Combined well plug/chemical heater assemblies for use in down-hole operations and associated heater cartridges

Abstract

The present invention provides a cartridge (1) for a chemical heater used in down-hole operations. The cartridge (1) comprises a quantity of a chemical reaction heat source (2) wrapped in a temporary coating (3) that is capable of maintaining the shape of the cartridge (1) prior to use but which is consumed during the burn of the heater. The present invention also provides a eutectic/bismuth based alloy well plugging/sealing tool (5). The tool (5) having a tubular heater body (6) with an internal cavity (8) capable of receiving a chemical heat source and a quantity of eutectic/bismuth based alloy (7) provided in thermal communication with the heater body (6) around an outer surface of the heater body (6). The tool has a sleeve (10) provided around an outer surface of the alloy (7), which insulates and/or mechanically protects the alloy (7) down-hole. In this way the sleeve (10) enables the diameter of tool (5) to be reduced whilst maintaining its functionality. In further aspect, the present invention also discloses the provision of a refractory lining (20) on the inner walls of the tubular heater body of chemical heaters, such as the heater (6) used in the eutectic/bismuth based alloy well plugging/sealing tool (5).

Claims

1. A cartridge for a chemical heater used in down-hole operations, the cartridge comprising a plurality of chemical reaction heat sources, wherein the plurality of chemical reaction heat sources are configured to define a shape of the cartridge, and wherein the plurality of chemical reaction heat sources are wrapped and completely surrounded in a temporary coating; whereby the temporary coating maintains the shape of the cartridge during insertion into a well, and whereby the temporary coating is consumed during the burn of the heater.

2. The cartridge of claim 1, wherein the heat source is wrapped in a plastic film.

3. The cartridge of claim 1 or 2, wherein the wrapped heat source is held within a flexible elongate surround member.

4. The cartridge of claim 1 or 2, comprising a flexible surround member, wherein the flexible surround is formed from one or more of the following: fibre glass, thin steel, carbon fibre, and synthetic fibre of a high tensile strength (e.g. Kevlar®).

5. The cartridge of claim 1 or 2, wherein the chemical reaction heat source is provided in the form of one or more blocks.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The various aspects of the present invention will now be described with reference to preferred embodiments shown in the drawings, wherein:

(2) FIG. 1 shows partially exposed view of a cartridge according to a first aspect of the present invention;

(3) FIG. 2 shows a cross-sectional view of a well plugging/sealing tool according to a second aspect of the present invention; and

(4) FIG. 3 shows a closer view of the well tool shown in FIG. 2.

DETAILED DESCRIPTION OF THE VARIOUS ASPECTS OF THE PRESENT INVENTION

(5) Although eutectic/bismuth based alloys are referred to throughout the present disclosure it is appreciated that low melt alloys' or low melting point alloys' may also be used interchangeably with the eutectic/bismuth based alloys used in the tools of the present invention. The low melting point alloy group is defined as those alloys that have a melting point of 385° C. or below.

(6) The various aspects of the present invention disclosed herein are considered particularly suitable for use in down-hole operations that take place within gas and oil wells. In particular the well plug of the present invention is considered particularly suitable for use in repair operations involving Open Hole Gravel Packs.

(7) The term ‘Open Hole Gravel Pack’ (OHGP) is used throughout to indicate when a screen is used to hold back proppant/sand in a completion. It will be appreciated that, in practise, this covers all gravel pack completions including open hole, cased hole and frac packs.

(8) Although the sealing and repair of Open Hole Gravel Pack is considered a particular suitable application of the present invention, it is envisioned that the various aspects of the present invention can also be employed in other well repair operations as well as in well abandonment.

(9) Given the main focus of the present invention, the preferred embodiments will be described from this point of view. However, it is envisioned that the apparatus and methods described could be usefully applied in other technical fields, such as those fields where underground conduits are to be plugged (e.g. water pipes).

(10) The first aspect of the present invention relates to a chemical heater cartridge 1 that is considered particularly suitable for use in chemical heaters that are deployed in various down-hole operations (e.g. forming eutectic/bismuth based alloy plugs).

(11) An example of a cartridge 1 in accordance with the first aspect of the present invention is shown in FIG. 1. The cartridge 1, which is preferably tubular in shape to suit the internal cavity of the heating tools in which it can be used, is formed from a solid block 2 of a chemical heat source material, such as thermite.

(12) In use the thermite material, for example, will undergo an extreme chemical reaction that generates a large amount of heat energy. It is this heat energy which is harnessed by a heater tool down a well to melt an alloy and form a plug.

(13) Although only one block of the material is shown in FIG. 1 it is anticipated that multiple blocks of chemical heat source material could be placed together in the cartridge 1. In particular, it is envisioned that a collection of blocks with different thermite mixtures could be placed together to create a specific heating pattern. More details on this are provided in WO 2014/096857 A2, which is an earlier disclosure by the inventors.

