NO20191144A1

NO20191144A1 - A well tool device comprising a heat insulation device and associated method for permanently plugging and abandoning a well

Info

Publication number: NO20191144A1
Application number: NO20191144A
Authority: NO
Inventors: Stian Tøndel; Gaute Sandvik
Original assignee: Interwell P&A As
Priority date: 2019-09-23
Filing date: 2019-09-23
Publication date: 2021-03-24

Description

The invention relates to a well tool device and a method for permanently plugging and abandoning a well.

Background of the invention

Plugging and abandonment operations, often referred to as P&A operations, are performed to permanently close oil and/or gas wells. Typically, this is performed by providing a permanent well barrier above the oil and/or gas producing rock types, typically in the cap rock in which the well has been drilled through.

To meet governmental requirements during plugging and abandonment (P&A) operations in a well, a deep set barrier must be installed as close to the potential source of inflow as possible, covering all leak paths. A permanent well barrier shall extend across the full cross section area of the well, including all annuli, and seal both vertically and horizontally in the well. This requires removal of tubing mechanically, or perforating tubulars followed by washing behind the tubulars. This will lead to that swarf and debris from for example mechanical milling, need to be cleaned out of all flowlines, including the BOP system, to the rig, either provided onshore or offshore. Normally cement is used for the purpose of P&A operations. However, the well barrier has to comply with all of the following requirements for a P&A plug; a) impermeability, b) long term integrity, c) non shrinking, d) ductility (non brittle) – able to withstand mechanical loads or impact, e) resistance to different chemicals/ substances (H2S, CO2 and hydrocarbons) and f) wetting - to ensure bonding to steel.

In WO 2013/135583 A1 (Interwell P&A AS) it is described a method of performing P&A operations, using a heat generating mixture (also denoted pyrotechnic mixture), e.g. a thermite mixture. Thermite is normally known as a pyrotechnic composition of a metal powder and a metal oxide. The metal powder and the metal oxide produce an exothermic oxidation-reduction reaction known as a thermite reaction. A number of metals can be the reducing agent, e.g. aluminium. If aluminium is the reducing agent, the reaction is called an aluminothermic reaction. Most of the varieties are not explosive, but may create short bursts of extremely high temperatures focused on a very small area for a short period of time. The temperatures may reach as high as 3000°C. In a first step in the method of WO2013/13558, it is provided an amount of a heat generating mixture (for example thermite) at a desired location in the well which heat generating mixture is thereafter ignited in order to start a heat generation process. It is also disclosed a tool for transporting the heat generating mixture into the well before ignition. Such a heat generating mixture may also be referred to as a pyrotechnic mixture.

During the last years, this technology has tested in test centers and in field trials , in order to verify that the permanent well barrier fulfills technical and regulatory requirements.

In some tests it was discovered that the permanent well barrier had thin layers or zones in which the bonding between the materials forming the permanent well barrier was weaker than other parts of the permanent well barrier.

An objective of the present invention is to provide a method for permanent plugging and abandonment of a well with a more homogenous permanent well barrier compared to prior art solutions.

Summary of the invention

According to the invention, it is at least partially prevented that molten material, i.e. melted pyrotechnic mixture and other materials melted by the heat generation process flow to an undesired location during the heat generation process.

It is described a well tool device for forming a permanent barrier in a well, comprising:

- a housing in which a compartment is provided;

- a pyrotechnic mixture provided within the compartment, where the pyrotechnic mixture is configured to generate heat during a heat generation process;

- the pyrotechnic mixture comprises a particulate of a first metal and a particulate metal oxide of a second metal in an over-stoichiometric amount relative to a red-ox reaction; where the first metal is oxidized to a metal oxide and the second metal is reduced to elementary metal;

- the first metal is a different metal than the second metal;

wherein that the well tool device further comprises:

- a heat insulation device provided below the pyrotechnic mixture.

The heat insulation device us preferably arranged such that, upon ignition of the pyrotechnic mixture, a smelting bath formed by the pyrotechnic mixture and surrounding materials are forced out sideways, i.e. radially or substantially horizontally, and is prevented from escaping downwardly in the well. In other words, the heat insulation device assists in that the reaction materials form a permanent barrier which penetrates surrounding materials mainly radially (and in a direction towards the surface of the well).

