Abstract:
A method and apparatus for connecting a component to a rod for use in downhole operations. Wherein the method and apparatus is design to reduce stress and the risk of failures in the connection during downhole operations. The method and apparatus having a connector assembly that is designed with only two wrench flats in order to minimize stress concentrations during operation. The method and apparatus having an optional intermediate alloy metallurgy.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     Embodiments of the present invention generally relate to a connector for connecting a rod with a component for use in boreholes such as oil and gas wells. More particularly, the invention relates to a connector having a stress reducing design including opposing planar portions in a substantially cylindrical body. More particularly still, the invention relates to a connector and rod having a higher alloy content.  
         [0003]     2. Description of the Related Art  
         [0004]     Modern oil and gas wells are typically drilled with a rotary drill bit and a circulating drilling fluid or “mud” system. The mud system (a) serves as a means for removing drill bit cuttings from the well as the borehole is advanced, (b) lubricates and cools the rotating drill bit, and (c) provides pressure within the borehole to balance internal pressures of formations penetrated by the borehole. Rotary motion is imparted to the drill bit by rotation of a drill string to which the bit is attached. Alternately, the bit is rotated by a mud motor which is attached to the drill string just above the drill bit. The mud motor is powered by the circulating mud system. Subsequent to the drilling of a well, or alternately at intermediate periods during the drilling process, the borehole is cased typically with steel casing, and the annulus between the borehole and the outer surface of the casing is filled with cement. The casing preserves the integrity of the borehole by preventing collapse or cave-in. The cement annulus hydraulically isolates formation zones penetrated by the borehole that are at different internal formation pressures.  
         [0005]     Numerous operations occur in the well borehole after casing is “set”. All operations require the insertion of some type of instrumentation or hardware within the borehole. Examples of typical borehole operations include: (a) setting packers and plugs to isolate producing zones; (b) inserting tubing within the casing and extending the tubing to the prospective producing zone; and (c) inserting, operating, and removing pumping systems from the borehole.  
         [0006]     Fluids can be produced from oil and gas wells by utilizing internal pressure within a producing zone to lift the fluid through the well borehole to the surface of the earth. If internal formation pressure is insufficient, artificial fluid lift means and methods must be used to transfer fluids from the producing zone and through the borehole to the surface of the earth.  
         [0007]     The most common artificial lift technology utilized in the domestic oil industry is the sucker rod pumping system. A sucker rod pumping system consists of a pumping unit that converts a rotary motion of a drive motor to a reciprocating motion of an artificial lift pump. A pump unit is connected to a polish rod and a sucker rod “string” which, in turn, operationally connects to a rod pump in the borehole. The string can consist of a group of connected, essentially rigid, steel sucker rod sections (commonly referred to as “joints”) in lengths of 25 or 30 feet (ft), and in diameters ranging from ⅝ inches (in.) to 1¼ in. Joints are sequentially connected or disconnected as the string is inserted or removed from the borehole, respectively. Alternately, a continuous sucker rod (hereafter referred to as COROD®) string can be used to operationally connect the pump unit at the surface of the earth to the rod pump positioned within the borehole.  
         [0008]     A COROD® and sucker rods have pin ends for connecting the rod to a pump, a motor, or another rod. The pin end has a wrench flat section which comprises four flat sections in the cross-sectional shape of a square. The wrench flat section allows an operator to grab the rod with a wrench and apply torque during connection. Because there are four flat sections at 90° angles the operator can move the wrench from one flat section to the next with only a quarter turn of the wrench.  
         [0009]     Many modern boreholes have a highly corrosive downhole environment. Traditional rods and connectors have been manufactured with a low alloy content. The typical rod has only up to 2% of common alloy elements such as Nickel, Chromium and Copper added to their metal chemistry. These low alloy rods are insufficient for use in corrosive borehole environments. To solve this problem in the past manufacturers applied coatings to the rods to prevent corrosion. However, these coatings tend to flake, or scratch off during bending and run in of the rod.  
