Patent Description:
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.

There are several technical and regulatory requirements for such permanent well barriers, some of which are a) impermeability of oil and/or gas through the permanent well barrier, b) long term integrity, c) non shrinking of the permanent well barrier, d) ductility (non brittle) - the permanent well barrier must be able to withstand mechanical loads or impact, e) resistance to different chemicals/ substances (H2S, C02 and hydrocarbons) and f) wetting - to ensure bonding to steel.

In <CIT> (Interwell P&A AS), it is disclosed a method for performing a P&A operation wherein a first step, it was provided an amount of a heat generating mixture (for example thermite) at a desired location in the well and thereafter to ignite the heat generating mixture 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.

In short, the above prior art will be described with reference to fig. In <FIG>, a well WE is shown to be provided through a section of a cap rock CR. The inner surface of a well bore WB is provided by an inner casing IC, where cement CM is provided in the annulus between the inner casing IC and the cap rock CR. It should be noted that some wells have several casings provided radially outside of each other, where cement or fluids are provided in the respective annuli. In <FIG>, it is shown that a lower barrier LB has been provided in the well bore WB. Above the lower barrier LB a heat insulating material HI, such as sand, has been provided. A well tool <NUM> has been lowered into the well above the heat insulating material HI by means of a wireline <NUM>. The well tool <NUM> comprises a housing <NUM> with a compartment <NUM> which contains a heat generating mixture <NUM> (for example thermite). An ignition device <NUM> is also provided in the compartment <NUM>. The ignition device <NUM> starts the heat generating process of the heat generating mixture <NUM>. The ignition device <NUM> may be time actuated or pressure actuated. Alternatively, the ignition device <NUM> may be actuated by means of a topside signal transferred via wire to the ignition device.

The result after the ignition is shown in <FIG>. Here it is shown that the elements of the well, i.e. inner casing IC, cement CE and cap rock CR have melted and thereafter hardened into one solid permanent well barrier PB containing constituents of rock, cement, steel and other elements being present in the well. Such other elements are the end product of the heat generation process, remains of the tool used to transport the heat generating mixture into the well, the ignition system etc..

This technology has been tested in test centers and in field trials, in order to verify that the permanent well barrier fulfills technical and regulatory requirements.

<CIT> describes that wells are sealed by means of thermite reaction charges inserted into the wells. The reaction charge can be diluted by addition of metal oxides, silica, or the like control reaction pressure, peak temperature, reaction rate, and expansion characteristics of the resulting thermite plug. The use of dilution of the thermite reactants can take the form of a thermite charge with specific layers, including relatively high and low reaction temperature layers. The ignition source can be oriented to achieve directional control on the product expansion including radial or axial expansion. The charge can be loaded with a large mass to compress the resulting thermite plug into the borehole wall and reduce its porosity during the reaction process. A further variation involves continuous feed of the thermite reactants to the reaction zone.

One object of the present invention is to provide a more efficient method for providing a permanent barrier in a well.

The present invention relates to a well tool system for forming a permanent barrier in a well, the system comprising:.

In many operations, the replenishment string will be pulled downwardly towards the heat generating process by means of gravity. Here, the elevating device is controlled to brake or to slow down the movement of the replenishment string. However, in some operations, gravity will not move the replenishment string sufficiently fast towards the heat generating process. Here, the elevating device is controlled to push the replenishment string towards the heat generating process.

In one aspect, the permanent barrier is a cap-rock to cap-rock permanent barrier extending across the whole cross-section of a wellbore.

The pyrotechnic mixture will, when ignited by the ignition device, start a heat generating exothermic reduction-oxidation process. The heat generating process is configured to melt the surroundings of the well at the location of the well tool device in the well.

In one aspect, the replenishment string has several properties in common with the tool string. They may have equal outer diameter. They may comprise several string sections having equal length. The string sections may have the same type of end connection interfaces for connection to other string sections.

In one aspect, the replenishment string comprises an elongated housing and a compartment within the elongated housing, wherein the compartment contains the first constituent and/or the second constituent.

In one aspect, a cross sectional area of the compartment may be equal to a cross sectional area of a compartment of the tool string. In one aspect, a material of the elongated housing may be equal to the material of the material of the housing of the tool string.

