Abstract:
An electrode for enhancing electrical conductivity between an oil or gas field downhole and the surrounding formation. The electrode may serve as a cathode to cooperate with a remote anode to produce an electric field through the formation. The electrode has an electrically conductive, elongated body with a proximal end adapted to be inserted into the production pipe and a distal end adapted to project into the formation. The body of the electrode has a series of radially-projecting flexible filaments. The filaments are composed of an electrically conductive material and are supported by the body so as to be electrically charged. At least one of the filaments project outwardly into engagement with the wall of the downhole. The filaments also project radially outward into the consolidated formation.

Description:
FIELD OF INVENTION 
       [0001]    The present invention relates to apparatus for enhancing the production of oil from subterranean oil reservoirs with the aid of electric current and, in particular, apparatus for enhancing the performance of the method described in U.S. Pat. No. 7,325,604, issued Feb. 5, 2008, the entire contents of which are incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    As set forth in more detail in U.S. Pat. No. 7,325,604, the oil bearing formation is tapped by drilling a downhole into the oil-bearing formation and providing an open end for the removal of oil. It has been found that the production of oil is enhanced by connecting a negative electrode to the open end and introducing a second electrode in proximity to the formation. A voltage difference is established between the first and second electrodes to create an electric field across the formation. The patent illustrates a downhole into a unconsolidated formation and includes a production pipe which lines the downhole where it enters the unconsolidated formation. In the patent, the terminal end of the production pipe serves as a cathode which cooperates with the second electrode serving as an anode. In consolidated formations, the downhole is drilled and the downhole serves as a conduit for the production of the oil. An electrode is mounted within the consolidated formation within the downhole where it enters the consolidated formation to cooperate with the remote electrode to establish an electric field through the formation. 
       SUMMARY OF THE INVENTION 
       [0003]    The present invention provides an improved electrode which may be mounted in the open end of the downhole to enhance the electrical field across the formation. 
         [0004]    More specifically, the present invention provides an electrode having a body body having a large plurality of resilient electrically conductive filaments projecting radially outward at each of the proximal and distal ends. In a preferred embodiment, the inner ends of the filaments are interconnected to form a string which extends along the length of the body to provide a continuous electrical path between the filaments at the proximal and distal ends of the body. 
         [0005]    In the design of most electrical equipment, the practice is to limit or eliminate any high stress points in which the gradient voltage may lead to a breakdown of the insulating material such as air or dielectric fluid. The present invention recognizes the desirability of proceeding contrary to this practice and to design the electrode to provide a plurality of stress points and thereby enhance the electric field created by the anode and cathode. 
         [0006]    More specifically, the present invention uses electrically-conductive filaments which terminate in points within the oil-bearing formation at the tips of the filaments to attract the electric field produced between the anode and cathode. 
         [0007]    In an embodiment of the invention for use in unconsolidated formations, where the downhole terminates in a production pipe projecting into the formation, the proximal end of the electrode body is positioned within the end of the production pipe and the pointed ends of the filaments contact and may dig into the interior wall of the production pipe adjacent the terminal end thereof to ensure good electrical contact between the electrode and the pipe. The distal end of the electrode body projects into the unconsolidated formation to cooperate with the remote anode to produce the electric field. 
         [0008]    In a second embodiment of the invention, the electrode is mounted in the downhole of a consolidated formation and the filaments throughout the length of the electrode provide a cathode to cooperate with the remote anode to establish the electrical field through the formation. 
         [0009]    In a preferred embodiment, the inner ends of the filaments are mounted in an electrically-conductive strip to form a string which extends along the outer surface of the body continuously from end to end. 
         [0010]    Preferably, the body is hollow to provide an interior flow passage which permits oil to flow from the field to the pump for extraction. In addition, spacing may be provided between the filaments to provide one or more supplemental passages surrounding the body through which oil may flow from the field to the pump. 
