CHEMICAL HEAT SOURCES FOR USE IN DOWN-HOLE OPERATIONS

Abstract

A chemical reaction heat source for use in heaters for downhole applications is provided. The heat source has a solid fuel composition that comprises thermite and a binding agent. The binding agent serves to maintain the solid form of the solid fuel composition during burning and ensure a predetermined uniform heating pattern can be provided for longer. The solid fuel composition can be provided in the form of blocks. The solid fuel composition can also be provided in the form of a plurality of fragments that, during burning, behave more like powdered thermite and can flow.

Claims

1. A down-hole chemical heater comprising a chemical reaction heat source, said heat source having a solid fuel composition; and wherein the fuel composition comprises thermite and one or more binding agents that maintain the solid form of the solid fuel composition during burning.

2. The chemical heater of claim 1, wherein said one or more binding agents are selected from sodium silicate and magnesite.

3. The chemical heater of claim 1 or 2, wherein the solid fuel composition is provided in one or more solid blocks.

4. The chemical heater of claim 3, wherein at least one of the solid blocks further comprises a damping agent.

5. The chemical heater of claim 4, wherein the proportion of damping agent to thermite varies from block to block.

6. The chemical heater of claim 3 wherein at least one of said solid blocks comprises a conduit running there through.

7. The chemical heater of claim 6, wherein each conduit receives a wicking fuel composition that burns quicker and/or hotter than the solid fuel composition.

8. The chemical heater of any one of claims 4 to 7, wherein said solid blocks are configured to be stacked one on top of another.

9. The chemical heater of claim 8, wherein said binding agents make up between about 5-35% by weight of the fuel composition.

10. The chemical reaction heat source of claim 1, further comprising an outer layer of a wicking fuel composition that burns quicker and/or hotter than the solid fuel composition.

11. The chemical heater of claim 1, further comprising an outer layer of an oxidizing agent.

12. A method of manufacturing a down-hole chemical heater, said method comprising: preparing a fuel composition comprising a mixture of thermite and one or more binding agents that maintain the solid form of the fuel composition during burning; forming the fuel composition in to one or more blocks; and inserting the blocks in a heater body.

13. The method of claim 12, wherein said one or more binding agents are selected from sodium silicate and magnesite.

14. The method of claim 12 or 13, wherein the step of forming the fuel composition in to one or more blocks comprises putting the mixture into one or more moulds.

15. The method of claim 14, wherein the step of forming the fuel composition in to one or more blocks comprises: freezing said moulded blocks; removing the blocks from said moulds; and heating said blocks.

16. The method of claim 14, wherein the step of forming the fuel composition in to one or more blocks comprises heating the blocks within said moulds.

17. The method of claims 12, wherein the fuel composition further comprises a damping agent.

18. The method of claim 17, wherein the fuel composition is compressed to form said one or more blocks.

19. The method of claim 18, wherein the fuel composition blocks are cylindrical in shape and have a predefined diameter.

20. The method of claim 19, wherein the ratio of binding agent and/or damping agent to thermite is increased in line with an increase in the predefined diameter of the blocks.

21. The method of claim 20, wherein the density of the fuel composition blocks is increased to reduce the burn rate provided by the heater.

22. The method of claim 20, wherein the density of the fuel composition blocks is decreased to increase the burn rate provided by the heater.

23. The method of claim 21, wherein the density is increased by reducing the grain size of the thermite used in the fuel composition.

24. The method of claim 22, wherein the density is decreased by increasing the grain size of the thermite.

25. The method of claims 21, wherein the density of the fuel composition blocks is controlled by the extent to which the fuel composition is compressed during the formation of the blocks.

26. The method of claim 12, further comprising providing the blocks with a wicking fuel composition that burns quicker and/or hotter than the fuel composition, wherein the wicking fuel composition is provided in at least one conduit running through the blocks and/or as an outer layer of the blocks.

