Abstract:
An electric submersible pump and motor assembly for downhole applications has an electric motor having a stationary nonrotating through bore, a pump driven by the electric motor, a deployment line upon which the electric motor and pump may be lowered down through a production tube, and a seal for sealing the assembly against the production tube. An inlet upstream of the seal through which well bore fluid may flow extends through the pump and the stationary nonrotating through bore of the motor, and the fluid may exit through an outlet open to the well bore downstream of the seal.

Description:
FIELD OF THE INVENTION 
   This invention relates to electric submersible pumps that can be deployed on a wireline or length of coiled tubing. 
   BACKGROUND OF THE INVENTION 
   Electrical submersible pumps are commonly used in oil and gas wells for producing large volumes of well fluid. An electrical submersible pump (hereinafter referred to “ESP”) normally has a centrifugal pump with a large number of stages of impellers and diffusers. The pump is driven by a downhole motor, which is a large three-phase motor. A seal section separates the motor from the pump to equalize the internal pressure of lubricant within the motor to the pressure of the well bore. Often, additional components will be included, such as a gas separator, a sand separator and a pressure and temperature measuring module. 
   An ESP is normally installed by securing it to a string of production tubing and lowering the ESP assembly into the well. Production tubing is made up of sections of pipe, each being about 30 feet in length. The well will be ‘dead’, that is not be capable of flowing under its own pressure, while the pump and tubing are lowered into the well. To prevent the possibility of a blowout, a kill fluid may be loaded in the well, the kill fluid having a weight that provides a hydrostatic pressure significantly greater than that of the formation pressure. During operation, the pump draws from well fluid in the casing and discharges it up through the production tubing. While kill fluid provides safety, it can damage the formation by encroaching into the formation. Sometimes it is difficult to achieve desired flow from the earth formation after kill fluid has been employed. The kill fluid adds expense to a workover and must be disposed of afterward. ESP&#39;s have to be retrieved periodically, generally around every 18 months, to repair or replace the components of the ESP. It would be advantageous to avoid using a kill fluid. However, in wells that are ‘live’, that is, wells that contain enough pressure to flow or potentially have pressure at the surface, there is no satisfactory way to retrieve an ESP and reinstall an ESP on conventional production tubing. 
   Coiled tubing has been used for a number of years for deploying various tools in wells, including wells that are live. A pressure controller, often referred to as a stripper and blowout preventer, is mounted at the upper end of the well to seal around the coiled tubing while the coiled tubing is moving into or out of the well. The coiled tubing comprises steel tubing that wraps around a large reel. An injector grips the coiled tubing and forces it from the reel into the well. The preferred type of coiled tubing for an ESP has a power cable inserted through the bore of the coiled tubing. Various systems are employed to support the power cable to the coiled tubing to avoid the power cable parting from the coiled tubing under its own weight. Some systems utilize anchors that engage the coiled tubing and are spaced along the length of the coiled tubing. Another uses a liquid to provide buoyancy to the cable within the coiled tubing. In the coiled tubing deployed systems, the pump discharges into a liner or in casing. A packer separates the intake of the pump from the discharge into the casings. Although there are some patents and technical literature dealing with deploying ESP&#39;s on coiled tubing, only a few installations have been done to date, and to date they have only been installed inside large casings, where the oil can flow around the outside of the motor and the pump intake is on the housing diameter. 
   In addition wireline has also been used to deploy ESP&#39;s, both these means are very cost effective and have a dramatic impact on the cost of deploying an ESP into a well. 
   OBJECTS OF THE INVENTION 
   It is an object of this invention to be able to provide an electric submersible pump that can conveniently be lowered on a wireline or coiled tubing. 
   Another object is to be able to provide an ESP that may be used without killing the well it is to be deployed in. 
   SUMMARY OF THE INVENTION 
   According to the invention there is provided an electric submersible pump and motor assembly for downhole applications, comprising an electric motor, a pump driven by the electric motor, a deployment line upon which the electric motor and pump may be lowered down through a production tube, and a sealing means for sealing the assembly against the production tube, the motor having a stationary non-rotating through bore, the assembly having an inlet upstream of the sealing means through which well bore fluid may flow, which leads through the pump and the stationary non-rotating through bore of the motor, and an outlet open to the well bore downstream of the sealing means through which the well bore fluid may exit. 
   According to another aspect of the invention there is provided a submersible pump and motor assembly for downhole applications, comprising a motor, a pump driven by the motor, and an inflatable packer for sealing the assembly against the production tube. The fluid from the pump is constrained by a burst disc to enter the inflatable packer through a one-way valve, such that the burst disc breaks to allow the pumped well fluid access to the outlet when the inflatable packer has been fully inflated. 
   Such an assembly can be manufactured with a small diameter, making the assembly especially suitable for relatively small-bore applications. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The following FIGS. will be used to describe embodiments of the invention which are given as examples and not intended to be limiting. 
       FIG. 1  is a side view of the through tubing ESP in situ in the lowermost part of a production tubing tailpipe. 
       FIG. 2  is an end view cross section XX of  FIG. 1   
       FIG. 3  is an end view cross section ZZ of  FIG. 1   
       FIG. 4  is an end view cross section YY of  FIG. 1   
       FIG. 5  is a side view of the through tubing ESP in situ in the lowermost part of a production tubing tailpipe with a discharge packer inflated. 
       FIG. 6  is a side view of the through tubing ESP in situ in the lowermost part of a production tubing tailpipe pumping fluid. 
