Downhole platform tool and method of clearing well tubing and casing with exothermic chemicals employing a downhole platform tool

Abstract

The invention relates to a temporary, movable base to be used with an exothermic chemical section milling step in a subterranean well prior to the plug and abandonment step. The temporary base might be melted, consumed, moved or destroyed when exposed to the increased temperature and pressure caused by the exothermic chemical section milling.

Description

[0001] DOWNHOLE PLATFORM TOOL AND METHOD OF CLEARING WELL TUBING AND CASING WITH EXOTHERMIC CHEMICALS EMPLOYING A DOWNHOLE PLATFORM TOOL

[0002] Field of the Invention

[0003] The present invention relates to the technical field of downhole operations in oil / gas wellbores, and in particular to operations associated with the use of exothermic chemical reaction heat sources to clear well tubing and / or casing from a downhole target region and tools for use in such.

[0004] Background of the Invention

[0005] When an oil / gas well reaches the end of its useful life it should be permanently plugged and abandoned. In this process, the well tubing is removed, and a long section of the casing is removed with a downhole method called section milling.

[0006] Section milling involves the deployment of a milling tool to a downhole target region wherein the milling tool is operated to mill a section of well tubing and casing within the target region to create a window that extends across the entire cross-section of the well bore.

[0007] Once the casing has been removed, low melt temperature, metal alloys or cement can be placed across the cross-section of the cleared well bore to create a "rock to rock" plug, sealing the well and protecting the environment.

[0008] Mechanical section milling is typically a slow, expensive method to remove the casing one small metal chip at a time much like machining parts with tool insert in a machine shop.

[0009] Traditional mechanical section milling may soon be replaced with faster, lower cost, more efficient, exothermic chemical tubing and casing removal.

[0010] An alternative clearance method to section milling is exothermic chemical tubing and casing removal, which uses chemicals that either react with well tubing and casing thereby consuming it or chemicals that generate heat within the target region that melts the well tubing / casing. International patent application WO 2015150828 A2, describes a method of exothermic chemical well tubing / casing removal which involves perforating the well tubing / casing in a downhole target region before the chemical agent is activated to clear the well tubing / casing. The methods disclosed in the earlier application were developed by the inventor of the present invention.

[0011] In order to optimise the amount of exothermic chemical needed to clear the well tubing / casing in the downhole target region the use of a supporting platform or base has been considered.

[0012] US 9,494,011 describes the use of a thermite reaction to form a fixed platform below a downhole target region so that a main thermite reaction can be carried out above the platform / base. The primary aim of disclosed method is to form a plug within the downhole target zone from the materials that result from the melting of well tubing / casing by the thermite reaction (e.g., reacted thermite, melted well tubing, etc).

[0013] Summary of the Invention

[0014] The present invention provides a downhole platform tool in accordance with claim 1 . The downhole platform tool is deployed within a downhole target region to provide a supporting platform, onto which a suitable quantity of a chemical reaction heat source can be delivered.

[0015] The supporting platform is provided by the plate which occludes the inner diameter of the tool’s tubular main body and prevents the undesirable flow of fluids in a down hole direction, that is to say the plate prevents the loss of fluids down hole.

[0016] However, in contrast to the fixed platform employed in the method of US 9,494,011 , the downhole platform tool of the present invention is configured to fail in the face of the increased temperature and pressure in the target region caused by the activation of the chemical reaction heat source in the target region.

[0017] The downhole platform tool of the present invention essentially acts as a moveable base that remains in place long enough for the heat generated by the activated chemical reaction heat source to melt the well tubing and / or casing in the target region. The materials that result from the clearance of well tubing / casing (e.g., reacted chemicals, melted well tubing, etc... ) accumulate on top of the downhole platform tool until such time as it fails, wherein the materials are released to fall down hole away from the target region.

[0018] The movable base provided by the downhole platform tool of the present invention is a technology breakthrough, allowing large lengths of tubing and casing to be removed at one time by melting or consuming the steel with an exothermic reaction and allowing the movable base to move, open, melt, or be consumed. This will allow the reactants from the exothermic chemical tubing and casing removal step to flow down the well bore, leaving the section milled area free for the "rock to rock" plug to be placed.

