GB2601185A

GB2601185A - Improvements relating to downhole heater assemblies and methods of operating such

Info

Publication number: GB2601185A
Application number: GB2018390.1A
Authority: GB
Inventors: Carragher Paul
Original assignee: Bisn Tec Ltd
Current assignee: Bisn Tec Ltd
Priority date: 2020-11-23
Filing date: 2020-11-23
Publication date: 2022-05-25
Also published as: AU2021384004A1; GB2603561A; GB2603562B; EP4248055A1; US20240102360A1; WO2022106826A1; GB2603561B; GB2603562A; GB202018390D0

Abstract

The present invention relates to a downhole heater assembly 10 comprising at least one heating tool 11 with a delivery support connection point 13, by which the heating tool is connectable to delivery means such as wireline 14. The assembly is provided with a baffle 15 configured to be positionable in the borehole at a location between said heater tool and said delivery means. When in position said baffle acts to restrict the movement of heated fluids produced during the operation of the heating tool so as to at least partially replicate the fluid flow conditions found in the test vessel in which the heating tool's configuration was originally tested. The present invention also provides associated methods that employ a baffle between a heating tool and the above ground delivery means used to deploy the heating tool downhole.

Description

IMPROVEMENTS RELATING TO DOWNHOLE HEATER

ASSEMBLIES AND METHODS OF OPERATING SUCH

Field of the Invention

The present invention relates to downhole heating operations carried out in boreholes and underground conduits, such as oil/gas wells, and heater assemblies for use therein.

Background of the Invention

Downhole heater assemblies are commonly employed in downhole operations that are associated with the formation, maintenance and abandonment of boreholes, to such as oil/gas wells.

As detailed in a number of the applicant's earlier filings, such as International PCT applications WO 2011/151271 Al, WO 2014/096857 A2 and WO 2014/096858 A2, downhole heater assemblies can be used to deploy eutectic alloys, such as bismuth-containing alloys, to plug wells or repair existing plugs in wells.

Also, as detailed in the International PCT application WO 2015/150828 A2, downhole heater assemblies can be used to clear well casing and other well tubing from boreholes and underground conduits, such as oil/gas wells.

The two most commonly used heat sources in downhole heater assemblies are electrical heat sources or chemical reaction heat sources.

The operation of each of these heat sources in a downhole environment presents various challenges, some of which are common to both heat sources and some of which are specifically associated with a particular heat source.

Addressing these challenges can involve extensive testing of heater assemblies. However, the costs involved in running tools down existing operational boreholes can be prohibitive, particularly in the case of oil/gas wells.

In order to provide a suitable environment for testing downhole heater assemblies more economically, test vessels are commonly used. However, the extent to which these test vessels can replicate real downhole conditions can be limited.

Such limitations can lead to situations where the heating results achieved during the operation of a heater assembly in a test vessel vary from to those delivered by the same heater configurations in the real downhole conditions of an operational borehole.

Summary of the Invention

With a view to addressing the discrepancies between the performance of heater assemblies under test conditions and their performance in operational conditions the present invention provides a method of heating a downhole target region of a borehole using a downhole heater assembly according to claim 1 and a downhole heater assembly according to claim 9.

In this regard, the present invention provides a method of heating a downhole target region of a borehole using a downhole heater assembly, said method comprising: delivering a heating tool to the target region of the borehole using a delivery support connected to an above-ground delivery means; positioning a baffle in the borehole at a location between the heating tool and the delivery means, wherein the baffle is configured to at least partially restrict the flow of fluids within the borehole; operating the heating tool so as to generate heat within the target region of the borehole; and retrieving the baffle and the heating tool from the borehole.

Typically boreholes contain downhole fluids. It will be appreciated therefore that when a heater is used to apply heat to a tool or structure (e.g. well plug, well casing or another type of downhole tubing) at least some of the heat energy generated by the heater is lost to the downhole fluids.

This energy loss is exacerbated by the fact that as the fluids in the heater's target region heat up they tend to rise upwards, only to be replaced by cooler downhole fluids. The ongoing effect of this fluid movement can have a noticeable impact on the amount of the heater's energy by redirecting heat from the heater's intended target (i.e. well tool or structure).

