Abstract:
A downhole apparatus and method for depositing metal at a desired area in a well casing. In one embodiment the apparatus comprises an oxygen tank filled with oxygen, a fuel tank filled with fuel, and a metal depositing device. An inert gas, such as nitrogen, may be supplied to dampen the heat generated by the metal depositing device. In an alternate embodiment, the apparatus comprises a gas tank with nitrous oxide therein and a sparking device to initiate a decomposition reaction to separate the nitrous oxide into its oxygen and nitrogen components. The metal depositing device may be adapted for flame spraying, plasma spraying or welding. A steering head is provided to reciprocate and rotate the apparatus so that the metal depositing device may be directed to the desired area in the casing. A camera and light are disposed at the bottom of the apparatus so that the interior of a well casing is illuminated and an image is transmitted to the operator for proper actuation of the steering sub. Details of a flame spraying method are disclosed.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to the repair and connection of downhole casing in a wellbore, and more particularly, to a tool system and method for repairing damaged areas, closing gaps between casing sections and filling other openings in well casing by flame spraying, plasma spraying, welding and other similar methods. 
     2. Description of the Prior Art 
     When well casing is installed in a wellbore, there may be gaps formed between casing joints. This is a particular problem, for example, between a lateral casing and the wall to which it is welded. Such gaps can be from several inches to as much as twenty feet or more. Closing this gap is a very difficult and time-consuming operation. This is also true in repairing a large damaged area or filling other openings in casing. 
     Filling such gaps or damaged areas using wire feeder type welding apparatus, either electric or laser type welders, may in fact prove to be impossible. In such cases, the problems associated with such openings may require different operations in the well, and in extreme cases may mean abandonment of that particular wellbore and the drilling of a new well. Obviously, this is a very undesirable situation, and there is thus a need for equipment and techniques to fill gaps or make repairs quickly and easily within the casing in the wellbore. 
     The present invention solves this problem by providing an apparatus and method for using techniques such as flame spray or plasma spray technology to do the job. It is estimated with this apparatus that about one-half pound per minute of metal may be deposited to the desired area in the casing, so even large areas can be repaired quickly. Unlike standard above-ground welding techniques, flame spraying or plasma spraying allow the metal to be applied directly to the bare wellbore and not just to the metal of the casing. In this way, the thickness of the deposited layer of metal can be built up as needed and spread out to adjacent casing surfaces. Like welding, the filled area becomes an integral part of the adjacent casing section or sections. 
     SUMMARY OF THE INVENTION 
     The present invention provides methods and apparatus for downhole welding to repair downhole casing in a wellbore and/or to close other openings in the casing or between sections of casing. This is accomplished by flame spraying, plasma spraying, welding, or other techniques for applying metallic material. 
     Thus, the invention may be described as a method of closing an opening in a wellbore casing string comprising the step of filling the opening with metallic material while the casing string is positioned in the wellbore. The opening in the wellbore casing string may be a damaged area of the casing string, a gap formed at adjacent ends of a pair of casing sections, or any other opening in the casing string. 
     A preferred embodiment of the apparatus comprises an oxygen supply such as a tank, a fuel tank, a metal supply, and metal depositing means in communication with the oxygen tank, fuel tank and metal supply such that heat is generated by the mixture of oxygen and fuel, and heated metal is deposited in the opening of the well casing and adhered thereto. 
     The fuel tank is filled with a fuel preferably from the group consisting of liquefied petroleum gas, kerosene and acetylene. The liquefied petroleum gas may include, for example, butane or propane. 
     The apparatus may comprise meters for metering flow of oxygen from the oxygen tank and fuel from the fuel tank. When the fuel is kerosene, the flow of oxygen is preferably less than about 280 standard cubic feet per gallon of kerosene. 
     The apparatus may additionally comprise a camera and a light disposed adjacent to the camera for lighting an area toward which the camera is directed. The operator may use the camera to guide the spray head to a desired area in the casing. This guiding of the spray head may be carried out by a steering sub adapted for connection to a tool string whereby the spray head may be rotated and reciprocated within the casing so that the spray head may be directed to the desired area in the casing. 
     In a preferred embodiment, the metal supply is a quantity of metal powder, and the metal depositing means comprises a powder container in which the metal powder is disposed. The metal depositing means further comprises a spray head in communication with the oxygen tank, fuel tank and powder container such that the mixture is a mixture of oxygen, fuel and metal powder which is discharged as a metallized flame spray from the spray head. 
     In this flame spray embodiment, the apparatus preferably further comprises an inert gas tank in communication with the powder container. The inert gas tank is filled with an inert gas which pushes the metal powder into the spray head. The inert gas is preferably selected from the group consisting of nitrogen and argon. The inert gas is also mixed with the mixture of oxygen, fuel and powder in order to boost flame speed of the flame discharged from the spray head. 