[0019] The movable base is a temporary plugging device to place the exothermic chemical reaction material at the target location, hold it in place during part of the chemical reaction phase, open or move allowing the reactants to flow down the well, thus creating a large, open area in the well. These new optimized tools and processes make chemical section milling efficient, cost effective, and much faster than mechanical section milling.

[0020] Preferably the anchoring means may comprise a quantity of low melting alloy, which has a melting point of less than 300°C, that can be melted downhole to anchor the tool against a surrounding well tubing or casing within the downhole target region; wherein preferably the low melting alloy is a bismuth based alloy.

[0021] By using an alloy with a low melting point it is possible to pre-configure the anchoring means to fail, whereby the tool would become dislodged from the target region and fall down the well bore along with the slag produced by the chemical milling of the well tubing and casing.

[0022] Alternatively, the anchoring means may comprise a mechanical packer, slips or a modified bridge plug. It is envisaged that further preferably the mechanical anchoring means may be configured to fail under pre-determined loads so that the entire tool becomes dislodged and falls down the well bore. In this way, once the accumulated slag created during the chemical milling of the well tubing and casing reaches a certain weight, the anchoring means fail and the tool and the slag fall down hole. Preferably the plate is formed from a structurally strong metal that has a melting point of at least 500°C and preferably at least 1000°C. Rendering the plate resistant to increased temperatures and pressure allows another component of the tool to act as the pre-configure point of failure.

[0023] In one preferred embodiment the plate may be secured to the tubular main body by a retaining means configured to fail when the temperature and / or pressure within the target region exceeds predetermined limits such that the plate is released from the tubular main body. This allows the plate to be disconnected from the rest of the tool thereby allowing the passage of material (e.g., well fluids and slag) through the main tubular body and down the well bore.

[0024] In a further preferred embodiment the retaining means may comprise a cap portion, of which the plate forms an integral part, that is releasably secured on the leading end of the tubular main body.

[0025] Preferably the retaining means may comprise a low melting alloy or metal that has a melting point of less than 300°C. In this way the retaining means can be configured to fail in the increased temperatures generated during the chemical milling of the well tubing and casing.

[0026] Further preferably, in embodiments where both the anchoring means and the retaining means comprise a low melting alloy, the anchoring means may comprise an alloy with a higher melting point that the alloy or metal used to form the retaining means such that the retaining means fail before the anchoring means.

[0027] Additionally or alternatively, the anchoring means comprise a greater quantity of alloy than the retaining means. In this way there is less alloy securing the plate to the tool that there is alloy securing the tool in the well tubing, which ensures that the retaining means fail first.

[0028] Preferably, when the plate is formed from a structurally strong heat resistant material (e.g., steel), the plate may comprise at least one through port, arranged parallel to a central axis of the plate, that is plugged with a low melting alloy that has a melting point of less than 300°C. This arrangement facilitates the partial failure of the plate, which allows for the escape of the slag formed by the chemical milling of the well tubing and casing to pass through the plate and fall down the well bore. Alternatively the plate may be formed from a material that is configured to fail at a predetermined temperature, said material being selected from a group consisting of: thin metal; foil; foil on top of a carboard substrate; a substrate made of plastic, metal or an elastomer, such as rubber; a low melting alloy that melts at less than 300°C; a combination of metal and plastic; a plastic; and combinations thereof. In this way the entire plate can be configured to fail leaving the slag formed by the chemical milling of the well tubing and casing free to fall down the well bore.

[0029] Preferably the interior of the tubular main body may be provided with a seat upon which the plate sits. Further preferably the plate may be hingeably mounted to the seat such that the plate can pivot in an up-hole direction and open a pathway through the inner diameter of the tubular main body. The provision of the hinged plate helps to reduce the resistance encountered by the tool when it is deployed downhole through the well fluids by permitting the passage of fluid.

[0030] Preferably the down-hole end of the tool may further comprise a mule shoe. The mule shoe makes it easier to run the tool down the well tubing to the target region.

[0031] The present invention also provides a method of clearing well tubing and / or casing from a downhole target region of a well bore using a chemical reaction heat source in accordance with claim 15.

