Abstract:
A shroud for use with a submergible pumping system. The shroud is disposed over a submergible motor and includes fluid channels for conducting heat away from the submergible motor. The shroud is formed from a sheet material, such as sheet metal, to permit its use in wellbores having a narrow annular space between the submergible pumping system and the interior surface of the wellbore casing. The sheet material includes longitudinal corrugations to facilitate fluid flow while strengthening the construction of the shroud.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to a system and method for pumping a production fluid from a subterranean well, and particularly to an electric submergible pumping system having a shroud formed from a sheet material. 
     BACKGROUND OF THE INVENTION 
     Pumping systems, such as electric submergible pumping systems are utilized in pumping oil and/or other production fluids from producing wells. A typical submergible pumping system includes components, such as a motor, motor protector, submergible pump and pump intake. In certain applications, a shroud is disposed about certain of the submergible components. For example, a shroud may be employed around the submergible motor to extend upwardly to the pump intake, where it is fastened to the submergible pumping system. Thus, the production fluid is drawn through the shroud, past the motor and into the pump intake. The produced fluid acts as a coolant when drawn past the submerged electric motor. 
     Conventional shrouds are formed from tubing having an inside diameter larger than the outside diameter of the submergible pumping system components. However, when the annular space between the well casing and the motor is relatively small, much of that space is taken by the wall thickness of the shroud tubing. In fact, in some situations the diameter of the tubing must be reduced to a point that the annular flow space becomes too small to provide sufficient fluid to the pump. This can starve the pump and ultimately damage the pump components. The narrow flow passage is also susceptible to clogging due to deposits or debris in the production fluid. 
     It would be advantageous to be able to utilize a downhole shroud in a narrow bore wellbore without undue utilization of the cross-sectional wellbore space potentially available as a fluid flow passage. 
     SUMMARY OF THE INVENTION 
     The present invention features a device for directing a production fluid along a motor used in a submergible pumping system deployable in a wellbore. The device includes a motor shroud sized to fit within a wellbore. The motor shroud includes a wall that defines an inner flow path of sufficient size to receive the motor therein. The wall of the motor shroud is corrugated to form a plurality of downflow and upflow passages, and a channel for the electrical power cable. 
     According to another aspect of the present invention, a submergible pumping system is provided for use in pumping a production fluid from a subterranean well. The system includes a submergible pump having a pump intake. Additionally, the system includes a submergible motor operably coupled to the submergible pump. A motor shroud is disposed over at least the submergible motor and the pump intake. The motor shroud is formed by a wall of sheet material. Typically, the sheet material is a sheet metal formed as a corrugated sheet. 
     According to another aspect of the invention, a method is provided for cooling a downhole component of a submergible pumping system disposed in a narrow wellbore. The method includes placing a corrugated sheet material around the downhole component to form an interior flow path between the sheet material and the downhole component. Additionally, an exterior flow path is formed between the sheet material and the narrow wellbore. The method further includes drawing a wellbore fluid through the exterior flow path in a first direction. Also, the method includes drawing the wellbore fluid through the interior flow path in a second direction. 
     According to another aspect of the present invention, a method is provided for assembling and deploying a submergible pumping system in a wellbore. The submergible pumping system has a plurality of submergible components and a shroud disposed about at least one of the submergible components. The shroud includes a deformable sidewall and an upper attachment end by which the shroud is coupled to at least one of the submergible components. The method includes assembling the shroud and those submergible components that are at least partially contained within the shroud. The method further includes mounting a first clamp about the shroud and a second clamp about at least one of the submergible components above the deformable sidewall. The method further includes supporting the clamps proximate an upper opening of the wellbore. Additionally, the method includes assembling the remainder of the submergible pumping system above the clamps. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will hereafter be described with reference to the accompanying drawings, wherein like reference numerals denote like elements, and: 
     FIG. 1 is a front elevational view of a wellbore in which an exemplary submergible pumping system, according to a preferred embodiment of the present invention, is deployed; 
     FIG. 2 is a cross-sectional view taken generally along line  2 — 2  of FIG. 1; 
     FIG. 3 is a cross-sectional view taken generally along  3 — 3  of FIG. 1; 
     FIG. 3A is an enlarged view of region  3 A— 3 A of FIG. 3; 
     FIG. 4 is an expanded view of the portion encircled by line  4 — 4  in FIG. 1; 
     FIG. 5 is an expanded view of the portion encircled by line  5 — 5  in FIG. 1; 
     FIG. 6 is a perspective view of an upper attachment portion of the shroud illustrated in FIG. 1; 
     FIG. 6A is a longitudinal cross-sectional view of a power cable extending through the upper attachment portion illustrated in FIG. 6; 
     FIG. 7 is a front elevational view of an alternate embodiment of the system illustrated in FIG. 1; 
     FIG. 7A is an enlarged portion encircled by the line  7 A— 7 A of FIG. 7; and 
     FIG. 8 is a front elevational view of the system illustrated in FIG. 1 suspended from an assembly clamp. 
