Abstract:
An electric submersible pump has one or more components coated with a biocide-incorporated coating for the purpose of controlling the activity of bacteria. The portions exposed to well fluid are coated for inhibiting bacteria from growing. Both centrifugal and progressing cavity pumps are applicable.

Description:
RELATED APPLICATIONS 
     This application is a divisional application of U.S. patent application Ser. No. 10/016,393, filed Dec. 10, 2001 now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention generally relates to bacterial corrosion protection in electric submersible pump (ESP) industry. More specifically, the present invention relates to ESP with corrosion preventing coating as well as a method of reducing the content and inhibiting the growth and activity of bacteria, especially sessile bacteria such as sulfate reducing bacteria (SRB) in ESP components. 
     2. Description of the Related Art 
     Electrical submersible well pumps for deep wells are normally installed within casing on a string of tubing. Usually the tubing is made up of sections of pipe which are screwed together. The motor is supplied with power through a power cable that is strapped alongside the tubing. The pump is typically located above the motor and connected to the lower end of the tubing. The pump pumps fluid through the tubing to the surface. One type of a pump, a centrifugal pump, uses a large number of stages and is particularly suited for large pumping volume requirements. 
     For lesser pumping volume requirements, a progressing cavity or PC pump may be employed. PC pumps utilize a helical rotor that is rotated inside an elastomeric stator which has double helical cavities. PC pumps may be surface driven or bottom driven. Surface driven PC pumps have a rod which extends down to the pump in the well, whereas bottom driven PC pumps are driven by electric motors located in the well. 
     Water flooding is widely used in the petroleum industry to affect the recovery of oil. This process increases the total yield of oil present in a formation beyond what is usually recovered in the primary process. It is desirable in this process to maintain a high rate of water injection with a minimum expenditure of energy. Any impediment to the free entry of water to oil-bearing formations seriously reduces the efficiency of the recovery operation. 
     Water flooding systems provide an ideal environment for growth and proliferation of biofilms. Large amounts of water are transported through these systems and injected into oil bearing formations in an effort to maintain reservoir pressure or to increase the mobility of oil through the formation to producing wells. The large surface area of the water distribution network encourages biofouling, which is the attachment and growth of bacteria on the pipe walls. 
     Biofouling caused by anaerobic bacteria is compounded in water floods by the practice of removing oxygen from the water before injection. The removal of oxygen is done to minimize corrosion of equipment; however, the anoxic conditions provide an ideal environment for the growth of sulfate reducing bacteria (SRB) in the biofilms. This phenomenon is observed both on the injection side and producing side of the water flood operation. The metabolic activity of these bacteria can lead to accelerated corrosion rates, plugging of filters, health hazards from the sulfide production, and eventual souring of the formation (a sour well contains hydrogen sulfide). 
     A common method used to control biofouling in the art is regular application of a biocide. The biocide is generally selected based on its performance in a standard laboratory evaluation test. Glutaraldehyde (pentanedial), which is a highly effective quick-kill biocide, is commonly used to control biofouling. Usually, the biocide is added to the system periodically in predetermined dosage regimes. However, such commonly used method has some disadvantages: it requires large quantity and periodic addition of the biocide, which can increase the cost. Besides, glutaraldehyde is unstable on storage, if not stored properly. 
     Therefore, there is clearly a need for an improved method to protect electric submersible pump components from microbiologically induced corrosion with long-lasting effect. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the invention to provide an improved method to protect electric submersible pump (ESP) components from microbiologically induced corrosion. 
     Specifically, the invention discloses that one or more biocides can be included in coatings which are to be used on ESP stage sets and components to control the activity of bacteria, especially sessile bacteria such as sulfate reducing bacteria (SRB). Various components of ESP that can be coated with biocide-incorporated coatings include head and base of the centrifugal pump, or intake and discharge of the progressing cavity pump. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A and 1B  comprise an elevational view of an electrical submersible pump (ESP) assembly supported on tubing within casing in a well and having an internal coating in accordance with this invention. 
         FIG. 2  is a cross-sectional view the pump of  FIG. 1   
         FIG. 3  is an enlarged cross-sectional view of a portion of the pump of  FIG. 1 . 
         FIGS. 4A and 4B  comprise a sectional side view of a progressing cavity (PC) pump on an upper end of a pump assembly showing intake ports and discharge of the pump, wherein the biocide-incorporating coating is applied in accordance with the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to  FIGS. 1A and 1B , electrical submersible pump (ESP) assembly is designated generally  10 . Usually, tubing  12  is run within casing  14  from the surface to provide a conduit to support ESP assembly  10  and carry produced fluids to ground surface. ESP assembly  10  includes a motor  16  that drives a pump  18 . Motor  16  and pump  18  are typically separated by a seal section  20 . Seal section  20  equalizes pressure of lubricant within motor  16  with that of the tubing annulus. Motor  16  is normally a three-phase electrical motor. Pump  18  is typically a centrifugal pump, although it might also be a progressing cavity pump. 