[0032] It is envisaged that, although not essential, it is preferable that the well tubing in the target region has perforations. In the event that the well tubing is unperforated, a pre-perforation step may preferably be employed before the downhole platform tool is deployed into the target region.

[0033] By employing the above method it is possible, in the first instance, to provide a platform upon which an exothermic chemical reaction heat source can accumulate and then, in the second instance, clear both the well tubing / casing and the slag created by the chemical milling step as well as the platform. This leaves a clearance window within the target region into which a suitable rock to rock abandonment plug can be installed.

[0034] Preferably the method employs the downhole platform tool of the present invention. Preferably the exothermic chemical reaction heat source is thermite or a thermite based mixture. Further preferably the exothermic chemical reaction heat source is delivered down hole in the form of a liquid. It is envisaged that said liquid can be delivered down hole using work string or coiled tubing or even using a downhole tool with a dump bailer.

[0035] As noted above, preferably the method may further comprise the step of perforating the innermost well tubing or casing in the target region prior to anchoring the downhole platform tool within the target region.

[0036] In situations where the innermost well tubing comprises perforations and the anchoring means of the downhole platform tool comprises a low melting alloy that has a melting point of less than 300°C, it is considered preferable that the downhole platform tool is aligned with said perforations so that the alloy of the anchoring means can flow therethrough. In this way the alloy anchoring means can fulfil the dual purpose of securing the tool in place within the well tubing and forming an annular alloy seal in the annulus between the well tubing and the casing.

[0037] The present invention also provides a method of abandoning a well bore in accordance with claim 21. The abandonment method utilizes the well tubing / casing clearance method of the present invention to create a clearance window within a downhole target region before deploying an abandonment plug in the window.

[0038] Although it is envisaged that the plug may be in the form of cement, preferably the abandonment plug is formed from a bismuth based alloy, which expands upon cooling to form a gas tight seal that extends across the entire cross-section of the well bore.

[0039] Brief Description of the Drawings

[0040] The present invention will now be described with reference to the preferred embodiments shown in the drawings, wherein:

[0041] Figure 1 A shows a downhole target region with a perforated well tubing before the deployment of a downhole platform tool; Figure 1 B shows the downhole target region of Figure 1A following the installation of a downhole platform tool to form a moveable base adjacent to perforations in the well tubing;

[0042] Figure 1 C shows the downhole target region of Figure 1 B following the delivery of exothermic material onto the moveable base;

[0043] Figure 1 D shows the downhole target region of Figure 1 C once the well tubing and casing in the target region have been melted by the exothermic material and the moveable base has moved downward;

[0044] Figure 2 shows a preferred embodiment of a downhole platform tool according to the present invention;

[0045] Figure 3 shows the downhole platform tool of Figure 2 deployed below the perforations in a well tubing;

[0046] Figure 3A shows the downhole platform tool of Figure 2 deployed adjacent the perforations in a well tubing;

[0047] Figure 4 shows an alternative preferred embodiment of the downhole platform tool according to the present invention deployed within a downhole target region;

[0048] Figure 4A shows the downhole platform tool of Figure 4 after the occluding plate has been removed;

[0049] Figure 5 shows a further alternative embodiment of the downhole platform tool in a closed state and in an open state; and

[0050] Figure 6 shows a downhole platform tool of the present invention with a mechanical anchoring means.

[0051] Detailed Description of the Preferred Embodiments

[0052] The apparatus and methods of the present invention will be described with reference to various examples of downhole platform tools and their use to provide moveable bases in downhole regions of wellbores that are to be subject to exothermic chemical removal of well tubing and / or casing. The inventors foresee that the tools and methods of the present invention are particularly suitable for oil / gas wellbores. However, it is envisaged that the present invention may also be applied in the removal of tubing from other forms of boreholes.

[0053] The preferred embodiments will be described as being used in combination with exothermic chemical reaction heat sources, such as thermite and thermite blends, in order to melt well tubing and casing within a downhole target region. As noted above, the use of exothermic chemical reaction heat sources to clear well tubing and casing is described in WO 2015150828 A2.

