EP4424973A1

EP4424973A1 - Annular barrier

Info

Publication number: EP4424973A1
Application number: EP23160016.4A
Authority: EP
Inventors: Ricardo REVES VASQUES
Original assignee: Welltec Manufacturing Center Completions Aps
Current assignee: Welltec Manufacturing Center Completions Aps
Priority date: 2023-03-03
Filing date: 2023-03-03
Publication date: 2024-09-04

Abstract

The present invention relates to an annular barrier for expansion in an annulus between a first well tubular metal structure and an inner face of a borehole or a second well tubular metal structure for providing zone isolation between a first zone and a second zone of the annulus, the annular barrier having a first axial extension, where the annular barrier comprises a tubular metal part for mounting as part of the first well tubular metal structure, the tubular metal part having an outer face, an expandable metal sleeve surrounding the tubular metal part and having an outer face facing towards the inner face of the borehole or the second well tubular metal structure and an inner face facing the outer face of the tubular metal part, a second axial extension along the first axial extension, and each end of the expandable metal sleeve being connected with the tubular metal part, an annular space between the expandable metal sleeve and the tubular metal part, an expansion opening in the tubular metal part through which fluid may enter the annular space in order to expand the expandable metal sleeve, and wherein the annular barrier further comprises a eutectic material which in a first condition is arranged on the outer face of the tubular metal part in a first axial position different from the second axial extension of the expandable metal sleeve, and in a second condition and a second axial position the eutectic material abuts a face of the expandable metal sleeve, and in an intermediate condition the eutectic material is positioned between the first axial position and the second axial position. The invention also relates to a downhole system comprising the annular barrier and a downhole tool string comprising a heating unit for heating the eutectic material.

Description

The present invention relates to an annular barrier for expansion in an annulus between a first well tubular metal structure and an inner face of a borehole or a second well tubular metal structure for providing zone isolation between a first zone and a second zone of the annulus. The invention also relates to a downhole system comprising the annular barrier and a downhole tool string.
In salt formations, the borehole of an oil or gas well may decrease over time, challenging the completion components, casings and liners arranged therein as these are dimensioned to the borehole as drilled. Annular barriers may be arranged along the casing or liner for providing zonal isolation, and annular barriers abutting the wall of the borehole are thus squeezed as the salt formation enlarges. Some annular barriers are made of flexible material able to flex as the salt formation enlarges and still provide a proper seal; however, if the salt formation continues to enlarge, the annular barriers can no longer provide a proper seal, and thus the zonal isolation is broken.
It is an object of the present invention to wholly or partly overcome the above disadvantages and drawbacks of the prior art. More specifically, it is an object to provide an improved annular barrier which is suitable for implementation into salt formations.
The above objects, together with numerous other objects, advantages and features, which will become evident from the below description, are accomplished by a solution in accordance with the present invention by an annular barrier for expansion in an annulus between a first well tubular metal structure and an inner face of a borehole or a second well tubular metal structure for providing zone isolation between a first zone and a second zone of the annulus, the annular barrier having a first axial extension, where the annular barrier comprises:

a tubular metal part for mounting as part of the first well tubular metal structure, the tubular metal part having an outer face,
an expandable metal sleeve surrounding the tubular metal part and having an outer face facing towards the inner face of the borehole or the second well tubular metal structure and an inner face facing the outer face of the tubular metal part, a second axial extension along the first axial extension, and each end of the expandable metal sleeve being connected with the tubular metal part,
an annular space between the expandable metal sleeve and the tubular metal part,
an expansion opening in the tubular metal part through which fluid may enter the annular space in order to expand the expandable metal sleeve, and

