The invention relates to a well operation tool for forming a permanent well barrier which extends across a full cross section area of a well, including all annuli, and seal both vertically and horizontally in the well in a pressurized environment such as a subsurface environment, in water, subsea, downhole etc., as well as methods of forming said permanent well barrier using a well operation tool.

Background of the invention

When igniting and combusting an ignition material in a container in a pressurized environment, i.e. an environment of overpressure, there is a risk of ingress or inflow of surrounding pressurized fluids disturbing or, even worse, killing the ignition process before it has had the time to finish and or react. This may be an issue if the ignition material, i.e. the material which is ignited (typically black powder, metal, oxides etc.), upon ignition melts a hole in the container where the process takes place or if the container collapses due change in properties of the container as a result of heating, which may lead to that the differential pressure between the outside and the inside of the container collapses the container. This process may be an igniting process, such as a chemical reaction if metal and oxide are used as the ignition materials. Metal and oxide release a significant amount of heat during reaction, which heat may potentially melt a housing surrounding the combustion chamber, by creating a hole or similar in the combustion chamber. If the melting of the housing or similar occurs before the process has started or too early in the process, there is a risk that the surrounding pressurized fluids may enter the combustion chamber possibly killing the ignition process. If surrounding

pressurized fluids enter the process and expels the melt away from the area which is to be melted, the result may be that the desired operation is not fulfilled/finished satisfactorily. Additionally, if there is a significant overpressure on the outside of the combustion chamber/housing, a weakening of the housing due to heating from the exothermic reaction may result in a collapse of the housing due to the large pressure differential between the inside of the combustion chamber/housing and the surrounding pressurized fluids, which may lead to a risk of stopping or killing the igniting process.

Document WO 2015/1 16261 Al describes different embodiments of sealing a well by using thermite. One of said embodiments relates to a method of sealing a well, comprising the steps of; a) lowering a cylinder of thermite reaction charge into a well proximate to a target plug zone location where the well is to be plugged, b) igniting the thermite material, the ignited thermite material forming a reaction zone, and c) continuously supplying additional thermite reaction charge from the cylinder to the reaction zone after performing the ignition step. The cylinder has an upper and a lower end, and wherein the igniting step b) comprises igniting the lower end of the cylinder. However, tests have proved that this method will not give a satisfying ignition/reaction process. In this document, the initial heat generated from the thermite reaction will weaken the cylinder material. The large pressure differential between the inside of the cylinder and the surrounding pressurized fluids will lead to a collapse of the cylinder, which again will prevent continuous supply of additional thermite reaction charge from the cylinder and hence stop or at least delay the igniting process.

Therefore, it is an objective of the invention to provide a more reliable ignition and combustion in a pressurized environment and by this ensure that the combustion do not stop and the melt does not get expelled from the designated area.

More specifically, an objective of the invention is to prevent, minimize, or at least delaying or reducing, the inflow of surrounding pressurized fluids during an ignition process or when the melt penetrates the tool and gets exposed to the surrounding overpressurized environment.

A third objective is to enable ignition by continuous feed of ignition material without the risk of collapse of the housing or ingress of fluids or gasses during the ignition or burning process.

Summary of the invention The applicant has devised and embodied a solution which provides a successful ignition in an over-pressurized environment compared to prior art solutions.

The invention is applicable for use in plugging and abandonment (P&A) of wells, for permanently sealing a storage of nuclear waste (i.e. radioactive material), C02, etc. In locations below the water table, the pressure may be substantial and thus, have to be taken into account if the ignition process takes place in these locations. In addition, in order to make sure that a proper seal has been made, it may be advantageous to make the seal at the depth of the cap rock in the well. The cap rock, i.e. the natural geological sealing rock may be at different depths at different locations. The invention is set forth and characterized in the independent claims, whereas the dependent claims describe alternative embodiments of the invention.

