Abstract:
A standoff for providing a fluid-tight seal for an electrical connection in a well between an electrical conductor extending from down hole of the well and a power source conductor extending from an above-ground power source is enclosed by and extends through and further into the wellbore. The power source conductor extends down hole to a connector for connecting the power source conductor to the electrical conductor. The standoff includes a rigid tube adapted to extend through a wellhead barrier of the well and terminate at a lower end. A rubber boot surrounds the rigid tube. An electrical insulative tubular body has a hole forming a first inner surface surrounding the power source cable between the lower end of the rigid tube and the connector, the rubber boot surrounding the tubular body. A sleeve is placed at one end of the tubular body and has a second, larger hole coaxial with the first hole and forming a second inner surface. An internal surface is formed between the first and second inner surfaces, the lip surrounding a portion of the rigid tube adjacent the lower end and the internal shoulder engages the lower end of the rigid tube for preventing the rubber boot from extruding between the tubular body and the rigid tube when pressurized and evenly distributing the compressive force on the end of the standoff. On the other end of the standoff, a washer sits atop the electrical connector and supports the insulation.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a non-provisional application claiming priority to U.S. Provisional Application No. 61/090,209, filed by applicant herein on 19 Aug. 2008. 
    
    
     TECHNICAL FIELD OF INVENTION 
     The present invention relates to an electrical connection device; specifically, to a high-pressure, high-temperature resistant standoff to insulate an electrical conductor preventing failure in a wellbore. 
     BACKGROUND OF THE INVENTION 
     Electrical connectors for oil wells using electrical submersible pumps (ESPs) are subjected to a variety of harsh and demanding operating environments. As worldwide demand for oil has increased, demand for ESP service in deeper and more challenging environments have presented the pump manufacturer and the companies providing service and peripheral equipment to the pump companies with a number of difficult problems. The continual pressurization and depressurization of well connectors has heretofore led to early and catastrophic failures of ESP systems. The advent of the electrical connectors shown in the prior art and referenced below has dramatically improved the failure rate among ESP installations and led to widespread commercial success of this form of electrical connector. However, recent failures caused by arc over of the electrical conductor in the electrical connectors described in the prior art, particularly in deep, hot and high-pressure wells have exposed additional problems not heretofore understood or appreciated and provided the impetus for further study and this solution to the problems previously incapable of solution. The improvements in this application are expected to make such wells as successful with ESP completions as experienced in non-troublesome wells. 
     STATEMENT OF THE PRIOR ART 
     This application is an improvement over the standoff disclosed in U.S. Pat. No. 5,642,780 issued Jul. 1, 1997 to Boyd B. Moore, which is incorporated herein by reference to show the state of the prior art and the problems overcome by the present invention. 
     SUMMARY OF THE PRESENT INVENTION 
     A high-temperature, high-pressure standoff for providing a fluid-tight seal for an electrical connection in a well between an electrical conductor extending from down hole of the well and a power source conductor extending from an above-ground power source enclosed by and extending through and further into the wellbore in a rigid tube surrounding an electrical conductor and an insulating sheath over the electrical conductor terminating in a rubber boot surrounding the rigid tube, the power source conductor extending down hole to a connector socket for connecting the power source conductor to the electrical conductor. The high-temperature, high-pressure standoff within said connector is fabricated with an electrically resistive metal sleeve having a first inner surface having an inner diameter permitting the rigid tube to be inserted therein and a second inner surface having an inner diameter permitting the electrical conductor and an insulating sheath to be inserted therein and an inner shoulder between said first and second inner surfaces having a width approximating the width of the rigid tube to seat an end of the rigid tube; an electrically insulative tubular body having a hole forming an inner surface surrounding the power source conductor between the lower end of the rigid tube and the connector, the rubber boot coaxially surrounding the tubular body and conductor; and, an electrically resistive washer intermediate the end of the tubular body and insulating sheath and a conductor socket for connecting the conductor. 