By having eutectic material arranged on the outer face of the tubular metal part, the sealing ability of the annular barrier can easily be re-established by heating the eutectic material as then the eutectic material changes condition to a flowable condition and re-arranges itself between the expandable metal sleeve and the borehole, and as the eutectic material changes condition to a solid state, the volume of the eutectic material enlarges and provides a new proper seal. Thus, an annular barrier having such eutectic material is suitable for implementation into a salt formation as the annular barrier is still able to provide a proper seal over time when the salt formation has enlarged.
Also, the annular barrier may further comprise a fluid communication channel having a first opening in a first axial channel position, and the fluid communication channel extending towards a second opening in a second axial channel position, where the second axial channel position overlaps or abuts an axial position of the expandable metal sleeve, and the eutectic material is in the first condition arranged upstream to the first opening, and in the second condition the eutectic material abuts the face of the expandable metal sleeve downstream to the second opening.
Moreover, the first axial channel position may be closer to the first axial position than to the second axial position.
Further, the fluid communication channel may be a tube.
In addition, the tube may be a metal tube metallically connected with the tubular metal part.
Furthermore, one of the ends of the expandable metal sleeve may be connected with the tubular metal part by means of a connection part, and the fluid communication channel may extend through the connection part, providing fluid communication to the annular space.
Also, in the second condition the eutectic material may overlap the second axial extension.
Moreover, the second opening may be arranged to overlap the second axial extension of the expandable metal sleeve.
Further, the fluid communication channel may be arranged to partly abut part of the outer face of the expandable metal sleeve.
In addition, the annular barrier may further comprise a chamber arranged on the outer face of the tubular metal part; in the first condition, the eutectic material is in powder form arranged in the chamber.
Furthermore, the eutectic material may be a solid block of eutectic material.
Also, the chamber may have a chamber opening in fluid communication with the first opening of the fluid communication channel.
Moreover, the eutectic material may comprise bismuth or an alloy of bismuth.
Further, the eutectic material may be a post-transition metal material such as bismuth or a bismuth alloy in one monolithic whole as a block or in powder form.
In addition, in the first condition the eutectic material may have a first volume, and in the intermediate condition the eutectic material may have a second volume being smaller than the first volume.
Furthermore, in the second condition the eutectic material may be arranged at least partly on the outer face of the expandable metal sleeve.
Also, in the second condition the eutectic material may be arranged at least partly in the annular space.
Moreover, the annular barrier may further comprise an equalising fluid channel providing fluid communication between the annular space and the annulus for allowing fluid within the annular space to flow out of the annular space when the eutectic material is displacing the fluid.
Further, the equalising fluid channel may have a first aperture in fluid communication with the annular space and a second aperture in fluid communication with the second zone.
In addition, the first opening and the second opening may be arranged in the connection part.
Furthermore, the annular barrier may also comprise a valve unit for controlling fluid communication between the expansion opening and the annular space via a conduit.
Moreover, the conduit may be used as the fluid communication channel.
Also, the valve unit may be fluidly connected to the equalising fluid channel.
Moreover, the expandable metal sleeve may be provided with a sealing unit on the outer face of the expandable metal sleeve.
Further, the sealing unit may be arranged in a circumferential groove of the expandable metal sleeve.
In addition, the sealing unit may further comprise an annular sealing element and a retaining element.
Furthermore, the sealing unit may comprise an intermediate element.
Also, at least the retaining element may comprise a post-transition metal material such as bismuth or a bismuth alloy.
Moreover, the annular sealing element may be made of elastomer, natural or synthetic rubber, polymer or a similar material.
Further, in the first condition the first opening may abut the eutectic material.
In addition, the first opening may comprise a plug at least partly made of a eutectic compound or alloy.
Furthermore, in the first condition the eutectic material may extend at least partly around a circumference of the tubular metal part.
Also, in the second condition the eutectic material may extend fully around the circumference of the tubular metal part.
Moreover, the first well tubular metal structure may have a higher melting point than that of the eutectic material.
Further, the eutectic material may have a first outer diameter when being in the first condition, and the first outer diameter may be smaller or equal to an outer diameter of the expandable metal sleeve in an unexpanded condition of the expandable metal sleeve.
In addition, in the intermediate condition the eutectic material may be at least partly in a liquid state.
Furthermore, the first zone may be a production zone, and the eutectic material may be arranged in the second zone. When the eutectic material enters the annular space, displacing fluid in the annular space, the lower pressure in the first zone will assist the fluid out of the annular space through the equalising fluid channel due to the lower pressure in the production zone.
Finally, the invention relates to a downhole system comprising the annular barrier and a downhole tool string comprising a heating unit for heating the eutectic material.
The invention and its many advantages will be described in more detail below with reference to the accompanying schematic drawings, which for the purpose of illustration show some non-limiting embodiments and in which:

Fig. 1 shows a cross-sectional view of an annular barrier having a block of eutectic material in a first condition,
Fig. 2A shows a cross-sectional view of another annular barrier having a eutectic material in a first condition,
Fig. 2B shows a cross-sectional view of the annular barrier of Fig. 2A having a eutectic material in a second condition,
Fig. 3 shows a cross-sectional view of part of another annular barrier having a block of eutectic material in a first condition,
Fig. 4 shows a cross-sectional view of part of yet another annular barrier having a chamber with powdered eutectic material in a first condition,
Fig. 5 shows a cross-sectional view of part of yet another annular barrier having a block of eutectic material in a first condition, and
Fig. 6 shows a cross-sectional view of another annular barrier having a eutectic material in a first condition.

