Abstract:
A method of manufacturing a submergible machine protector bag comprising providing a tubular woven sleeve of reinforcing material, fitting the sleeve over a mandrel, embedding the sleeve in a waterproof elastomeric material to form a bag body and removing the bag body from the mandrel.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of United Kingdom Patent Application No. 0618231.5 filed Sep. 15, 2006. The disclosure of the above application is incorporated herein by reference. 
       FIELD 
       [0002]    The present disclosure relates to protector bags for submergible (submersible) electric motors or other machines for use for example down-hole in a wellbore. 
       BACKGROUND 
       [0003]    The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. Electric submergible pumps are widely used throughout the world for recovering subterranean fluids to the earth&#39;s surface. For the long term successful operation of such submergible pumping systems, the electric motor must be supplied with uncontaminated motor cooling oil. This cooling oil is partially contained within one or more elastomeric bags within a motor protector. Unfortunately, in wellbore environments with elevated temperatures, such as greater than about 300° F. (150° C.), conventional motor protector bags rapidly deteriorate and split so that the cooling oil will become contaminated by wellbore fluids. This contamination can directly lead to shortened operational life, which in turn will cause the premature shutting-in of the well, and the costly removal and repair of the submergible pumping system. 
         [0004]    Specifically, the elastomeric motor protector bags are generally cylindrical in shape and are sealed within an oil filled housing, with the purpose of providing an expandable volume to accommodate expansion of the cooling oil during operation. The bags are filled with oil at the time of installation to an expanded state. With the rise of temperature caused by immersion in the wellbore, as well as the thermal expansion caused by the operation of the electric motor, the oil expands and is accommodated by further expansion of the bag. When the electric motor is turned off, the cooling oil cools and contracts. This contraction allows the motor protector bag to deflate. The repeated expanding and contraction of the elastomeric bag can cause splitting or cracks in the bag under certain conditions. 
         [0005]    A known motor protector bag is described in U.S. Pat. No. 6,537,628, on which the above paragraphs are based, and to which the reader is referred. That bag however is difficult to manufacture economically and furthermore the effectiveness of the reinforcement is limited. The present invention at least in its preferred embodiments can provide a solution to these shortcomings. 
       SUMMARY 
       [0006]    According to one aspect of the invention there is provided a method of manufacturing a submergible machine protector bag comprising providing a tubular woven sleeve of reinforcing material, fitting the sleeve over a mandrel, embedding the sleeve in a waterproof elastomeric material to form a bag body and removing the bag body from the mandrel. 
         [0007]    By “embedded” we mean that the sleeve is at least to some extent set into the waterproof elastomeric material, and is not just disposed on its surface. By “mandrel” we mean any mandrel, core or former suitable for having a bag body moulded about it. 
         [0008]    In another aspect of the invention there is provided a submergible machine protector bag comprising a woven tubular sleeve of reinforcing material embedded in a bag body of waterproof elastomeric material. 
         [0009]    Preferably the sleeve is of smaller diameter than the mandrel, and is expanded to fit over the mandrel. The sleeve may be a knitted tube or sock. 
         [0010]    The sleeve may have elasticity to permit said expansion. The elasticity may be provided by elastomeric material in the sleeve, which elasticity subsequently may be substantially eliminated. 
         [0011]    The elasticity may be eliminated by decomposition of the elastomeric material in the sleeve. 
         [0012]    The elastomeric material in the sleeve may be natural rubber in the threads from which the sleeve is woven. Alternatively it may be a soft fluorocarbon elastomer, for example in the range 55 to 70 nominal IHRD, preferably about 60 nominal IHRD. 
         [0013]    The sleeve may be woven from thread containing or consisting of poly (p-phenylene-2, 6-benzobisoxazole) fibre (PBO fibre). 
         [0014]    Alternatively or in addition it may be woven from thread containing or consisting of carbon fibre and/or glass fibre. 
         [0015]    The sleeve may be positioned relative to the mandrel so that it is embedded in a radially inner surface of the bag body. 