Typically, in order to accommodate the cooling effect caused by downhole fluids the heating capacity of the downhole heaters is increased accordingly. In the case of 30 chemical based heaters this can be achieved by increasing the amount of the heating material (e.g. thermite and thermite based mixes) carried by the heater and/or by using a heating mixture that burns hotter.

With that said, there is always a need to strike a balance between the size and weight of a heater and its heating capacity. It is with this design aim in mind that 5 manufacturers of downhole heaters employ test vessels so that they can simulate the environmental conditions that are found in operational boreholes.

Using a test vessel it is possible to trial different heater configurations (e.g. heater dimensions, chemical heat source composition and/or quantities) in a more economical manner than would be possible using operational boreholes.

Test vessels can be configured to reproduce a range of conditions found in operational boreholes, such are borehole diameter, and borehole ambient temperature and pressure.

Practical limitations on the size of test vessels can limit the depths that are achievable which means that it is not possible to accurately simulate the level of heat dissipation caused by the borehole fluids in an operational borehole. This is because an operational borehole generally contains much greater quantities of fluid, thus providing much greater capacity for heat to be lost to said fluid.

Ultimately it is this difference between the environment created in the test vessel environment and the environment within the operational borehole, for which a particular heater is being designed, that reduces the level of precision achievable in the heater's configuration; for example in the formulation and quantification of the chemical reaction heat source material used in the heater.

The method of the present invention addresses this problem by deploying a baffle within an operational borehole at the same time as a heating tool.

By way of the baffle, which is configured to sit within the borehole and restrict the flow of fluids within the borehole, the method of the present invention adapts the downhole environment of the operational borehole to bring it closer to that is achievable in the test vessel.

That is to say, rather than the downhole heater being separated from the surface by potentially thousands of feet of downhole fluid that is free to rise and fall under the heat energy generated by the heater, the baffle is used to curtail the movement of downhole fluids to such an extent that the operational borehole behaves more like the test vessel, in which the heater is typically only associated with a maximum of 21m (approx. 70 feet) of fluid.

It will be appreciated that employing the method of the present invention will enable more precise configuration of a downhole heater because it brings the environmental conditions of the test vessel and the operational borehole closer together, that is, at least with regard to the level of heat energy lost from a heater to downhole fluids.

Preferably the method of the present invention involves delivering the heater and the baffle downhole at the same time. Alternatively the baffle may be positioned downhole after the heater has been delivered to the target region.

Regardless of whether the heater and the baffle are delivered in the same operation or in separate operations, the method may preferably involve providing the baffle on the same delivery support that is used to deploy the heater. Typical examples of the most common delivery support employed in the deployment of downhole heaters include slick-line, wireline, coil and drill pipe.

In this regard it is envisaged that associating the baffle with the same delivery support (e.g. a wireline) that is used to deliver the heating tool down the borehole removes the need for additional delivery runs, thereby simplifying the process.

However it is also envisaged that the baffle may be delivered using a separate delivery mechanism without departing from the general concept of the present invention.

Preferably the method may further comprise the step of delivering the baffle downhole in an unexpanded or partially expanded state and then, once in position downhole, expanding the baffle towards the walls of the borehole so as to increase the extent to which the baffle restricts the flow of fluids within the borehole.

It is envisioned that delivering the baffle downhole whilst either unexpanded or only partially expanded can aid the passage of the baffle down a borehole, which may include restrictions and other obstructions that might otherwise impede the delivery 30 route.

Further preferably the full expansion of the baffle may be co-ordinated with the operation of the heating tool. To this end, the expansion of the baffle may preferably be controlled by the heating tool.

Alternatively the expansion of the baffle may be controlled by separate control means. In addition, it is envisaged that the baffle may be urged to expand by the upwards flow of fluid caused by the heat generated by the heater.

Preferably the baffle may be positioned up to 6m (approx. 20 feet) away from the heating tool. Further preferably the distance between the baffle and the heating tool may be in the region of 0.3 to 1.0m (approx. 1 to 3 feet). In this way the baffle can create a volume of free flowing fluid in a region of the borehole between the heating tool and the surface, where the delivery means are located, that is similar to that provided in a test vessel.

Preferably the step of operating the heating tool may comprise the use of a chemical reaction heat source, such as a thermite based material, to generate the heat within the target region. Although chemical heaters are considered preferable, it is envisioned that the method the present invention could also be employed for other types of downhole heaters, such as electrical heaters.