The solution at least partially prevents that molten material, i.e. melted pyrotechnic mixture and other materials melted by the heat generation process flow away from the heat generation process due to gravity, e.g. axially if the well tool device is arranged in a vertical wellbore.

In an aspect, the heat insulation device may comprise a closed bottom section and a side section protruding upwardly and along the periphery of the bottom section.

In order to provide a larger smelting bath with reduced risk of smelt escaping sideways, the heat insulation device may form a cup-shaped, bowl-shaped or concave-shape where the reaction takes place.

The heat insulation element may be provided as different sections connected or fixed to each other, alternatively, it can be manufactured as one single body which is provided within the lower housing section or which is connected to the lower housing section.

The heat insulation device may have a longitudinal center axis and a radial cross section perpendicular to the longitudinal center axis and the heat insulation device may extend over parts of the radial cross section of the well tool device.

The heat insulation device may extend over a complete cross section of the well tool device. This prevent that the smelt bath (reaction materials) escapes downwardly and allows smelt bath to form.

The heat insulation device may comprise graphite, carbon or ceramic material.

Graphite (either synthetic or natural carbon-based), carbon materials and ceramic materials have a very high melting temperature (3800 K ~3523 °C) and will withstand the temperatures which occurs upon ignition of the pyrotechnic mixture. Thus, the smelt from the pyrotechnic mixture will be prevented from falling downwardly by the heat insulation device.

The well tool device may further comprise an igniter for igniting the pyrotechnic mixture.

In one aspect, the igniter may be arranged within the compartment. There may be several igniters provided at different positions in the compartment, preferably arranged along the longitudinal extension of the compartment, either side-by-side or in a spaced apart relationship. In aspects where the intermediate housing section is the consumable housing section, the igniter may be provided in the upper, intermediate or lower housing section. The igniter can also be provided axially aligned throughout the entire length of the tool.

In another aspect, the well tool device itself does not comprise an igniter, as the pyrotechnic mixture is ignited by heat from an adjacent well tool device. This adjacent well tool device may comprise an igniter.

The housing may comprise a lower housing section, an intermediate housing section and an upper housing section, wherein at least one of the housings is formed of different material than at least one other of the housings. I.e., when the well tool device is installed in a well, the lower housing section is the part of the well tool device closest to the bottom of the well whereas the upper housing section is the part of the well tool device closest to the top of the well.

The lower housing section may comprise the heat insulation device.

In one aspect, the height of the intermediate housing section is equal to or more than 30% of a total height) of the lower housing section, the intermediate housing section and the upper housing section.

In one aspect, the housing is cylindrical.

The lower housing section may comprise a bottom section, a sidewall and an open top end and the heat insulation device may be arranged inside the lower housing section.

The lower housing section may comprise an open bottom end, a sidewall and an open top end and the heat insulation device may comprise a flange portion connectable to the lower housing section. This may have the advantage that a larger smelting bath with reduced risk of smelt escaping sideways is formed.

The lower housing section may comprise a closed bottom end, a sidewall and an open top which form a cup or bowl or concave shape where the reaction takes place.

The lower housing section may be formed of a material of a relatively larger strength compared to the intermediate housing section. Such material may be a material for increased strength, such as steel, which has a relatively high melting temperature and which is a relatively strong and cost effective material. However, other materials with the desired properties can be used.

The intermediate housing section may be a consumable housing section made from a material which is consumed during the heat generation process.

The intermediate housing section can be made from one of the reactants consumed during the reaction process. The reactant material can be aluminium. Aluminum can further reduce the weight of the well tool device). However, other reactants than aluminium can be used. In principle, any metals which both can function as a reactant material (i.e. «fuel» in the chemical reaction) and which have an impact on structural strength can be used, such as, but not limited to: Aluminium, Magnesium, Mangan, Vanadium,Chrom, Titanium, Cobalt, Molybdenum, boron. In addition, alloys with specific function can also be used.