         [0016]    Alternatively it may be positioned to be embedded in the radially outer surface of the bag body, or to be embedded between the radially inner and radially outer surfaces. 
         [0017]    The method may comprise providing a layer of elastomeric material on the mandrel before fitting the sleeve over the mandrel and preferably partially curing the layer before fitting the sleeve over the mandrel. 
         [0018]    A further layer of elastomeric material may be provided radially outwardly of the sleeve, and the two layers of elastomeric material may be merged into a single layer through interstices of the sleeve. 
         [0019]    The bag may be formed by press-moulding the waterproof elastomeric material. 
         [0020]    The method preferably includes providing the waterproof elastomeric material or at least one said layer thereof as a strip, and winding it around the mandrel. 
         [0021]    The sleeve may be used to hold in place an end section of the waterproof elastomeric material before press-moulding thereof. 
         [0022]    The material of the sleeve may be surface treated to promote adhesion thereof to the elastomeric material. 
         [0023]    Preferably the surface treatment causes a chemical bond to form between the surface of the sleeve material and the elastomeric material. The surface treatment may be a plasma treatment. 
         [0024]    The invention also provides a submergible machine encased in a protector bag as set forth above. 
         [0025]    Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
     
     
       DRAWINGS 
         [0026]    The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
           [0027]    The invention now will be described merely by way of example with reference to the accompanying drawings, wherein: 
           [0028]      FIG. 1  (taken from U.S. Pat. No. 6,537,628) shows a known motor protector bag. 
           [0029]      FIG. 2  illustrates a method according to the invention; 
           [0030]      FIGS. 3 ,  4  and  5  show details of three embodiments of bags according to the invention; and 
           [0031]      FIGS. 6 ,  7  and  8  illustrate further embodiments of the method of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0032]    The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. 
         [0033]    For the purposes of the following discussion it will be assumed that the elastomeric bag of the present invention is used within an oil-filled electric motor protector of the type used with submergible electric motors to be suspended within wellbores. However, it should be understood that the present invention can be used within any other type of downhole or surface motor, pump, turbine or other industrial machine that requires the use of an elastomeric body to contain it or to contain oil supplied to it. 
         [0034]    As has been briefly described above the present invention is a reinforced elastomeric bag for use within an oil-filled electric motor protector. Electric motor protectors are well known to those skilled in the art, and they provide the capability for thermal expansion of the electric motor&#39;s cooling oil, they provide isolation of the cooling oil from wellbore fluids, and they usually contain thrust bearings to absorb the axial loading of the pump that is connected thereto.  FIG. 1  illustrates one preferred embodiment of a motor protector  10  of the present invention connected, in any well known manner, between a pump  12  and an electric motor  14 . The arrangement of the motor protector  10 , the pump  12  and the electric motor  14  is commonly referred to as an electric submergible pumping system or “esp”  16 .  FIG. 1  shows the esp  16  suspended within a wellbore  18  that penetrates one or more earthen formations  20 . 
         [0035]    The interior of the motor protector  10  contains one or more generally cylindrical elastomeric bags  22 , which are clamped on each end by annular brackets or rings  24  across spaced inner housings  26 . The interior  28  of each bag  22  is filled with cooling oil that is conveyed to and from the electric motor  14  through internal passages (not shown) in the protector  10  and the motor  14 , as is well known to those skilled in the art. The elastomeric bag  22  is preferably formed as a single continuous body, without a seam or weld, and has a thickened portion or bead  30  adjacent each mouth or end opening  32 . 
         [0036]    The bag body is preferably formed primarily from an elastomeric material that provides desired elasticity at temperatures above 300° F. (150° C.). Suitable elastomeric materials include tetrafluoroethylene-propylene copolymers, vinylidene fluoride hexafluoropropylene copolymers, virtually saturated acrylonitrile-butadiene copolymers, vinylidene fluoride-perfluoromethylvinylethertetrafluoroethylene terpolymers, vinylidene fluoride hexafluoropropylene tetrafluoroethylene terpolymers, ethylene propylene diene monomer-based polymers, and combinations thereof. One or more bonded layers of such material(s) can be used as desired. 
