be protected to operate longer and more reliably while significantly reducing the length of the ESP  20  system. 
         [0029]    Referring to  FIG. 2 , an alternative embodiment is illustrated that is similar to the embodiment shown in  FIG. 1 . However, in this embodiment, an additional expansion chamber  56  is shown coupled in series with the primary expansion chamber  50 . The primary function of this embodiment is to provide an additional expansion chamber for redundancy proposes. The additional expansion chamber  56  can also provide additional expansion and contraction capability to the subsea system. As in the embodiment of  FIG. 1 , the oil line  42  allows hot motor oil from the base of the motor  22  to expand out into a bellows  54  inside the expansion chamber  50 . However, capsule line  48  connects to the additional expansion chamber  56  outside of bellows  58  to allow formation fluid in the capsule  30  to travel up to a second chamber within expansion chamber  56  defined by the expansion chamber housing  57  and the external surface of the bellows  58 . The interior of bellows  58  is connected by a line  51  to the exterior of bellows  54 . As in the embodiment of  FIG. 1 , the bellows  54 ,  58  of both expansion chambers  50 ,  56  have check valves  49 ,  59  that allow oil to flow from one chamber to the next during prefilling. Thus, the oil inside bellows  54 ,  58  does not communicate with the formation fluid held in the additional expansion chamber  56  although the formation fluid can communicate with oil external to the bellows  58  in the additional expansion chamber  56 . The capsule line  48  passes through a connector  45  that passes through the cap  32  to allow the capsule line  48  to communicate with the interior of the capsule  30  exposed to the formation fluid. The coupling line  51  connects the second chamber within the primary expansion chamber  50 , which contains oil, and is defined by the expansion chamber housing  52  and the external surface of the bellows  54 , to the interior of bellows  58  of the additional expansion chamber  56 , which is also filled with oil. The use of multiple expansion chambers as in this example can further increase reliability by including redundancy. If one expansion chamber fails or leaks, the second expansion chamber can protect the subsea system. As in the embodiment of  FIG. 1 , the ESP system of this embodiment may be horizontally mounted or inclined on a skid  60  ( FIG. 3 ), or vertically mounted with a caisson  100  ( FIG. 4 ) in the seafloor, as explained below. 
         [0030]    In the embodiment shown in  FIG. 4 , the capsule  30  and the ESP  20  within can be housed in a caisson  100 . The caisson  100  can be partially or completely submerged in the seabed and can be several hundred feet deep. The connections and ESP  20  arrangement are identical in this embodiment to those shown in the embodiment of  FIG. 1 . However, the pump  24  discharges production fluid from the capsule  30  through outlet  36  and into the caisson  100  instead of a production flow line. An outlet port  104  on the caisson  100  connects to a production fluid riser or flow line. The caisson  100  can be used to separate gas in the production fluid to thereby increase pumping efficiency. The expansion chamber  50  would be located proximate and external the caisson  100  to allow for expansion of the motor oil. Alternatively, multiple expansion chambers could be utilized as in the embodiment of  FIG. 2 . Also, in another alternate, the production fluid could flow into the upper end of caisson  100  down around capsule  30 . The fluid flows up capsule  30  and is pumped out cap  33 . 
         [0031]    Referring to  FIG. 5 , an alternative embodiment is illustrated that is similar to the embodiment shown in  FIG. 1 . However, in this embodiment, multiple ESP systems,  20 ,  70  are shown connected in series, each with its own expansion chamber  50 ,  84 . A primary ESP  20  within a capsule  30  is shown connected in series to ESP  70  within a capsule  76  to provide additional pressure boosting capacity. The discharge outlet  36  of the primary ESP  20  connects to the inlet port  72  of the secondary ESP  70 . A pump  71  then discharges production fluid through a discharge outlet  74  in the secondary ESP  70 . The discharge outlet  74  can connect to a production flow line or riser. 
         [0032]    Continuing to refer to  FIG. 5 , the arrangement of the secondary ESP  70  is identical to that of the primary ESP  20 . An oil line  80  passes through a connector  81  that passes through a cap  87  to allow the oil line  80  to communicate with the base of the motor  73 . The oil line  80  allows hot motor oil from the base of the motor  73  to expand out into a bellows  88  inside the expansion chamber  84 . A capsule line  82  passes through a connector  83  that passes through the cap  87  to allow the capsule line  82  to communicate with the interior of the capsule  76  exposed to the formation fluid. The capsule line  82  allows formation fluid in the capsule  76  to travel up to a second chamber within the expansion chamber  84  defined by the expansion chamber housing  86  and the external surface of the bellows  88 . Both the primary ESP  20  and the secondary ESP  70  have standard subsea connectors  31 ,  85  that pass through their respective caps  32 ,  87  to connect with the base of the motors  22 ,  73 . The subsea connectors  31 ,  85  allow a power umbilical (not shown) to provide electrical power to the motors  22 ,  73  via the subsea connectors  31 ,  85 . Each of the ESP systems can be electrically connected in parallel by running separate umbilicals from a main power umbilical (not shown). 