First embodiment, using a gas-releasing material for pressurizing the housing

According to the present invention inflow or ingress of surrounding pressurized fluids, e.g. water, hydrocarbons (oil, gas, condensate), are prevented, or at least, delayed. After ignition of the ignition material, the present invention ensures the presence of a sufficient pressure inside the combustion chamber to prevent inflow of the surrounding pressurized fluids. Hence, the ignition process is allowed to continue without disturbances from fluid inflow for a longer period of time than prior art solutions. Even if the housing surrounding the combustion chamber melts, i.e. if there is a hole in the housing, or collapses, the present invention will secure that the surrounding fluids are prevented from inflow.

The pressurized environment may be subsea or in geological formations such as downhole environment. However, the invention may also be used in atmospheric pressure conditions. When used subsea, the surrounding environment is typically water and the pressure is equal to the hydrostatic column of water above the position where the housing is used. If arranged in a well, the density of the well fluid is often higher than the density of water (density water = 1000 kg/m ³ ), resulting in an even heavier hydrostatic column than in pure water conditions. The pressure exerted by the hydrostatic column of water is a linear function in relation to the water depth, i.e. :

10 meter water depth ~ 1 bar

50 meter water depth ~ 5 bar

500 meter water depth ~ 50 bar

Hence, the hydrostatic column may create a significant pressure on the outside of the combustion chamber, and thus, a potential pressure difference between the inside of the combustion chamber and the outside of the combustion

chamber/housing is large if not compensated for. Therefore, the present invention has significant effect if used in areas of large pressure.

If used downhole, the pressurized environment may be water, air, hydrocarbon fluids, a gel used in displacement of another fluid, or a mixture thereof, which fluids may have a great variety of pressures, often significantly large pressures, which large pressures may incur problems in relation to the igniting process if there is pressure communication between the inside and the outside of the housing.

According to the present invention, it is provided a well operation tool for forming a permanent well barrier which extends across a full cross section area of a well, including all annuli, and seal both vertically and horizontally in the well in a pressurized environment, the pressurized environment having a pressure above 1 atmospheric pressure, the well operation tool comprises:

- a sealed housing;

- a combustion chamber provided within the housing;

- an ignition material provided within the combustion chamber;

- an ignition tool at least partly extending into the combustion chamber;

- a gas producing material provided within the combustion chamber;

wherein the gas producing material is adapted to release gas when subjected to a temperature above a threshold value due to ignition of the ignition material. Thus, the temperature increase due to ignition of the ignition material increases the pressure inside the combustion chamber. It is clear that the reaction in the ignition material (after ignition) may also contribute to the pressure increase inside the combustion chamber if the ignition material releases gas upon heating. The pressure increase due to the temperature increase causing the gas producing material releasing gas, results in an increased pressure inside the combustion chamber Then, if the melting of the housing or collapse of the housing takes place prior to the complete of the igniting process, i.e. the reaction process, the pressure increase resulting from the gas release of the gas producing material, prevent, or at least delays, the inflow of pressurized fluids from the surrounding pressurized

environment. If used in a well, the well may be a vertical well, a horizontal well, or a declined well (i.e. a well forming any angle between 0 and 180 degrees relative a vertical axis).

A well operation tool shall be understood as any tool which can be used anywhere inside a well, i.e. anywhere in a well extending from a surface location (topside on a floating vessel or on surface on land) down to the end of the well. Alternatively, the tool may be used in applications including removal of a well element such as a X- mas tree or similar. In the latter applications, the well operation tool may be used on the outside of the well itself for removal of a well element connected to the well. Examples of the latter applications may be to lower the well operation tool down to a subsea wellhead, either inside or outside of the well, and use it for removal of a component forming part of the well. In these situations, either the water (if arranged outside the well) or any other fluids inside the piping (riser, tubing etc.) may create the pressurized environment. According to the invention, the housing and or the combustion chamber may be gas- tight and may be made of a material able to withstand large differential pressures between an outside of the housing/combustion chamber and an inside of the housing. According to an aspect, the housing and combustion chamber can be separate elements or, alternatively, they may be formed of the same element. The combustion chamber is an enclosed space in which combustion takes place.