All the figures are highly schematic and not necessarily to scale, and they show only those parts which are necessary in order to elucidate the invention, other parts being omitted or merely suggested.
Fig. 1 shows an annular barrier 1 in its expanded state in an annulus 103 between a first well tubular metal structure 3a and an inner face 4 of a borehole 5 for providing zone isolation between a first zone 101 and a second zone 102 of the annulus. The annular barrier 1 has a first axial extension 2 along which it extends along the longitudinal extension of the well tubular metal structure 3a and the borehole 5. The annular barrier 1 comprises a tubular metal part 6 for mounting as part of the first well tubular metal structure 3a. The tubular metal part 6 has an outer face 7 facing the inner face 4 of the borehole 5. The annular barrier 1 further comprises an expandable metal sleeve 8 surrounding the tubular metal part 6 and having an outer face 9 facing towards the inner face 4 of the borehole 5 and an inner face 10 facing the outer face 7 of the tubular metal part. The expandable metal sleeve 8 has a second axial extension 22 along the first axial extension representing the length of the expandable metal sleeve. Each end 31, 32 of the expandable metal sleeve 8 is connected with the tubular metal part 6 for enclosing an annular space 11 between the expandable metal sleeve and the tubular metal part. An expansion opening 12 is arranged in the tubular metal part 6 through which fluid may enter the annular space 11 in order to expand the expandable metal sleeve 8. The annular barrier further comprises a eutectic material 14 which in a first condition is arranged on the outer face 7 of the tubular metal part 6 in a first axial position 51 different from the second axial extension 22 of the expandable metal sleeve 8 along the first axial extension 2, so that the eutectic material 14 is arranged outside the annular space 11 and the expandable metal sleeve.
By having eutectic material 14 arranged on the outer face 7 of the tubular metal part 6, the sealing ability of the annular barrier 1 can easily be re-established by heating the eutectic material as then the eutectic material changes condition to a flowable condition and re-arranges itself between the expandable metal sleeve 8 and the borehole 5, and as the eutectic material changes condition to a solid state, the volume of the eutectic material enlarges and provides a new proper seal. The flowable or even liquified eutectic material 14 is thus able to enter smaller gaps than when the eutectic material is in its solid state, and upon solidification the eutectic material increases in volume and fills up the gap even better. Thus, an annular barrier having such eutectic material is suitable for implementation into a salt formation as the annular barrier is then still able to provide a proper seal even after some time when the salt formation has enlarged.
When entering a downhole tool string 50 comprising a heating unit 54 for heating the eutectic material 14 from within the first well tubular metal structure 3a/tubular metal part 6, the eutectic material 14 becomes flowable and flows down in relation to a top 61 of the well and towards the expanded expandable metal sleeve 8 for resting on top of a sealing unit 27 along the circumference of the annular barrier 1 barrier - as indicated by the dotted line and reference 14' as representing the eutectic material in the second condition. This may occur many years after having set the annular barrier 1 in order to plug and abandon the well, or if the sealing of the annular barrier has become less efficient due to formation changes, such a salt formation.
In Fig. 2A, the eutectic material 14 is in the first condition on the outer face 7 of the tubular metal part 6 in the first axial position 51, which is different from the second axial extension 22 of the expandable metal sleeve 8 along the first axial extension 2. After being heated, the eutectic material 14 becomes flowable and flows to a second axial position 52 and a second condition where the eutectic material abuts the face 9, 10 of the expandable metal sleeve 8, as shown in Fig. 2B. When being in the flowable condition, the eutectic material 14 is in an intermediate condition where the eutectic material is positioned between the first axial position 51 and the second axial position 52.