27. The method of claim 12, further comprising providing the blocks with an outer layer of an oxidizing agent.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0066] The present invention will now be described with reference to the drawings, wherein:

[0067] FIG. 1 shows a preferred embodiment of a chemical reaction heat source of the present invention;

[0068] FIG. 2 shows a plan view of an alternative preferred embodiment of the present invention; and

[0069] FIG. 3 shows a flow diagram of the steps involved in a preferred embodiment of the method of manufacturing the fuel composition crumble of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0070] Although the present invention is considered particularly appropriate for use in plugging both vertical and non-vertical wells (with or without well casings) it is appreciated that the heaters of the present invention have characteristics which make them suitable for a range of other down-hole applications too.

[0071] For example the described aspects of the present invention can be used together with the methods and apparatus described in WO2011/151271 to facilitate the squeezing off and repairing of wells.

[0072] Further, whilst the chemical heat source of the present invention is described herein primarily in relation to its use in the plugging of oil and gas wells, it is envisaged that chemical heat source of the present invention would provide benefits when plugging other forms of underground conduits, such as water pipes for example.

[0073] In a preferred embodiment of the chemical reaction heat source 1 of the present invention the solid fuel composition is provided in the form of a stacked arrangement of blocks 2, 3 and 4 that, in use, are housed within a heater body.

[0074] In order to maintain the solidity of the blocks during burning, the fuel composition used to form each block comprises one or more binding agents as well as thermite. The role of the binding agent, preferable examples of which include sodium silicate and magnesite, is to maintain its structure, and thus a solid shape, at high temperatures so as to prevent the thermite from becoming molten and flowing like a liquid.

[0075] By maintaining the original solid shape of the fuel composition block it is possible to achieve a fixed, consistent heat distribution pattern for a longer period of time, thus achieving a more uniform heating of the eutectic alloy (e.g., Bismuth-based alloy) being used in, for example: a well plug, annulus packer or a squeezing off operation.

[0076] The provision of a consistent heat distribution pattern is considered particularly advantageous in down-hole operations within substantially horizontal wells because unbound burning thermite can flow under the force of gravity and settle on the lower regions of a heater. This reduces the heat applied to any alloy in the upper regions, which can impair the plug formation process.

[0077] Preferably the binding agent/binder constitutes up to 35% by weight of the fuel composition, although amounts of binding agent can be as low as 5% in many applications.

[0078] Whilst it is envisioned that the binder may provide a damping effect to the fuel composition, in preferred embodiments of the present invention a separate damper agent (e.g., sand or magnesite) may also be added to the fuel composition.

[0079] In a preferred example, the fuel composition of the present invention comprises between 5-15% by weight sodium silicate and between 10-35% by weight of magnesite. In this composition the magnesite has a dual role as both a binding agent and a damping agent.

[0080] It is envisaged that each of the solid fuel composition blocks 2, 3, 4 in the heat source 1 shown in FIG. 1 is capable of generating a certain level of heat, the level of which is predetermined by the ratio of thermite to damping agent (e.g., sand) in the composition mix of that particular block.

[0081] It will be appreciated that a range of predetermined mixes, which are capable of generating a range of predetermined temperatures, can be produced by varying the levels of thermite from 99% to 1% by mixing the thermite with a damping agent. The damping agents (or combustion suppressing agents as they may also be referred to herein) preferably take the form of silica or sand. However, it is envisaged that alternative forms of damping agent may also be adopted without departing from the general inventive concept of the present invention.

[0082] It is appreciated that by arranging blocks with differing heating abilities in specific stacking orders it is possible to create a chemical reaction heat source that generates a heat distribution pattern appropriate to the type of heater it is being used in.

[0083] FIG. 1 shows an example of a chemical reaction heat source 1 with a block stacking arrangement that creates a distinct heating pattern.

[0084] It is appreciated that, due to the variations in damping provided from block to block, the passage of the chemical reaction (and the associated heat generation) through the heat source 1 can also be variable.

[0085] On some occasions this may be desirable, however it is envisaged that there are many occasions where a more uniform heat distribution pattern is required across the entire heat source 1. One example of which might be when dealing with a heat source of an increased length, for instance a heater that is 10-20 ft or about 3-6 meters long.