[0054] WO 2015150828 A2 also describes the use of chemicals that consume, rather than melt, the well tubing / casing to clear a downhole target region. It is envisaged that the tools of the present invention might also be used to provide a moveable base that supports such chemicals. As such, the present invention also contemplates that the various methods and downhole platform tools described herein might also employed using chemicals that consume the well tubing / casing in place of the exothermic chemical reaction heat sources referred to in the preferred embodiments.

[0055] WO 2015150828 A2 also describes that it is beneficial to perforate the well tubing in the downhole target region in order to enhance the effectiveness of the exothermic chemical reaction heat sources and the consuming chemicals. In view of this, the preferred embodiments are shown as being deployed within perforated well tubing 5. However, whilst not as preferable, it is envisaged that the various aspects of the present invention could also be practically applied in unperforated well tubing.

[0056] Turning now to Figures 1A to 1 D, the general process of chemical section milling in accordance with the present invention will now be described as having the following steps: a) Perforate the tubing string. (There is no need to remove the tubing string). b) Place the movable base in or below the perforations depending on the type. c) Run work string or coiled tubing the target depth at or just above the movable base. d) Pump the exothermic material into the well. e) Remove the work string or coiled tubing from the well. f) Run the starter into the well, locating it in the volume of exothermic material. g) Start the exothermic chemical reaction. h) Melt or consume the tubing and casing. i) Move, open, melt, or consume the movable base. j) The reactants will flow down the well, where they will cool and solidify. k) The area of the well is now free of tubing and casing. l) Clean the well bore and place the "rock to rock" plug. m) Abandon the well.

[0057] Figures 1 A to 1 D provide a graphical representation of some the above steps. Figure 1A represents step a), in which a well tubing 5 is located within a well casing 1 that in turn is located within a well bore 27. The well tubing 5 has been perforated using known techniques (e.g., perforating gun, laser cutting).

[0058] If there is enough room, the downhole platform tool and the perforating guns might be run on one trip into the well. This would make the process faster and less expensive. In such embodiments of the method of the present invention, the perforating guns would be run to the target depth, fire, perforate, then move down placing the downhole platform tool at the lower section of the perforated tubing.

[0059] Figure 1 B shows step b), wherein a downhole platform tool has been deployed within the perforated well tubing 5 at a location adjacent the perforations to form a moveable base 19.

[0060] It is envisaged that the downhole platform tool could alternatively be deployed downhole of the perforations (using either alloy anchoring means or mechanical anchoring means, such as a packer). However, the benefit of deploying the downhole platform tool adjacent to the perforations is that, if alloy anchoring means are used, the alloy can flow into the annulus between the well tubing 5 and the casing 1 and form an annular alloy seal at the same time as securing the moveable base 19 in position.

[0061] Figure 1 C shows step e), wherein the exothermic chemical reaction heat source 21 has been delivered on top of the moveable base 19. The perforations in the well tubing 5 allow the exothermic chemical reaction heat source, which is preferably in the form of a liquid or is fragmented so that it can flow in a manner similar to a liquid, to pass into the annulus between the well tubing 5 and the surrounding casing 1.

[0062] If the exothermic material is being pumped in the well, the coiled tubing or tubing end can be located above the moveable base formed by the downhole platform tool. This will ensure that the exothermic material is placed exactly on target and not scattered up and down the well prior to starting the reaction.

[0063] Figure 1 D shows step k), wherein the slag 25 formed of reactants of the exothermic chemical reaction heat source and melted well tubing / casing has fallen down hole from the target region along with the moveable base 19 to leave a clearance window 23 within the target region.

[0064] Since the volume of the reactants and melted steel, can move down with the movable base, the volume of the well that is opened is maximized when compared to the same operation with a fixed base, such as that described in US 9,494,011. The minimized amount of exothermic chemicals is utilized making the method of the present invention cost effective and efficient. The movable base is an important part of the system as the reactants and the melted steel may move down the well hundreds of feet.

[0065] Although not shown, it will be appreciated that steps I) and m) can then take place to locate a plug within the cleared space that extends from one side of the well bore to the other side in a ‘rock to rock’ arrangement. The plug would preferably, although not essentially, be formed from a bismuth based alloy due to the alloy’s ability to expand when it cools.