       FIG. 7  is a side view of the through tubing ESP in situ in the lowermost part of a production tubing tailpipe deflating the packer 
       FIG. 8  is a side view of a electrical powered pump about to be docked into a standing valve 
       FIG. 9  is a similar side view as  FIG. 8  with the ESP docked into the standing valve. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to  FIGS. 1 to 7  there is shown a well casing  1  with production tubing  2  disposed inside the well casing. The electrical submersible pump consists of a braided wireline  3  secured to the ESP in a rope socket  4 , the electrical conductors terminating  5  at an electric motor assembly  7 , an inflatable packer  6 , a pump  8  attached to and driven by the electric motor assembly  7 , the pump having a pump inlet  9 . A chamber  14  leads from the pump through the center of the motor, exiting through assembly outlet  25 . Referring particularly to  FIG. 2 , the motor has a center  10  that remains stationary during operation, an outside housing  11  which similarly remains stationary, and a rotating part  12  on which magnets  13  are mounted. 
   Referring to  FIG. 1 , the ESP is lowered down the production tubing  2  until the required depth is reached, usually at the lower end of the production tubing, the assembly (or at least the lower end of the assembly) being submerged beneath the well fluid. Referring to  FIG. 5 , when the assembly is at the correct depth, the electric motor is turned on to drive the pump  8 , which draws fluid through the pump inlet  9  along passage  18  and into the chamber  14 . The chamber  14  is initially sealed by a burst disc  17  at its upper end from the assembly outlet  25 . Referring to  FIG. 5 , as the pump  8  operates and pressure in the chamber  14  increases, fluid in the chamber  14  flows through a check valve  16  to inflate packer  15 , securing the ESP in position and sealing it against the production tube  2 . 
   Referring to  FIG. 6 , once the packer  15  has been fully inflated, the pressure in the chamber  14  continues to increase until the burst disc  17  ruptures, allowing fluid in the chamber  14  to exit the assembly through the assembly outlet  25 . The packer  15  remains fully energized, securing the ESP in position and sealing it against the production tubing  2 , since fluid in the packer  15  cannot pass back through the check valve  16 . The pump  8  now displaces fluid from the well beneath the packer  15  through the pump inlet  9  into the chamber  14  and out of the assembly through the assembly outlet  25  into the annulus of the production tubing  2 , and up to the surface. 
   Referring to  FIG. 6   a , the upper housing section  20  and lower housing section  21  are attached by a bolt  19 , the head  23  of the bolt  19  rests upon two spacers  24 ,  26  held in an extended relationship by shear pins  27 . The shear pins are sufficient to support the weight of the lower housing section  21  when the ESP is being lowered down the production tube. When the packer  15  is fully inflated and engaged with the production tubing  2 , the force needed to move the ESP is greater than the shear pins  27  can bear. Referring also to  FIG. 7 , if the well operator wishes to retrieve the ESP, sufficient tension is applied to the wireline so that the separation force between the upper and lower housing sections exceeds the force the shear pins  27  can withstand, so the upper spacer  24  slips inside the lower spacer  26  and the head  23  of the bolt  19  rests upon the lower spacer  26 . This allows the upper housing section  20  and lower housing section  21  to separate a predetermined amount. Referring to  FIG. 7 , part of the lower housing initially covers a packer outlet port  22 . However, once the upper and lower housing sections  20 ,  21  separate through the breaking of the shear pins, this packer outlet port  22  opens to lead to the production tube annulus. The fluid in the packer is at a greater pressure than the fluid surrounding the ESP, and the packer deflates, disengaging with the inner surface of the production tubing  2  and allowing the ESP to be pulled to the surface. 
   Ideally, the positive displacement pump  8  used is one more fully described in WO 2008/032126, but whose basic operation will be described here for completeness. As can be seen from  FIG. 3 , the inner bore  41  of the ESP housing is elliptical. The moving parts of the pump include a cylinder block  42  with a radial bore  43 , having cylinders  44  which can move along the bore but which are biased outwardly by springs. When the motor  7  rotates the block  42 , the cylinders  44  are moved radially inward and outward by the elliptical inner surface  41  of the housing. Using ball bearing valves (not shown) above and beneath the bore  43 , fluid is drawn upward into the bore  43  as the cylinders  44  travel radially outward, and then ejected above the bore  43  where it is directed into axial bores  9  as the cylinders  44  return inward. The pump has several similar but differently aligned cylinders and bores stacked in series,  FIG. 4  showing the cross section of another cylinder block and piston set further down the pump. Of course various types of known pump may be used in this invention. 
     FIGS. 8 and 9  is an another means of separating the pump inlet from the pump discharge. In this example, a standing valve assembly  30  is latched into a nipple profile  31  in the tubing. The standing valve assembly has seals  32  and a check valve  33 . This keeps any fluid pumped from the well inside the tubing, unlike the embodiment shown in  FIGS. 1 to 7 . The ESP is lowered into the well on wireline. At its lower end it has a stab in seal  34  which locates in bore  35  of the standing valve, so that when in the landed position shown in  FIG. 9  the pump inlet  49  is separated from the pump discharge  50  by the standing valve assembly  30 . The pump  8  again pumps the fluid up the center of the motor  7  and into the tubing annulus. If this was a gas well, excess fluid can be produced up the tubing while gas is produced up the casing annulus  36 . 
   Although the embodiments described here are shown as deployed on a wireline, they could also be deployed on tubing (whether coiled tubing or a tubing string), so that a further path up the well bore is provided. With paths being provided by such deployment tubing and the annulus between the ESP and the production tube, pumped fluid could be drawn up one flowpath, while gas was allowed to flow up the other flow path, in a similar manner to the arrangement shown in  FIGS. 8 and 9 . 
   Alternative embodiments using the principles disclosed will suggest themselves to those skilled in the art upon studying the foregoing description and the drawings. It is intended that such alternatives are included within the scope of the invention, which is limited only by the claims.