[0086] In situations where a more uniform heat distribution pattern is required it is envisaged that it is advantageous to utilize a wicking fuel composition, either on the surface of the solid fuel blocks or housed within the blocks.

[0087] Essentially the wicking fuel composition provides a quicker route for the chemical reaction/burning to spread through the blocks of a chemical reaction heat source. To this end, the wicking fuel composition necessarily burns quicker and/or hotter than the fuel composition used to form the blocks. This may mean that the wicking fuel composition is pure thermite, although it does not necessarily preclude the presence of a damping agent at a lower proportion to that used in the associated blocks.

[0088] In the preferred embodiment shown in FIG. 1 the wicking fuel composition 5 is received within a conduit that runs through the center of the heat source 1 that is formed by the stacking of blocks 2, 3 and 4. In order to achieve a single conduit extending through the entire heat source 1 each block must be provided with a separate conduit that is in alignment with its neighbors.

[0089] It is envisaged that, although FIG. 1 only shows a single conduit running through the entire length of the stack, it may be advantageous to provide more than one conduit per block.

[0090] FIG. 2 shows a plan view of a heat source 1a with an alternative arrangement of conduits containing a wicking composition 5a. It is envisaged that providing a plurality of conduits in a block might be particularly desirable when the block is subject to higher damping as it would enable chemical reactions to be triggered in several regions of the block at the same time (i.e., rather than from the center outwards). Such an arrangement may also be employed in blocks of a larger diameter, for example. Indeed, it is envisaged that this approach can be adopted in combination with any of the other aspects of the present invention.

[0091] Although FIG. 1 shows the conduit running through the entire length of the heat source 1 it is envisaged that a conduit may not be required in every block in a stack. An example where this might be the case is where the block itself is capable of transmitting the chemical reaction/heat quickly to the next block in a stack (i.e., the block is not a substantial obstruction). This may be the case when the block is small, or it is formed from a sufficiently fast/hot burning fuel composition.

[0092] Although not shown in the Figures it is also appreciated that pure thermite powder may be provided in and around the region where the igniter and the first fuel composition block come into contact. In this way the chemical reaction is given the best chance of being successfully initiated.

[0093] As mentioned above, in addition to the ingredients of the solid fuel composition block, other aspects of the block can be adjusted to alter the burn rate delivered by a given block.

[0094] For example, a cylindrical block with an outer diameter of about 5 cm (2 inches) that has 73% density would burn at approximately 2.4 seconds per cm (6 seconds per inch). However, if the same mixture is used to form a cylindrical block of the same density but with an outer diameter of about 10 cm (4 inches) the burn rate increases to approximately 0.4 seconds per cm (1 second per inch).

[0095] By way of further example, if the same fuel composition mixture was used to form a cylindrical block with an outer diameter of about 5 cm (2 inches) but with a density of 60% then the block would burn at a rate of 0.4 seconds per cm (1 second per inch). However, if a similar cylindrical block was made with its density increased to 80% then the burn rate decreases to approximately 12 seconds per cm (30 seconds per inch).

[0096] It is envisioned that these observations can be used to help produce fuel composition blocks to suit a range of needs. Whether that be retaining a consistent burn rate across a range of different sized heaters or achieving a range of different burn rates within a single heater.

[0097] It is appreciated that various methods can be employed during the manufacturing process to ensure that the fuel composition blocks of the present invention are produced with a desired shaped block.

[0098] The mixture of the fuel composition that is formed from thermite, one or more binding agents and possibly, additional damping agents tends to have fluid consistency.

[0099] By way of an example the thermite, which is preferably provided in a granular form, can be mixed with a sodium silicate solution to form the fuel composition. The sodium silicate solution may preferably have water content in the region of 60-70%.

[0100] It is only once the mixture has been heated (or cooked) that the fuel composition takes on a more solid form; the heating preferably takes place in a suitable oven.

[0101] The process of making the fuel composition blocks employed in the present invention essentially involves the steps of: [0102] Mixing the various ingredients (i.e. thermite, binding agent, damping agent) to produce the fuel composition; [0103] Molding the fuel composition into the desired block shape(s); [0104] Heating the molded fuel composition to cook the blocks so that they become solid.