     In an alternate embodiment, rather than oxygen, a tank may be filled with a gas such as nitrous oxide (N 2 O) and decomposed into oxygen and nitrogen by adding heat, such as by a sparking device. The decomposition reaction creates additional heat which continues the reaction thus providing oxygen for combustion of the fuel and nitrogen as an inert gas. Additional nitrogen may be added by means of a separate tank, through the casing or a tube from the surface. 
     One purpose of the inert gas is to keep the combustion temperature controlled so that it does not become excessive. Thus, the heat is dampened to prevent heat damage to the well casing. The inert gas also helps improve vision through a camera by clearing the smoke caused by the combustion. 
     A tube may be inserted into the well casing adjacent to the tool to evacuate the fumes, thus also aiding and improving vision through the camera. 
     In still another embodiment, the nitrogen tank may be eliminated and nitrogen pumped down the well annulus to dampen the combustion temperature and clear the smoke. 
     Stated in another way, the apparatus of the present invention may be described as one for spraying metal into a desired area of a well casing from the inside of the well casing, the apparatus comprising a steering sub adapted for connection to a tool string, a housing attached to the steering sub such that the steering sub may be used to provide movement of the housing with respect to the tool string, an oxygen tank in the housing wherein the oxygen tank has a quantity of pressurized oxygen therein, an inert gas tank in the housing wherein the inert gas tank has a quantity of pressurized inert gas therein, a fuel tank in the housing wherein the fuel tank has a quantity of fuel therein, a powder container in the housing wherein the powder container has a quantity of metal powder therein and is in communication with the inert gas tank such that the pressurized inert gas tends to push the metal powder out of the powder container, and a spray head connected to the housing and in communication with the oxygen tank, fuel tank and powder container such that fuel, oxygen, inert gas and metal powder are mixed in the spray head and discharged therefrom as a flame spray whereby metal may be deposited on the desired area in the casing. 
     Numerous objects and advantages of the invention will become apparent as the following detailed description of the preferred embodiment is read in conjunction with the drawing which illustrates such embodiment. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates a first embodiment of the downhole flame spray welding tool system of the present invention positioned in a well casing. 
     FIG. 2 shows an alternate embodiment of the flame spray welding tool. 
     FIG. 3 illustrates one embodiment technique for supplying inert gas. 
     FIG. 4 shows an additional embodiment technique for supplying inert gas. 
     FIG. 5 presents a further embodiment technique for supplying inert gas. 
     FIG. 6 illustrates still another embodiment technique for supplying inert gas. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawing, a first embodiment of the apparatus of the present invention is shown and generally designated by the numeral  10 . First embodiment apparatus  10  is connected to the lower end of a tool string  12  which is positioned in casing  14  of a wellbore  16 . 
     In the drawing, apparatus  10  is illustrated as a flame spray apparatus which is a preferred embodiment. Apparatus  10  comprises a housing  18  which is connected to tool string  12  by a steering sub  20 . Steering sub  20  comprises a shaft portion  22  which is actuated by a drive portion  24 . Drive portion  24  may be electrically controlled and include means for reciprocating and rotating shaft  22  and thus reciprocating and rotating housing  18 . 
     In the upper portion of housing  18  is an oxygen tank  26  which is filled with a quantity of pressurized oxygen. An oxygen equalizer  28  is disposed in housing  18  to insure that the pressure level in oxygen tank  26  is maintained at a desired level with respect to the pressure within a well annulus  30  defined between apparatus  10  and casing  14 , as will be further described herein. 
     Below oxygen tank  26  is an inert gas tank  32 . Inert gas tank  32  is filled with a quantity of pressurized inert gas. The inert gas in inert gas tank  32  may be any desirable gas of this type, such as argon or nitrogen. However, the invention is not intended to be limited to a particular inert gas. An inert gas equalizer  34  is disposed in housing  18  to insure that the pressure of the inert gas in inert gas tank  32  is maintained at a desired level with respect to the pressure in well annulus  30 . 
     A fuel tank  36  is disposed below inert gas tank  32 . Fuel tank  36  is filled with any suitable fuel. For example, but not by way of limitation, the fluid may be kerosene, acetylene or a liquefied petroleum gas, such as butane or propane. 
     A powder container  38  is disposed below fuel tank  36  and is filled with a quantity of metal powder of a kind known in the art. Normally, the metal powder is iron-based, although that is not necessarily the case, and in certain conditions other metals may be used. Basically, any material that will adhere to the well casing as a result of a flame spray process, and is compatible with the fluids being handled in the well, would be suitable. 
     A spray head  40  extends away from a lower portion of housing  18 . Spray head  40  includes a mixing portion  42  and a nozzle portion  44 . 