         [0010]     A COROD® and sucker rods are particularly susceptible to fatigue failure caused by continuous use of the rod to operate downhole tools and pumps. Fatigue failure occurs with frequency at the fillet of the square wrench flats. The discontinuity at the fillet creates a stress concentration. The stress concentration will eventually cause the rod to fail which causes loss of time and equipment. Fatigue failure is of particular concern when using progressive cavity pumps and deviated wellbore applications where eccentricity facilitates bending and flexing of the rod connection(s).  
         [0011]     There is a need for a connector for connecting a rod to another downhole component that reduces stress in the connector. There is a further need for a more even distribution of stresses in the connector in order to prevent fatigue failure. There is yet a further need for a corrosion resistant rod and connector.  
       SUMMARY OF THE INVENTION  
       [0012]     In one aspect a connector for connecting a rod to a wellbore component has a first end for connecting to the component, a second end for connecting the body to the rod and a cross section defining a cylindrical shape with opposing planar portions for engagement with a torquing member. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]     So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.  
         [0014]      FIG. 1  is a cross sectional view of a wellbore illustrating a rod connector for use with a spooled rod.  
         [0015]      FIG. 2  is a cross sectional view of a wellbore illustrating a rod connector for use with a jointed rod.  
         [0016]      FIG. 3  is a view of a connector assembly of the present invention.  
         [0017]      FIG. 4  is a cross-sectional view of the connector assembly of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0018]     The apparatus and method of the present invention allow for connection of a rod for use in a downhole operation with a component. The connector allows the rod to operate downhole equipment while reducing the amount of stress in the connection which leads to failures.  
         [0019]      FIG. 1  depicts a cross-sectional view of a wellbore  100 . As illustrated, the wellbore  100  has a string of casing  102  fixed in formation  104  by cured cement  106 . The wellbore  100  also includes a first component  108 , shown schematically, connected to a rod  110  by a connector assembly  112 . In one embodiment the connector assembly  112  couples the first component  108  to the rod  110 , which is a spooled or continuous rod (COROD®). The COROD® can be of any diameter that is capable of being wound and unwound around a spool  114 .  
         [0020]     In operation the spool  114  with the rod  110  wound around the spool  114  is brought to the wellbore  100 . The connector assembly  112  is then connected to the first component  108 , described in more detail below, and an end of rod  110 . The spool  114  then actuates and lowers the first component  108  by unspooling the rod  110 . When the first component  108  reaches a desired depth in the wellbore  100  the spool  114  stops. In one embodiment the rod  110  is then cut and another connector assembly  112  (not shown) is coupled to the rod and a second component  200 , shown in  FIG. 2 . In one embodiment, the end of the rod  110  with the second component  200  is connected in the same manner as the end with the first component  108 .  
         [0021]      FIG. 2  shows the rod  110  as a series of rods or joints  202 . The joints  202  are of any length desired. In an embodiment the joints  202  are 25 to 30 feet in length. The joints  202  couple together in the same way as the components  108  and  200  are coupled to the rod with connector assembly  112 , described in more detail below. The first component  108  couples to the joint  202 . The first component is then lowered into the wellbore  100 , until the top end of the joint  202  is near the top of the wellbore. Another joint  202  then couples to the first installed joint. This is repeated until the rod  110  is the desired length. The second component then couples to the rod  110 .  
         [0022]     Although rod  110  is shown as a spooled rod and a jointed rod it should be appreciated that the rod may be any rod for use in downhole operations, such as a COROD®, a sucker rod, jointed rod, etc. Further, it should be appreciated that the rod  110  could be a solid rod or a tubular having a bore through the center. The rod  110  can be of any desired diameter in order to meet the specific requirements of the operation.  
         [0023]     The rod  110  and connector assembly  112  may be of any metallurgical make-up. In an alternative embodiment the rod  110  and the connector  112  have increased alloy content. In another embodiment, the rod  110  and the connector  112  have an intermediate alloy level between stainless steel and low alloy carbon steel. The alloy content in another embodiment could be in the range of greater than 2½% Cr. to less than 13% Cr. In another embodiment the alloy content would be approximately 5Cr-½Mo alloy steel, similarly replicating ASME SA193 Grade B5. Although, the alloy used is discussed in respect to Cr, it should be appreciated that any alloying metal could be used such as nickel (Ni.), molybdenum (Mo.), copper (Cu.), vanadium (V.), etc. Further, the metallurgy described above can be used on any rod and any connector used in downhole operations.  