In prior art, the whole housing was made from steel. According to the invention, the amount of steel in the solid permanent barrier resulting from the heat generat ion process is reduced. Hence, the solid permanent barrier will be more homogenous, thereby avoiding or at least reducing weaker layers or zones in the permanent well barrier.

The first metal is more reactive than the second metal as defined in a reactivi ty series of metals.

The first metal may be one of the following metals: Mg, Al, Ti, Mn, V, Zn, Cr, Mo, Co, Ni, Sn, Pb, Cu, or B.

In a preferred embodiment, the first metal is aluminum or an aluminum alloy.

The metal oxide of the second metal may be one of: copper(II) oxide, chromium(III) oxide, iron(II, III) oxide, manganese(IV) oxide, silicon dioxide, boron trioxide, or lead(II, IV) oxide.

It is further described a method of forming a permanent barrier in a well using a well tool device, wherein the well tool device comprises: a housing in which a compartment is provided, a pyrotechnic mixture provided within the compartment , wherein the pyrotechnic mixture comprises a particulate of a first metal and a particulate metal oxide of a second metal in an over-stoichiometric amount relative to a red-ox reaction; where the first metal is oxidized to a metal oxide and the second metal is reduced to elementary metal; the first metal is a different metal than the second metal, and a heat insulation device provided below the pyrotechnic mixture, wherein the method comprises the steps of:

- lowering the well tool device to a melting position in the well,

- igniting the pyrotechnic mixture, thereby starting a heat generating process which takes place above the heat insulation device.

In an aspect, the method further comprises a step of allowing pyrotechnic mixture to be fed to the heat generating process.

The advantage of said method steps may, i.a. result in that melted materials are prevented from escaping the heat generating process to a position below (e.g. gravity) the by the heat insulation device and that the melted materials from the heat generating process instead is guided to expand radially guided by the heat insulation device.

As used herein, the term “pyrotechnic mixture” is a particulate mixture of a first metal and an oxide of a second material, which when heated to an ignition temperature will react spontaneously in an exothermic and self-sustained chemical reaction where the first metal is oxidized to a metal oxide and the second metal is reduced to elementary metal. I.e. the pyrotechnic mixture can be defined as any substance or mixture of substances designed to produce an effect by heat, light, sound, gas/smoke or a combination of these, as a result of non-detonative selfsustaining exothermic chemical reactions. Pyrotechnic substances do not rely on oxygen from external sources to sustain the reaction.

An example of a possible reaction may be the the reaction between particulate ferric oxide and particulate aluminium:

Other examples are presented in the detailed description below.

After ignition, the pyrotechnic mixture will burn with a temperature of up to 3000°C and melt a great part of the proximate surrounding materials, with or without the addition of any additional metal or other meltable materials to the well.

The surrounding materials may include any material normally present in the well, and can be selected from a group comprising, but not limited to: tubulars, e.g. casing, tubing and liner, cement, formation sand, cap rock etc. The heat from the ignited mixture will melt a sufficient amount of said materials. When the pyrotechnic mixture has burnt out, the melted materials will solidify forming a reservoir sealing barrier. If the ignition is at the cap rock, the reservoir sealing barrier melts and bonds in a transition area with the cap rock forming a continuous cap rock - to - cap rock barrier. This reservoir sealing barrier seals from inflow from any reservoir(s) below the reservoir sealing barrier. The operation is particularly suitable in vertical sections of the well, but may also be suitable in deviating or diverging sections such as horizontal sections or sections differing from a vertical section.

The sufficient amount of pyrotechnic mixture, e.g. thermite mixture, varies dependent on which operation that is to be performed as well as the design well path. As an example, NORSOK standard D-010, which relates to well integrity in drilling and well operations, defines that a cement plug shall be at least 50 meters and in some operations up to 200 meters when used in abandonment operations. For example, one may fill whole of the inner volume of the pipe. A pipe having an inner diameter of 0,2286 m (95/8”) has a capacity of 0,037 m<3 >per meter pipe. In order to provide a 50 meter plug by means of the method according to the invention, one would need 1,85 m<3 >pyrotechnic mixture comprising thermite. Similarly, if a cement plug of 200 meters is required, the amount of first pyrotechnic mixture needed would be 7,4 m<3>. It should though be understood that other plug dimensions may be used, as the plug provided by means of the invention will have other properties than cement and the NORSOK standard may not be relevant for all applications and operations. Any amount of pyrotechnic mixture may be used, dependent on the desired operation, the properties of the pyrotechnic mixture and the materials.