         [0011]    Although the invention has been developed primarily for the enhancement of production of crude oil from underground formations, it is believed that it is effective to enhance the recovery of other carbonaceous fluids, such as natural gas, from underground formations. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The invention will be described in greater detail with reference to the accompanying drawings, in which: 
           [0013]      FIG. 1  is a diagrammatic illustration of an oil field embodying an electrode in a production pipe in an unconsolidated formation in accordance with the present invention; 
           [0014]      FIG. 2  is an enlarged perspective view of the lower end of the production pipe, with a portion broken away to illustrate the electrode shown in  FIG. 1  in which the string of filaments is wound about the body in an open helix; 
           [0015]      FIG. 3  is a cross sectional view of the production pipe providing a plan view of the electrode shown in  FIG. 2 ; 
           [0016]      FIG. 4  is a perspective view similar to  FIG. 2  of a second embodiment of electrode of the invention in which the string of filaments is wound around the body in a closed helix; 
           [0017]      FIG. 5  is a cross sectional view similar to  FIG. 3 , showing the embodiment shown in  FIG. 4 ; 
           [0018]      FIG. 6  is a perspective view similar to  FIG. 2  of a third embodiment of the invention in which multiple strings of filaments extend axially along the length of the body; 
           [0019]      FIG. 7  is a cross sectional view similar to  FIG. 3 , showing the embodiment shown in  FIG. 6 ; and 
           [0020]      FIG. 8  is a diagrammatic illustration similar to  FIG. 1  of an oil field embodying an electrode in accordance with the present invention mounted in the downhole within a consolidated formation. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0021]      FIG. 1  illustrates an oil-producing well  13  of the type shown in U.S. Pat. No. 7,325,604. The well has a vertical down hole which passes through the overburden  12  into an unconsolidated oil-bearing formation  11 . In the illustrated embodiment, the down hole has a production pipe  18  which extends throughout the length of the hole and has a terminal end  16  within the formation  11 . As described in detail in U.S. Pat. No. 7,325,604, an electric source  20  has a positive terminal  21  connected to an anode  22  which is preferably of titanium and is embedded in the electric field remote from the well  13 . A negative terminal  23  is connected to the pipe so that the terminal end  16  of the pipe serves as a cathode for establishing an electric field through the formation. The terminal end of the pipe is preferably made of stainless steel or another electrically-conductive material. The electric field enhances the flow of oil into the pipe  18  where a pump  24  is operative to pump the oil from the formation to conventional machinery  25  at the head of the well for collecting the oil product for refining and distribution. Although the diagrammatic representation in  FIG. 1  shows the pipe  18  within a vertical downhole, the production pipe may extend horizontally or at an angle to penetrate an oil-bearing formation which is remote from the head of the well. 
         [0022]    As shown in  FIGS. 1-3 , adjacent the terminal end  16  of the pipe  18  an electrode  30  is mounted to project into the unconsolidated formation  11 . The electrode  30  comprises a hollow cylindrical body, preferably of an electrically-conductive material, such as stainless steel or another electrically-conductive material. As shown in  FIG. 2 , the body  31  has a plurality of filaments  33  projecting radially from the body along its length. In the present instance, the filaments are interconnected along their length by a conductive strip  34  to form a string  35  of filaments which is wound helically around the outer circumference of the body  31 . As shown in  FIGS. 1 and 2 , approximately half of the convolutions of the helically-wound string  35  are contained within the pipe  18  and the remaining convolutions extend outwardly into the oil-bearing formation  11 . In the illustrated embodiment of the invention, the filaments comprise wires of rectangular cross section free ends are beveled as shown in  FIG. 3  to provide a pointed end for engaging the inner surface of the pipe  18  adjacent its terminal end  16 . 
         [0023]    In accordance with the invention, the beveled ends of the filaments create a plurality of electrical stress points at the outer radial ends of the filaments  33  throughout the length of the electrode  30 . The stress points within the terminal end of the pipe  18  are effective to dig into the inner peripheral surface of the pipe  18  to provide a good electrical interconnection between the electrode and the pipe. Within the oil-bearing formation, the terminal ends of the filaments provide a plurality of electrical stress points which attract the electrical charge which provides the electric field within the formation. 
         [0024]    In a preferred embodiment, the filaments may be made of standard wire in a round or square configuration and ranging in diameters from very fine to a quarter inch. The ends of the filaments may be beveled by grinding the outer perimeter by the string of filaments after they are wound on the body  31 . The filaments may alternatively be formed with individual needle points prior to being assembled into the string  35 . The filaments must be sufficiently flexible to flex at their outer ends to conform to any irregularities in the interior surface of the terminal end portion of the pipe  18  but be of sufficient stiffness to insure good electrical contact between the filaments and the pipe. 
         [0025]    Although the preferred form of the invention includes the flexible strip  34  mounting the individual filaments, it may be found preferable to form the string  35  in a manner so that the filaments and the strip are integrally united at the inner ends of the filaments, but with sufficient flexibility to enable to string to be wound circumferentially on the body  31 . 
