Abstract:
An exothermic well tool and method of use for the repair of failure spots along a section of a first tubular conduit, such as casing, are provided wherein the housing of the tool is heated to at least a temperature approximately in excess of that required to activate and melt an exothermic metal alloy composition and may include an ignitable starter fuel charge with a series of solid activation fuel charges spaced throughout the chamber. The tool may also include a length of a second tubular conduit for positioning around the exterior of the housing to define an annular area relative to the first tubular conduit for deposit of a low temperature metal alloy therein.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     (1) Field of the Invention  
         [0002]     The invention relates to an apparatus and method for the repair of failure spots along a first tubular conduit, such as casing, in a subterranean well.  
         [0003]     (2) Brief Description of the Prior Art  
         [0004]     Subterranean wells, such as oil, gas or water wells, oftentimes are completed with the introduction and cementing in place a long string of tubular sections of metallic casing. Since the expected production life of such a well has been known to last decades, and in view of the fact that the abrasive well fluids and treatment chemicals flowing interiorally of the casing often result in defects, such as small holes, pock marks leading to small holes and cracks, (“failure spots”) it is not at all surprising that a failure in circulation of the fluids oftentimes results, with the holes eventually getting larger and larger and even penetrating through the cement securing the casing within the well. It is therefore necessary from time to time to inspect the casing for such defects and attempt to repair them, as opposed to retrieving the entire casing string and running and setting another string of casing.  
         [0005]     The present invention addresses the problems as set forth above.  
       SUMMARY OF THE INVENTION  
       [0006]     The present invention provides an exothermic well tool and method for heating a low temperature metal alloy for the repair of failure spots along a section of a first tubular conduit, such as, for example, casing. The well tool comprises an elongated heat conducting housing having a cylindrical interior chamber. The interior of the chamber is heated by an electrically ignitable fuel system and the heat is transferred through the housing and into a low temperature eutectic metal alloy composition previously deposited within the well. The eutectic alloy composition is caused to melt and free flow within the well to seek the failure spots and plug or otherwise treat them to abate the failures. Preferably, means are provided at one end of the housing for introducing, positioning and retrieving the tool within the well. An electrically ignitable starter fuel charge is placed within the chamber. Means are provided for electrically igniting the starter fuel charge. Throughout the interior of the housing are disposed a series of solid activation fuel charges. A primary slow burning ignition fuel charge surrounds the solid fuel activation charges and is ignited by the solid fuel activation charges.  
         [0007]     Prior to igniting the fuels within the tool, the tool is placed in alignment in the well for straddling the particular failure spot or spots. A second tubular conduit, or repair conduit section, is run into place in the annular area between the exterior of the housing of the tool and the interior of the first conduit member. The lowermost end of this second or repair conduit includes a retaining seal extending outwardly for sealing contact with the interior of the first conduit member. After the second or repair conduit is in place, and the well tool housing are run to location, a fluid containing a low temperature melting, or eutectic, alloy is placed into the annular area above the seal and between the exterior of the well tool housing and the interior of the casing section to be repaired. As the eutectic alloy is slowly melted during activation of the well tool, the alloy in the fluid flow and the failure spots are plugged and sealed. Thereafter, the well tool housing is retrieved from the well and the second tubular string, or repair section, may be left in the well to straddle the failure spots, leaving the original casing intact with the failure spots repaired and the casing integrity enhanced for normal subterranean operations. If desired, the second tubular string of casing or tubing may be perforated thereafter if the repaired section is within a producing zone or section of the well. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]      FIG. 1  is a vertical longitudinal sectional schematic view of a section of casing including failure spots to be repaired.  
         [0009]      FIG. 2  is a view similar to that of  FIG. 1 , illustrating the insertion of the second, or repair, tubular conduit with a retainer seal disposed at its lower end to form an annular area between the second conduit and the interior of the casing.  
         [0010]      FIG. 3  is an illustration similar to that of  FIGS. 1 and 2 , and depicting through vertical cross-section the well tool housing including the various fuel deposits.  
         [0011]      FIG. 4  is an illustration similar to that of  FIG. 1 , illustrating the repaired casing conduit after the well tool housing has been retrieved, the failure spots repaired, and the secondary conduit retrieved. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0012]     Now referring to  FIG. 1 , there is shown a subterranean well W. The well W includes previously run and set a first conduit string or casing C- 1 . As shown the casing string C- 1  has a series of small holes or defects H located longitudinally and radially around a section of the casing C- 1 .  
         [0013]     As shown in  FIG. 1  the apparatus  100  of the present invention is preferably run into the well W on wire line  101 , of conventional and known nature. Alternatively, it may be run into the well W on tubing or electric line. If means other than electric line are used to run and set the apparatus  100 , an electric line  103  is provided form the top of the well W and connected to a source of electric energy at the top or other location in the well W and is connected at the lower end to an electric starter charge  104  within an upper starter charge chamber section  105  within an elongated heat conducting housing  106 . The housing preferably is made of metal, such as an alloy steel or the like. The major requirement for the construction of the housing  106  is that it is enabled to conduct, or transfer, heat, sufficiently to melt the exteriorally deposited eutectic alloy material, discussed in detain below. The chamber section  105  is the uppermost portion of a continuing cylindrical interior chamber  107  defined within the interior of the housing  106 . A one-way check valve  108  is positioned at the upper end of the housing  106  to vent pressure exceeding a pre-set limit within the housing  106  during ignition of the various fuels required to activate the apparatus  100 .  