     This high-temperature, high-pressure standoff is preferably formed from a high voltage, high strength, ceramic insulator material, but can formed from a high voltage, high strength, glass-filled insulator phenolic material. 
     The high-temperature, high-pressure standoff ceramic insulator compound can be composed essentially of 99.5% Al 2 O 3  by weight. Alternatively, but less preferably, the high-temperature, high-pressure standoff ceramic insulator compound can be composed essentially of composed essentially SiO 2 , 46%, MgO 17%, Al 2 O 3  16%, K 2 O 10%, B 2 O 3  7%, and F 4% (by weight). 
     The high-temperature, high-pressure standoff additionally can additional provide a washer placed between the high-temperature, high-pressure standoff and the connector socket to evenly distribute the compressive forces between the socket and the standoff. Both the washer and the electrically resistive metal sleeve may be fabricated from materials such as stainless steel or a material having a conductivity of not more than 1.45 E +06 Siemens/M. 
     This new improved standoff arrangement permits an electrical connector for electrically connections to a conductor extending from down hole in a well to a power source conductor, said electrical connector comprising a rigid tube enclosing said source conductor; the connector socket electrically terminating the end of the power source conductor past the end of the rigid tube; permitting a sleeve having a longitudinal hole therethrough having a bore accommodating the rigid tube on one end and providing an interior shoulder against which said rigid tube engages while permitting the source conductor to extend therethrough surrounding the power source conductor between the end of the rigid tube and said connector socket; an insulating tubular standoff having a hole forming an inner surface permitting the passage of the electrical conductor; and a rubber boot surrounding said connector socket and said standoff. The washer placed between the insulating tubular standoff and the connector socket fully and evenly distributes the compressive forces imposed on the tubular standoff by the connector socket, making these successful electrical connector arrangements to be used in harsh, deed, high-temperature and high-pressure well environments. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a partial sectional view illustrating a standoff according to the prior art. 
         FIG. 2  is a partial cross-sectional view of the female end of the standoff assembly described in the prior art showing details of the counterbored shoulder failure mechanism experienced by the prior art devices in hot, high-pressure wellbores which prompted the present improvement over the prior art standoff. 
         FIG. 3  is a partial cross-sectional view of the female end of the standoff assembly showing the solution to the deformation or creep experienced by the standoff after prolonged exposure to high-temperature and high-pressure. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     U.S. Pat. No. 5,642,780 issued on Jul. 1, 1997, to Moore, is incorporated herein by reference to show the state of the art prior to the present application. Detailed reference to this patent and the drawings shown therein will make understanding the scope and purpose of the present invention readily comprehensible. As shown in  FIG. 1 , an insulated conductor cable is inserted in a wellbore and connected to a splice preferably made of a non-ferromagnetic, electrically conductive material, such as stainless steel, for example, or the like. The top fitting  100  is preferably a ferrule-type fitting, such as, for example, Swagelok®, or the like, so that the top fitting  100  is fixedly attached to the rigid tube  15 . 
     The top fitting  100  is preferably a close fit having a relatively tight tolerance around the rigid tube  15 . The top fitting  100  is preferably tightened to crimp the rigid tube  15  to form a fluid seal. This choking effect of the rigid tube  15  by the top fitting  100  further prevents fluid flow from the wellbore to atmospheric pressure outside the wellhead (not shown). 
     The top stop  102  includes a corresponding threaded hole  102   b  for receiving the screw which aligns with an outer sleeve slid around the top stop  102  so that the outer holes and holes  102   b  are aligned, and a screw (not shown) is screwed into the threaded hole  102   b  through the hole of the outer sleeve and tightened to the rigid tube  15  to affix the outer sleeve to the top stop  102 , which is attached to or integrally formed with the top fitting  100 . 