     FIG. 8A is a perspective view of a portion of a multi-section shroud, according to an alternate embodiment of the shroud illustrated in FIG. 8; and 
     FIG. 9 is a perspective view of an alternate embodiment of the system illustrated in FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring generally to FIG. 1, an exemplary pumping system  10 , such as an electric submergible pumping system, is illustrated. Pumping system  10  may comprise a variety of components depending on the particular application or environment in which it is used. Typically, system  10  includes at least a submergible pump  12 , a submergible motor  14 , a motor protector  16  and a pump intake housing  18  having an intake opening  20  through which a production fluid, such as petroleum, is drawn into intake housing  18  by pump  12 . 
     In the illustrated example, pumping system  10  is designed for deployment in a well  22  within a geological formation  24  containing desirable production fluids, e.g. water or petroleum. In a typical application, a wellbore  26  is drilled and lined with a wellbore casing  28 . Wellbore casing  28  includes a plurality of openings or perforations  30  through which production fluids flow from geological formation  24  into wellbore  26 . 
     Pumping system  10  is deployed in wellbore  26  by a deployment system  32  that may have a variety of forms and configurations. For example, deployment system  32  may comprise tubing, e.g. production tubing  34 , connected to submergible pump  12  by a connector/discharge head  36 . 
     It should be noted that the illustrated submergible pumping system  10  is merely an exemplary embodiment. Other components can be added to the system, other configurations of components can be utilized, and other deployment systems may be implemented. Additionally, the production fluids may be pumped to the surface through tubing  34  or through the annulus formed between deployment system  32  and wellbore casing  28 . 
     Pumping system  10  further includes a shroud  38  disposed about one or more of the submergible pumping system components. For example, shroud  38  preferably is disposed about submergible motor  14 , motor protector  16  and fluid intake  20 . 
     Shroud  38  is disposed within wellbore  26  such that a pair of fluid flow paths are formed. For example, an external fluid flow path  40  is disposed between shroud  38  and an interior surface  42  of wellbore casing  28 . Furthermore, an interior fluid flow path  44  is disposed between shroud  38  and the enclosed submergible components, e.g. motor  14  and motor protector  16 . Thus, when pump  12  is powered by motor  14 , a low pressure area (suction) is created at intake  20 . This suction draws wellbore fluid downwardly from perforations  30  through exterior fluid flow path  40 . The fluid is drawn around a bottom end  46  of shroud  38  and upwardly through interior fluid flow path  44  to intake  20 . The fluid is then discharged upwardly through production tubing  34  via submergible pump  12 . The flow of fluid past, for example, submergible motor  14  removes heat created by motor  14  during operation. 
     Shroud  38  is formed from a sheet material  48  to occupy a minimal amount of the cross-sectional annular space between the submergible system components and interior surface  42  of casing  28 . Preferably, shroud  38  is formed from sheet metal having a thickness less than approximately ⅛ of an inch. As illustrated best in FIGS. 2 and 3, shroud  38  preferably is corrugated. In other words, sheet material  48  forms a wall  50  about submergible motor  14 , motor protector  16  and intake  20  that has longitudinal corrugations running from bottom end  46  to intake  20 . The corrugations of wall  50  are formed as a series of alternating ridges and grooves. For example, wall  50  includes an interior surface  52  that has a series of alternating ridges  54  and grooves  56 . Grooves  56  form interior fluid flow path  44  that permit fluid to flow upwardly past submergible motor  14  and motor protector  16  to intake  20 . Preferably, ridges  54  are disposed against the submergible pumping system components, e.g. motor  14 , to further help dissipate heat as production fluid flows past the exterior of shroud  38 . 
