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.

<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. Various combinations and permutations of the above inventive concepts are described.

<CIT> describes composition for a plug for wellbores undergoing plugging and abandonment operations.

<CIT> describes a to-be-abandoned underground wellbore is plugged along any desired longitudinal interval and radial extent by: - dropping capsules filled with a grout, pyrotechnic, swelling, bismuth, clay, bentonite, hardening, sintering, and/or other plug generating material into the wellbore at selected time intervals; - inducing the capsules to accumulate above a downhole cement or other barrier in the wellbore; - inducing the accumulated capsules to disintegrate and to release the plug generating material into the wellbore; and - inducing the released plug generating material to generate a fluid tight barrier of a desired length and radial extent within the wellbore.

<CIT> describes a method is provided for plugging a wellbore having a casing and cement surrounding the casing and traversing a formation, which involves configuring and using at least one tool located in the wellbore to deliver composite material to a target area in the wellbore, wherein the composite material includes metal alloy and an exothermal reactant. The at least one tool is further configured and used to apply heat or spark to the composite material in the target area to ignite the exothermal reactant of the composite material and melt the metal alloy of the composite material. The melted metal alloy of the composite material is permitted to solidify to form a plug at the target area in the wellbore.

<CIT> describes a method and apparatus for creating a fluid seal in a subterranean well structure having a fluid seal defect. The method comprises introducing a meltable repair material proximate a structure in a subterranean well which has a fluid seal defect or enhanced seal capacity is required or it is desired to temporarily or permanently hydraulically isolate a portion the well or strengthen the structural integrity of well tubulars or tubular hangers. Exothermic reactant materials are located proximate the meltable repair material. The exothermic reactant material is ignited or an exothermic reaction otherwise initiated which supplies heat to and melts the meltable repair material into a molten mass. The molten mass flows and solidifies across the structure and the fluid seal defect to effect a fluid seal in the subterranean well structure or the structural integrity is enhanced.

<CIT> describes a method of plugging a well by employing a tool to remove a portion of a casing at a section of the well to be plugged. A plugging material is employed on a blocking device of the well to plug the wellbore. An exothermic fluid is deployed downhole and is activated to solidify and form a cast in place plug that fills the section to be plugged of the well.

<CIT> describes a method for electric ignition of an exothermic mixture employed in well for plugging the wells. The ignitor is described to include a compartment and a housing. A mixture of metal and oxide are included in the compartment and along with a first and second electrode connectable to the power supply to ignite the mixture.

<CIT> describes a method for cementing wells. The method employs coloring agent in a water soluble bag into a portion of spacer or scavenging fluid, pumping the spacer or scavenger and cementing slurry down the casing to the bottom of the hole. Further, the casing volume is displaced and then pumping is stopped to allow the cement slurry to harden.

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. 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.

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

One object is to provide a method of constructing a well which may be efficiently abandoned when it is desired to permanently abandon the well.

The present invention relates to a method for providing a permanent barrier in a well, wherein the method comprises the steps of:.

The step of lowering the second constituent comprises:.

Here, the second constituent is allowed to settle as sediment above the first constituent.

As used herein, the term "particulate" is referring to a material comprising a plurality of smaller particles. The particulate material may be in powder form or in a granule form.

In one aspect, the amounts of metal oxide and the metal are mixed in a stochiometric ratio.

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

In one aspect, the steps a) and b) and the subsequent steps step c1) and c2) are performed alternatingly, allowing a multi-layered sediment to form at the desired location.

In one aspect, the second constituent is a solid object in the form of a spear, a cylinder etc. The second constituent, for example in the form of a spear, may be pushed or forced down into the settled first constituent. The second constituent, for example in the form of a cylinder, may be lowered first. Then, the second constituent may be lowered to fill the annular space radially outside of the cylinder.

In one aspect, the step of lowering the second constituent comprises:.

Alternatively, the second constituent may be separated from contact with the first constituent until the step of igniting the pyrotechnic mixture. The second constituent may for example be separated from contact with the first constituent by means of a foil, a sheet etc., which will easily be melted by the heat from the igniter. Alternatively, the second constituent may be separated from contact with the first constituent by means of a separating mechanism, for example a mechanically, electrically or chemically controlled separating mechanism.