         [0033]    Alternatively, stages in the pump of the secondary ESP can be inverted, as shown in  FIG. 6 . The embodiment shown in  FIG. 6  is identical to the embodiment shown in  FIG. 5 , with multiple ESPs  20 ,  90  and expansion chambers  50 ,  84 . However, the secondary ESP  90  has a pump  94  with inverted stages relative to pump  71  of  FIG. 5  that allow for production flow in the opposite direction. Thus, the discharge outlet  36  of the primary ESP  20  connects to the inlet port  95  of the secondary ESP  90 . In a non-inverted stage arrangement, such as in  FIG. 5 , inlet port  95  would be the discharge outlet. The inverted stage pump  94  then discharges production fluid into the capsule  93 , where the fluid flows external to the motor  92  and seal section  96  and out of the capsule  93  through a discharge outlet  97  at one end of the capsule  93 . The discharge outlet  97  passes through a cap  99  that is identical to the cap  32  on the primary capsule  30 . The discharge outlet  97  can further connect to a production flow line or riser. In this case the bellows  88  of the expansion chamber  84  connected to the secondary pump system  90  will be balancing the oil pressure with the discharge fluid pressure. 
         [0034]    The serially connected ESP systems in the embodiments shown in  FIGS. 5 and 6  can be mounted inclined or horizontally on a skid  60  as in  FIG. 3  or mounted in a caisson  100  as shown in  FIG. 4 . Further the multiple expansion chambers can be mounted on the skid  60  ( FIG. 3 ) or on the seabed. 
         [0035]    Referring to  FIG. 7 , an alternative embodiment is illustrated that is similar to the embodiment shown in  FIG. 1 . However, in this embodiment, the ESP  20  uses a standard ESP arrangement instead of an inverted arrangement. Thus, the motor  110  is located below the pump  112  and a seal section  114  is located between. Further, the production fluid will flow into the capsule  30  through a port  124  at one end of the capsule  30 . Port  124  connects to a flow line carrying production fluid from a well. The pump  112  discharges the production fluid through a piece of tubing  126  that passes through the cap  32 . The discharge tubing  126  can connect to a flow line or riser, as in the embodiment of  FIG. 1 . The base of the motor  110  in this example is at the end of the capsule  30  opposite the cap  32 . A power cable  122  runs through an electrical penetrator  120  in the cap  32  ( FIGS. 11 and 12 ) and connects to motor  110  to energize it. In this embodiment the oil line  42  connects to the bellows  54  of the expansion chamber  50  and extends down into the capsule  30  to communicate with the motor  110 . As in the embodiment of  FIG. 1 , the capsule line  48  allows formation fluid in the capsule  30  to travel up to a second chamber within the expansion chamber  50  defined by the expansion chamber housing  52  and the external surface of the bellows  54 . 
         [0036]    Alternatively, the seal section  114  shown in  FIG. 7  could be replaced with a battery of mechanical seals  130 , as shown in  FIG. 8 . The embodiment shown in  FIG. 8  is identical to the embodiment shown in  FIG. 7 , with the ESP  20  in a standard ESP arrangement and expansion chamber  50 . However, replacing the seal section with the battery of mechanical seals  130  may require the addition of an internal expansion chamber  128  within that capsule  30  and at the base of the motor  110 . In this embodiment then, the external expansion chamber  50  can function as a redundant expansion chamber to prevent the internal expansion chamber  128  from overexpanding. 
         [0037]    The ESP systems in the embodiments shown in  FIGS. 7 and 8  can be mounted inclined or horizontally on a skid  60  as in  FIG. 3  or mounted in a caisson  100  as shown in  FIG. 4 . Further the multiple expansion chambers can be mounted on the skid  60  ( FIG. 3 ) or on the seabed. 
         [0038]    During operation of an ESP  20 , the heat generated in the motor raises the temperature of the motor oil, causing it to expand. This expansion can lead to oil migrating outside of the motor and seal section, resulting in less oil for protecting the motor and possible contamination of other parts of the ESP  20 . Further, a leak caused by the expanded oil can result in formation fluid contaminating the motor oil, which is typically rated for a particular differential pressure. The conventional way of dealing with these problems requires the use of internal expansion chambers that add significant length to the ESP system, making for additional assembly and handling of the ESP at the rig and during running operations. In addition, the reliability of the expansion chamber at the seal section and thus that of the ESP  20  is compromised if the oil expansion exceeds the maximum capacity of the internal expansion chamber. Thus, by locating an expansion chamber  50  on the seabed externally to the capsule  30 , or on a skid that supports capsule  30 , the length of the ESP  20  could advantageously be reduced and the reliability of the ESP  20  could advantageously be increased. 
         [0039]    While the invention has been shown in only one 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.