In one aspect, the well tool system comprises a setting tool provided between the replenishment string and the well tool device, wherein the setting tool is configured to disconnect the replenishment string from the well tool device.

In one aspect, the well tool device comprises an anchoring device for anchoring of the well tool device to the well.

In one aspect, the anchoring device is set by gravity, i.e. the weight above the anchoring device will cause the anchoring device to radially expand into contact with the well.

In one aspect, the setting tool is configured to radially expand the anchoring device of the well tool device before disconnecting the replenishment string from the well tool device.

In one aspect, the replenishment housing is made of the first constituent and/or the second constituent.

In one aspect, the first constituent comprises bismuth oxide and the second constituent comprises aluminum.

In one aspect, the elevating device is located topside.

In one aspect, the tool string is a drill pipe type of string, a coiled tubing type of string, or a wireline type of string.

In one aspect, the elevating device is a top drive or rotary table when the tool string is a drill pipe type of string, a reel drive or injector when the tool string is a coiled tubing type of string or a reel drive when the tool string is a wireline type of string.

In one aspect, the sensor is an optic fiber sensor guided in the longitudinal direction of the replenishment string.

In one aspect, the replenishment string comprises one or more further ignition devices provided within or adjacent to the pyrotechnic mixture.

The one or more further ignition devices may restart the heat generating process again, should the heat generating process stop for some reason.

In one aspect, the replenishment string further comprises an electric wire connected to the one or more further ignition devices for igniting the ignition devices.

In one aspect, the pyrotechnic mixture provided in a lower end of the replenishment string has a first set of properties; wherein the pyrotechnic mixture provided in an upper end of the replenishment string has a second set of properties being different from the first set of properties; and wherein the elevating device, is configured to control the movement of the replenishment string towards the heat generating process based on the first set and the second set of properties.

In one aspect, the first and second set of properties being different may be the particle size of the first and/or second constituents, additives used in the pyrotechnic mixture, etc..

Embodiments of the present invention will be described in detail below with reference to the enclosed drawings, wherein:.

It is now referred to <FIG>, where it is shown a well tool system <NUM> for forming a permanent barrier in a well WE.

In the lower end, the system comprises a well tool device <NUM> comprising a pyrotechnic mixture <NUM> and an ignition device <NUM> provided within or adjacent to the pyrotechnic mixture <NUM>, wherein the pyrotechnic mixture <NUM> comprises a first constituent <NUM> in the form of a metal oxide and a second constituent <NUM> in the form of a metal. This well tool device <NUM> may be the prior art well tool device <NUM>.

In the present embodiment, there are some differences with respect to the prior art well tool device <NUM>. A first difference is that the well tool device comprises an anchor <NUM> for securing the well tool device <NUM> relative to the inner surface of the well. The anchor <NUM> may prevent upwardly directed movement of the well tool device <NUM> (for example caused by the heat generating mixture forcing the upper part of the well tool device <NUM> upwardly), it may prevent downwardly directed movement (for example caused by gravity) or both.

A second difference is that in the present embodiment, the metal oxide is bismuth oxide, also referred to as bismuth(III) oxide or Bi2O3 and the metal is aluminum Al or an aluminum alloy.

The pyrotechnic mixture <NUM> will, when ignited by the ignition device <NUM>, start a heat generating exothermic reduction-oxidation process:.

This type of pyrotechnic mixture <NUM> is often referred to as thermite, and the heat generating reaction is often referred to as a thermite reaction.

The heat will melt the surroundings at the location of the well tool device, such as casing, cement, and possibly also parts of the formation radially outside of the casing and cement. It should be noted that there may be two or more casings outside of each other. The annulus between the casings may be fluid-filled, filled with cement, gravel or other materials. After cooling, a cap-rock to cap-rock permanent barrier extending across the whole cross-section of a wellbore may be the result. Hence, the result may be similar to the result shown in <FIG>.

The system <NUM> further comprises a string connected to the upper end of the well tool device <NUM> by means of a setting tool <NUM>. The upper end of the string is connected to an elevating device <NUM>, which is used to move the string and the well tool device <NUM> up and down to its desired location in the well.

The system <NUM> comprises different substrings. First, the system <NUM> comprises an upper tool string indicated in <FIG> as reference number <NUM>. Second, the system <NUM> comprises a replenishment string <NUM> connected between the setting tool <NUM> and the tool string <NUM>.