The desired amount of pyrotechnic mixture is prepared at the surface and positioned in the well tool device. The mixture may for example be a granular or powder mixture. The well tool device may be any well tool device suitable for lowering into a well, and may preferably have a circular cross section of the same, or smaller size as the inner diameter of any present tubing, other pipe(s) or open hole section(s) in the well bore. Dependent on the desired operation, the well tool device, or a set of a number of well tool devices, may be a short or a long well tool device. In a P&A operation, where the need of a large melting area is desired, the set of well tool devices may be several meters, ranging from 1 meter to 1000 meters.

In an aspect, a timer can be arranged in connection with the igniter. A timer function might be favorable for example in situations where a number of wells are to be abandoned at nearby locations, e.g. from the same template. If used offshore, the timer in each well may be set to ignite at the same time, or at different times, subsequent to that the operation vessel has left the location. This reduces the risk of personal injury.

The pyrotechnic mixture may comprise a thermite mixture, however other pyrotechnic mixtures might be used.

As used herein, the term “the first metal is more reactive than the second metal” means that the first metal of the pyrotechnic mixture has a higher reactivity than the second metal of the metal oxide. The reactivity of metals is determined empirically and given in reactivity series well known to the person skilled in the art. An example of a reactivity series of metals is found in e.g. Wikipedia: https://en.wikipedia.org/wiki/Reactivity_series

The relative terms “upper”, “lower”, “below”, “above”, “higher” etc. shall be understood in their normal sense and as seen in a cartesian coordinate system. When mentioned in relation to a well, “upper” or “above” shall be understood as a position closer to the surface of the well (relative to another component), contrary to the terms “lower” or “below” which shall be understood as a position further away from the surface of the well (relative another component).

By the use of the described invention, all operations can be performed onshore and, if in water, from a light well intervention vessel or similar, and the need for a costly rig is eliminated. Prior to the ignition of the pyrotechnic mixture, the well may be pressure tested to check if the seal is tight. This might be performed by using pressure sensors or other methods of pressure testing known to the person skilled in the art.

The invention will now be described in non-limiting embodiments and with reference to the attached drawings, wherein:

Brief description of the drawings

Fig. 1A is an overview of a setup of a prior art well tool device 10 as disclosed in the Applicant’s own publication WO 2013/135583 A prior to the ignition of the pyrotechnic mixture;

Fig. 1B shows the situation after ignition of the pyrotechnic mixture when a permanent barrier has formed in the well;

Fig. 2 shows a well tool device 10 according to the present invention prior to the ignition of the pyrotechnic mixture;

Fig. 3A shows a well tool device;

Fig. 3B is a cross-section view along line A – A in Fig. 3A;

Figs. 4A-H show examples of the relationship between the heat insulation device and the lower housing section;

Detailed description of a preferential embodiment

Fig. 1A shows an overview of a setup of a prior art system disclosed in the Applicant’s own publication WO 2013/135583 A. Fig. 1A indicates the situation prior to the ignition of a pyrotechnic mixture 40. A vertical well bore WB has been drilled in a formation F. The wellbore WB is provided with casing CA cemented to the formation wall (not shown), and a tubing or liner TBG in the lowermost part of the well bore WB. In a lower part of the well bore WB a first permanent plug 4 has been set. A first high temperature resistant element 5, such as ceramic element or glass element, is arranged above the first permanent plug 4 to protect the first permanent plug 4. A pyrotechnic mixture 40, e.g. a thermite mixture, is arranged above the first high temperature resistant element 5. Similarly, there may be arranged a second high temperature resistant element 7 as well as a second permanent plug element 8 above the pyrotechnic mixture 40. In addition, an igniter 50, for ignition of the pyrotechnic mixture 40, can be arranged in connection with the pyrotechnic mixture 40. A timer element 9 may be arranged to time set the detonation of the igniter 50, and thus the pyrotechnic mixture 40.