(14) As will be appreciated from FIG. 1, the block 2 is surrounded by a wrap 3. The wrap 3, which is preferably a shrink wrap of a plastic film material (e.g. PVC), serves to maintain the shape of the wrapped block 2 and, in the case of multiple blocks, keep the blocks closely packed together. This is important because it prevents the formation of gaps between the blocks 2 during transport, which can affect the progression of the cartridge's burn during the chemical reaction.

(15) The final outer layer of the cartridge 1 is provided by the tubular surround 4, which is preferably formed from a material with insulating properties such as fibre glass. In use, when the cartridge is housed within the cavity of a heater body (not shown), the tubular surround 4 provides an element of protection to the walls of the heater body.

(16) Protecting the heater walls in this way allows for the option of reducing the thickness of the heater body without increasing the risk of the heater walls being melted by the heat given out by the cartridge 1.

(17) FIG. 1 shows an exposed view of the cartridge 1 so that the various layers can be appreciated. In the complete cartridge the wrap 3 would completely surround the blocks of chemical heat source material 2 and the surround 4 would form the outer surface of the cartridge 1.

(18) FIG. 2 shows a well plugging/sealing tool 5 in accordance with a second aspect of the present invention. Although it is envisaged that the cartridge of the first aspect of the present invention may be used with the tool 5, this is not essential. The assembly is shown without a cartridge to avoid overcomplicating the drawing. This is also the case with FIG. 3.

(19) The well plugging/sealing tool 5 is formed from a centrally located heater body 6 made, for example, from steel, aluminium, stainless steel, carbon fibre, high temperature plastic. The heater body 6 is provided with a suitable eutectic/bismuth based alloy 7 along majority of its outside length.

(20) The heater body 6 is also provided with a cavity 8 that, in use, receives a chemical heat source material, which may advantageously, but not essentially, be in the form of the cartridge of the first aspect of the present invention. As noted above, using the cartridge of the present invention within the cavity 8 of the heater body 6 would allow the thickness of the heater body walls to be reduced without making the heater body more vulnerable to melting by the heat generated within its cavity.

(21) However it is envisaged that the internal walls of the heater body 6 might alternatively, or additionally, be protected by coating the inner walls of the heater body that define the cavity 8 with a lining of refractory material 20 (shown as dashed line for ease of identification).

(22) Preferably the walls of the cavity are coated with zirconium oxide (ZrO.sub.2), otherwise known as zirconium dioxide or zirconia. However alternatives refractory materials are envisaged, with suitable alternative including fibre glass, Kevlar® and other ceramic materials such as aluminium oxide and magnesium oxide.

(23) It is also envisaged that the zirconium oxide may also be partially stabilized using dopants such as yttrium oxide, magnesium oxide, calcium oxide, and cerium (III) oxide.

(24) In a preferred embodiment, the zirconium oxide coating is applied to the inner walls of the heater body 6 using a drip process. The preferred coating process involves dripping a suitable water-based slurry containing zirconium oxide (an example of which is PyroPaint 634ZO, available from Aremco, 707-B Executive Boulevard, Valley Cottage, N.Y. 10989) in to a tubular heater body that is titled at an angle of between 5-30 degrees.

(25) Before the slurry is applied, the internal cavity of the tubular heater body is first treated with a phosphoric acid solution and then rinsed with clean water to as to clean the inner walls of the tubular heater body to ensure the walls are ready to receive the coating. It will be appreciated that other acids, such as hydrochloric acid, may also be used to treat the tubular heater body.

(26) Alternative methods for cleaning the inner walls in preparation for receiving the coating include: sand blasting, grit blasting, mechanical roughening (e.g. sanding down). The skilled person will appreciate that further alternative methods might be employed without departing from the present invention.

(27) Once clean, the tubular heater body is rotated at a rate of between 20 to 60 revolutions per minute (RPM) as the slurry is dripped into the cavity of the tubular heater body via the elevated opening at the end of the tubing. In this way the inner walls of the tubular heater body are coated with the zirconium oxide slurry.

(28) Once the coating has been applied, the tubular heater body is placed in an oven and cured at about 90° C. for around 1 to 4 hours. Using this method it has been possible to achieve a coating thickness of between 0.002 inches and 0.020 inches on the inner walls of the heater body.

(29) Once the coating is cured, the heater end tubes are capped off with welded and/or threaded plugs and filled with the thermite chemical heat source.

(30) Although the drip process is considered preferable due to its economic efficiency, it is envisaged that the coating may be applied using alternative approaches such as vapour deposition and spraying (including thermal spraying).

(31) It is envisaged that the above coating process can be used to apply the refractory lining to a variety of tubular heater bodies; that is to say heaters with or without the features of the externally mounted alloy and protective sleeve.

(32) The heater body 6 and the alloy 7 are mounted to connection means 9 such that the tool 5 can be attached to a well deployment tool (not shown) for delivery down-hole.

(33) A sleeve 10 is provided on the outer surface of a majority (preferably about ⅔ of the total length) of the well plugging/sealing tool 5. The sleeve 10 acts with the heater body 6 to almost completely envelop the alloy 7 with an annular space between the sleeve and the heater body 6.