In <FIG>, the tool string <NUM> and the replenishment string <NUM> are a drill pipe type of string, comprising several string sections 70a, 90a, 90b, 90c connected to each other by means of connection interfaces <NUM>, <NUM> in their upper end being connectable to connection interfaces <NUM>, <NUM> in their lower end. In <FIG>, a height H90 of the replenishment string <NUM> is indicated to comprise three drill pipe sections, each drill pipe section having a height of ca <NUM> - <NUM> feet (<NUM> - <NUM> meter). It should be noted that the total height of the tool string <NUM> typically will be much longer than the height H90 of the replenishment string <NUM>.

The drill pipe type of string is rigid, enabling it to be pushed actively into the well. The drill pipe type of string has a relatively high weight, and can therefore also be lowered relatively fast into the well by gravity. It is now referred to <FIG>. Here it is shown that the replenishment string <NUM> comprises an elongated housing <NUM> and a compartment <NUM> within the elongated housing <NUM>, wherein the compartment <NUM> contains the first constituent <NUM> and/or the second constituent <NUM>.

The entire replenishment string <NUM> may comprise the same type of pyrotechnic mixture <NUM>. Alternatively, each section 90a, 90b, 90c may comprise different types of pyrotechnic mixtures <NUM>. In yet an alternative, as indicated in <FIG>, one section of drill pipe may comprise layers 40a, 40b, 40c of different pyrotechnic mixtures <NUM>.

The term "different type" may refer to other metal oxides and metals than the abovementioned bismuth oxide and aluminum. One alternative embodiment is iron oxide and aluminum, but there are various other metal oxides and metals.

The term "different type" may also refer to different particle size of the first and/or second constituents used in the respective layers of the pyrotechnic mixture <NUM>, it may refer to different additives used in respective layers of pyrotechnic mixture <NUM>, etc..

It should be noted that the pyrotechnic mixture <NUM> is provided stationary with respect to the housing <NUM>. Hence, the pyrotechnic mixture <NUM> should not move up in the compartment <NUM> within the housing <NUM> due to the pressure difference between the well pressure and the pressure topside. In the same way, the pyrotechnic mixture <NUM> should not down and out from the compartment <NUM> within the housing <NUM> due to gravity. The pressure above the pyrotechnic mixture <NUM> may be balanced with the well pressure as the replenishment string <NUM> is lowered into the well, to reduce a differential pressure between the inside and the outside of the housing <NUM>.

The pyrotechnic mixture <NUM> may be held stationary with respect to the housing <NUM> by means of binding agents. The pyrotechnic mixture <NUM> may be provided as solid blocks or discs, where the inner surface of the housing <NUM> comprises restrictions which are holding these blocks or discs stationary. These restrictions may not be a part of the housing itself, but may be provided by means of a sleeve inserted into the housing.

It is now referred to <FIG>. Here, the tool string <NUM> and the replenishment string <NUM> are a coiled tubing type of string. The coiled tubing type of string is also rigid, enabling it to be pushed actively into the well. Even though being lighter than the string of the first embodiment, also the coiled tubing can be lowered into the well by gravity.

Similar to the drill pipe in the first embodiment, also here the replenishment string <NUM> is a longitudinal extension of the tool string <NUM>, and the cross sectional area of the compartment <NUM> may be equal to a cross sectional area of a compartment of the tool string <NUM>.

As is known, coiled tubing are typically stored as one continuous string reeled up on a drum, where the movement of the coiled tubing up and down in the well is performed by a reel drive rotating the drum and/or by an injector 80b pushing or pulling the coiled tubing into or out from the well.

In <FIG>, it is shown that the replenishment string <NUM> comprises a housing <NUM> and a compartment <NUM> within the housing <NUM> filled with pyrotechnic mixture <NUM>. Here, the housing <NUM> is a pipe. It should be noted that also here, there may be layers of different pyrotechnic mixtures <NUM>, as described in the first embodiment above.

In <FIG>, the housing <NUM> is made by rolling the material of the housing and joining the end surfaces of the material, as indicated by the joint 93a.

The embodiment in <FIG> corresponds to the embodiment in <FIG>. Here, the joint 93a is formed by overlapping end surfaces of the material.