Fig. 1B shows the situation after ignition of the pyrotechnic mixture when a permanent barrier PB has formed in the well. As is clear from Fig. 1B, all surrounding materials close to the position of the pyrotechnic mixture of Fig. 1A have been subject to heat from the ignition of the pyrotechnic mixture 40 and melted due to this heat.

Fig. 2 shows a well tool device 10 according to the present invention, prior to the ignition of the pyrotechnic mixture 40. The well tool device 10 is lowered in the well bore WB to the depth of the cap rock CR e.g. by using a lowering tool such as a wire line tool WLT. A vertical well bore WB has been drilled in a formation F through the cap rock CR and into the reservoir R. The reservoir R may be any reservoir R holding a natural resource such as hydrocarbons (oil/gas/condensates), water, geothermal energy (heat etc.) or serve as an injection reservoir for nuclear waste, CO2 capture, radioactive materials etc.

The well bore is provided with casing CA cemented with cement CE to the formation wall, and a tubing or liner TBG in the lowermost part of the well bore WB. In a lower part of the well a first permanent plug 4 has been set. A first high temperature resistant element 5, such as ceramic element or glass element or a plug formed of a pyrotechnic mixture with a lower reaction temperature such that it may solidify inside the tubing or liner TBG, is arranged above the first permanent plug 4 in order to protect the first permanent plug 4. However, the presence of the f irst permanent plug 4 and the first high temperature resistant element 5 is optional as there may be other means or material which provide the same effect as these elements. For example, a heat insulation device, possibly in combination with a permanent plug, may form an integral part of the well tool device 10. Then the need of an additional high temperature resistant element 5 below the well tool device 10 may be superfluous.

Further referring to Fig. 2, the well tool device 10 may further comprise a housing 20. The housing 20 may enclose a fluid tight compartment 30, in which compartment 30 the pyrotechnic mixture 40 can be arranged. A heat insulating device 60 can be arranged in a lower part of the well tool device 10. An igniter head 11 or igniter can be arranged in connection with the pyrotechnic mixture 40.

The lowering tool, e.g. wire line tool WLT 2, may be used for lowering at least one of the first permanent plug 4, the first high temperature resistant element 5, the pyrotechnic mixture 40 and/or the igniter 50.

Fig. 3A shows a well tool device 10 which can be used in the setup of Fig. 2, while Fig. 3B is a cross-section view along line A – A in Fig. 3A.

Referring to Figs. 3A and 3B the well tool device 10 comprises a housing 20 in which a compartment 30 is provided, where a pyrotechnic mixture 40 is provided within the compartment 30. The pyrotechnic mixture 40 is here shown as grey dots, illustrating the particles forming the pyrotechnic mixture 40. The pyrotechnic mixture 40 may comprise a particulate of a first metal and a particulate metal oxide of a second metal, different from the first metal, in an over-stoichiometric amount relative to a red-ox reaction where the first metal is oxidized to a metal oxide and the second metal is reduced to elementary metal.

The disclosed housing 20 is cylindrical and has a longitudinal center axis illustrated as a dashed line I-I. The total height of the housing 20 is illustrated as height H20tot.

The housing 20 comprises a lower housing section 20a, an intermediate housing section 20b and an upper housing section 20c. The upper housing section 20c is connected to a wireline 2. The lower housing section 20a has a height H20a, the intermediate section H20b has a height H20b and the upper housing section 20c has a height H20c, where the total height H20tot equals the sum of H20a, H20b and H20c. The height H20b may be 70 – 90% of the height H20tot. As an example, H20tot may be 4 meters, and H20b may be 3,2 meters.

It should be noted that the upper and lower housing sections 20a, 20b in Fig.3A are drawn with thicker lines than the intermediate housing section 20b. This is done for illustration purposes only and is not representative of the material thickness of these housing sections.