     The rigid tube  15  extends past the connector to a lower end  110 , which engages a standoff  112 . The electrical conductor means  11  extends beyond the lower end  110  of the rigid tube  15  through the standoff  112  to the upper end  114   a  of a female connector socket  114 . The insulation  113  of the electrical conductor means  11  is stripped off exposing the conductor element portion  11 ′, which is crimped and/or soldered to electrically and mechanically connect it to the female connector socket  114 , as is well known to those skilled in this art. 
     The female connector socket  114  includes a socket portion at its opposing end for receiving a male connector pin (not shown). It is noted that the particular male and female connectors described herein could be reversed, or otherwise replaced with other slideable connector means as known, so that the prior invention was not limited by any particular connector means. The male connector pin and the female connector socket  114  are formed of any suitable electric conducting material such as copper, or the like, and each is formed by a plurality of longitudinally extending portions which are configured to axially align and mate. A similar connection configuration is more fully described in the U.S. Pat. No. 4,614,392, which is hereby incorporated by reference as if copied verbatim herein. In this manner, the male connector pin and the female connector socket  114  are coupled together for electrically connecting the down hole cable conductors to the electrical conductor means  11 . 
     As previously noted in the cited prior art, three similar down hole cable conductors are found in the normal installation, although only one is shown herein. The conductor cable extends upwards from the ESP to penetrate a connector, where the cable is electrically and mechanically connected to the male connector pin in a similar manner as described for the electrical conductor means  11  and the female connector socket  114 . 
     A female boot  120 , preferably molded from rubber, is formed to surround the rigid tube  15 , the standoff  112  and the female connector socket  114  for electrically isolating the conducting portions from the outer sleeve. The female boot  120  includes a longitudinal passage for receiving a projecting end portion of a male boot. The male boot is inserted into the female boot  120  and locked. The male boot also molded from rubber, is formed to surround the electrical conductor and the male connector pin for electrical isolation from the enclosing outer sleeve. The male and female boots  120  have outer surfaces which are preferably snugly fill the outer sleeve. The outer sleeve is thus electrically isolated from the conductive portions of the electrical conductor connectors. 
     In operation of most wells, the entrained gas and oil exerts a significant amount of pressure which may be applied against the barrier or wellhead. The fluid within the wellbore forms a fluid column which rises and falls depending upon the formation pressure and whether the down hole pump is turned on or off. When the pump is turned off, the fluid column typically rises causing a high-pressure area surrounding the connectors. This high-pressure in these types of wells can still reach the pressure rating of the wellhead, which could be 5,000 to 10,000 psi or more. In contrast, the surrounding air outside the wellhead is at relatively low pressure. In current ESP production schemes, well connectors are being used far deeper in the wellbore and are often found under cowls having multiple pump installations deep within the well and approaching total bottom depth where geophysical temperatures and pressures are significantly higher than those experienced near the wellhead. 
     Due to this high-pressure, the male and female boots  120  typically become saturated with well fluids. When the ESP is turned on, it pumps fluid up the production tubing typically causing the fluid column to fall, so that the annular area surrounding the connector below the wellhead becomes relatively depressurized. The fluid impregnated male and female boots  120  can not release the fluid fast enough, so that a pressure differential exists between the inside of the electrical connector and the surrounding depressurized area. The rubber of the male and female boots  120  tends to expand to force the male and female boots  120  apart, which would otherwise separate a male connector pin from the female connector socket  114 . Due to the top stop  102 , the bottom stop (not shown) and the outer sleeve, the rubber boots  120  are confined and cannot readily expand so that the connector remains intact. Further, since the top fitting  100  is fixedly attached to the rigid tube and attached to or integrally formed with the top stop  102 , the rigid tube  15  is not forced out of the connector, so that the connector remains intact throughout the expansion and contraction phases of the well cycle. 