In Figs. 2A and 2B, the annular barrier 1 further comprises a fluid communication channel 15 having a first opening 16 in a first axial channel position 21, and the fluid communication channel extends towards a second opening 17 in a second axial channel position 22. In Figs. 2A and 2B, the second axial channel position 22 overlaps an axial position 23 of the expandable metal sleeve 8 and abuts the expandable metal sleeve. The eutectic material 14 is in the first condition arranged upstream to the first opening 16, and in the second condition the eutectic material abuts the inner face 10 of the expandable metal sleeve 8 downstream to the second opening 17. In the intermediate position, the eutectic material 14 is flowing in the fluid communication channel 15 in order to move to the second axial channel position 22. The first axial channel position 21 is closer to the first axial position 51 than the second axial position 52. The fluid communication channel 15 may be a tube 18 as shown in Fig. 2A. The tube 18 is a metal tube, such as a hollow heat tube, e.g. of cobber, metallically connected with the tubular metal part 6, as shown in Fig. 3, so that the heating unit of the downhole tool string 50 is able to heat the tube and thus keep the eutectic material flowable. The first well tubular metal structure 3a has a higher melting point than that of the eutectic material 14 so that only the eutectic material changes to a flowable condition. The tube 18 may also be heated by other means, such as electric wires or thermite, even though not shown.
In the second axial position 52 and the second condition of the eutectic material 14, the eutectic material is, in Fig. 2B, positioned inside the annular space 11, but may also be positioned outside the expandable metal sleeve 8 sealing between the outer face 9 of the expandable metal sleeve and the inner face 4 of the borehole 5 or the well tubular metal structure 3 (shown in Fig. 6). Thus, in the second condition the eutectic material 14 may be arranged both inside and outside the expandable metal sleeve 8, which is suitable for plug and abandonment of the well or part of the well when sidetracking above the abandoned part. As the eutectic material 14 such as bismuth alloy is metallic, the eutectic material, in the second condition when positioned between the expandable metal sleeve 8 and the first well tubular metal structure 3a, provides a full metal-to-metal seal which is very strong. When the eutectic material 14 is positioned between the expandable metal sleeve 8 and the wall of the borehole 5, the sealing ability of the eutectic material is less efficient.
In the first condition shown in Fig. 2A, the eutectic material 14 has a first volume V1, and in the intermediate condition the eutectic material has a second volume being smaller than the first volume. The eutectic material 14 comprises bismuth or an alloy of bismuth, and the eutectic material is thus a post-transition metal material such as bismuth or a bismuth alloy in one monolithic whole as a block or in powder form.
In the first condition, the eutectic material 14 extends at least partly around a circumference of the tubular metal part 6, either in the form of separate elements, an open-ended ring-shaped element or a full ring. In the second condition, the eutectic material 14 extends fully around the circumference of the tubular metal part 6, as the eutectic material flows in the intermediate condition and evenly self-distributes around the circumference of the tubular metal part 6 when positioned inside the annular space 11, or around the circumference of the expandable metal sleeve 8 when positioned outside the expandable metal sleeve.
As shown in Fig. 3, one of the ends of the expandable metal sleeve 8 is connected with the tubular metal part 6 by means of a connection part 41, 42, and in Figs. 2A and 2B both the first end 31 and the second end 32 of the expandable metal sleeve 8 is connected to the tubular metal part 6 by means of a first connection part 41 and a second connection part 42. In Fig. 5, the fluid communication channel 15 extends through the connection part 41, 42, providing fluid communication to the annular space 11. In Figs. 3 and 4, the fluid communication channel 15 is arranged to partly abut part of the outer face 9 of the expandable metal sleeve 8 so as to guide the eutectic material 14 in its flowable intermediate condition to the outside of the expandable metal sleeve on top of the sealing unit 27. Thus, in the second condition the eutectic material 14 overlaps the second axial extension. The second opening 17 is arranged to overlap the second axial extension 22 of the expandable metal sleeve 8.
As shown in Fig. 4, the annular barrier 1 further comprises a chamber 19 arranged on the outer face 7 of the tubular metal part 6, and in the first condition the eutectic material 14 is in powder form and arranged in the chamber. The chamber 14 has a chamber opening 20 in fluid communication with the first opening 16 of the fluid communication channel 15. The tube 18 forming the fluid communication channel 15 may also comprise powered eutectic material 14. In the first condition, the first opening 16 is abutting the eutectic material 14. In Figs. 1, 2A, 3, 5 and 6, the eutectic material 14 is a solid block of eutectic material. In Fig. 5, the first opening 16 and the second opening 17 are both arranged in the first connection part 41, and the first opening 16 comprises a plug 28 which may at least partly be made of a eutectic compound or alloy so that the plug is removed when heated, e.g. by the heating unit 54 of the downhole tool string 50 or other means such as thermite or electric wire.