In one aspect, the method comprises, prior to step a) a step of:.

In one aspect, the method comprises the step of:.

In one aspect, the first constituent is a particulate matter having a particle size of <NUM> to <NUM>.

In the above embodiments in which the second constituent is also a particulate constituent, the second constituent comprises particles having a particle size of <NUM> to <NUM>. It should be noted that the second constituent in at least some of the above embodiments may have a particle size above <NUM>.

In one aspect, the method further comprise the steps of:.

In one aspect, the heating tool may be lowered before step a). In one aspect, the heating tool may be lowered before step d). The heating tool is providing that the first, particulate constituent and/or the second, particulate constituent becomes heated to a temperature of ca <NUM> - <NUM>. It should be noted that this temperature interval is considerably lower than the temperature of ca. <NUM> needed to initiate the heat generation exothermic reduction-oxidation process.

As used herein, the term "sintering" is defined as the process of compacting and forming a solid mass of material by heat or pressure without melting it to the point of liquefaction. Above, the sintering is performed by exposing the first, particulate constituent and/or the second, particulate constituent to heat from the heating tool.

The sintering process will prevent that the particulate constituent and/or the second, particulate constituent become unintentionally flushed out from the annulus again.

In one aspect, the first, particulate constituent comprises bismuth oxide.

In one aspect, the second constituent comprises aluminum or an aluminum alloy.

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

It is now referred to <FIG>. Here it is shown a well WE comprising an inner casing IC cemented by means of cement CE within the formation, here indicated as a cap rock formation CR. A lower barrier LB has been set in the inner casing IC. Optionally, a heat insulation material HI may be provided above the lower barrier LB.

Then, a well tool device <NUM> has been lowered into the well above the lower barrier LB by means of a wireline. The well tool device <NUM> comprises a housing <NUM> in which a compartment is provided. The compartment within the housing <NUM> is filled with a pyrotechnic mixture <NUM> comprising a first constituent <NUM> and a second constituent <NUM>. The well tool device <NUM> further comprises an ignition device <NUM>. The first constituent <NUM> is a metal oxide and the second constituent <NUM> is a metal. The housing <NUM> may be made of steel, alternatively the housing <NUM> may be made of the second constituent <NUM>.

The well tool device <NUM> may have a cylindrical shape, i.e. having a circular cross sectional shape perpendicular to the longitudinal axis I-I. It should be noted that the well tool device <NUM> alternately may have a triangular, square or even polygonal circular cross sectional shape.

The above well tool device <NUM> may be the prior art well tool device <NUM> described in the introduction above with reference to <FIG>. It should be noted that in <FIG>, the housing <NUM> is indicated as a white rectangle, i.e. the content within the housing <NUM> is not indicated in <FIG>.

However, in the present embodiment, the well tool device is not identical to the prior art well tool device, as is apparent from the description below.

In the present embodiment, the metal oxide is bismuth oxide, also referred to as bismuth(III) oxide or Bi2O3. In the present embodiment, 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>.

In a subsequent step, which is also shown in <FIG>, a further amount of the first constituent <NUM> is lowered into the well. The further amount of the first constituent <NUM> is initially transported into the well by means of a container <NUM> suspended from a wireline <NUM>. The container <NUM> is then opened, as indicated by an arrow in <FIG>, which allows the further amount of the first constituent <NUM> to sink down to the well tool device <NUM>, more specifically to the annulus radially outside of the well tool device <NUM> and inside of the inner casing IC. Such a container <NUM> is often referred to as a bailer, and the operation of using such a container is often referred to as a bailing operation.

In a next step, the first particulate constituent <NUM> is allowed to sink down and to settle as sediment at the desired location by waiting a first predetermined period of time TP1. This will be obtained by gravity, as the first constituent and the second constituent have a density higher than the density of the well fluid. The time period TP will be depending on setting depth, estimations of viscosities and particle size/shape and the type of well fluids. Experiments conducted with settlement in water is <NUM>-<NUM> seconds per meter of fluid, which corresponds to an approximate settling time at <NUM> depth of <NUM>,<NUM>-<NUM> hours. (more than one hour for each <NUM>).