     An oxygen line  46  interconnects oxygen tank  26  with mixing portion  42  of spray head  40 . An oxygen meter  48  may be disposed in oxygen line  46 . An oxygen mixing valve  50  is disposed in the lower end of oxygen line  46  within mixing portion  42  of spray head  40 . 
     A fuel line  52  extends from fuel tank  36  to mixing portion  42 , and a fuel meter  54  may be disposed in fuel line  52 . A fuel mixing valve  56  is disposed in the lower end of fuel line  52  within mixing portion  42  of spray head  40 . 
     A powder opening or line  58  communicates powder container  38  with mixing portion  42  of spray head  40 . A powder mixing valve  60  is disposed in powder line  58  within mixing portion  42 . 
     An inert gas line  62  interconnects inert gas tank  32  with powder container  34 . 
     Oxygen meter  48  and fuel meter  54  may be of any kind known in the art. In particular, an electronic flow meter which provides a signal at the surface is preferred, but the invention is not intended to be limited to only that configuration. 
     Oxygen mixing valve  50 , fuel mixing valve  56  and powder mixing valve  60  are also preferably electronically controlled from the surface so that the operator may adjust the amount of oxygen, fuel and metal powder passing therethrough, respectively. The pressurized inert gas in inert gas tank  32  forces the powder in powder container  38  outwardly through powder mixing valve  60  when the powder mixing valve is opened. 
     At the lower end of housing  18  is a camera  64 , of a kind known in the art with a light  66  on the lower end thereof. As will be further described herein, light  66  illuminates the inside of casing  14  so that a desired area  68  is illuminated, and the camera sends an image of area  68  to the operator. 
     The inert gas is used for a number of reasons. Most importantly, it is used to control the temperature as previously mentioned. It also provides a non-liquid, non-oxygen environment in which the process may take place. The inert gas also provides a media to deliver the powdered metal. Additionally, the inert gas helps displace the smoke for a better view through camera  64 . 
     Referring to FIGS. 3-6, the inert gas, such as nitrogen, may be delivered to the desired location in the well bore in a number of ways. One method, shown generally in FIG. 3, is to use a separate tank in the tool. This is essentially the same as first embodiment  10  previously described. 
     Another technique would be to pump the inert gas down well casing  14  around the tool as shown in FIG.  4 . Smoke generated from combustion would be withdrawn from casing  14  by a vent tube  96 . 
     A further technique is shown in FIG. 5. A sealing means, such as a packer  98 , is used to seal between tool string  12  and casing  14 . A supply tube  100  extends from the surface through packer  98  and is used to supply the inert gas to the desired area in casing  14  adjacent to the tool. Smoke from combustion is vented from that area to a location in casing  14  above packer  98  through a vent tube  102 . 
     Still another technique is illustrated in FIG.  6 . In this version, a packer  104  is used to seal between tool string  12  and casing  14 . A vent tube  106  extends through packer  104  and is used to vent smoke as previously described. The inert gas is pumped down through tool string  12  and discharged through a supply port  108  below packer  104 . 
     Operation of the First Embodiment 
     Tool string  12  is made up with apparatus  10  at the lower end thereof and run into casing  14  of wellbore  16  such that the apparatus is generally near the desired area  68  in casing  12 . Area  68  may be any kind of opening in casing  14 . In the drawing, area  68  is illustrated as a damaged portion within casing  14  which leaves an exposed bare portion  70  of wellbore  14 . However, it should be understood that apparatus  10  is not limited only to the repair of damaged areas in casing  14 . Area  68  could also be an opening which is intended to be in the casing but which must be closed after certain well operations. Additionally, area  68  could be a gap between two adjacent sections of casing. Basically, the invention is intended to be used for closing or filling any type of opening in casing  14 , and not just the particular ones listed herein. 
     Exact positioning of nozzle portion  44  of spray head  40  with respect to area  68  in casing  14  is accomplished by actuating drive portion  24  of steering sub  20  as desired. Light  66  illuminates the interior of casing  14 , as previously mentioned, and camera  64  allows the operator to position nozzle portion  44  of spray head  40  as precisely as necessary. 
     Opening of oxygen mixing valve  50 , fuel mixing valve  56  and powder mixing valve  60  allow the oxygen, fuel and metal powder to flow into spray head  40  and subsequently out nozzle portion  44 . Oxygen meter  48  and fuel meter  54  allow for a proper combustible mixture of oxygen and fuel so that a metallized flame spray  72  is discharged from nozzle portion  44 . For example, for kerosene, a preferred flow rate of oxygen would be approximately 280 standard cubic feet of oxygen per gallon of kerosene. This may vary depending upon well conditions and the size of nozzle portion  44 . The control of flow of oxygen from oxygen tank  26  is important so that a proper combustion is obtained with the oxygen and fuel. An improper flow of oxygen can cause burn-up of the steel of casing  14  and thus destroy more of the casing rather than repair it or otherwise close it. 