[0066] Figure 2 shows a preferred embodiment of a downhole platform tool 19a of the present invention. The tool 19a consists of a tubular main body 31 with metal sealing alloy 11 cast on the outside thereof at an up-hole location and a plate 9 in a fixed location near the bottom of the tubular main body 31 at a down-hole location. It will be appreciated that terms ‘up-hole’ and ‘down-hole’ are intended to differentiate between the end of the tool that is closed to the surface of the well bore (i.e. , the up-hole portion) and the end of the tool that is at the leading end of the tool (i.e., the down-hole portion).

[0067] Although not shown, it is envisaged that the downhole platform tool shown in Figure 2 can be run in the well with a heater, which can then be operated to melt the sealing metal 11 . When the alloy 11 cools and solidifies it acts as anchoring means and holds the tool 19a in position within the well tubing in a downhole target region. In preferred operations the tool is positioned in the lower most perforated area of a well tubing so that the perforations are clear to allow the passage of the exothermic chemical reaction heat source into the annulus.

[0068] By locating the anchoring means of alloy 11 on the tubular main body 31 at the up-hole end of the tool 19a and the plate 9 within the tubular main body 31 at the down-hole end of the tool 19a a clearance is provided within the tubular main body 31 . This clearance defines a sump volume 39.

[0069] It is envisaged that the length of the sump volume 39 might be very short (say less than 1 inch) or it may be very long (in the order of hundreds of feet). However, the sump volume must be long enough to accommodate the heater, starter, and running tool components. In situations where a large sump volume is not needed, it might be just long enough to keep the heater away from the plate 9 to avoid damage during installation into the well.

[0070] The length of the tubular main body 31 can be extended to increase the size of the sump volume in order to accommodate sufficient volumes of exothermic chemical reaction heat source to melt larger tubing and casing volumes.

[0071] The tubular main body 31 of the downhole platform tool 31 is preferably made from steel so that it maintains its structural integrity within the downhole environment even after the exothermic chemical reaction heat source has been activated.

[0072] There is a mule shoe 41 included at the leading (i.e., down-hole) end of the tool 19a to make it easier to run the tool into the well tubing 5, through the perforated section of tubing and to the target depth. The plate 9 can be formed from a similar material to the tubular main body 31 (e.g., steel). In such arrangements, the plate 9 itself does not form the point of failure of the downhole platform tool. Instead the point of failure can be provided by the retaining means (not shown) employed to secure the plate 9 to the tubular main body 31.

[0073] Alternatively, it is envisioned that the point of failure can be provided by the anchoring means used to secure the tool 19a in position within the well tubing 5. In embodiments where the anchoring means take the form of an alloy seal (e.g., Figures 2, 3 and 3A), it is envisaged that the combination of the heat generated by the exothermic chemical reaction heat source and the weight of the slag produced during the clearance of the well tubing / casing by the exothermic chemical reaction heat source can dislodge the tool 19a so that it can move down hole.

[0074] As noted above, it is envisaged that the alloy based anchoring means 11 of the downhole platform tool 19a allows it to be secured both below the perforations in a well tubing 5 (as shown in Figure 3) and in line with the perforations in a well tubing 5 (as shown in Figure 3A).

[0075] With regard to Figure 3A it will be appreciated that in operations where the tool is positioned in line with the perforations the alloy of the anchoring means achieves a dual purpose of both securing the tool 19a in position and also creating annular alloy seal 11 a.

[0076] Figure 4 shows three key states of an alternative preferred embodiment of the downhole platform tool 19b, which differs from the tool 19a shown in Figures 2, 3 and 3A by virtue of the fact that the occluding plate takes the form of a flapper plate 7 supported by an annular seat 33 that is secured to inside of the tubular main body 31 of the tool 19b.

[0077] Although not essential, it is envisaged that the flapper plate 7 is preferable hingeably mounted to the seat 33 such that the flapper plate can move to permit the passage of fluids through the main tubular body via orifice 13. This is considered beneficial as it will reduce the fluid resistance from downhole fluids when the downhole platform tool 19b is delivered down the well bore to the target region. The first state of the downhole platform tool 19b is shown in the first stage of Figure 4, wherein the flapper plate 7 is not covering the central orifice 13 of the seat 33 and well fluids are able to pass therethrough.