The housing may be formed of a material which enables the operator to control the strength, and also the melting temperature of the housing. The material can withstand large pressure differentials between the inside of the housing and the outside of the housing. For example, the inner volume of the housing, i.e. the pressure in the combustion chamber may be atmospheric pressure and the outside may be 500 bar or more. Similarly, the pressure in the inner volume may be larger than the outside pressure. Thus, the housing is able to withstand large pressure differentials both between the inner volume of the housing and the outside of the housing, and vice versa. Such materials may be any desired materials, including aluminum, aluminum alloys (e.g. 7075-T6), steel and composite materials such as carbon fiber. However, any other materials may also be used, such as steel, polymer etc., chosen to meet the demands in the specific project. The pressure-sealing of the housing may be done by welding, using o-ring(s) or other means of sealing.

After a while, when the ignition has started, firstly the gas producing material according to the present invention will provide for a pressure increase inside the combustion chamber and, if there is a hole in the combustion chamber or housing (and open to the surrounding environment), the pressure increase provided for by the gas producing material will prevent inflow of pressurized fluids and, in addition the heat generated from the ignition process will create a "heat front" against the fluids in the pressurized environment, preventing inflow.

A gas producing material shall be understood as any material or element which, when subjected to a temperature above a threshold temperature or pre-defined temperature, generates gas which again result in an increase of the pressure within the housing. The gas producing material is a volatile composition releasing gas upon heating above a threshold temperature. The gas producing material may be a solid media such as a polymer material, a carbonate, wooden material, or

alternatively a chemical composition, or combinations thereof. The polymers may include, but are not limited to Energetic polymers e.g. Glycidyl azide polymer, 3- nitratomethyl-3-methyloxetane or glycidyl nitrate. However other materials may be used. Hence, the gas producing material can be considered to be a pressure increasing material.

Alternatively, the gas producing material may be pellets, which pellets are mixed with the ignition material. If the ignition material comprises a binding agent, the gas producing material may form part of the binding agent. The term "exothermic mixture" shall be understood as any mixture which, when it reacts, enables a chemical or physical reaction that releases heat, e.g. a thermite reaction. That is, the reaction is exothermic if the medium in which the reaction takes place produces heat. This reaction gives net energy to its surroundings.

The amount of gas producing material depends on the demands in the specific project, such as:

Volume of the combustion chamber,

Amount of ignition material,

Pressure in the surrounding environment,

Composition of the ignition material,

- Composition of the gas producing material,

Material of the sealed housing,

Expected temperature within the combustion chamber,

etc. In an aspect, the ignition material comprises an oxide and a metal arranged to create an exothermic reaction upon ignition. The term exothermic mixture shall be understood as any mixture which, when it reacts, enables a chemical or physical reaction that releases heat, e.g. a thermite reaction. That is, the reaction is exothermic if the medium in which the reaction takes place produces heat. This reaction gives net energy to its surroundings. The exothermic mixture may comprise e.g. a thermite mixture. Thermite is normally known as an exothermic 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.

According to an aspect, the exothermic reaction is an aluminothermic reaction.

According to an aspect, the released gas from the temperature increase of the gas producing material provides for a pressure increase inside the combustion chamber, which pressure increase is sufficient to prevent inflow from the pressurized environment. The potential inflow may be a result of collapse of the housing and or, if there is melted a hole in the housing, by the heat generated from the ignition and subsequent reaction of ignition material. Such inflow may, as discussed above, be any kind of pressurized fluid or other material present in the pressurized

environment. Furthermore, the pressure increase inside the combustion chamber does not have to balance off the pressure in the pressurized environment for the invention to provide for the desired effect. In some instances, the pressure increase may result in a pressure which is less than the pressure in the pressurized

environment and still provide for the desired effect, alternatively in combination with the "heat front" generated from the ignition process as discussed above.