     Flame spray  72  contains the metal powder therein which is directed into area  68  to gradually close or fill the opening. An advantage to a metal flame spray is that it may be discharged directly on exposed portion  70  of the wellbore. That is, the flame spray does not need to be directed to the metal forming casing  14  at all times. The metal will gradually build up and close area  68  and, of course, permanently adhere to the adjacent metal of casing  14 . 
     As previously mentioned, the pressurized inert gas in inert gas tank  32  forces the metal powder in powder container  38  into spray head  40  so that it is mixed with the oxygen and fuel to form the appropriate flame spray. Another advantage of the inert gas is that it will also boost flame speed out of nozzle portion  44  of spray head  40  so that less time is necessary to fill area  68 . 
     Another purpose of the inert gas is to reduce the combustion temperature of the fuel to prevent heat damage to casing  14 . The inert gas also helps clear smoke caused by the combustion which improves the vision available through camera  64 . 
     A tube  74  may be inserted in annulus  30  such that a lower end  76  of the tube is near nozzle portion  44 . The pressure in tube  74  may be lowered in a manner known in the art to evacuate fumes of combustion from annulus  30  to improve vision through camera  64 . The position of tube  74  in FIG. 1 is for illustrative purposes only. It will be understood by those skilled in the art, that the tube would not be positioned directly between flame spray  72  and exposed portion  70 . Rather, it would preferably be to one side so that it is not damaged by the heat. 
     Referring now to FIG. 2, a second embodiment of the apparatus of the present invention is shown and generally designated by the numeral  80 . Like first embodiment  10 , the second embodiment is connected to the lower end of a tool string  12  which is positioned in casing  14  of wellbore  16 . 
     Second embodiment apparatus  80  is similar to first embodiment apparatus  10  except that the second embodiment does not include a separate oxygen tank  26  and inert gas tank  32 . Rather, a single gas tank  82  is provided along with fuel tank  36  and powder container  38 . Gas tank  82  has a sparking device  84 , such as a spark plug, disposed therein. 
     Gas tank  82  is filled with a gas such as nitrous oxide (N 2 O) which can be decomposed into oxygen and the inert gas nitrogen when heat is applied thereto from sparking device  84 . 
     A gas equalizer  86  ensures that the pressure of the gas in gas tank  82  is maintained at a desired level with respect to the pressure in well annulus  30 . 
     Housing  78  has a spray head  40  substantially identical to that previously described for first embodiment  10 . A gas mixing valve  88  is included in spray head  40  along with the same fuel mixing valve and powder mixing valve previously described. 
     A first gas line  90  inner connects gas tank  82  with gas mixing valve  88  and may have a gas meter  92  disposed therein. A second gas line  94  inner connects gas tank  82  with powder container  38  so the pressure is applied to the powder to force it outwardly through powder mixing valve  60 . 
     Operation of the Second Embodiment 
     Tool string  12  is made up with apparatus  80  at the lower end thereof and run into casing  14  of wellbore  16  such that the apparatus is generally near the desired area  68  in casing  12  in a manner substantially identical to first embodiment  10 . 
     By applying electrical power to sparking device  84 , heat is applied to the nitrous oxide in gas tank  82  to start decomposing the gas into its separate components of nitrogen and oxygen. The decomposition reaction creates additional heat which continues the reaction. The mixture of oxygen and nitrogen is discharged through gas mixing valve  88  where the oxygen combines with the fuel to create combustion. The rest of the operation is substantially the same as the first embodiment. 
     In still another embodiment, rather than having an inert gas stored separately in the tool as in first embodiment  10  or created by decomposing nitrous oxide as in the second embodiment, the inert gas may be totally eliminated from the tool itself and pumped down well annulus  30 . In this event, another means must be provided to apply pressure to powder container  38 , such as by using oxygen to force the powder out of the tool during operation. It will be seen that in all of these cases, the nitrogen is thus provided in the area around nozzle portion  44  so that the heat of combustion is dampened which reduces the combustion temperature so that heat damage does not occur to casing  14 . Also, in any of these embodiments, the nitrogen may be used to clear the smoke caused by the combustion so that the view through camera  66  is improved. 
     In using the apparatus and method of the present invention, it is contemplated that about one-half pound per minute of metal may be deposited in the target area. 
     In addition to the flame spray embodiment shown and described, the invention could utilize any other means for depositing metal. For example, but not by way of limitation, a metallized plasma spray, welding, etc., could be used. 
     It will be seen, therefore, that the apparatus and method of the present invention are well adapted to carry out the ends and advantages mentioned, as well as those inherent therein. While a presently preferred embodiment of the apparatus and method have been described for the purposes of this disclosure, numerous changes in the arrangement and construction of parts in the apparatus and steps in the method may be made by those skilled in the art. All such changes are encompassed within the scope and spirit of the appended claims.