     Referring now to  FIG. 2 , pump  18  has a cylindrical housing  21 . An adapter  22  on its lower end connects pump  18  to motor  16  ( FIG. 1 ). A plurality of pump stages are located in housing  21 . As shown also in  FIG. 3 , each stage has a impeller  23  with a plurality of passages  24  that lead upward and outward from a central inlet. Each impeller  23  fits within a diffuser  25 , which has a plurality of passages  26  that lead inward and upward. A shaft  29  that is supported in housing  21  by radial bearings  27 ,  28 , extends through each impeller  23  and diffuser  25 . Impellers  23  are secured to shaft  29  by keys for rotation with shaft  29 , while diffusers  25  are stationarily mounted in housing  21 . 
     Shaft  29  is connected to another shaft (not shown) extending upward from seal section  20  ( FIG. 1 ), which in turn is driven by motor  16 . A discharge head  30  at the upper end of housing  21  connects pump  18  to tubing  12  ( FIG. 1 ). Discharge head  30  has an internal passage for the discharge of well fluid into tubing  12 . Caps  31  shown in  FIG. 2  on discharge head  30  and adapter  22  are used only during transporting pump  18  and will be removed when pump  18  is to be installed in a well. 
     Biocide-incorporated coatings can be applied to various internal/external surfaces of pump  18 .  FIG. 3  illustrates biocide-incorporated coatings  32  formed on all surfaces that come into contact with the well fluid. This includes passages  24  of impeller  23  and passages  26  of diffusers  25 , as well as exterior portions of impellers  23  and diffusers  25 . Additionally such coatings  32  may be formed in the internal passages of adapter  22  and discharge head  30 . Coatings  32  may also be formed on bearings  27 ,  28  and in the space in housing  21  above the upper pump stage and below upper bearing  28 . 
     Referring now to  FIGS. 4A and 4B , a progressing cavity (PC) pump  37  is driven by motor  38 . PC pump  37  has a metal rotor  39  which has an exterior helical configuration and a splined lower end. Rotor  39  has undulations with small diameter portions  40  and large diameter portions  42  that give rotor  39  a curved profile relative to axis  32 . Rotor  39  orbitally rotates within an elastomeric stator  41  which is located in pump housing  13 . Stator  41  has double helical cavities located along axis  32  through which rotor  39  orbits. A housing  42  made of a plurality of tubular sections encloses stator  41  and rotor  39 . 
     Specifically referring to  FIG. 4A , a plurality of intake ports  47  are located in the lower portion of pump housing  42 . The upper end of housing  42  is secured to a string of production tubing  48  by a coupling  49 . Well fluid pumped by pump  37  is drawn in through intake ports  47  and  35  and discharged tubing  48 . The internal portions of housing  42  that are exposed to well fluid may also have a biocide-incorporated coating. This includes both the intake portion and the discharge portion. 
     Examples of the biocides that have been used in the art to kill bacteria generally include various salts of metals, such as copper, arsenic, tin, lead, and zinc, as well as organic poisons. In addition to the above, bromine, glutaraldehyde, and possibly chlorine are the primary compounds to be used in accordance with the present invention. Other possible biocides include organic compounds, such as acrolein, formaldehyde, sodium dichlorophenol, acetate salts of coco amines, acetate salts of coco diamines, acetate salts of tallow diamines, alkyl amino, alkyl dimethyl ammonium chloride, alkyl phosphates, coco dimethyl ammonium chloride, paraformaldehyde, sodium salts of phenols, and substituted phenols, and inorganic compounds, such as sodium hydroxide, calcium sulfate. 
     The above mentioned biocides can be present in a dry and granular state before mixing with the liquid coatings. Alternatively, the biocides can be present in a liquid state in a microscopic time release capsule before mixing with the liquid coatings. After mixing, the coatings can be applied either by dipping or spraying (liquid or dry). For example, dry spraying would be electrostatic. 
     The invention has significant advantages. When biocides are incorporated in the coatings and then applied to the ESP components, no periodic addition of the biocides is needed. This may reduce the cost dramatically. Also, the incorporation of biocides in the coatings would prolong the life span of the biocides, especially for those that are not stable on storage, such as glutaraldehyde. 
     While the invention has been shown in only some 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.