Patent Application
20060037749
(1) Field of the Invention
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.
(2) Brief Description of the Prior Art
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.
The present invention addresses the problems as set forth above.
The present invention provides a well tool and method for heating a low and higher temperature melting metal alloy charge 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 housing having a cylindrical interior chamber and a lower end. The chamber is formed by first and sections therein. The housing also has proximate its lower end a circumferentially extending dissolvable sacrificial wall means for initially isolating the chambers from the exterior of the housing and, upon melting of the metal alloys, providing a passageway through the housing to permit the alloys to flow out of the housing and into the well. A first, low temperature melting eutectic metal alloy charge is deposited within one of the first and second sections of the chamber. A second, higher temperature melting metal alloy charge is deposited within the other of the first and second sections of the chamber. The second, higher temperature metal alloy charge produces, upon melting, a metal precipitate, which, in turn, is used, in combination with the first metal alloy charge, to repair the failure spots, as hereinafter described. Means are provided at one end of the housing for introducing, positioning and retrieving the tool within the well. An ignitable fuel system is also carried within the chamber. Finally, means for igniting the fuel system is provided, whereby, upon activation of the igniting means, the fuel system is ignited sufficient to heat and melt the first lower temperature melting eutectic metal alloy charge and thereafter sufficient to heat and melt the second higher temperature melting metal alloy charge to produce the metal precipitate, such as iron, whereby, upon said melting of said alloy charges, the sacrificial wall is dissolved to provide said passageway for the flow of the first metal alloy and the precipitate through the housing and into the well.
The tool and method of its use further includes a number of additional features and steps, provided by other elements. For example, the tool may include a ceramic or other heat resistant plug carried on said well tool at the lower end of the housing and positionable within the well for bridging the failure spots on the tubular conduit. Upon completion of the operation and method, the plug is caused to be separated or released from the housing, and the housing is retrieved to the top surface of the well and the plug is left in position within the well.
Now referring to
As shown in
The chamber 107 within the housing 106 contains a homogeneous stabilized ignition or fast burning fuel charge 109. 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 bum 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 housing 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.
The invention contemplates use of two metal alloy substances, or charges, for providing the molten metal composite and precipitate for repair of the failure spots H in the well W. The first, or lower temperature melting eutectic metallic alloy LTA is deposited into the first, or uppermost chamber section 105 above the uppermost end of a second, higher temperature melting metal alloy HTA housed within chamber section 105A. The eutectic composition LTA is 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 composition LTA 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. In summary, when reference herein is made to a low temperature alloy composition, or “a first, lower temperature melting eutectic melting metal alloy”, I mean to refer to these exemplary compositions and to metallic compositions which melt at temperatures of no more than about 1,100 degrees F.
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.
The second, higher temperature elting alloy HTA is deposited within the chamber section 105A. Such alloy composition will melt at temperatures of about 2,400 degrees F., and greater, to form a metal precipitate, such as iron. Modem high temperature alloys have undergone little change in chemical composition in the past thirty years. Most possible combinations of iron, nickel, cobalt, chromium, molybdenum, tungsten, titanium, aluminum, colombium and trace elements have been produced and are available from a number of commercial sources which form a precipitate upon melting:
Other grades in this group include the more highly alloyed exhaust valve steels such as AMS 5700 (aircraft) and the 21-23% chromium manganese alloys with the commercial designations 21-2N, 21-4N, 21-12N and 23-8N. The latter three grades are age hardenable. The age hardening, engine valve type grades are used up to 1400° F. (760° C.), but provide fairly low strength at the upper end of their temperature capability.
Now, with first reference to
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.