         [0024]      FIG. 3  depicts a view of the connector assembly  112  according to one embodiment of the present invention. The connector assembly  112  includes a body  300 , a first end  302  and a second end  304 . In one embodiment, the first end  302  has threads  306 . As shown, the threads  306  are the male or pin of the connection; however, it should be appreciated that the threads  306  could be in any form to facilitate connection to another member such as a female or box end, a clamp, a flange, etc. The first end  302  adapts for easy connection to the components  108  and  200  or another connector assembly  112 . The first end  302  couples to the body  300 .  
         [0025]     The body  300  is substantially cylindrical and has two full diameter sections  308  on each end of the body  300 . Between the full diameter sections  308  is an engaging section  310 . The engaging section  310  includes planar portions  312 . The planar portions  312  are substantially parallel and adapted to be engaged by a tool  400 , shown in  FIG. 4 . The tool  400  is any tool for applying or resisting torque in the rod  110  such as a wrench, spanner, etc. As shown in  FIG. 4  the planar portions  312  are arranged at edges  402  to transition smoothly from flat to the natural cylindrical diameter of the body  300 . This differs from prior connectors that had a square arrangement, thus having four 90° angles. It should be appreciated that when applying torque to a rod or tubular the highest stress concentrations are on the outer edge of the rod or tubular. In an arrangement with sharp angles the torque load is further concentrated at the angles. Thus, the engaging section  310  reduces stress concentrations in the connector assembly  112  by having tangential edges  402  rather than the angles of the prior art. It should be appreciated that the body  300  can be of any size and configuration so long as the edges  402  of the planar portions  312  have a smooth transition to the rest of the body.  
         [0026]     The body  300  couples to the second end  304  of the connector assembly  112 . Each end of the second end  304  adapts to couple to the rod  110  and the body  300  respectively. The second end  304  may be adapted to be the same diameter as the rod  110 , and further be adapted to match the diameter of the body  300  on the other end. The second end  304  is welded directly to the rod  110 , although it should be appreciated that any connection could be used such as clamps, threads, flanges, etc.  
         [0027]     The first component has an adapter  116  shown schematically. The adapter  116  is arranged to connect to the first end  302 . In one embodiment the adapter  116  is a female or box connection attached to a shaft that couples to the first component  108 . The adapter  116  with the first component  108  is then brought into engagement with the first end  302 . The tool  400  then engages the planar portions  312 . The connection is made between the adapter  116  and the first end  302  by rotating the adapter  116  while the tool  400  prevents rotation of the connector assembly  112 . In another embodiment the connection is made when the adapter  116  is held stationary while the tool  400  torques the connector  112 . It should be appreciated that the adapter could be any connector adapted to connect to the first end  302 . The connection of the connector assembly  112  to the second component  200  or another connector assembly is performed in the same manner as described above and thus will not detailed here.  
         [0028]     In one embodiment the first component is a downhole pump such as a reciprocating pump, a progressive cavity pump. The second component is a motor for rotating the rod  110 . As the second component  200  rotates the rod  110 , the rod  110  turns and torques the connector  112  and transfers rotation to the adapter  116  and thus transfers rotation to the shaft of the pump, not shown. As described above due to the improved design of the connector assembly  112 , stresses in the connector assembly  112  and the risk of failure are greatly reduced over the life of the rod.  
         [0029]     Although the first component  108  is described as a pump, it should be appreciated that the first component  108  could be any tool or component used in downhole operations such as a packer, an expander, a cutting tool, a valve, an anchor, etc. It should further be appreciated that the second component  200  could be any tool or component used at the surface of a wellbore such as, but not limited to a spider, a rotary table, a pipe spinner, a power tong, a top drive, an elevator, the spool, a human operator, etc.  
         [0030]     While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.