The present invention also provides a downhole heater assembly comprising at least one heating tool with a delivery support connection point, by which the heating tool is connectable to delivery means via a delivery support such that said heating tool can be delivered to and retrieved from a downhole target region of a borehole; and wherein the assembly further comprises a baffle configured to be positionable in the borehole at a location between said heater tool and said delivery means, said baffle being configured to restrict the movement of heated fluids produced during the operation of the heating tool.

It is envisaged that the delivery support is preferably selected from a group consisting of slick line, wireline, coil, drill pipe. However, it is envisaged that any support that is capable of connecting the above ground delivery means to the heater assembly at a controllable depth could be employed without departing from the scope of the present invention.

It will be appreciated that the assembly of the present invention can be operated in accordance with the method of the present invention to achieve heating results that are more consistent with those achieved during pre-deployment testing in test vessels.

Preferably the baffle may be located between the heating tool and the delivery support connection point. In this arrangement the baffle may be provided as single combined unit with the heater.

Alternatively, the downhole heater assembly may further comprise a delivery support connected to the delivery support connection point and wherein the baffle is located on the delivery support. In this arrangement the baffle is provided as a separate unit to the heater. One of the benefits of positioning the baffle on the delivery support rather than on the heating tool is that a greater range of separation between the baffle and the heater can be achieved.

In a further alternative, the baffle could be delivered downhole using a secondary delivery support. This arrangement provided the additional advantage that the distance between the baffle and the heater tool can be adjusted without the need to retrieve the baffle and reattach it to the delivery support at a new position.

Preferably the baffle may be configured to be expandable towards the walls of the borehole so as to increase the extent to which the baffle restricts fluid movement zo within the borehole.

As noted above, providing the baffle as an expandable component can make it easier to deliver the baffle down hole, especially where there are restrictions or obstructions in the hole.

In addition, it is envisioned that the level of expansion of the baffle could be variable so as to allow adjustment of the extent to which the baffle restricts the movement of fluids within the borehole during and possibly in the period following after the operation of the heating tool.

Preferably the means by which the expansion of the baffle is achieved may be selected from hydraulic means, pneumatic means, mechanical means and combinations thereof.

Preferably the assembly may comprise control means that co-ordinate the operation of the heating tool and the expansion of the baffle.

Further preferably the control means that control the expansion of the baffle are provided on the heating tool.

Preferably, the baffle may be urged to expand and/or contract by way of one or more resilient biasing means. Further preferably the baffle may comprise a canopy of flexible material connected to an umbrella spring mechanism.

It is envisaged that the umbrella spring mechanism will provide a framework for the flexible material to expand, and thereby restrict fluid flow within the borehole, or 10 contract, and thereby ease the passage of the baffle downhole.

As an alternative to varying the size of the baffle by expansion/contraction, is in envisaged that the baffle may be provided with ports and/or valves that can be opened and closed to adjust the level of fluid restriction provided by the baffle.

In addition, it is also envisaged that some baffle embodiments, such as hydraulically/pneumatically inflatable variants, may benefit for the provision of ports and/or valves.

Preferably the baffle may be positioned a distance of up to 6m (approx. 20 feet) away from the heating tool. Further preferably the distance between the baffle and the heating tool may be in the region of 0.3 to 1.0m (approx. 1 to 3 feet). As noted above, the spacing provided between the heater tool and the baffle can create a volume of free flowing fluid in a region of the borehole between the heating tool and the surface, where the delivery means are located, that is similar to that provided in a test vessel Preferably the heating tool employs a chemical reaction based heat source, such as zs therm ite or a therm ite based mixture.

Preferably the baffle may comprise insulating means to reduce the amount of heat energy lost from the region of the borehole between the heater tool and the baffle.

In this way the baffle restricts the loss of heat due to convection (i.e. as heated fluids rise upwards in the borehole) and due to conduction (i.e. heat energy from the heated fluids passes through the baffle to the downhole fluids on the other side of the baffle).

The present invention also provides for a method of deploying a eutectic/bismuth based alloy based tool in which the alloy is delivered to a downhole target region and then is melted using the heating method of the present invention.

Further, the present invention provides for a method of clearing an underground conduit from a borehole in which the underground conduit is melted using the heating method of the present invention.