[0105] It is appreciated that one way of ensuring that the fuel composition remains in the desired block shape throughout the manufacture process is to keep the fuel composition in a mold throughout the cooking process. Once the blocks of fuel composition have been cooked, and have solidified, they can be removed from the molds.

[0106] However, for practical reasons it is considered preferable, wherever possible, to avoid the use of mold during the cooking step. To this end it is envisaged that the fuel composition mixture can be solidified prior to heating so that the blocks retain their shape without the need for a mold. This reduces the total number of molds required.

[0107] In cases where the fuel composition comprises sodium silicate, for example, one approach for solidifying the block shape prior to cooking is to evenly distribute CO.sub.2through the mixture before the cooking step. Subjecting the mixture to CO.sub.2 in this way makes the blocks solid enough to be handled so that they can be placed in an oven without the need for a mold.

[0108] However, this approach is not considered ideal for achieving a uniform burn rate throughout the block. This is because as the CO.sub.2 passes through the mixture it reacts with sodium silicate in the fuel composition and forms sodium dioxide, which acts as an accelerant, and sodium carbonate, which acts as a damping agent.

[0109] The essentially random nature with which the accelerant and damping agent are formed within the final fuel composition mixture prevents the production of blocks having a consistent and repeatable burn rate, which is undesirable.

[0110] It is also noted that if the fuel composition is exposed to too much CO.sub.2 the blocks formed can become too brittle and fragile, which is also undesirable.

[0111] In view of the practical difficulties of both the above-described approaches for retaining the shape of the fuel composition blocks prior to cooking, a further approach was required. To this end the present invention provides an alternative solution.

[0112] A preferable method of maintaining the molded shapes of the fuel composition blocks prior to cooking involves freezing the blocks. It has been discovered that subjecting the blocks to temperatures in the range of between ?20 to ?80? C. causes the water present in fuel composition, an example of which would be the water present in the sodium silicate solution, to freeze and thereby solidify the entire block.

[0113] It is noted that when using temperatures towards the lower end of the above range to freeze the blocks the freezing process is carried out for a shorter period of time. At higher temperatures within the stated range the process can continue for longer.

[0114] This allows the blocks to be handled, removed from their molds and placed into the oven.

[0115] Once in the oven, the blocks are heated at temperatures of about 250? C. for about 3 hours until the blocks are cooked solid. However, the skilled person will appreciate that the blocks can be cooked at different temperatures and for different lengths of time without departing from the general concept of the present invention.

[0116] It was surprisingly discovered that the frozen blocks do not melt during the heating process but rather the water in the fuel composition blocks changes directly from a solid form to a vapor without triggering any chemical changes at all.

[0117] As a result, this alternative approach facilitates the formation of fuel composition blocks with highly uniform burn rates (unlike CO.sub.2 formed blocks) without the need to keep the mixture in the mold until it has been cooked.

[0118] It will be appreciated from the above-described features that the present invention allows the heating characteristics of a given heater to be predefined to suit the particular needs of any given down-hole task by effectively adjusting the arrangement blocks to achieve the most appropriate heat distribution pattern and then maintaining their relative positions during the burning process.

[0119] The method of manufacturing the fuel composition crumble of the present invention will now be described with reference to FIG. 3, which shows a flow diagram of the key stages of the production process.

[0120] It will be appreciated that the initial steps of the crumble manufacture process are essentially the same as those employed to produce the solid fuel composition blocks of the present invention; with the additional fragmentation stage being the main distinction. In view of this it is appreciated that the above description of the manufacture process for the blocks is also applicable to the method of manufacturing the fuel composition crumble.

[0121] Referring now to FIG. 3, it can be seen that in the first stage of manufacture the various constituents of the fuel composition are mixed together in a mixing container 10. The constituents shown are thermite 11, a binding agent such as sodium silicate 12, and a damping agent such as sand or magnesite 13.

[0122] For the sake of clarity the thermite is represented by the symbol +, the binding agent is represented by the symbol ?, and the damping agent is represented by the symbol ? (i.e. a triangle).