[0078] The flapper can be propped and held open with the running, starting tool (not show) and then unpropped and allowed to close when the heater is pulled from the well.

[0079] Once the tool 19b has been secured in position with its anchoring means (as with tool 19a alloy is used to secure the tool in place within the well tubing 5), the flapper plate 7 can rest fully on the seat 33 and prevent the passage of fluids in a down hole direction. Thus the flapper plate 7 provides a base for the exothermic chemical reaction heat source to be delivered onto.

[0080] It is envisaged that the flapper plate could once again be formed from a heat resistance material, such as steel, to ensure that it does not represent the point of failure for the tool. However, in the tool 19b shown in Figure 4 the flapper plate is preferably formed from a material that will fail under the conditions (e.g., increased heat and pressure) created by the activation of the exothermic chemical reaction heat source in the target region.

[0081] In order to render the flapper plate consumable it is envisaged that is could be made of one or more of these materials: thin metal; foil; foil on top of a cardboard substrate; or a substrate made of plastic, metal, rubber (an elastomer), or an engineering; plastic, a high strength composite; low melt temperature (e.g., less than 300°C), metal sealing alloy, such as a bismuth based alloy; a combination of metal and plastic; a plastic that is consumed; certain non-metallic compounds can increase the energy output of an exothermic reaction like thermite.

[0082] The flapper plate 7, and possibly also the seat 33, could also be constructed from a thin metal can containing any or many of the following: Low melt temperature (e.g., less than 300°C), metal sealing alloy, such as a bismuth based alloy beads; Plastic beads; Plastic flakes; Plastic strands; Cement; Ceramic; Resin impregnated cloth; Fiberglass; Aluminium; Plastic sheet.

[0083] It will be appreciated that the above materials could also be employed to render any plate included in the downhole platform tool of the present invention and not just the flapper plate 7. However in cases where alloy based anchoring means are employed in combination with an alloy based plate / flapper plate, it is envisaged that the melting point of the anchoring alloy should be higher than that of the plate to ensure that it is the plate, and not the anchoring means, that provide the point of failure for the tool.

[0084] If the plate is made of more than one material, parts of the plate may be melted or consumed, or it constructed from a high strength, high temperature resistant material it may be partially melted, opened, or consumed.

[0085] Turning now to the final stage show in Figure 4, wherein the flapper plate has been consumed and the slag formed of reactants of the exothermic chemical reaction heat source and melted well tubing / casing has fallen down hole from the target region to leave a clearance window within the target region. It will be appreciated that the seat 33 forms an orifice 13, regulating the flow of the heated reactant products following the exothermic chemical tubing and casing removal step.

[0086] Figure 5 show two key states of a further embodiment of a downhole platform tool 19c of the present invention. In the first stage shown in Figure 5, the two-part construction of the tool 19c can be appreciated. The anchoring means 11 , which are once again alloy based, are provided on the up-hole end of the tubular main body 31 of the tool 19c. This represents the first part of the tool.

[0087] The plate 9 is integral with a second tubular body 12 in the form of a cap which is secured over the leading end of the tubular main body by alloy-based retaining means 14. It is essential that the alloy used to form the retaining means fails before the anchoring means. It is appreciated that this can be achieved by either employing a smaller quantity of alloy in the retaining means, employing an alloy with a lower melting point in the retaining means or a combination of both.

[0088] In a further alternative arrangement of the plate, which could be incorporated into any one of the downhole platform tools described so far without requiring significant re-engineering, the plate may be formed from a main body of heat resistant material (e.g., steel) that comprises one or more ports that pass through the main body from its up-hole facing surface to its down-hole facing surface. Each port is plugged with a material that has a much lower melting point that the main body of the plug such that, under the increased temperatures created by the activation of the exothermic chemical reaction heat source, the plugs melt to open up the ports in the plate. The ports then allow the slag formed of reactants of the exothermic chemical reaction heat source and melted well tubing / casing to pass through the plate and fall down the well bore.