Brief Description of the Drawings

The present invention will be described with reference to a preferred embodiment, wherein: Figure 1 shows the main stages of a preferred embodiment of the method of the present invention; Figure 2 shows an alternative embodiment of the heater assembly of the present invention; and Figure 3 shows the expansion and contraction of the baffle shown in Figure 2. Detailed Description of the Preferred Embodiments It is envisaged that the downhole heating method of the present invention can be employed in downhole operations carried out a variety of underground conduits.

However the method of the present invention is considered to be particularly useful for use in downhole operations conducted in oil/gas wells.

Examples of downhole operations in which the heating method of the present invention can be employed include the deployment and/or removal of eutectic/bismuth-based alloy plugs, thermally deformed annular packers (TDAPs), and other downhole tools employing such alloys.

In this regard, reference is made to the applicant's earlier published International PCT applications WO 2011/151271 Al, WO 2014/096857 A2 and WO 2014/096858 A2 It is also envisioned that the heating method of the present invention may also be employed in the removal of downhole well conduits, such as well casing/tubing, using chemical reaction based heater assemblies. In this regard, reference is made to WO 201 5/1 50828 A2.

In the light of the range of downhole operations in which the method of the present invention can be employed, for the sake of clarity the preferred embodiment of the present invention represented in Figure 1 shows the steps relating to the delivery and operation of the heating tool without the heater's target (e.g. well plug/tool).

It will be appreciated that depending on the nature of the downhole operation being carried out, additional tools may or may not be employed in tandem with the heating tool. For example, in the case of a downhole operation to deploy a eutectic/bismuthbased alloy plug, a suitable alloy could be mounted -either directly or by way of an additional mandrel into which the heater is received -around the outside of the heating tool. In this way the alloy can be delivered to a target region of a borehole (typically an oil/gas well, but not exclusively so) using the heater assembly and then melted by the heat given off to effect the formation of a plug within the borehole as the alloy cools, solidifies and, in the case of preferred alloys, expands.

Referring now to Figure 1, the key stages of the downhole heating method of the present invention will now be described with regard to the use of a heating tool 3 in an underground conduit 1 that is located in a borehole 2. Preferably, the conduit 1 may be in the form of an oil/gas well casing or tubing. However the skilled person will appreciate that the method of the present invention could also be employed in other forms of underground conduit that contain fluids, such as water wells and mining bore holes.

In the first stage (A) of the method, a delivery support in the form of a wireline 4 is used to deliver the heating tool 3 downhole into the conduit 2 located in a borehole 1 that has been created (e.g. by drilling) in a formation.

The wireline 4 connects the heating tool 3 to delivery means (not shown) that are located at the surface and which can be operated to lower and raise the heating tool 30 within the borehole. As noted above, wireline is just one example of a delivery support that is used to connect the heating tool to the above ground delivery means.

The skilled person will appreciate that alternative connection systems may be employed without departing from the general concept of the present invention.

Using the delivery means the heating tool 3 can be delivered to a target region of the borehole and, once the heating operation has been effected, retrieved from the borehole to the surface.

It will be appreciated that conventional mechanisms (e.g. crossover tool) can be used to attach the heating tool 3 to the delivery means via the wireline 4.

In the second stage (B) of the method, a baffle 5 is positioned within the borehole at a pre-determined distance from the heating tool 3.

Preferably the baffle 5 is attached to the wireline 4 once a pre-determined amount of wireline 3 has been reeled off by the above ground delivery means. In this way the clearance between the heating tool 3 and the baffle 5 can be precisely controlled.

With that said, it is appreciated that alternative mechanisms for delivering the baffle 5 downhole can also be employed without departing from the general concept of the present invention, provided they enable the distance between the heating tool 3 and the baffle 5 to be accurately monitored and controlled.

In one such alternative arrangement the baffle 5 may be mounted on a secondary delivery support/means (not shown). In this way, the baffle 5 can be raised and lowered downhole independently of the heating tool 3.

The ability to separately control the depth to which the heating tool and the baffle are delivered gives the operator increased flexibility when setting the clearance between the heating tool 3 and the baffle 5.

It is envisioned that the method of the present invention affords the operator the freedom to vary the distance between the heating tool 3 and the baffle to achieve both large and small clearances. With that said, the preferred distance between the heating tool and the baffle should be no more than 6m (approx. 20 feet) because this represents the limit of the clearance that can be achieved using test vessels. Clearances of between around 0.3 to 1.0m are considered particularly suitable.