The housing sections 20a, 20b, 20c may be connected to each other by means of threaded connections, by means of fasteners such as screws etc., or by other means. In Fig. 3A, the lower housing section 20a comprises a heat insulation device 60, to at least partially prevent or delay that molten material flow to an undesired location such as e.g. axially downwards, during the heat generation process. The heat insulation device 60 may for example comprise carbon, graphite or a ceramic material.

The well tool device 10 may further comprise an igniter 50 adapted to heat at least a part of the pyrotechnic mixture 40 to its ignition temperature. Hence, when the pyrotechnic mixture is ignited, a pyrotechnic heat generating process starts, resulting in that casing and other parts outside of casing (cement, formation (i.e. cap rock) etc.) will start to melt. When the pyrotechnic heat generation process ends, a permanent barrier will have formed.

In fig. 3A, reference number 21 refers to a section of the housing 20. In Fig. 3A, the section 21 of the housing 20 corresponds to the intermediate section 20b of the housing 20.

The section 20b of the housing 20 may be made from a material being a constituent of the pyrotechnic mixture 40, e.g. preferably the first metal in the pyrotechnic mixture 40. Hence, during the heat generation process, the material of the section 21 will be consumed. In fig. 3A, the upper housing section 20c may be made of a steel material, similar to the steel material used for the entire housing 20 in prior art, whereas the lower housing section 20a may be made of steel and support the heat insulation device 60. Alternatively, the lower housing section 20a may be the heat insulation device 60. Hence, the total amount of steel material is reduced. It is assumed that this contributes to a more homogenous permanent well barrier after the heat generation process.

Fig. 4A shows a cylindrical lower housing section 20a with open top and the hemispheric heat insulation device 60 inside the lower housing section 20a.

Fig. 4B shows a cylindrical lower housing section 20a with an open top where the heat insulation device 60 forms part of the lower housing section 20a.

Fig. 4C shows a hemispheric lower housing section 20a with an open top and the heat insulation device 60 arranged inside the hemispheric lower housing section 20a. The lower housing section 20a is illustrated as reinforced relative the intermediate housing section 20b and may e.g. be made of steel.

Fig. 4D shows a cylindrical lower housing section 20a with an open top where the lower housing section 20a comprises the heat insulation device 60. The lower housing section 20a is illustrated as reinforced relative the intermediate housing section 20b and may e.g. be made of steel.

Fig. 4E shows an example of the lower housing section 20a and/or the heat insulation device 60 having a frusto-conical shape tapering downwards and with an open top for receiving the pyrotechnic mixture 40 (not shown in Fig. 4E).

Fig. 4F shows an example of the lower housing section 20a and/or the heat insulation device 60 having a hemispheric or round bowl shape with an open top for receiving the pyrotechnic mixture 40 (not shown in Fig. 4F).

Fig. 4G shows an example of the lower housing section 20a and/or the heat insulation device 60 having a cylindrical shape with open top for receiving the pyrotechnic mixture 40 (not shown in Fig. 4G).

Fig. 4H shows an example of the lower housing section 20a and/or the heat insulation device 60 having a cylindrical shape with open top for receiving the pyrotechnic mixture 40 (not shown in Fig. 4H). A bottom part of the lower housing section 20a and/or the heat insulation device 60 is connected to a flange portion 62 for connection to the housing 20.

The pyrotechnic mixture 40 and the pyrotechnic process will be described in detail below.

The pyrotechnic process

The pyrotechnic mixture 40 comprises a particulate of a first metal and a particulate metal oxide of a second metal in an over-stoichiometric amount relative to a red-ox reaction.

The first metal is oxidized to a metal oxide and the second metal is reduced to elementary metal where the first metal is a different metal than the second metal. Heat is a result of this reaction.

One example of such a pyrotechnic mixture is the following:

Fe2O3 + 2 Al → 2 Fe Al2O3 + heat (1)

Here, the first metal is aluminum (Al) and the second metal is iron oxide (Fe2O3). The first metal is oxidized to the metal oxide aluminum oxide (Al2O3) and the second metal is reduced to the elementary metal iron (Fe). Heat is produced during this process, which often is referred to as a thermite process.