[0089] Although alloy retaining means are employed in the embodiment shown in Figure 5, it is envisaged that alternative mechanical retaining means, which can be configured to fail under pre-determined loads (e.g., shear pins, bolts and rings) may also be employed to ensure that the retaining means act as the point of failure for the tool.

[0090] Turning now to the second stage shown in Figure 5, the downhole platform tool 19c is shown after the alloy retaining means have melted and the cap, which comprises the occluding plate 9, have fallen away with the slag formed of reactants of the exothermic chemical reaction heat source and melted well tubing / casing.

[0091] In contrast to the embodiments shown in the majority of the figures, Figure 6 shows a preferred embodiment of a downhole platform tool 19d of the present invention which employs mechanical anchoring means rather than an alloy based approach. The mechanical anchoring means could take the form of a permanent packer, an anchor with slips, a modified bridge plug or a downhole tool could be used to anchor the tool within the well tubing to provide a movable base near the lowest perforations in the tubing.

[0092] As with the alloy based anchoring means, the mechanical anchoring means 17a are positioned on the outside of the main tubular body 31 at the up-hole end of the tool 19d. A flapper plate 7 is provided within the main tubular body at the downhole end of the tool. Although the seat 33 has been omitted from the figure, it is envisaged that it would also be present.

[0093] In order to provide the tool 19d with a point of failure, the flapper plate is preferably made from one or more of the suitable consumable materials listed above. With that said, it is envisaged that if the flapper tool could still be formed from a heat resistant material, such as steel, provided the point of failure is achieved in another way.

[0094] For example, retaining means that are configured to fail under the conditions created by the activation of the exothermic chemical reaction heat source (e.g., shear pins or meltable alloy) could be used to temporarily secure the flapper plate to the seat.

[0095] Alternatively, the mechanical anchoring means 17a could be configured to fail under a pre-determined load, such that the weight of the slag formed during the clearance of the well tubing / casing by the exothermic chemical reaction heat source can dislodge the tool 19d and free it to fall down the well bore.

[0096] Although it is envisaged that the increased temperature generated by the exothermic chemical reaction heat source should be sufficient to melt the alloy used by the anchoring means and the plate retaining means of the downhole platform tool, in some embodiments it may be considered beneficial for the tool to comprise a second exothermic reaction source, such as thermite or modified thermite, which is activated by the exothermic chemical tubing and casing removal reaction carried out by the main delivery of exothermic chemical reaction heat source.

[0097] Reference Table Clauses

[0098] The present invention will now be described in general terms with reference to the following clauses, wherein:

[0099] 1 . A movable base for an exothermic chemical tubing and casing removal that is moved, opened, melted or consumed with the heat and or pressure generated from the exothermic chemical reaction.

[0100] 2. One or more components of the movable base are moved, opened, melted or consumed.

[0101] 3. A movable base for an exothermic chemical tubing and casing removal that is moved or opened at or near the end of the exothermic chemical reaction which removed the tubing and casing from a section of the well bore.

[0102] 4. A movable base for an exothermic chemical tubing and casing removal that can be moved or opened utilizing an exothermic chemical reaction.

[0103] 5. The method of using the movable base with a chemical reaction.

Claims

Claims1 . A downhole platform tool for deployment in a downhole target region of a well bore that comprises a well tubing and / or casing, said tool comprising: a tubular main body with an inner diameter and anchoring means provided on the outside thereof adjacent to an up-hole end of the tool, wherein, in use, the anchoring means secure the tool in place within said well tubing and / or casing in the downhole target region; a plate arranged adjacent to a down-hole end of the tool to occlude the inner diameter of the tubular main body and thereby restrict the movement of fluid through the target region in at least a direction of flow that moves from up-hole to down-hole; and wherein the anchoring means and / or the plate are configured to fail when the temperature and / or pressure within the target region exceeds predetermined limits, and thereby open a pathway within the well bore that permits the movement of fluid through the target region.

2. The tool of claim 1 , wherein the anchoring means comprises a quantity of low melting alloy, which has a melting point of less than 300°C, that can be melted downhole to anchor the tool against a surrounding well tubing or casing within the downhole target region; wherein preferably the low melting alloy is a bismuth based alloy.