Ultimately the method of the present invention allows the operator to recreate the volumes of fluid that are heated in the test vessel during testing in a real life operational borehole, which, without the baffle, would have considerably greater volumes of fluid. As noted above, the larger the volume of fluid in the downhole environment, the greater the extent to which heat energy can be dissipated by fluid movements within the target region.

Rather than seeking to develop testing equipment that more closely resembles downhole environments (i.e. by making bigger test vessels), the method of the present invention allows an operator to curtail an operational borehole by deploying the baffle 5 within a pre-determined distance of the heating tool 3 so that it more closely resembles the environment within which the heating tool's configuration was developed and tested.

As will be appreciated from the second stage (B) shown in Figure 1, preferably the baffle 5 is deployed downhole in an unexpanded, or at very least only partially expanded state. This makes it easier to avoid potential restrictions and obstructions in the borehole on route to the target region. In addition, it makes it easier for the baffle to pass through the downhole fluids.

It is envisioned that other mechanisms may be employed to ease the passage of the baffle downhole. For instance, the baffle, which in most cases would have a circular shape when viewed in plan so as to correspond with the cross-sectional shape of the borehole, may be provided with one or more through ports so that fluids can pass through the baffle when it is being lowered/raised within the borehole.

In those arrangements where the baffle is provided with one or more through-ports, the baffle may further preferably be provided with closure valves that can be actuated to close the through-ports. In this way, once the baffle is in position downhole, the through-ports can be closed by valves to better restrict the flow of fluids within the borehole.

In the embodiment of the present invention shown in Figure 1 the baffle 5 is provided as an inflatable member that is configured to expand once it is in position downhole.

It is envisaged that the expansion of the baffle can be achieved using either hydraulic means or pneumatic means to inflate it.

The skilled person will appreciate that other mechanisms for increasing the diameter of the baffle, such as mechanical (e.g. spring-actuated), could be employed without departing from the scope of the present invention.

Turning now to the third stage (C), the baffle 5 is shown in its expanded state. In its expanded state the extent to which the movement of fluids up-hole is restricted.

It is envisioned that the baffle 5 may be locked in position by virtue of its expansion against the inside of the well tubing 1 walls. Alternatively, or additionally, the baffle may be locked in position at a pre-determined distance from the heating tool 4 by securing itself to the wireline 4.

Control means for actuation the expansion and/or positional locking of the baffle may preferably be provided on the heating tool, although alternatively they could be provided at the surface with the delivery means/secondary delivery means.

Once the heating tool 3 and the baffle 5 are in positioned in their spaced apart downhole locations (i.e. the heating tool in the target region and the baffle a pre-determined distance up-hole of the heating tool) the heating tool 3 can be operated to commence the generation of heat 6 in the target region.

As noted above, the heating tool of the present invention is preferably a chemical reaction based heater that uses a thermite or thermate based mixture to generate heat. However, it is envisioned that the benefits of the present invention could also be delivered using downhole heaters that employ other heat sources (e.g. electrical).

In the final stage (D) shown in Figure 1 the heating tool 3 is generating heat 6 which can be employed to melt a eutectic/bismuth-based alloy to form a plug or alternatively to clear away unwanted underground conduits/structures (e.g. well casing/tubing). However in addition, the heat generated by the heating tool also heats the fluid present in the target region of the borehole.

The downhole fluid heated by the energy given off by the heating tool 3 is caused to rise up the borehole, as represented by arrows 7. In downhole heating operations carried out prior to the development of the present invention heated fluid would be free to rise up-hole unrestricted.

This would set up a continuous flow of heated fluids upwards away from the heating tool, which would have a noticeable dissipating effect on the heat generated by the heating tool. The dissipating effect caused by the free movement of heated fluid would cause the heating tool to perform its primary heating task less effectively that might be expected from the testing of a particular heater configuration.

However, by deploying a baffle 5 up-hole of the heating tool 3, the extent to which heated fluids can rise up the borehole is restricted. As is demonstrated in the final stage (D) shown in Figure 1, the continued rise of the heated fluid 7 is restricted by the baffle (as represented by arrows 8).