         [0037]    To increase the tear resistance of the elastomeric material one or more reinforcing materials is added. For example tetrafluroethylene, aromatic p-polyamides, aromatic o, m-polyamides, fibreglass, ferrous metal, nonferrous metal, and combinations thereof of the particles, threads and/or weave, are dispersed within, bonded to or layered within the elastomeric material in manners to improve the tear resistance of the bag  22  at elevated temperatures, such as at temperatures of greater than about 300° F. (150° C.). 
         [0038]    In U.S. Pat. No. 6,537,628 (from which the above description is largely taken), it is suggested that the elastomeric material be reinforced with woven material which is wrapped around a form mandrel before the bag is moulded around it. Alternatively it is applied by hand after the bag has been moulded and vulcanized, and is bonded or glued to it. We consider that neither of these techniques is satisfactory. The woven material is in sheet form and, where its edges overlap, the integrity of the bag depends in that region entirely on the strength of the bond between the elastomeric material and the woven sheet material. Furthermore when the sheet material is glued to the surface of the bag, the integrity of the whole structure depends on the strength of the adhesive bond. 
         [0039]    In the present invention, the reinforcing material is provided in the form of a tube, preferably a knitted tube or sock, preferably seamless. Referring to  FIG. 2 , the sock  40  is of smaller diameter than the main body  42  of a mandrel  44  but due to its knitted form it can be expanded to fit over it, as shown in the successive views in  FIG. 2 . The elastomeric bag material is then moulded around the mandrel in the conventional manner. This process results in the bag material being forced through the interstices of the woven sock, ideally right through to the surface of the mandrel. Alternatively if the liquid elastomer is injected into the mould from within the mandrel, it passes outwardly through the interstices of the sock. The moulded product is then cured, and subsequently removed from the mandrel eg. by expanding it with compressed air applied from within the mandrel, or via a separate removable collar inserted between the product and the mandrel. Alternatively a collapsible mould core could be employed. 
         [0040]    The tube or sock  40  is shown in  FIG. 2  to be of uniform diameter. If preferred it could be made of a more bottle-like shape approximating to the shape of the mandrel. This would enable some reduction in the degree of elasticity in the tube  40  necessary for it to fit over the larger part of the mandrel. Thus, in general the tube  40  can be made of varying diameter as appropriate to the required finished shape of the protector bag as determined by the mandrel. 
         [0041]    The resulting product is shown in  FIG. 3 . Whilst it is shown to be of circular cross-section, other cross-sections are possible. It can be seen from  FIG. 3  that the reinforcing sock is firmly embedded in the inner surface  46  of the bag. In an alternative technique, some of the bag material  48  is applied to the mandrel and cured before the sock is fitted. Then the remainder of the bag material is moulded around the sock. Depending on how much material is applied to the mandrel before the sock is fitted, the sock  40  can be located between the radially inner  46  and radially outer surfaces  50  of the finished bag ( FIG. 4 ) or can be embedded in its radially outer surface  50  ( FIG. 5 ). Of course, if desired the reinforcing material can be made to extend throughout the radial thickness of the bag. To achieve this the sock is woven so as to have a thickness roughly equal to the bag thickness, and the bag is made by injection moulding of initially liquid material that can flow through the interstices of the woven material without distorting it. 
         [0042]    A suitable fibre material from which to weave the sock is PBO, ie. poly (p-phenylene-2, 6-benzobisoxazole). This is available for example under the trade name ZYLON from the Toyobo Co Limited. 