     Similarly, wall  50  includes an exterior surface  58  that has a series of alternating ridges  60  and grooves  62 . Grooves  62  are formed on an opposite side of wall  50  from interior ridges  54 , and ridges  60  are formed on an opposite side of wall  50  from interior grooves  56 . Effectively, interior grooves  56  are separated from exterior grooves  62  by a plurality of sidewalls  63 . The exterior grooves  62  form exterior fluid flow path  40  along which fluid flows from perforations  30  downwardly to the bottom end  46  of shroud  38 . 
     In the illustrated embodiment, the grooves and ridges are of varying size. For example, interior grooves  56  become progressively larger in cross-sectional area moving from one side of shroud  38  to the other. This design permits the enclosure of a power cable  64  in one of the larger or largest interior grooves  56 , as illustrated best in FIG.  3 . Power cable  64  may be a conventional power cable utilized in providing power to submergible motor  14 . 
     As illustrated in FIG. 4, an end ring  66  is attached to the interior of wall  50  proximate bottom end  46 . End ring  66  preferably is a metallic ring having an outer profile that matingly engages and supports the interior surface  52  of shroud  38 , to which it is attached by, for example, welding. End ring  66  has one or more axial openings  68  to communicate the external flow path  40  with the interior flow path  44 . End ring  66  also includes a central axial opening  69 . 
     As illustrated in FIG. 5, shroud  38  preferably is attached to at least one of the submergible pumping system components proximate an upper end  70  of shroud  38 . For example, shroud  38  may be affixed to intake housing  18  above intake openings  20 , as illustrated in FIGS. 1 and 5. 
     In the preferred embodiment, a plurality of lugs  72  are utilized to secure sheet material wall  50  to intake housing  18 . As illustrated in FIG. 6, each lug  72  includes a base end  74  that matingly engages a corresponding interior groove  56  to block fluid flow therethrough. This ensures that the fluid properly travels downwardly through the exterior grooves of shroud  38  and then upwardly to intake opening  20  through the interior grooves of shroud  38 . The lower end  74  of each lug  72  may be attached to wall  50  by, for instance, welding. Several lugs  72  also include an upper tapered portion  76  having an aperture  78  therethrough. Aperture  78  is designed to receive a fastener  80  therethrough, as illustrated best in FIG.  5 . An exemplary fastener is a bolt designed for threaded engagement with corresponding threaded apertures  82  disposed in intake housing  18 , or in a rotatable member attached to intake housing  18 . 
     If power cable  64  is directed through one of the interior grooves  56 , one of the lugs  72  must be formed to accommodate the power cable. Such a lug is illustrated in FIG.  6  and includes a truncated upper tapered portion  84  having an interior channel  86  for receiving power cable  64  therethrough. Upper portion  84  includes a pair of side tabs or wings  88  having apertures  90  therethrough. Apertures  90  are designed to receive corresponding fasteners  80  for threaded engagement with intake housing  18 . To prevent fluid leakage past cable  64 , a tapered packing  91  may be inserted between cable  64  and interior channel  86  during field installation, as illustrated in FIG.  6 A. Tapered packing  91  may be either preformed or flexible, so that it wraps around cable  64 . Packing  91  preferably is formed of a deformable material, such as lead, rubber or plastic. 
     As illustrated in FIGS. 7 and 7A, pumping system  10  may be modified by the addition of a lower scraper  92 , sometimes referred to as a bullnose scraper. Bullnose scraper  92  includes a plurality of scraper ribs  94  designed to scrape unwanted debris or materials from the interior of casing  28  during deployment of submergible pumping system  10 . The removal of such debris and deposits helps prevent damage to the sheet material forming shroud  38  and ensures that external flow path  40  is not obstructed. 