         [0026]    The presence of the electrode  30  within the terminal end of the pipe  18  may impede the flow of oil from the formation  11  to the pump  24 . To minimize the impedance, the hollow interior  36  of the body  31  provides an open flow path from the formation to the pump. An additional flow path is provided by the open winding of the string  35  about the outer perimeter of the body  31 . The additional flow path is the helical space  37  between the convolutions of the string  35  in its helical disposition about the body  31 . 
         [0027]    A second embodiment of the invention is illustrated in  FIGS. 4 and 5 . In this embodiment of the invention, the electrode is made similarly to the above-described electrode  30  and consists of an electrode  40  having an elongated body  41  which, in the present instance, is a hollow cylindrical element. The electrode  40  is provided with a string  45  of radially projecting filaments  43  which are interconnected at their base by a connecting strip  44  which is wound helically about the outer circumference of the hollow body  41 . In the present embodiment, the string  45  is wound about the body  41  in a close-wound helix. In other respects, the strings  45  of filaments  43  may be identical to the strings  35  of filaments  33  of the first embodiment and further description is deemed unnecessary. 
         [0028]    In the second embodiment of the invention, the string  45  is closely wound with little or no spacing between the helical convolutions of the string. The close helical winding of the string  45  about the body  41  tends to impede the flow of oil between the outer periphery of the body  41  and the inner periphery of the pipe  18  adjacent the terminal end  16 . To reduce the impedance, the hollow interior  46  of the body  41  provides a flow path from the formation  11  to the pump  24 . A limited flow path may be available between the filaments of the string  45 . To provide a greater flow in the path between the body  41  and the interior wall of the pipe  18 , the contour of the outer perimeter of the electrode may be shaped to provide a clear flow path between the formation and the pump  24 . The clear flow path may be achieved by designing the string during assembly with a selected group of the filaments  33  which are shorter than the remaining so as to provide a clearance space between the ends of the selected filaments and the interior wall of the pipe. This additional flow path may be achieved by including selected shorter filaments in the string during assembly of the string. Alternatively, the electrode may be shaped following its manufacture to grind away the outer ends of selected filaments along a path extending throughout the length of the electrode, to thereby provide an additional path which is unimpeded extending from the distal end to the proximal end of the electrode. 
         [0029]    A third embodiment of the invention is illustrated in  FIGS. 6 and 7 . In this embodiment of the invention, the electrode is made similarly to the above-described electrode  30  and consists of an electrode  50  having an elongated body  51  which, in the present instance, is a hollow cylindrical body. The electrode  50  includes a plurality of strings  55  which extend axially along the outer periphery of the hollow body  51 . The strings  55  are formed similarly to the strings  35  and  45  of the previously described embodiments consisting of filaments  53  and a base strip  54 . The bases  54  of the strings  55  are spaced about the outer perimeter of the hollow body  51  to provide open channels  57  therebetween which extend the full length of the electrode. The electrode of this embodiment provides less impedance to the flow of oil from the formation  11  to the pump  24 . In this embodiment of the invention will also permit the hollow body  51  to be replaced by a solid body (not shown). 
         [0030]      FIG. 8  illustrates the first embodiment of the invention mounted in the downhole which penetrates in a consolidated formation containing a carbonaceous fluid such as natural gas. In this illustration, the well has a vertical downhole which passes through the overburden  110  into a consolidated formation  111  containing a carbonaceous fluid. The downhole  118  has a terminal end within the formation  111 . An electric source  20  has a positive terminal  21  connected to an anode  22 , as described above. A negative terminal  23  is connected to the casing of the pump  24 . An electrode  130  is connected to the pump casing by an electrical conduit  131 . The electrode  130  is similar to the electrode  30  described above but includes a connection to the electrical conduit  131 . The electric source  20  generates an electric field within the formation and enhances the flow of oil into the downhole  118  where a pump  24  may be provided to pump the carbonaceous fluid from the formation to conventional machinery  25  at the head of the well for collecting the product for refining and/or distribution. The pointed ends of the filaments of the electrode  130  create a plurality of electrical stress points throughout the length of the electrode  130  which attract the electrical charge which provides the electrical field within the formation. In this embodiment, as in each of the three embodiments of electrode shown in  FIGS. 1-7 , the electrode provides passageways for the flow of carbonaceous fluid within the downhole. 
         [0031]    All of the embodiments of the present invention are effective to enhance the electrical field created by the anode and the cathode of the source  20 . The electrode may be retro-fitted to an existing well to improve the recovery of carbonaceous fluid from the underground formation. 
         [0032]    While particular embodiments of the present invention have been illustrated and described, it is not intended to limit the invention to such disclosure but changes and modifications may be made therein and thereto within the scope of the following claims.