According to an aspect, the released gas from the temperature increase of the gas producing material provides for a pressure increase inside the combustion chamber, which pressure is at least equal to, or higher, than the pressure of the pressurized environment. According to an aspect the, the gas producing material releases nitrogen gas, but also other types of gases may be used. Nitrogen gas, or any other inert gases such as argon or other, may be preferred because they are relatively cheap and noble gases which hardly react with any other chemicals.

According to an aspect of the invention, the ignition material is adapted to be continuously fed after ignition of the ignition material. The ignition material may then be arranged in a housing formed as a cylinder or column of ignition material which is ignited by the ignition tool in the lower part such that reaction material is continuously fed by the force of gravity after the ignition material has been ignited. If gravity (or alternatively a mechanical force applied either as a replacement for gravity or in combination with gravity) is the feeding principle, the velocity of the reaction is relative slower than the velocity created by the gravity or mechanical supply, such that "fresh", i.e. undisturbed ignition material is supplied faster than the reaction. As a result, after reaction, the reaction zone formed in the well is in the range of 20 - 40% of the height of the column of ignition material prior to ignition. For example, if the initial height of the ignition material is 3 meters, the reaction zone will be approximately 1 meter. By having the tool with the gas releasing material in the same housing as the ignition material, building up the pressure inside the housing during reaction of the ignition material, the ignition or reaction process is allowed to continue even if the housing is weakened or if there is a large pressure in the pressurized environment.

In an aspect, the pressurized environment is surrounding water, such as seawater or fresh water. However, if the well has been displaced, the displacement fluid or material, such as displacement gel, may be the surrounding pressurized fluid.

According to another aspect, the pressurized environment is a downhole well, such as a hydrocarbon well, a water well or an earth heat well, where the surrounding fluids may be water, oil, gas, mud or a mixture of these. The well operation tool may be secured in the well by using known anchoring devices, such as slips. This will prevent the well operation tool from being blown upwards or downwards when the pressure inside the tool is released. This may particularly desired when the pressure inside the tool is higher than the surrounding pressurized environment. It is further described a method of forming a permanent well barrier which extends across a full cross section area of the well, including all annuli, and seal both vertically and horizontally in the well by preventing inflow of a fluid into a well operation tool, the well operation tool comprising a pressure-sealed housing and a combustion chamber provided within the housing, wherein the method comprises the steps of:

- arranging an ignition material, an ignition device and a gas producing material within the combustion chamber;

- positioning the well operation tool in a pressurized environment, the pressurized environment, having a pressure above 1 atmospheric pressure,

- igniting the ignition material by use of the ignition tool, thereby generating heat which provides for release of gas from the gas producing material when subjected to a temperature above a threshold value.

In an aspect, the method may further comprise the step of selecting an amount of the gas producing material based on expected pressure of the pressurized environment, wherein the selected amount is sufficient to increase the pressure inside the combustion chamber to prevent inflow from the pressurized environment. The potential inflow may be a result of collapse of the housing and or if there is melted a hole in the housing, by the heat generated from the ignition and subsequent reaction in the ignition material. Furthermore, the pressure increase inside the combustion chamber does not have to balance off the pressure in the pressurized environment for the invention to provide for the desired effect. In some instances, the pressure increase may result in a pressure which is less than the pressure in the pressurized environment and still provide for the desired effect, alternatively in combination with the "heat front" generated from the ignition process as discussed above.

According to an aspect, the method may further comprise the step of selecting an amount of the gas producing material based on expected pressure of the pressurized environment, wherein the selected amount is sufficient to provide for a pressure inside the combustion chamber which pressure is at least equal to, or higher, than the pressure of the pressurized environment.

In an aspect, the method further comprises the step of continuously feeding ignition material after ignition of the ignition material. The ignition material may then be formed of a cylinder or column of ignition material which is ignited by the ignition tool in the lower part such that reaction material is continuously fed by the force of gravity and/or by another applied pressure/ force such as mechanical pressure/force after the ignition material has been ignited.