     Scraper  92  also includes an axial opening  96 . Axial opening  96  is sized to receive a mounting stud  98  that is mounted to and extends from a motor base  100  of submergible motor  14 . Stud  98  includes a shoulder  102  and a distal threaded region  104  designed for threaded engagement with a retainer nut  106 . Retainer nut  106  secures bullnose scraper  92  on stud  98  between shoulder  102  and retainer nut  106 . The opening  69  in end ring  66  is sized to receive stud  98  therethrough. The stud  98  transfers any resistance thrust encountered during deployment to the motor rather than to the sheet metal shroud  38 , the motor being stronger than the shroud. Also, should the sheet metal shroud  38  become detached from the intake housing  18 , as by corrosion, the bullnose scraper  92  and stud  98  enable the shroud to be retrieved from the well. 
     Submergible pumping system  10  may also include an upper scraper  108  mounted above submergible pump  12  and shroud  38 . Upper scraper  108  includes a plurality of whole or partial scraper rings  110 . Scraper rings  110  are primarily designed to scrape deposits and other collected material from the interior of wellbore casing  28  when submergible pumping system  10  is removed from a wellbore location. The scrapers facilitate the removal of submergible pumping system  10  while limiting damage to shroud  38  and other submergible pumping system components. 
     As illustrated in FIG. 8, a special clamp  112  may be used to facilitate deployment of the pumping system into the shroud. Clamp  112  mounts on the shroud by fasteners, such as bolts, that pass engagingly through holes in the clamp and thread into holes  113  (see FIG. 6) in lugs  76 . The inside diameter of clamp  112  may be slightly larger than the outside diameter of shroud  38 , so that the fastener bolts tend to expand the diameter of the shroud when tightened, facilitating insertion of the submergible pumping system  10  into the shroud. 
     The clamp  112  may be formed of two separable semicircular halves, as would be known to those of ordinary skill in the art. Each half has two lugs  114  that allow fasteners to join the two halves into a complete circle, that encircles the shroud. Lugs  114  also serve to support the clamp  112  and shroud  38  on a wellhead  115  during deployment. 
     A preferred exemplary sequence of installation is as follows: 
     1. Clamp  112  is attached to the shroud lugs  76 . 
     2. Clamp  112  is used to lift the shroud  38  and lower it into wellbore  26 , so that the clamp lugs  114  rest on the wellhead  115 . 
     3. Motor  14  with stud  98  attached to the lower end, protector  16 , and intake  18  are lowered into shroud  38 , either singly or as a subassembly. (If singly, conventional submergible pumping system clamps may be utilized and placed on shroud clamp  112  to support the submergible pumping system components without causing stress to the shroud itself.) 
     4. During deployment of the submergible pumping system components into the shroud  38 , the electrical power cable  64  is deployed into a sufficiently large internal groove  56  of shroud  38  such that it passes through channel  86  of the special lug  72 . 
     5. When intake housing  18  is proximate the top end of shroud  38 , fasteners  80 , such as bolts, pass non-engagingly through apertures (not shown) in shroud clamp  112 . These fasteners then pass engagingly through holes  78  and  90  in lugs  76  (see FIG. 6) and thread into holes  82  in the intake housing  18  or holes in a rotatable ring mounted on intake housing  18 . 
     6. Fasteners attaching clamp  112  to shroud  38  are then removed. Subsequently, fasteners  80  may be fully tightened, slightly reducing the diameter of the shroud, so that it seals effectively to the intake. 
     7. Clamp  112  is removed from shroud  38 . 
     8. The submergible pumping system string  10  and shroud  38  are lifted clear of the wellhead  115 . 
     9. Bullnose scraper  92  and retainer nut  106  are mounted on the lower end of stud  98 , which protrudes from lower end ring opening  69 . 
     10. The submergible pumping system string is then lowered into wellbore  26 , and the balance of the submergible pumping system is deployed, as would be known to those skilled in the art. 
     In some applications, it may be advantageous to divide shroud  38  into multiple sections. For example, if the required length of the shroud is greater than can be transported or installed in a single piece, the shroud may be divided into multiple sections, as illustrated in FIG.  8 A. In the exemplary embodiment illustrated, shroud  38  includes a plurality of shroud sections  120  that are joined together. 