         [0014]     The housing  106  contains a primary, slow burning, homogeneous stabilized ignition fuel charge  109 , which may have an additive in it to avoid the formation of an iron precipitant, in order to avoid a reaction which will burn a hole through the lower end of the housing  106 . Any commercially available source of a mixture of iron oxide and aluminum which is used in, for example, explosives for perforating guns or like actuations within a subterranean well, may be used. Additives which assist in the burning of a material under water, such as boron nitrate may also be added. The fuel charge  109  may also include an additive such as magnesium for more controlled burning. The aluminum may be finely ground to increase the rate of burn. However, it is preferable to retard the burn rate of this fuel  109  so that energy is not lost in the exhaust. To control the rate of burn of the fuel  109  to achieve maximum burn without excessive exhaust loss, a binder, such as starch, may be added to slow the rate of burn, as well as an additive that expands upon heating to raise the melting point of the fuel mixture charge  109  and to permit the fuel charge  109  to harden quickly as it is introduced into the chamber  107 . Such expansion and hardening agents are commercially available from a host of sources and are well known to those skilled in the fuel composite arts for well tool usage. An additive, such as a dispersant, may also be provided to keep iron particles moving in the fuel mixture charge  109  so that they do not decant to the bottom of the fuel charge  109  but react and hit the matrix and “freeze” in place such that iron pellets are scattered through the fuel charge  109  instead of providing an iron plate at the bottom of the chamber  107  at the bottom of the housing  106 .  
         [0015]     Interspaced longitudinally and radially within the fuel charge  109  are a series of solid activation fuel charges  110  in tubular housing  111 . The tubular housings  111  may be made of any material that will contain activation fuel charge  110  and separate it from the primary fuel charge  109 , yet quickly burn at a relatively low temperature to permit the fuel charges  109  to disperse quickly into the primary fuel charge  109 . Thus, the tubular housings  111  may be made of a light cardboard of known construction. Again, the particular primary fuel charge will be well known to those skilled in these arts and are commercially available.  
         [0016]     The primary fuel charge  109  is topped off with an electrically ignitable starter fuel charge  112  within the uppermost end or portion of the chamber  107 . The starter fuel charge composition may be one of a number of commercially available fuels well known to those skilled in these arts.  
         [0017]     The method and apparatus of the present invention may also include a length of second tubular conduit  113  having first and seconds  113 -A,  113 -B and introduceable within the well W for positioning within the well W exteriorally around the housing  111 . An annular area  114  is defined within the well W and interiorally of the first tubular conduit C- 1  for deposit of a low temperature metal alloy eutectic composition EC. The eutectic composition EC is placed in the annulus area  114  in the form of pellets, in a carrier fluid. The word “eutectic” describes an alloy, which, like pure metals, has a single melting point. This melting point is usually lower than that of any of the constituent metals. Thus, for example, pure Tin melts at 449.4 degrees F., and pure Indium melts at 313.5 degrees F., but combined in a proportion of 48% Tin and 52% Indium, they form a eutectic which melts at 243 degrees F. Generally speaking, the eutectic alloy of the present invention will be a composition of various ranges of Bismuth, Lead, Tin, Cadmium and Indium. Occasionally, if a higher melting point is desired, only Bismuth and Tin or Lead need be used. The chief component of this composition EC is Bismuth, which is a heavy coarse crystalline metal that expands when it solidifies. Water and Antimony also expand but Bismuth expands much more than the former, namely 3.3% of its volume. When Bismuth is alloyed with other materials, such a Lead, Tin, Cadmium and Indium, this expansion is modified according to the relative percentages of Bismuth and other components present. As a general rule, Bismuth alloys of approximately 50 percent Bismuth exhibit little change of volume during solidification. Alloys containing more than this tend to expand during solidification and those containing less tend to shrink during solidification. After solidification, alloys containing both Bismuth and Lead in optimum proportions grow in the solid state many hours afterwards. Bismuth alloys that do not contain Lead expand during solidification, with negligible shrinkage while cooling to room temperature.  
         [0018]     Most molten metals when solidified in molds or annular areas shrink and pull away from the molds or annular areas or other containers. However, eutectic fusible alloys expand and push against their container when they solidify and are thus excellent materials for use as plugging agents for correcting failure spots in well tubular conduits, such as casing.  
         [0019]     The second tubular conduit  113  has proximate its first or lower end  113 -B a retaining seal means  115  for sealing the low temperature metal alloy in the annular area  114  and preventing it from being deposited in the well W below the area containing the failure spots or defects H.  
       OPERATION  
       [0020]     After the casing C- 1  has been inspected and found to have failure spots or defects H, The second tubular string of casing  113  is run into place. Thereafter, the housing  106  of the apparatus  100  is run into the well W on conventional tubing, coiled tubing, wire line, or the like to a location where it straddles the area of the casing C- 1  containing the failure sport H. The annular area  114  is then filled with a carrier fluid containing the eutectic alloy EC. Thereafter, the respective charges are remotely activated which, in turn, ignites the quick fuel spot charges  110  which, in turn, heats and burns the slow stabilized fuel  109 , resulting in the high energy heating of the housing  106 . This heat is then transferred into the eutectic alloy EC to melt it such that it flows and seeks the defects H and plugs or bridges them to enhance the integrity of the casing C- 1 . Thereafter, the housing  106  is removed from the well W and perforation through the second tubular conduit  113  , or normal production operations, may be continued.  
         [0021]     Although the invention has been described in terms of specified embodiments which are set forth in detail, it should be understood that this is by illustration only that the invention is not necessarily limited thereto, since alternative embodiments and operating techniques will become apparent to those skilled in the art in view of the disclosure. Accordingly, modifications are contemplated which can be made without departing from the spirit of the described invention.