Second embodiment, pressurizing the well operation tool before positioning the tool in the well

According to a second embodiment it is described a well operation tool for forming a permanent well barrier which extends across a full cross section area of a well, including all annuli, and seal both vertically and horizontally in the well in a pressurized environment, the pressurized environment having a pressure above 1 atmospheric pressure, wherein the well operation tool comprises:

- a sealed housing comprising an inner volume;

- a combustion chamber provided within the housing;

- an ignition material provided within the combustion chamber;

- an ignition tool for igniting the ignition material;

wherein the inner volume of the sealed housing is adapted to be pressurized before it is placed in the pressurized environment. The sealed housing is preferably pressure sealed. The pressure applied to the inner volume may be equal to, or higher than the expected pressure of the pressurized environment where the well operation tool is to be positioned. By doing this, one achieve the same effect as in the first embodiment, i.e. to prevent, minimize or delay inflow or ingress of surrounding pressurized fluids, e.g. water, hydrocarbons (oil, gas, condensate). After ignition of the ignition material, it is ensured presence of a sufficient pressure inside the combustion chamber to prevent inflow of the surrounding pressurized fluids. Hence, the ignition process is allowed to continue without disturbances from fluid inflow for a longer period of time than prior art solutions. Even if the housing surrounding the combustion chamber melts, i.e. if there is a hole in the housing, or collapses, the present invention will secure that the surrounding fluids are prevented from inflow. Means used for pressurizing the inner volume may be any means known for pressurizing high pressure source or any device which can increase pressure etc. The housing may then be provided with an interface for connection to the high pressure source, such as a valve or similar. The high pressure source may be nitrogen gas or any other gas or other fluid with sufficient pressure.

The housing is thus made of a material which is adapted to resist large differential pressure between the inside of the housing and the outside of the housing, i.e. if the pressure applied to the inner volume is large, and the housing is in atmospheric environment, the pressure difference between the inside and the outside of the housing may be substantial and the housing shall comply with such pressure differences. The material of the housing may be the same as for the housing in the first embodiment, including aluminum, aluminum alloys (e.g. 7075-T6), steel and composite materials such as carbon fiber. However, any other materials may also be used, such as steel, polymer etc., chosen to meet the demands in the specific project. The pressure-sealing of the housing may be done by welding, using o-ring(s) or other means of sealing. The second embodiment further relates to a method of forming a permanent well barrier which extends across a full cross section area of a well, including all annuli, and seal both vertically and horizontally in the well, by preventing inflow of a fluid into a well operation tool, the well operation tool comprising a pressure-sealed housing having an inner volume, a combustion chamber provided in the inner volume of the housing, wherein the method comprises the steps of:

- arranging an ignition material, an ignition tool within the combustion chamber;

- pressurizing the inner volume of the housing;

- positioning the well operation tool in a pressurized environment having a pressure above 1 atmospheric pressure.

Other features and functions of the well operation tool and the method will be similar to the features described in relation to the first embodiment.

Further, it is clear that according to an aspect, a combination of the first and second embodiment is possible, i.e. to pressurize the inner volume of the housing before it is placed in the pressurized environment and then use a gas producing material which further pressurizes the inner volume of the housing when subjected to a temperature above a threshold value.

According to both embodiments of the invention, the invention may for example be used in well abandonment operations as described in WO 2013/135583 A2, i.e. be used to form a permanent well barrier which extends across the full cross section area of the well, including all annuli, and seal both vertically and horizontally in the well. The present invention assists in forming of the permanent well barrier by substantial radial melting of surrounding materials such as pipes, cement and formation sand, thereby creating a permanent well barrier which is formed by melted well operation tool, pipes, cement and formation sand.