     Multiple shroud sections  120  may be joined by overlapping shroud section ends or by sheet metal splicing channels that are attached to both sections. For example, a joint member  122  or  151 , in the form of a sheet metal splicing channel, may be sized for mating engagement with the joined shroud sections  120  along either interior surface  52  or exterior surface  58 . In the example illustrated, joint member  122  is disposed on the exterior of shroud sections  120  and matingly engages exterior grooves  62 , while joint member  151  is disposed on the interior and matingly engages interior groove  44 . The sheet metal splicing channel may be joined to shroud sections  120  by appropriate fasteners, such as screws, rivets or other fastening methods or mechanisms. In the embodiment illustrated, a plurality of fasteners  124 , e.g. screws or rivets, are disposed through sidewalls  63  of each shroud section  120 . Typically, the sheet metal channel  122  also includes corresponding sidewalls  126  that each lie adjacent a sidewall  63 , as best illustrated in FIG.  8 A. Fasteners  124  are disposed through adjacent sidewalls  63  and  126  to secure each shroud section  120  to joint member  122  or  151 . 
     During deployment of the overall pumping system  10 , each shroud section  120  is supported at the wellhead by an appropriate clamp, similar to clamp  112  discussed above. The clamp, however, preferably is designed for attachment to a shroud section by fasteners, such as screws, that pass through holes  128  formed in sidewalls  63 , generally at the upper end of a given shroud section  120 . The clamp is designed to support a given shroud section, via fasteners extending through sidewalls  63 , to avoid interference with pumping system components as they are inserted into the shroud section  120 . Once the supported shroud section  120  is attached to the next sequential shroud section, the clamp may be removed, and holes  128  plugged. Holes  128  may be plugged with, for example, short plugging screws that do not extend beyond the maximum outer diameter of the shroud or the minimum inner diameter of the shroud. 
     Another embodiment of a multi-section shroud is illustrated in FIG.  9 . In this system, at least some of the submergible pumping system components, e.g. motor  14  and motor protector  16 , are partially encased in sections of shroud  38  before the submergible components are joined together and installed in the well. 
     In this embodiment, shroud  38  includes a plurality of shroud sections  140  that are fastened to each submergible component. Each shroud section may be attached to a corresponding submergible component by, for example, screws, rivets, welding, adhesives, etc. In the embodiment illustrated, each shroud section  140  includes a plurality of openings  142  disposed radially therethrough at the base of each exterior groove  62 . Holes  142  are located for alignment with corresponding threaded openings  144  extending radially inwardly into the outer wall of the submergible component to which that particular shroud section  140  is attached. Appropriate fasteners  146 , such as screws, are inserted through holes  142  and threadably engaged with threaded openings  144  to secure each shroud section  140  to a corresponding submergible component, as illustrated in FIG.  9 . 
     Attachment of shroud sections  140  directly to submergible components facilitates attachment of the bullnose scraper  92  when, for example, the required length of a unitary shroud would be to great to lift the shroud clear of the wellhead during installation. In this system, the bullnose scraper  92  may be attached to the lowermost submergible section before it is installed in the well. Additionally, a sectional shroud of the type illustrated permits access to certain areas of the submergible components to permit joining of the submergible components and to facilitate the overall installation procedure. Exemplary access areas include clamp grooves, end flanges, fluid ports, electrical connections, etc. 
     When an access area is no longer needed, that area is covered by a supplemental shroud section  148 . In the embodiment illustrated, each supplemental shroud section  148  is divided into a pair of components  150  that have ridges and grooves corresponding to the ridges and grooves of the sequential shroud sections  140 . It should be noted that a variety of single piece or multiple piece supplemental shroud sections  148  can be designed. 
     The illustrated components  150  include a plurality of holes  142  located for alignment with corresponding threaded openings  144 . As described above with respect to each shroud section  140 , fasteners, such as screws  146 , may be inserted through holes  142  in each component  150  and threadably engaged with a corresponding threaded opening  144  formed in the enclosed, submergible components. Upon installation of the supplemental shroud section  148 , the entire shroud  38  is completed to permit the appropriate flow of fluid along external grooves  62  and internal grooves  56 . 
     It will be understood that the foregoing description is of preferred embodiments of this invention, and that the invention is not limited to the specific forms shown. For example, a variety of materials potentially may be used in constructing the shroud; various other or additional components can be contained within the shroud or mounted above the shroud; varying numbers and sizes of corrugations may be formed in the shroud; and the sequence and arrangement of the pumping system components and installation procedure can be changed to suit a specific pumping application. These and other modifications may be made in the design and arrangement of the elements without departing from the scope of the invention as expressed in the appended claims.