Further, the extent to which the fluid flow is restricted can be set to correspond to that achieved in the test vessel in which the heating tool configuration was tested. This enables the operator to more efficiently and accurately configure the heating tool's characteristics (e.g. heater size, heat source type and quantity).

Preventing the loss of heated fluids up-hole means that the heat generated by the heating tool is better contained in the desired target region, which helps improves the heating efficiency of the heating tool and, in the case of chemical heaters, allows the weight/size of the heating tool to be reduced. This, in turn, enhances an operator's ability to deploy heating tools in boreholes with more restricted access.

Figure 2 shows an alternative preferred embodiment of the heater assembly 10 of 20 the present invention which employs a mechanical baffle arrangement rather than an inflatable arrangement.

The heater 11, which is shown in a truncated form for sake of scale, is provided with a setting tool 12 that essentially houses the control mechanisms for operating the heater (e.g. ignition means in the case of a chemical heater).

The setting tool is then connected via a delivery support connection point 13 to a delivery support, which is again shown as a wireline 14 but could be any suitable connection line, pipe or coil. The baffle 15 is located between the connection point 13 and the setting tool 12 of the heater 11.

In Figure 2 the baffle 15 is shown in an expanded state, wherein the baffle extends 30 beyond the outer diameter of the heater 11. The expansion mechanism of the baffle shown in Figure 2 will now be described with reference to Figure 3, in which the baffle is shown in both an unexpanded state and an expanded state.

The baffle 15 comprises a central shaft 16 that is connected between the setting tool 12 of the heater 11 and the delivery support connection point 13. A collar 17 is fixed in position on the shaft 16. Attached to the collar 17 is a web of flexible material 18 that essentially forms a canopy that is capable of changing shape to accommodate the expansion and contraction of the baffle 15. It will be appreciated that the flexible material should be resistant to the downhole environment within which the assembly 10 is to be deployed. It is envisaged that a suitable flexible material for use in the baffle is silicone rubber. However the skilled person will appreciate that other flexible materials could be suitably be employed.

The baffle 15 further comprises a plurality of resiliently biased expansion bands 20 that are secured at their respective ends to the connection point 13 and a moveable collar 19, which is slideably mounted on the central shaft 16. In this way the unsecured middle portions of the bands are free to bend and flex in a radial direction relative to the central shaft.

It is envisaged that the resiliently biased expansion bands 20 may be formed from flexible strips of a suitable spring metal. However the skilled person will appreciate that an alternative resilient material may be employed without departing from the scope of the present invention.

In the preferred embodiment the moveable collar 19 is urged away from the setting tool 12 by way of actuation means 21, which may take the form of a coiled spring. It is envisaged that the actuation means 21 can be used to control the distance between the connection point 13 and the collar 19, which in turn will control the extent to which the resiliently biased expansion bands 20 can be deformed.

In this regard the actuation means 21 can limit the extent to which the collar 19 can move up and down the central shaft, which in turn limits the extent to which baffle can be expanded or contracted.

The central portion of the canopy of flexible material 18 is attached to the fixed collar 17 whilst the periphery of the canopy is attached to each of the plurality of resiliently biased expansion bands 20. By connecting the flexible material to the middle portions of the resiliently biased expansion bands 20, the baffle can be operated to expand and contract the flexible material so that the extent to which it can restrict the flow of fluid past the baffle is varied.

That is, when the resiliently biased expansion bands 20 are forced radially outwards they pull the flexible material outwards to form an expanded fluid blocking structure.

Also, when the resiliently biased expansion bands 20 move radially inwards they pull in the flexible material and contract the fluid blocking structure.

It is envisaged that preferably, at rest, the bands will extend outwards beyond the outer diameter of the rest of the heater assembly 10 so that the canopy of flexible material will at least partially block the borehole and, in so doing, restrict the flow of fluids within the borehole.

However, the flexible nature of the bands allows the baffle to compress, as necessary, to accommodate narrowed portions of the borehole that might be encountered during the heater assembly's deployment. Once past the narrowed portion of a borehole, the resilient nature of the bands will cause the baffle to once again return to its expanded state, in which the baffle restricts the flow of fluid within the borehole.

It is further envisaged that, in use, the canopy may be caused to expand even further under the influence of heated fluids rising within the borehole. That is rising fluid 20 could become trapped by partially opened canopy and then urge it to open further.