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

Brief description of the drawings

Fig. 1 shows an embodiment of the invention prior to ignition; Fig. 2 shows an embodiment of the invention prior to ignition with an alternative positioning of the ignitor and gas producing material compared to Fig. 1 ;

Fig. 3 shows an embodiment of the invention prior to ignition where the ignition material and gas producing material have been mixed to form a mixture;

Fig. 4 shows an embodiment of the invention prior to ignition where the ignition material and gas producing material have been mixed to form a mixture, with an alternative positioning of the ignitor compared to Fig. 3;

Fig. 5 shows the situation after ignition, where melt has collected in the bottom and gas on top;

Fig. 6 shows the situation after ignition, at a later stage of the reaction than in Fig. 5, where melt has collected in the bottom and migrated radially outwardly through surrounding pipes, cement and formation;

Fig. 7 shows an embodiment of the well operation tool comprising slips for anchoring the tool to the wall of the wellbore/casing;

Fig. 8 shows the principle of the invention prior to the ignition of the ignition material in the combustion chamber, and the different pressures inside and outside of the housing;

Fig. 9 shows the principle situation after ignition of the ignition material, when the temperature has risen above the threshold value of the gas producing material such that gas has been released; Detailed description of a preferential embodiment

Fig. 1 shows an embodiment of the invention prior to ignition. The Figure discloses a well operation tool 1 for use in a pressurized environment 2. The pressurized environment 2 may have a pressure above 1 atmospheric pressure. The pressurized environment 2 may be subsurface, in water, subsea, downhole etc. and may contain any pressurized fluids such as water, oil, gas, mud or mixtures of these. The well operation tool 1 comprises a pressure-sealed housing 3 which encompasses a combustion chamber 4, i.e. the combustion chamber 4 is provided within the housing 3. An ignition material 5 and an ignition tool 6 for igniting the ignition material 5 are provided within the combustion chamber 4, in a lower part of the combustion chamber 4. A gas producing material 7 is provided within the

combustion chamber 4. A base 10 for reaction tool is arranged below (i.e. further down the well 100) the well operation tool 1. The base 10 may include a heat shield, i.e. an element which has a high resistance to heat such as ceramic or glass (sand), and may be in the form of a bridge plug. Ignition cables 9 may be arranged in connection with the ignition tool 6 to induce ignition. The ignition can be electrical ignition, but other ignitions may be used such as chemical ignition. A positioning system 8 may be connected to the well operation tool 1 for positioning the well operation tool 1 at a desired position in the well 100 or subsea. The positioning system 8 may be e-line cable, coiled tubing or any other system providing the desired effect of positioning of the well operation tool 1. Initially, i.e. prior to ignition, there is atmospheric pressure in the combustion chamber 4, i.e. inside the housing.

In a second embodiment, having a plurality of the similar features as the features described in relation to Fig. 1 , i.e. the first embodiment, the inner volume of the sealed housing 3 is adapted to be pressurized before it is placed in the pressurized environment 2. Thus, in this second embodiment the gas producing material may be superfluous. Means used for pressurizing the inner volume may be any means known for pressurizing high pressure source or any device which can increase pressure etc. The housing may then be provided with an interface for connection to the high pressure source, such as a valve or similar. The high pressure source may be nitrogen gas or any other gas or other fluid with sufficient pressure.

Further, it is clear that according to an aspect, a combination of the first and second embodiments are possible, i.e. to pressurize the inner volume of the housing 3 before it is placed in the pressurized environment 2 and then use a gas producing material which further pressurizes the inner volume of the housing 3 when subjected to a temperature above a threshold value.

Fig. 2 shows an embodiment of the invention prior to ignition with an alternative positioning of the ignitor and gas producing material compared to Fig. 1. The ignition tool 6 could alternatively be positioned anywhere in the housing 3. Fig. 3 shows an embodiment of the invention prior to ignition where the ignition material and gas producing material have been mixed to form a mixture 1 1. The other elements forming the well operation tool are similar to the one described in relation to Figures 1 and 2. Fig. 4 shows an embodiment of the invention prior to ignition where the ignition material and gas producing material have been mixed to form a mixture 1 1 , with an alternative positioning of the ignition tool 6 compared to Fig. 3. The ignition tool 6 could alternatively be positioned anywhere in the housing 3.