One difference between coiled tubing and drill pipe is that the drill pipe typically can be lowered one length of drill pipe section before a pause is required to join a further drill pipe section on top of the previous drill pipe section. The typical length of such a drill pipe section is <NUM>. Coiled tubing can be lowered continuously into the well without any such pause.

It is now referred to <FIG>. Here, the tool string <NUM> is a wireline type of tool string. As a wireline is flexible, it cannot be pushed actively into the well. As is known a wireline does not comprise a central bore or compartment in which the pyrotechnic mixture <NUM> may be located.

As a first example (shown in <FIG>), the replenishment string <NUM> comprises a flexible housing <NUM> in the form of a hose (for example similar to a fire hose, a garden hose etc. with a suitable outer diameter), filled with pyrotechnic mixture <NUM>. Hence, also the replenishment string <NUM> will be relatively flexible. Here, the lower end of the wireline <NUM> is connected to the upper end of the hose <NUM>.

As a second example (shown in <FIG>), the wireline <NUM> is continued inside the flexible housing <NUM> as a replenishment wireline <NUM>, to ensure that weight of the well tool device <NUM> and the setting tool <NUM> can be carried by the replenishment string <NUM>.

As a third example, the replenishment string <NUM> comprises a more rigid housing <NUM>, for example a section of coiled tubing etc. filled with pyrotechnic mixture <NUM>. Here, the cross section of the replenishment string <NUM> will be similar to one of <FIG> d.

As is known, wireline is typically stored reeled up on a drum, where the movement of the wireline up and down in the well is performed by a reel drive rotating the drum. In all of the above examples, gravity must be used when lowering the replenishment <NUM> towards the heat generating process.

It is now referred to <FIG>. Even though the replenishment string <NUM> here is of the drill pipe type, the features of the fourth embodiment can be used with the other types of replenishment strings as well.

In <FIG> it is shown that the replenishment string <NUM> comprises a fiber optic sensor <NUM>, which may be of the type fibre Bragg gratingLight reflected from the fiber optic sensor <NUM> changes dependent on temperature and/or the length of the fiber. This information can be used by the elevating device <NUM> to control the speed of the movement of the replenishment string <NUM> towards the heat generating process based on signals from the one or the plurality of sensors <NUM>.

Of course, other types of sensors may be used for this purpose, for example a number of spaced apart temperature sensors will also give information about the temperature at different positions in the replenishment string <NUM>.

In <FIG> it is further shown that the replenishment string <NUM> comprises an ignition device <NUM> and an electric wire <NUM> connected to the ignition device <NUM>. The ignition device <NUM> may restart the heat generating process again, should the heat generating process stop for some reason. The conditions for restating the heat generating process may be detected by the fiber optic sensor <NUM>.

It is now referred to <FIG>. Here it is shown an embodiment of the system <NUM> without a setting tool <NUM>. Hence, here the well tool device <NUM> is secured below the replenishment string <NUM>, and there is no release of the replenishment string <NUM> from the well tool device <NUM> before ignition of the ignition device <NUM> of the well tool device <NUM>. However, as the material of the housing of the well tool device <NUM> or the housing of the replenishment string <NUM> will melt by the heat of the heat generation process or be consumed as part of the heat generation process, it will still be possible to move the replenishment string up and down relative to the location of the heat generation process.

Again, even though <FIG> shows the wireline type of tool string <NUM>, the fifth embodiment may be used for the other types of string as well.

It is now referred to <FIG>. Here it is shown an embodiment of the system <NUM> without an anchoring device <NUM>. Here, the well tool device <NUM> is lowered until it is supported by the lower barrier LB and/or heat insulation material HI and then the well tool device <NUM> is released from the replenishment string <NUM> by means of the setting tool <NUM> before ignition of the ignition device <NUM> of the well tool device <NUM>. Hence, the setting tool <NUM> is only a releasing tool. After ignition, the replenishment string <NUM> is moved relative to the location of the heat generation process.

Again, even though <FIG> shows the wireline type of tool string <NUM>, the sixth embodiment may be used for the other types of string as well.

The operation of the first embodiment will now be described. It should be noted that the same or similar operation may be performed for the other embodiments as well.