The annular barrier 1 may further comprise an equalising fluid channel 24 as shown in Figs. 2A and 2B. The equalising fluid channel 24 provides fluid communication between the annular space 11 and the annulus 103 for allowing fluid within the annular space to flow out of the annular space when the eutectic material 14 is displacing the fluid. The equalising fluid channel 24 may be fluidly connected to a valve unit 25, shown in Fig. 1, so that the equalising fluid channel 24 is also used as a conduit 38 controlling fluid communication between the expansion opening and the annular space 11 via the conduit 38, as shown in Fig. 1. In another annular barrier 1, part of the conduit 38 is used as the fluid communication channel 15. In Figs. 2A and 2B, the equalising fluid channel 24 has a first aperture 33 in fluid communication with the annular space 11 and a second aperture 34 in fluid communication with the second zone.
In order to provide a better seal when the expandable metal sleeve 8 is expanded to abut the inner face 4 of the borehole 5 or another well tubular metal structure, the expandable metal sleeve is provided with a plurality of sealing units 27 on the outer face 9 of the expandable metal sleeve 8, as shown in Fig. 1. The sealing units 27 are arranged in a circumferential groove 29 of the expandable metal sleeve 8. At the groove 29, the expandable metal sleeve 8 has a first thickness t₁, and between two grooves the expandable metal sleeve has a second thickness t₂ being greater than the first thickness. The sealing unit 27 further comprises an annular sealing element 35 and a retaining element 36. The retaining element 36 is a wound ring so that the retaining element is able to partly unwind as the expandable metal sleeve 8 is expanded, providing a proper back-up to the annular sealing element 35. In Fig. 6, an intermediate sealing element 37 is arranged between the annular sealing element 35 and the retaining element 36 so that the retaining element does not rupture the annular sealing element as it unwinds during expansion. In order to keep the annular sealing element 35 in the groove 29, the annular sealing element has different widths w1, w2, w3, where w2 is greater than w1, but smaller than w3. In one annular barrier 1, the retaining element 36 comprises a post-transition metal material such as bismuth or a bismuth alloy. The annular sealing element 35 is made of elastomer, natural or synthetic rubber, polymer or a similar material.
As shown in Figs. 3-5, the eutectic material 14 has a first outer diameter O1 when being in the first condition, and the first outer diameter is smaller or equal to an outer diameter O2 of the expandable metal sleeve 8 in an unexpanded condition. In this way, the eutectic material 14 is not hindering insertion of the annular barrier 1 into the well. In the intermediate condition, the eutectic material 14 may be at least partly in a liquid state.
The first zone 101 may be a production zone, and the eutectic material 14 is arranged in the second zone 102 so that when the eutectic material enters the annular space 11 displacing fluid in the annular space, the lower pressure in the first zone will assist the fluid out of the annular space through the equalising fluid channel 24 due to the lower pressure in the production zone. In some wells, the pressure in the non-producing zone is lower than the pressure in the producing zone, and in such wells the eutectic material is in its first condition arranged in the second non-producing zone.
As shown in Figs. 1 and 6, a downhole system 100 is disclosed comprising the annular barrier 1 and the downhole tool string 50 comprising the heating unit 54 for heating the eutectic material 14.
By "fluid" or "well fluid" is meant any kind of fluid that may be present in oil or gas wells downhole, such as natural gas, oil, oil mud, crude oil, water, etc. By "gas" is meant any kind of gas composition present in a well, completion or open hole, and by "oil" is meant any kind of oil composition, such as crude oil, an oil-containing fluid, etc. Gas, oil and water fluids may thus all comprise other elements or substances than gas, oil and/or water, respectively.
By "annular barrier" is meant an annular barrier comprising a tubular metal part mounted as part of the well tubular metal structure and an expandable metal sleeve surrounding and connected to the tubular metal part defining an annular barrier space.
By "casing" or "well tubular metal structure" is meant any kind of pipe, tubing, tubular, liner, string, etc., used downhole in relation to oil or natural gas production.
In the event that the tool is not submergible all the way into the casing, a downhole tractor can be used to push the tool all the way into position in the well. The downhole tractor may have projectable arms having wheels, wherein the wheels contact the inner surface of the casing for propelling the tractor and the tool forward in the casing. A downhole tractor is any kind of driving tool capable of pushing or pulling tools in a well downhole, such as a Well Tractor^®.
Although the invention has been described above in connection with preferred embodiments of the invention, it will be evident to a person skilled in the art that several modifications are conceivable without departing from the invention as defined by the following claims.