Fig. 5 shows the situation after ignition, where melt 13 has collected in the bottom of the combustion chamber 4 and the released gas 12 from either the gas producing material or the mixture of ignition material and gas producing material on top.

Fig. 6 shows the situation after ignition, at a later stage of the reaction than in Fig. 5, where the melt 13 has collected in the bottom of the combustion chamber 4 and migrated radially outwardly through surrounding pipes, cement and formation. This is visually shown by comparing the radial extension of the melt 13 of Figure 5 vs. Fig. 6. A permanent well barrier is thus formed when the melt 13 solidifies, which extends across the full cross section area of the well 100, including all annuli, well operation tool, pipes, cement and formation sand and seal both vertically and horizontally in the well 100. The melt 13 may further fill voids in the formation. Ignition material 5 may be continuously fed by gravity (and or with mechanical force) to the reaction zone. After ignition and reaction, the melt 13 is in bottom of the combustion chamber and gas 12 on top.

Fig. 7 shows an embodiment of the well operation tool comprising slips for anchoring the tool to the wall of the wellbore/casing. The slips 15 function to hold the well operation tool 1 in place due to overpressure on the inside of the housing 3 relative the pressurized environment when the reaction melts the housing 3.

Fig. 8 shows an embodiment of the invention prior to the ignition of the ignition material 5 in the combustion chamber 4. Fig. 8 discloses a well operation tool 1 for use in a pressurized environment 2, the pressurized environment 2 having a pressure PE above 1 atmospheric pressure. The pressurized environment 2 may be

subsurface, in water, subsea, downhole etc. and may contain any pressurized fluids such as water, oil, gas, mud or mixtures of these. The well operation tool 1 comprises a pressure-sealed housing 3 which encompasses a combustion chamber 4, i.e. the combustion chamber 4 is provided within the housing 3. An ignition material 5 and an ignition tool 6 for igniting the ignition material 5 are provided within the combustion chamber 4. A gas producing material 7 is provided within the combustion chamber 4. In Fig. 8, the pressure Po within the combustion chamber 4 is 1 atmospheric pressure, which is the pressure prior to ignition of the ignition material 5. Fig. 9 shows the situation after ignition of the ignition material 5 and when the temperature has risen above the threshold value of the gas producing material 7 such that gas has released or generated 12 from the gas producing material 7 building up, i.e. increasing, the pressure Pi inside the combustion chamber 4. Now, after ignition of the ignition material, the pressure Pi within the combustion chamber 4 is above 1 atmospheric pressure due to a temperature inside the combustion chamber 4 above a threshold value for the gas producing material 7, which gas producing material 7 therefore has released gas 12.

In use, after ignition of the ignition material 5 , there is a risk parts of the housing 3 is melted providing one or more holes in the housing 3 or, alternatively, that the housing 3 collapses due to change in properties, e.g. less strength, after being heated. If there was not a gas producing material 7, the surrounding fluids (fluids in the pressurized environment 2) would enter the combustion chamber 3 due to overpressure and or large pressure differential between the outside of the housing 3 compared to the inside of the housing 3 (i.e. in the combustion chamber 4). Thus, by using the invention, the pressure inside the combustion chamber 4/housing 3 is increased by the gas released from the gas producing material 7, thereby providing a pressure increase which prevents inflow from the pressurized environment 2. This pressure increase may result in an equal pressure or a higher pressure on the inside of the combustion chamber 3 compared to the outside of the combustion chamber 4/housing 3. This will prevent, and in some situations even completely prevent, inflow of surrounding pressurized fluids from the pressurized environment 2.

By the arrangement of the embodiments of the Figures a proposed solution to the object of the invention is explained, which is to provide a reliable tool, as well as a method of obtaining an ignition in a pressurized environment using said tool.

The invention is herein described in non-limiting embodiments. The skilled person will understand that the embodiments may be varied and modified without departing from the scope of the invention as set forth in the attached claims.