         [0043]    To assist the integration of the sock with the bag material, the sock material can be surface-treated eg. by Chemosil® 5150, applied by dipping or brushing, and carried in a suitable solvent such as industrial methyl alcohol, for example at a concentration of 50% by volume. The sock material alternatively can be plasma-treated to alter the surface chemistry of the fibres or remove unwanted process aids, lubricants etc or other contaminants from the surface of the fibres to promote adhesion so that they bond directly to the bag material. The sock material then chemically bonds to the bag material rather than being dependent solely on mechanical adhesion. This is particularly advantageous when the sock is embedded in the inner or outer surface of the bag. 
         [0044]    The plasma treatment typically comprises placing the sock in a treatment chamber and exposing it at chamber ambient temperature to a plasma formed by exciting a gas (for example ammonia, argon, water vapour, air, oxygen or nitrogen or a mixture thereof) in an electric field at low pressure (for example in the range 10 −1  to 10 −3  Pa). The excited gas forms ions, free radicals or other reactive species which react with (particularly organic) impurities from the sock material surface to form oxides or other volatile compounds which are then pumped out of the chamber. The plasma treatment can also increase the surface area of the material and modify its surface chemistry by ablation (micro-etching) and thereby improve its chemical and physical adhesive interaction with the elastomeric bag material. 
         [0045]    By using a tube of reinforcing material rather than wrapped sheet material the overlapping join of U.S. Pat. No. 6,537,628 is avoided. Preferably the tube is formed seamlessly by knitting it as a sock, but a tube can be made from sheet material by joining its edges eg. by sewing. However, the knitted construction can provide an inherently more resilient reinforcing structure then material woven as a sheet. This better enables the reinforcement to expand and contract with the bag material during use. The limitations on the choice of reinforcing material which were seen as a problem in U.S. Pat. No. 6,537,628 can thus be avoided to some extent, and reinforcing fibres having little inherent resiliency can be used, for example carbon fibre, glass fibre or aramids or some of the other conventional materials dismissed in U.S. Pat. No. 6,537,628 as unsuitable. 
         [0046]    Alternatively or in addition, temporary elasticity can be provided in the sock or tube by including elastic material in the thread from which it is woven, and then destroying that elasticity during subsequent processing. For example natural rubber (latex) threads can be included amongst the threads; this material will survive during the moulding and initial curing step but not the post cure (which can be as much a 12 hrs @ 230° C.) due to the elevated temperature. The temperatures encountered in use also are likely to be beyond the capability of latex. 
         [0047]    If permanent elasticity is required in the sock a heat resistant material can be included in the thread from which the sock is woven. For example a fine extruded cord of soft fluorocarbon elastomer, preferably of about 60 IHRD may be used, although the resulting sock would be harder to stretch over the mandrel then a comparable one containing latex. 
         [0048]      FIG. 6  is a flow chart for one embodiment of the method of producing a protector bag according to  FIG. 4 , by compression moulding. The embodiment presumes the use of two cores or mandrels (stages  52 ,  66 ), the bag on one being cured whilst the other is being laid-up (prepared). Uncured sheet rubber material of a tetrafluoroethylene/propylene (TFE/P) compound based on a blend of Asahi Glass&#39;s Aflas® 150P and 100H polymers, reinforced with carbon black and incorporating a peroxide cure system, is calendered (rolled) to a uniform thickness of 1 to 1.2 mm at stage  54 . It then is cut into strips 25 mm wide (stage  56 ). 
         [0049]    One of the strips is wound helically around a pre-heated mandrel or core (stage  58 ) to cover its circumferential surface as required for the finished shape of the bag. Advantageously the mandrel can be rotated eg. in the headstock of a lathe to facilitate this. The PBO sock or tube, having first been cut to length, is pulled over the first layer of rubber (stage  60 ). A second strip of rubber is then wound helically over the sock (stage  62 ); it may be found advantageous for this layer to be wound to the opposite hand to the first layer so that the strip edges in the two layers are not parallel. The assembly then is placed in a compression mould for 20 minutes at 160° C. wherein the two layers of rubber are compressed together and merge through the interstices of the sock, and abutting surfaces (both between the layers and between the edges of the strip forming each layer) fuse together and the completed make-up is subjected to compression moulding at elevated temperature. The resulting product consists of a single homogeneous layer of elastomeric material in which the sock is embedded. 