Claims

An annular barrier (1) for expansion in an annulus (103) between a first well tubular metal structure (3a) and an inner face (4) of a borehole (5) or a second well tubular metal structure (3) for providing zone isolation between a first zone (101) and a second zone (102) of the annulus, the annular barrier having a first axial extension (2), where the annular barrier comprises:
- a tubular metal part (6) for mounting as part of the first well tubular metal structure, the tubular metal part having an outer face (7),

- an expandable metal sleeve (8) surrounding the tubular metal part and having an outer face (9) facing towards the inner face of the borehole or the second well tubular metal structure and an inner face (10) facing the outer face of the tubular metal part, a second axial extension along the first axial extension, and each end (31, 32) of the expandable metal sleeve being connected with the tubular metal part,

- an annular space (11) between the expandable metal sleeve and the tubular metal part,

- an expansion opening (12) in the tubular metal part through which fluid may enter the annular space in order to expand the expandable metal sleeve, and wherein the annular barrier further comprises a eutectic material (14) which in a first condition is arranged on the outer face of the tubular metal part in a first axial position (51) different from the second axial extension of the expandable metal sleeve, and in a second condition and a second axial position (52) the eutectic material abuts a face (9, 10) of the expandable metal sleeve, and in an intermediate condition the eutectic material is positioned between the first axial position and the second axial position.
An annular barrier according to claim 1, further comprising a fluid communication channel (15) having a first opening (16) in a first axial channel position (21), and the fluid communication channel extending towards a second opening (17) in a second axial channel position (22), where the second axial channel position overlaps or abuts an axial position (23) of the expandable metal sleeve, and in the first condition the eutectic material is arranged upstream to the first opening, and in the second condition the eutectic material abuts the face of the expandable metal sleeve downstream to the second opening.
An annular barrier according to claim 2, wherein one of the ends of the expandable metal sleeve is connected with the tubular metal part by means of a connection part (41, 42), and the fluid communication channel extends through the connection part, providing fluid communication to the annular space.
An annular barrier according to any of the preceding claims, wherein in the second condition the eutectic material overlaps the second axial extension.
An annular barrier according to claim 2, wherein the fluid communication channel is arranged to partly abut part of the outer face of the expandable metal sleeve.
An annular barrier according to any of the preceding claims, further comprising a chamber (19) arranged on the outer face of the tubular metal part; in the first condition, the eutectic material is in powder form arranged in the chamber.
An annular barrier according to any of claims 1-5, wherein the eutectic material is a solid block of eutectic material.
An annular barrier according to claim 7 when dependent on claims 2-5, wherein the chamber has a chamber opening (20) in fluid communication with the first opening of the fluid communication channel.
An annular barrier according to any of the preceding claims, wherein in the second condition the eutectic material is arranged at least partly on the outer face of the expandable metal sleeve.
An annular barrier according to any of claims 1-9, wherein in the second condition the eutectic material is arranged at least partly in the annular space.
An annular barrier according to any of the preceding claims, further comprising an equalising fluid channel (24) providing fluid communication between the annular space and the annulus for allowing fluid within the annular space to flow out of the annular space when the eutectic material is displacing the fluid.
An annular barrier according to claim 3, wherein the first opening and the second opening are arranged in the connection part.
An annular barrier according to claims 2-5, wherein the first opening, in the first condition, is abutting the eutectic material.
An annular barrier according to any of the preceding claims, wherein in the first condition the eutectic material extends at least partly around a circumference of the tubular metal part.
Downhole system comprising the annular barrier according to any of claims 1-14 and a downhole tool string (50) comprising a heating unit (54) for heating the eutectic material.