3. The tool of claim 1 , wherein the anchoring means comprises a mechanical packer, slips or a modified bridge plug.

4. The tool of claim 1 , 2 or 3, wherein the plate is formed from a structurally strong metal that has a melting point of at least 500°C and preferably at least 1000°C.

5. The tool of claim 4, wherein the plate is secured to the tubular main body by a retaining means configured to fail when the temperature and / or pressure within the target region exceeds predetermined limits such that the plate is released from the tubular main body.

6. The tool of claim 5, wherein the retaining means comprises a cap portion, of which the plate forms an integral part, that is releasably secured on the leading end of the tubular main body.

7. The tool of claim 5 or 6, wherein the retaining means comprise a low melting alloy or metal that has a melting point of less than 300°C.

8. The tool of claim 7, wherein the anchoring means comprise an alloy with a higher melting point that the alloy or metal used to form the retaining means such that the retaining means fail before the anchoring means.

9. The tool of claim 7 or 8, wherein the anchoring means comprise a greater quantity of alloy than the retaining means.

10. The tool of claim 4, wherein the plate comprises at least one through port, arranged parallel to a central axis of the plate, that is plugged with a low melting alloy that has a melting point of less than 300°C.11 . The tool of claim 4, wherein the plate is formed from a material that is configured to fail at a predetermined temperature, said material being selected from a group consisting of: thin metal; foil; foil on top of a carboard substrate; a substrate made of plastic, metal or an elastomer, such as rubber; a low melting alloy that melts at less than 300°C; a combination of metal and plastic; a plastic; and combinations thereof.

12. The tool of any one of the preceding claims, wherein the interior of the tubular main body is provided with a seat upon which the plate sits.

13. The tool of claim 12, wherein the plate is hingeably mounted to the seat such that the plate can pivot in an up-hole direction and open a pathway through the inner diameter of the tubular main body.

14. The tool of any one of the preceding claims, wherein the down-hole end of the tool further comprises a mule shoe.

15. A method of clearing well tubing and / or casing from a downhole target region of a well bore using a chemical reaction heat source, said method comprising:providing a downhole platform tool down that is configured to fail at a predetermined temperature or pressure, said tool having a main tubular body with externally mounted anchoring means and an internally mounted occluding plate; deploying the downhole platform tool down the well bore via the innermost well tubing or casing and securing the tool in place within said innermost well tubing or casing using the anchoring means in order to create a platform in the target region; delivering the chemical reaction heat source into the target region so that it can accumulate on top of the platform; starting the exothermic chemical reaction of the chemical reaction heat source and allowing the temperature within the target region to increase, whereby the well tubing and / or casing within the target region are melted to form a molten mixture with the chemical reaction heat source; and continuing the heating of the target region until the anchoring means or the plate of the downhole platform fail under the increased temperature and / or pressure generated by the exothermic chemical reaction of the chemical reaction heat source and allowing the molten mixture to fall down hole away from the target region.

16. The method of claim 15, wherein the downhole platform tool used is in accordance with any one of claims 1 to 14.

17. The method of claim 15 or 16, wherein the exothermic chemical reaction heat source is thermite or a thermite based mixture.

18. The method of claim 16 or 17, wherein the exothermic chemical reaction heat source is delivered down hole in the form of a liquid.

19. The method of any one of claims 15 to 18, further comprising the step of perforating the innermost well tubing or casing in the target region prior to anchoring the downhole platform tool within the target region.

20. The method of any one of claims 15 to 19 when the innermost well tubing comprises perforations and the anchoring means of the downhole platform tool comprises a low melting alloy that has a melting point of less than 300°C, whereinthe downhole platform tool is aligned with said perforations so that the alloy of the anchoring means can flow therethrough.21 . A method of abandoning a well bore comprising: using the method of any one of claims 15 to 20 to clear a plug window within a downhole target region that extends across the entire cross-section of the well bore; and deploying a plug that extends across the entire cross-section of the well bore in the plug window cleared by the clearance method.

22. The method of claim 21 , wherein a bismuth based alloy is used to form the plug.

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