     Referring now to  FIG. 2 , a partial sectional view of the electrical connector is shown illustrating the failing standoff  112 . As shown, the standoff  112  preferably has a larger diameter than the female connector socket  114  for proper placement of the rubber female boot  120 . When the down hole pump is turned off, any fluid existing in the high-pressure area seeps inside the connector  23  and impregnates the male (not shown) and female boots  120 . A low pressure area exists inside the rigid tube  15  relative to the high pressure annular area outside the connector and the boots  120 . The pressurized fluid impregnated rubber of the boots  120  tends to expand within the connector, thereby forming a tighter seal on all passages through which well fluids might flow. It is undesirable for fluid to escape through the rigid tube  15  via the electrical conductive means  11  comprising the conductor element portion  11 ′ and the insulation  113 . 
     The standoff  112  of the prior art was formed of a reinforced, high voltage, high strength insulator material. The material was a glass-filled laminate phenolic material, such as Westinghouse G-10, for example. The standoff  112  had a hole  112   a  with a diameter for surrounding the insulation  113  of the electrical conductive means  11 , and a second, larger diameter hole  112   b  on one end extending part way into the standoff  112 . The second hole  112   b  was carefully counterbored to receive the rigid tube  15  to create a tight fit. The second hole  112   b  also formed an extension lip  112   c  for circumscribing the rigid tube  15 , and a shoulder  112   d  engaging the lower end  110  of the rigid tube  15 . In spite of the high-pressure, it was previously noted that the rubber of the female boot  120  could extend slightly between the extension lip  112   c  and the rigid tube  15 , but was previously thought to not penetrate all the way to the shoulder  112   d . In fact, the lower end  110  of the rigid tube  15  was previously believed to be forced into the shoulder  112   d  of the standoff  112  forming an effective fluid seal due to the pressure applied by the surrounding rubber, and the low pressure within the rigid tube  15 . The standoff  112  had what was believed to be a relatively wide flat face at a lower end  112   e  engaging the upper end  114   a , which is also relatively wide and flat, to thereby form a fluid seal. The hydraulic pressure differential was intended to force the female connector socket  114  against the lower end  112   e  of the standoff  112 . Thus, fluid was thought to be restrained or not permitted to escape past the standoff  112 , allowing for a greater seal. 
     These prior art standoffs work in most applications and can withstand pressures as high as 10,000 psi without failure. However, arc over failures have been experienced in deep, hot, high-pressure wells. Lab test of these connector with elevated temperature and pressures failed to reveal the failure mechanism until they were left in well-like conditions for extended periods of time. Failures appear to have been caused by the standoff being deformed over extended periods of time to well-like heat and pressure gradients. In these failures, the entire assembly is compressed by the hydrostatic build-up as the counterbore shoulder  112   d  is driven down against the stainless steel tubing  15  causing the laminate material of the standoff to deform, expand or crack  112   f , and eventually fail. 
     To overcome this problem, as shown in  FIG. 3 , a stainless steel sleeve  300  has been fabricated to fit between the steel tube  15  and the standoff  340 . This stainless steel sleeve  300  is counterbored to provide a flat shoulder  305  to seat the rigid tubing  15  and prevents the tubing from unduly compressing against the shoulder  305 . The fittened bottom  320  of the sleeve  300  fully seats on top of the standoff  340  and prevents the tubing  15  from being driven into the standoff  340 , correcting the problem as shown in  FIG. 2 , which is believed to be the principal cause of the prior failures. On the other end of the standoff  340 , a stainless steel washer  360  is placed around the conductor  11 ′ and between the upper surface  114   a  of electrical connector socket  114  and the standoff body  340  to prevent compressive forces from driving the socket between the edge of the standoff  340  and the insulator sheath  113 , each of which are supported by the upper surface  350  of washer  360 . These details are shown in greater detail in  FIG. 3 . The boot  120 , the cap  102  and hole  102   b  for anchoring the cap  102  and compressing a bushing around the tubing  15 , all function in the manner previously shown in the prior art. 