         [0050]    Full cure may or may not be completed in the moulding process. A post moulding process whereby the bag is placed in an autoclave or oven and subjected to a ‘ramped’ heated and cooling process may be employed. This process may take place whilst the bag is still on the mandrel or after it has been removed. The latter is preferred because otherwise the release of the mandrel or core for the manufacture of another bag is delayed. A suitable post-moulding even cure cycle is as follows (ramp up to 100° C. @ 50° C. per hour, dwell for 1 hour @ 100° C., ramp up to 180° C. @ 20° C. per hour, dwell for 1 hour @ 180° C., ramp down to room temperature @ 40° C. per hour). 
         [0051]    The finished bag is blown off the mandrel by means of compressed air supplied via a collar eg. of PEEK (polyetheretherketone) material inserted between the bag and the mandrel. Alternatively if a collapsible mandrel is used, the bag is removed by disassembling the mandrel and removing it from within the bag. 
         [0052]      FIG. 7  illustrates another embodiment of the method, for the production of a  FIG. 4  bag with a cone-shaped end. Steps corresponding to those of  FIG. 6  have the same reference numerals. In this embodiment the first rubber layer is not wound onto the core in strip form. Instead (stage  70 ) it is extruded as an uncured tube and fitted to the mandrel core, followed by the PBO sock (stage  74 ). Previously, the rubber sheet calendered as before at stage  54 , is cut or stamped out to provide accurate ‘CAD’ designed half-section developments (“laminates” or flat panels) which when formed around a conical end of the mandrel will form the end of the bag. The remainder of the sheet is cut or stamped into 25 mm and 12.7 mm wide strips (stage  72 ). 
         [0053]    The laminates are fitted under the end of the sock so as to contact the end of the rubber tube previously fitted to the mandrel. They are temporarily held in place by one turn of the narrower strip material (stage  76 ); some solvent may be applied to the rubber to assist temporary adhesion. Then the lay-up is completed by helically winding an outer layer of wider strip (stage  62 ). The subsequent stages  64 ,  66  and  68  then proceed as previously described. 
         [0054]    In this and the other embodiments the rubber overlaps the free end or ends of the sock by a small amount. If preferred, the edges of the strip can in each embodiment overlap each other slightly. 
         [0055]      FIG. 8  illustrates a method of producing a bag according to  FIG. 3 , with the sock embedded in the inner surface of the bag. Again, stages already described have the same reference numerals as in  FIGS. 6 and 7 . In this embodiment the AF90LS rubber sheet is calendered at stage  78  to 2.4 to 2.5 mm thickness (twice that in the previous examples, because there will be only one layer of material; it is cut into 25 mm strips at stage  56  as before. The PBO sock is pulled over the bare mandrel at stage  80  and the strip wound helically over it with slight overlap at stage  82 . Moulding and curing then proceeds as already described. The resultant bag has its sleeve  40  embedded in the inner surface of the bag. 
         [0056]    Compression moulding of the bag has the advantage that the tube or sock  40  is less likely to be displaced during the moulding operation because it is already held in position by the uncured rubber material when it is put in the mould. Excessive displacement of the tube  40 , in addition to resulting in a less repeatable product, may otherwise tear the tube fabric unless particular care is taken. Partial pre-curing (eg. to between 20% and 50% of full cure) of the inner layer of rubber in  FIGS. 6 and 7  may further support the tube against the hydrostatic forces experienced during the compression moulding step. 
         [0057]    Each feature disclosed in this specification (which term includes the claims) and/or shown in the drawings may be incorporated in the invention independently of other disclosed and/or illustrated features. A feature of one embodiment can be incorporated in another embodiment. 
         [0058]    Statements in this specification of the “objects of the invention” relate to preferred embodiments of the invention, but not necessarily to all embodiments of the invention falling within the claims.