It is now referred to <FIG>. Here it is shown that the well tool device <NUM> has been set above a lower barrier LB, similar to the situation in <FIG>. The anchoring device <NUM> has been radially expanded by means of the setting tool <NUM> and the tool string <NUM> and the replenishment string <NUM> has been lifted up a distance from the well tool device <NUM>. In some of the above embodiments, there is no setting tool <NUM> and hence no movement of the replenishment string <NUM> relative to the well tool device <NUM> before ignition. In some of the above embodiments, there is no anchoring device <NUM>, but the setting tool <NUM> releases the replenishment string <NUM> from the well tool device before ignition, allowing movement of the replenishment string <NUM> relative to the well tool device <NUM> before ignition.

The ignition device <NUM> of the well tool device <NUM> is now starting the heat generating process. The ignition device <NUM> may ignite based on an ignition signal sent via a wire (not shown in <FIG>), an ignition signal sent wirelessly or an ignition signal sent from circuitry (a timer etc. not shown in <FIG>) in the well tool device.

After the heat generating process has started, the elevating device <NUM> is controlling the movement of the replenishment string <NUM> down towards the heat generating process, and further amounts of the pyrotechnic mixture <NUM> is supplied to or replenished to the process.

It should be noted that in many cases, the replenishment string <NUM> will be pulled downwardly towards the heat generating process by means of gravity. Here, the elevating device <NUM> is braking the movement of the replenishment string <NUM>. However, in some operations, gravity will not move the replenishment string <NUM> sufficiently fast towards the heat generating process. Here, the elevating device <NUM> is controlled to push the replenishment string <NUM> towards the heat generating process.

According to the above, it is achieved that the reaction process can be tailored to different operational requirements. For example, the temperature can be increased in specific areas of the well cross section by rapid feeding and/or by adjusting the pyrotechnic mixture in some sections of the replenishment string.

Alternatively, the temperature may be decreased by slowing down the feeding to reduce impact on well elements and host rock/ geological formation.

One layer of pyrotechnic mixture may delay the continuation of the reaction to allow reaction materials to separate and increase bonding to the host rock before continuing the feed.

In addition, the feeding can be controlled in such a way that the total barrier length can be increased and that the barrier is in accordance with technical requirements and regulations at the desired location (i.e. the location of the well tool device and immediately above the location of the well tool device).

It should be noted at the pressure within the drill pipe string, i.e. the pressure inside the tool string <NUM> and the replenishment string <NUM> may be controlled from topside.

Moreover, the elevating device <NUM> may be configured to control the movement of the replenishment string <NUM> towards the heat generating process based on these first set and the second set of properties.

In an alternative embodiment, the well tool device <NUM> may be lowered in a separate operation from the replenishment string <NUM>. Hence, the replenishment string <NUM> does not need to carry the load of the well tool device <NUM>. Here, it is possible to use the metal of the pyrotechnic mixture <NUM> as a material of the housing <NUM> of the replenishment string <NUM>. Hence, the compartment <NUM> will contain a larger amount of metal oxide or the compartment <NUM> will contain only metal oxide.

Claim 1:
A well tool system (<NUM>) for forming a permanent barrier in a well (WE), the system comprising:
- a well tool device (<NUM>) comprising a pyrotechnic mixture (<NUM>) and an ignition device (<NUM>) provided within or adjacent to the pyrotechnic mixture (<NUM>), wherein the pyrotechnic mixture (<NUM>) comprises a first constituent (<NUM>) in the form of a metal oxide and a second constituent (<NUM>) in the form of a metal;
- a tool string (<NUM>) connected above the well tool device (<NUM>);
- an elevating device (<NUM>) connected to the well tool device (<NUM>) via the tool string (<NUM>);
- a replenishment string (<NUM>) connected between the well tool device (<NUM>) and the tool string (<NUM>),
wherein the replenishment string (<NUM>) comprises the first constituent (<NUM>) and/or the second constituent (<NUM>);
wherein the elevating device (<NUM>), after a heat generating process is started by means of the ignition device (<NUM>), is configured to control the movement of the replenishment string (<NUM>) towards the heat generating process;
characterized in that the replenishment string (<NUM>) comprises one or a plurality of sensors (<NUM>) for sensing the heat distribution along the replenishment string (<NUM>); and wherein the elevating device (<NUM>) is configured to control the movement of the replenishment string (<NUM>) towards the heat generating process based on signals from the one or the plurality of sensors (<NUM>).