In the above example, the first metal is more reactive than the second metal as defined in a reactivity series of metals.

In alternative embodiments for such a reaction, the first metal may be of the following metals Mg, Al, Ti, Mn, V, Zn, Cr, Mo, Co, Ni, Sn, Pb, Cu, or B and the metal oxide of the second metal is one of: copperII oxide, chromiumIII oxide, ironII, III oxide, manganeseIV oxide, silicon dioxide, boron trioxide, or leadII, IV oxide. When combining the above, the first metal is more reactive than the second metal as defined in a reactivity series of metals.

Some examples of alternative processes, in which the first metal is aluminum, are disclosed below:

It should be noted that the heat produced in the above processes will vary from process to process. In addition, the speed of the reaction will vary from process to process. Factors that can influence the above characteristics may be the selected materials reactivity and particle size. In an alternative process, aluminium (Al) can be swapped with magnesium in all of the above exemplified alternative processes.

As mentioned above, it is also possible to use magnesium as the first metal, as disclosed below:

As described above, at least a section 21 of the housing 20 is made of the first metal. Hence, the section 21 may be made of aluminum or an aluminum alloy, where the pyrotechnic reaction is one of reactions (1) – (6) above.

In a preferred embodiment, the first metal is aluminum or an aluminum alloy.

Suitable aluminum alloys may be the 6000/7000/8000 series of aluminum alloys, as defined by International Alloy Designation System (IADS). One preferred aluminum alloy is the 7075-T6 aluminum alloy.

Alternatively, the section 21 may be made of magnesium or a magnesium alloy, where the pyrotechnic reaction is reaction (7) above.

Magnesium alloys may comprise for example aluminum, zinc, manganese, silicon, copper, rare earth minerals and zirconium.

It should be noted that Fe2O3 is the metal oxide in both reaction (2) and (7) above. Hence, section 21 may also comprise an alloy containing both aluminum and magnesium.

It should be noted that even though the section 21 of the housing 20 is made of the first metal, the first metal may also be present as a particulate material together with the metal oxide of the second metal as a particulate material in the compartment 30. Hence, the pyrotechnic mixture 40 may comprise particulate material of the first metal and particulate material of the metal oxide of the second metal. In addition, the pyrotechnic mixture 40 may comprise additives. Such additives may be used to control (increase or decrease) temperature of the process, to control (increase or decrease) viscosity of the process, to control rheological or thermodynamic properties. Additives, such as silicates or clay minerals, may also be used to establish a more mineralogical suitability with the host rock in which the process is to be performed.

The embodiments disclosed in the figures provide a proposed solution to the object of the invention, which is to provide a method for permanent plugging and abandonment of a well with a homogenous permanent well barrier.

It should further be noted that the surface of the inner surface of the housing 20 may be coated. The effect of the coating is primarily to be able to control the heat transfer between an outside of the tool and an inside of the tool at different positions axially. Coating may be performed in order to control heat flux to surrounding elements and concentrate heat generated in reaction to specific positions axially in tool body. Furthermore, coating could be used to decrease heat impact from specific zones in tool, i.e. metal phase which has high conductivity and heat capacity towards the host rock, resulting in lower thermal shock and stress. In addition, coating could also be used to reduce heat loss through tool body resulting in premature solidification of oxide phases. Examples of coating can be liquid carbide coatings, zirconia-based oxides, aluminum oxide etc.

The invention is herein described in non-limiting embodiments. It should though be understood that the embodiments may be envisaged with a lower or higher number of permanent plugs and high temperature resistant elements. The skilled person will understand if it is desirable to set none, one, two or several permanent plugs dependent on the desired operation. Similarly, the number of high temperature resistant elements positioned in the well may vary from zero, one, two or several, dependent on the operation.