[0123] During the mixing stage the various constituents are thoroughly blended to disperse them evenly throughout the mixture. It is appreciated that standard mixing equipment known in the art can be employed to achieve this.

[0124] Once the mixture has been suitably blended it is preferably placed in a mold 14 to shape the mixture. In the example shown in FIG. 3 the mold shapes the mixture into a sheet configuration, which is preferably between 2-40 mm thick. However, it is envisaged that the mold may alternatively shape the mixture into a block shape. This would be the case for the solid fuel composition blocks of the present invention.

[0125] The shaped mixture is then subjected to heating temperatures of about 250? C. for around 3 hours to cook the shaped mixture and form the solid shaped block or sheet (in the case of the crumble). Once again it is appreciated that the cooking temperature and cooking time can be adjusted to suit the size of the shaped block or sheet that is being cooked.

[0126] Again, as discussed above, it is contemplated that the shaped mixture can be cooked with or without the mold 14.

[0127] Once the solid fuel composition has been formed it can either be used directly as a chemical reaction heat source for a heater in its molded shape (i.e., block) or it can be subjected to further processing to produce the fragmented solid fuel composition or crumble of the present invention.

[0128] As represented diagrammatically in FIG. 3, the various constituents are evenly distributed throughout the molded sheet of fuel composition 15. This even distribution is represented by the combined symbol formed from the +, ?, ?. This even distribution would also be present in the fuel composition blocks formed by this process.

[0129] In order to produce the fuel composition crumble the next stage is to subject the molded sheet 15 to mechanical impacts to break the sheet up into smaller fragments 17, which preferably have a rough diameter in the range of 100 ?m to 10 mm and further preferably between 500 ?m to 6 mm.

[0130] It is appreciated that the size of the fragments will, to a certain extent, be dictated by how fine or coarse the thermite powder being used in the mixture is. In this regard it is noted that because every fragment needs to have each of the constituents, using a coarser thermite powder increases the size of the thermite constituent, which in turn increases the overall size of the fragments.

[0131] In FIG. 3 the mechanical impact is shown as being delivered by a hammer 16. However, it is envisaged that the fragmentation step can be carried out in a wide variety of ways provided they achieve a controlled and consistent fragmentation of the sheet 15.

[0132] Preferably the plurality of fragments 17 produced in a particular batch are roughly the same size so that their burn characteristics are consistent throughout the crumble 18.

[0133] In this regard, so that the burn characteristics of a particular batch are consistent the deviation of the fragment sizes within the batch is preferably limited to no more than about 20% either side of the mid-point. By way of an example, if the mid-point fragment size is 1 mm, the smallest fragments are 0.8 mm and the largest fragments are 1.2 mm.

[0134] In order to achieve this, the fragmented fuel composition is filtered/sieved to ensure all the fragments within a particular batch fall within a predetermined size range.

[0135] Although the preferred range of sizes of the fragments of the present invention is between 100 ?m to 10 mm, it is appreciated that the size range within a particular batch may be narrower to ensure consistent burn characteristics of the fragments within the batch. Again, this is achieved by filtering out larger fragments and smaller particles from the fragmented fuel composition.

[0136] It is appreciated that larger fragments, removed by the filtering step, may be subjected to further fragmentation before being reintroduced into the filtered mixture.

[0137] As will be appreciated from the diagrammatic representation shown in FIG. 3, the fragments 17 constitute reactive clusters because they comprise all three constituents 11, 12, 13 as represented by the combined symbol formed from the +, ?, ?.

[0138] As a result, even after the fragments 17 have disturbed (i.e., during transport), the fragments 17 burn with much more consistent burn characteristics that would be possible with a powdered fuel composition made from the similar constituents (e.g., thermite, damping agent).

[0139] In this way the fragments burn with greater consistency than powdered fuel compositions and greater flowability than fuel composition blocks.

[0140] As with the solid fuel composition blocks of the present invention, the fragments of the fuel composition crumble can be placed within a heater body (not shown) and used as the chemical reaction heat source for the heater.