In an alternative arrangement of the mechanical arrangement shown in Figures 2 and 3, the actuation means 21 may be operated to force moveable collar 19 to slide up the shaft 16, thereby urging the resiliently biased expansion bands 20 outwards and opening the canopy.

It is envisaged that this arrangement could be employed in embodiments where the baffle's default position in the unexpanded state.

Claims

Claims 1. A method of heating a downhole target region of a borehole using a downhole heater assembly, said method comprising: a) delivering a heating tool to the target region of the borehole using a S delivery support connected to above-ground delivery means; b) positioning a baffle in the borehole at a location between the heating tool and the delivery means, wherein the baffle is configured to at least partially restrict the flow of fluids within the borehole; c) operating the heating tool so as to generate heat within the target region of the borehole; and d) retrieving the baffle and the heating tool from the borehole.
2. The method of claim 1, comprising providing the baffle on the delivery line/pipe.
3. The method of claim 1 or 2, wherein the baffle and the heater are delivered downhole at the same time.
4. The method of claim 1 or 2, wherein the baffle is positioned downhole after the heating tool has been delivered to the target region.
5. The method of claim 1, 2, 3 or 4, said method further comprising the step of delivering the baffle downhole in an unexpanded state and then expanding the baffle zo towards the walls of the borehole so as to increase the extent to which the baffle restricts the flow of fluids within the borehole.
6. The method of claim 5, wherein the expansion of the baffle is co-ordinated with the operation of heating tool.
7. The method of claim 5 or 6, wherein the expansion of the baffle is controlled by the heating tool.
8. The method of any of the preceding claims, wherein the baffle is positioned up to 20m (approx. 70 feet) above the heating tool, and preferably between 0.3 to 1.0m (approx. 1 to 3 feet).
9. The method of any of the preceding claims, wherein operating the heating tool comprises the use of a chemical reaction heat source, such as a therm ite based material, to generate the heat within the target region.
10. A downhole heater assembly comprising at least one heating tool with a delivery support connection point, by which the heating tool is connectable to delivery means via a delivery support such that said heating tool can be delivered to and retrieved from a downhole target region of a borehole; and wherein the assembly further comprises a baffle configured to be positionable in the borehole at a location between said heater tool and said delivery means, said baffle being configured to restrict the movement of heated fluids produced during the operation of the heating tool.
11. The downhole heater assembly of claim 10, wherein the baffle is located between the heating tool and the delivery support connection point.
12. The downhole heater assembly of claim 10, further comprising a delivery support connected to the delivery support connection point and wherein the baffle is located on the delivery support.
13. The downhole heater assembly of claim 10, 11 or 12, wherein the baffle is configured to be expandable towards the walls of the borehole so as to increase the extent to which the baffle restricts fluid movement within the borehole.
14. The downhole heater assembly of claim 13, wherein the mechanism by which the expansion of the baffle is achieved is selected from hydraulic means, pneumatic means, mechanical means and combinations thereof.
15. The downhole heater assembly of claim 13 or 14, wherein the assembly comprises control means that co-ordinate the operation of the heating tool and the expansion of the baffle.
16. The downhole heater assembly of any of claims 13, 14, or 15, wherein the control means that control the expansion of the baffle are provided on the heating tool.
17. The downhole heater assembly of any of claims 13 to 16, wherein the baffle is urged to expand and/or contract by way of one or more resilient biasing means.
18. The downhole heater assembly of claim 17, wherein the baffle comprises a canopy of flexible material connected to an umbrella spring mechanism.
19. The downhole heater assembly of any of claims 10 to 18, wherein the baffle is positioned a distance of up to 6m (approx. 20 feet) from the heating tool, and preferably between 0.3 to 1.0m (approx. 1 to 3 feet).
20. The downhole heater assembly of any of claims 10 to 19, wherein said at least one heating tool employs a chemical reaction based heat source.
21. The downhole heater assembly of any of claims 10 to 20, wherein the baffle comprises insulating means.
22. A method of deploying a eutectic/bismuth based alloy based tool in a downhole target region, said method comprising: delivering the eutectic/bismuth based alloy based tool to the downhole target region; heating the tool using the heating method of any of claims 1 to 9.
23. A method of clearing an underground conduit from a borehole, wherein the underground conduit is melted using the heating method of any of claims 1 to 9.