REFERENCE LIST:

Claims

1. A well tool device (10) for forming a permanent barrier in a well (WE), comprising:

- a housing (20) in which a compartment (30) is provided;

- a pyrotechnic mixture (40) provided within the compartment (30), where the pyrotechnic mixture (40) is configured to generate heat during a heat generation process;

- the pyrotechnic mixture (40) comprises a particulate of a first metal and a particulate metal oxide of a second metal in an over-stoichiometric amount relative to a red-ox reaction; where the first metal is oxidized to a metal oxide and the second metal is reduced to elementary metal;

- the first metal is a different metal than the second metal;

characterized in that the well tool device (10) further comprises:

- a heat insulation device (60) provided below the pyrotechnic mixture (40).

2. The well tool device (10) according to claim 1, wherein the heat insulation device (60) comprises a closed bottom section and a side section protruding upwardly and along the periphery of the bottom section.

3. The well tool device (10) according to any of the preceding claims, wherein the well tool device (10) the heat insulation device (60) has a longitudinal center axis and a radial cross section perpendicular to the longitudinal center axis and wherein the heat insulation device (60) extends over parts of the radial cross section of the well tool device (10).

4. The well tool device (10) according to any of the preceding claims 1-8, wherein the heat insulation device (60) extends over a complete cross section of the well tool device (10).

5. The well tool device according to any of the preceding claims, wherein the heat insulation device (60) comprises graphite, carbon or ceramic material.

6. The well tool device (10) according to claim 1 or 2, further comprising:

- an igniter (50) for igniting the pyrotechnic mixture (40).

7. The well tool device (10) according to any of the preceding claims, wherein the housing (20) comprises a lower housing section (20a), an intermediate housing section (20b) and an upper housing section (20c), wherein at least one of the housings (20a, 20b, 20c) is formed of different material than at least one other of the housings (20a, 20b, 20c).

8. The well tool device (10) according to claim 7, wherein the lower housing section (20a) comprises the heat insulation device (60).

9. The well tool device (10) according to any of the preceding claims 7 or 8, wherein the lower housing section (20a) comprises a bottom section, a sidewall and an open top end and wherein the heat insulation device (60) is arranged inside the lower housing section (20a).

10. The well tool device (10) according to any of the preceding claims 7-9, wherein the lower housing section (20a) comprises an open bottom end, a sidewall and an open top end and wherein the heat insulation device (60) comprises a flange portion (62) connectable to the lower housing section (20a).

11. The well tool device (10) according to claims 8 or 9, wherein the lower housing section (20a) is formed of a material of a relatively larger strength compared to the intermediate housing section (20b).

12. The well tool device (10) according to any of the preceding claims, wherein the intermediate housing section (20b) is a consumable housing section made from a material which is consumed during the heat generation process.

13. Well tool device (10) according to claim 1, where the first metal is more reactive than the second metal as defined in a reactivity series of metals.

14. Well tool device (10) according to any of the preceding claims, wherein the first metal is one of the following metals: Mg, Al, Ti, Mn, V, Zn, Cr, Mo, Co, Ni, Sn, Pb, Cu, or B.

15. Well tool device according to any one of the preceding claims, wherein the metal oxide of the second metal is one of: copper(II) oxide, chromium(III) oxide, iron(II, III) oxide, manganese(IV) oxide, silicon dioxide, boron trioxide, or lead(II, IV) oxide.

16. Method of forming a permanent barrier in a well (WE) using a well tool device (10), wherein the well tool device comprises: a housing (20) in which a compartment (30) is provided, a pyrotechnic mixture (40) provided within the compartment (30), wherein the pyrotechnic mixture (40) comprises a particulate of a first metal and a particulate metal oxide of a second metal in an over-stoichiometric amount relative to a red-ox reaction; where the first metal is oxidized to a metal oxide and the second metal is reduced to elementary metal; the first metal is a different metal than the second metal, and a heat insulation device (60) provided below the pyrotechnic mixture (40), wherein the method comprises the steps of:

- lowering the well tool device (10) to a melting position in the well,

- igniting the pyrotechnic mixture (40), thereby starting a heat generating process which takes place above the heat insulation device (60).

17. The method according to claim 12, where the method comprises the following step:

- allowing pyrotechnic mixture (40) to be fed to the heat generating process.