       FIG. 3  is a detailed partial cross sectional view of the top portion of the female end of the electrical connector where the insulative standoff  340  had previously been made of the material described in U.S. Pat. No. 5,642,780, a glass fiber laminated phenolic insulation which worked in most applications. However, in long hot and high-pressure environments, it was discovered the material degraded or deformed causing catastrophic failures. Applicant found in extended, high-temperature high-pressure applications that standoff made from ceramics, such as 99.5% alumina (Al 2 O 3 ), provided by CoorsTek, Inc. of Golden, Colo., and which is sold under the tradename, AD-995 is optimal for this application. Other alternative materials are Corning Glass Works Macor™ which is a compound of SiO 2 , 46%, MgO 17%, Al 2 O 3 16%, K 2 O 10%, B 2 O 3  7%, and F 4% (by weight), which can be machined, has a rated continuous use temperature of 800° C. and a peak temperature of 1000° C., a dielectric strength of at 785 V/mil yet providing a compressive strength of 50,000 psi provided adequate service in these environments. The alumina ceramic material for the standoff  340  provides a compressive strength at 20° C. of 2600 Mpa (377 psi×10 3 ), a Rockwell 45N hardness of 83, a maximum use temperature of 1750° C., 0 gas permeability, and 8.7 ac-kV/mm (220 acV/mil) dielectric strength. 
     The steel tube  15  is inserted in the sleeve  300  which provides a flat shoulder  305  to fully support the compressive force of the tube against which the end of the steel tube  110  fully sets. The counterbore of the prior art device encouraged the tube to lift and separate the laminate material  112  (as shown in  FIG. 2  at  112   f ). In the present embodiment, the stainless steel sleeve  300  fully distributes the load to the end of the standoff  340  evenly. The insulation around the conductor  113  is stripped off at the end of the standoff  340  and a stainless steel washer  360  is placed to support the standoff against the end of the socket  114 , into which is placed the bare conductor  11 ′. The compressive loading experienced by the standoff  340 , whether made from the preferred alumina material or from the less preferred Westinghouse G-10 material or the Corning Macor material is evenly distributed over the entire end of the standoff tube and are believed to therefore be well within the mechanical compressive strength of both materials. Additionally, by avoiding the counterboring found in preparing the prior art standoff device ( 112  of  FIGS. 1 and 2 ) that caused the failure, the cost of preparation of the entire assembly will be reduced since no careful counterboring need be done to the standoff  340  after the hole is drilled for the conductor and insulation sheath. This new arrangement minimizes machine shop spoilage of these small parts. Moreover, assembly of the standoff of the prior art embodiment required careful attention to the possibility of cracking the phenolic-resin standoff from forcing the rigid steel tube  15  into the seat in the counterbore  112  in  FIG. 1 . Installation cracking from inserting the steel tube  15  in the standoff  340  at an angle eliminated this problem, making installation easier and faster, minimizing costly downtime for the well. Additionally, with the prior art embodiment, care was required to avoid stressing the electrical connector to avoid cracking the standoff, after assembly. Often, when banding the electrical conductor cable to the production tubing, stress would be placed on the connection cracking the standoff on the interior of the connector splice while it remained out of the view of the installer. This cracking could lead to failure of the connection by arc-over. This care is no longer critical, making the connection more durable in normal field environments. 
     This new design provides a stronger, and therefore superior, insulation material to prevent the arc over failures experienced by the existing prior art designs. It is now appreciated that each of the three electrical connectors (of which only one is shown) for connecting the electrical conductor means provides an effective seal preventing fluid from escaping through the rigid tubes  15 , and remains intact during pressurization and depressurization occurrences in the well even in high-temperature conditions. This new overall design of these electrical connectors provides ESP service in both regular oil wells and in deep, hot and high-pressures well currently being put into production worldwide fostering enhanced market acceptance of ESP solutions. 
     While the particular invention as herein shown and disclosed in detail is fully capable of obtaining the objects and providing the advantages hereinbefore stated, it is to be understood that this disclosure is merely illustrative of the presently preferred embodiments of the invention and that no limitations are intended other than as described in the appended claims.