(34) As detailed above the sleeve 10 serves to protect the alloy 7. In a first instance the sleeve protects the alloy mechanically as the well plug travels down-hole to the target region. To achieve this, the sleeve is preferably made using a structurally strong and resilient material, such as thin steel or Kevlar® tubing. The mechanical protection is considered particularly necessary when the well plug assembly is being deployed in highly deviated wells (i.e. wells with not vertical orientations).

(35) In a second instance the sleeve protects the alloy by insulating it from the down-hole environment. To achieve this, the sleeve is preferably made using a material with suitable insulating properties, such as fibre glass. It is envisaged that while the sleeve does not necessarily need to provide mechanical protection, particularly in cases where the well path is more of a vertical nature, the insulating protection provided by the sleeve is considered to be applicable in most applications of the present invention.

(36) As detailed above, providing an insulating layer outside the alloy serves to not only retain heat within the well tool 5 for longer—thus achieving more efficient heat generation—but it also counters the loss of heat that might occur to fluids flowing passed the well tool within the target region.

(37) The well plugging/sealing tool 5 shown in FIG. 2 is provided with both a mechanically protective outer sleeve 10 (e.g. thin steel) and an insulating sleeve layer 10a (e.g. fibre glass). However it is envisaged that a composite material with suitable structural and heat retaining characteristic might be employed instead of the two layer sleeve arrangement.

(38) As can be seen from FIG. 2, the sleeve 10 only extends along a portion of the full length of the well plugging/sealing tool 5. As a result, a portion of the alloy and the heater are not shielded by the sleeve 10.

(39) The partial coverage of the alloy by the sleeve causes the covered alloy to become super-heated within the annular space between the heater and the sleeve because the alloy's only escape route is located at the point where the sleeve ends. It is envisaged that the positioning of the sleeve's end point can therefore be used to focus where the molten alloy is ejected into the surrounding well environment.

(40) By ejecting super-heated molten alloy in this way, rather than releasing it more slowly from along the entire length of the well plug, it is possible to get the alloy to travel much further before it cools and solidifies. This is considered particularly advantageous when forming seals in sand pack formations (i.e. OHGPs), because the alloy can penetrate much further into the sand pack before it finally sets—thus forming a better seal.

(41) The well tool 5 shown in FIG. 2 is also provided with wear pads 12 located on spacers 11 that project out radially from the sleeve 10 of the well tool 5. This arrangement serves to further protect the well tool from damage during its deployment down-hole.

(42) Although only a pair of wear pads 12 is shown in FIG. 2, it will be appreciated that the pads could be arranged periodically around the entire circumference of the outer surface of the well tool 5. It is also envisaged that multiple sets of wear pads could advantageously be positioned along the length of the well plug's outer surface.

(43) Advantageously the annular space between the heater 6 and the sleeve is not entirely filed with alloy 7. Instead, and as will be appreciated from FIGS. 2 and 3, a spacer element 13 is provided in the annular space above the alloy 7.

(44) The spacer element 13, which is preferably made from a structurally robust material such as steel, provides the well plug with a structurally reinforced region that can be more readily used by gripping machines to pick the well plug up during above-ground handling operations. It is envisaged that without the space element 13, a gripping machine would be more likely to crush the well plug due to the soft nature of eutectic/bismuth based alloys.

(45) Finally, the well tool 5 is provided with a skirt 14 on its leading end. The skirt 14, which is essentially an open ended tube attached to the end of the heater body 6, allows well fluids to flow in and out of the open end thereby removing heat from the system and allowing the alloy to cool as it moves away from the heater body 6.

(46) The above described features of the well plugging/sealing tool 5 will be further appreciated from FIG. 3, which show a more detailed view of the top end of the well plug together with part of a well deployment tool 15.

(47) As can be seen, the well plugging/sealing tool 5 is connected to a well deployment tool 15 via connection means 5. The connection means 5 also serves to hold the heater body 6 and the sleeve 10 together by way of grub screws 16 (sleeve to connection means) and 17 (heater body to connection means).

(48) Within the cavity 8 of the heater body is provided an ignition device 18, which is in operable communication with an operator at ground level via a linkage that passed through the connection means 9 and the well deployment tool 15.

(49) Also located within the cavity 8 is a spring 19. The spring 19, one end of which urges against the ignition device 18, is used to urge the blocks of the chemical heat source material housed in the cavity together so as to illuminate unwanted gaps between the blocks (not shown). Preferably the spring is provided with a washer (not shown) that increases the surface area pushing against the blocks.

(50) The positioning of the spacer element 13 relative to the alloy 7 within the annular space provide between the heater body 6 and the sleeve 10 will be better appreciated from FIG. 3. In particular it will be noted that the spacer is located in a region that is not aligned with the heater cavity 8 into which the chemical heat source material is received. The alloy, however, is aligned with the heater cavity so as to ensure it is adequately heated by the chemical reaction heat source (e.g. thermite).