In the present example, the second constituent <NUM> was lowered into the well as part of the well tool device <NUM>. Hence, by the first constituent <NUM> lowered into the well in the housing <NUM> of the well tool device <NUM> and the container <NUM>, and by the second constituent <NUM> lowered as part of (i.e. either as a particulates in the compartment of the housing <NUM> or as the material of the housing <NUM> itself) the well tool device <NUM>, the entire inner diameter of the inner casing contains constituents of the pyrotechnic mixture <NUM>.

The amounts of the first and second constituents are preferably determined and measured before the operation starts, to ensure that a stochiometric ratio between the first and second constituents are present in the well.

By allowing the first, particulate constituent <NUM> to settle as sediment, the available space at the desired location may be filled entirely with the pyrotechnic mixture <NUM>, causing the well fluid, typically water, to be displaced upwardly. Hence, a more efficient heat generating process may be achieved.

It should be noted that there may be alternative ways of lowering the further amount of the first constituent <NUM> into the well. In some wells it may be possible to lower the second constituent <NUM> from the topside of the well, i.e. to omit the use of the container <NUM>.

It should also be noted that the it is possible that also the second constituent <NUM> is a particulate constituent <NUM>. In such a case, the first constituent <NUM> and the second constituent <NUM> may be mixed before lowering them to the desired location. Due to the above period of time TP1, the second particulate constituent <NUM> is allowed to settle as sediment together with the first particulate constituent <NUM>. It should be noted that due to different densities of the two constituents, the second constituent <NUM> and the first constituent <NUM> may settle in different layers.

Hence, in yet an alternative, it is possible to first lower a first amount of the first particulate constituent <NUM> and then wait the predetermined period of time TP1, then to lower a first amount of the second particulate constituent <NUM> and then wait a second predetermined period of time TP2. Then, a second amount of the first particulate constituent <NUM> is lowered and this amount is allowed to settle during a third period of time TP3 and then again a second amount of the second particulate constituent <NUM> are allowed to settle during a fourth period of time TP4. Hence, a layered or multilayered structure of the pyrotechnic mixture is achieved.

As used herein, the term "particulate" is referring to a material comprising a plurality of smaller particles. The particulate material may be in powder form or in a granule form. Typically, the particles have a size of <NUM> - <NUM>.

It is now referred to <FIG>. Here it is shown that the well WE comprises a restriction RE, which is so narrow that the well tool device <NUM> in <FIG> cannot pass the restriction RE.

In a first step, the first particulate constituent <NUM> is lowered into the well, for example as described in example <NUM> above.

In a second step, the second constituent <NUM> in the form of a solid object, shown in <FIG> as a spear <NUM>, is lowered into the first particulate constituent <NUM>, where the pointed end of the spear will make it easier for the solid object to penetrate down into the first particulate constituent <NUM>. As aluminum is a relatively light material, additional weight may be set on top of the spear to force it down. Alternatively, the spear may have a through bore, where a gas or liquid is flowing out from the end of the spear, thereby creating turbulence in the particulate metal oxide adjacent to the outer surface of the spear, making it easier to push or force the spear down. The outer diameter of the spear is less than the inner diameter of the restriction RE.

The ignition device <NUM> is here secured to the outside of, or provided in a compartment within, the spear.

Also here, the first particulate constituent <NUM> is allowed to sink down and to settle as sediment at the desired location by waiting a first predetermined period of time TP1.

In <FIG> it is shown that the height H45 of the level of the first constituent <NUM> is substantially equal to the height H46 of the spear <NUM>.

In an alternative embodiment, the second constituent <NUM> in the form of the solid object is lowered first, and then the first particulate constituent <NUM> is lowered to the annulus outside of the solid object. Also here, the pointed end of the spear may be useful in order to pass the restriction. However, the pointed end is not a required, the object may be cylindrical.

In yet an alternative embodiment, the spear may comprise threads for rotating the spear down into the metal oxide. A rotation tool anchored to the inner casing above the spear is then needed.

It is now referred to <FIG>. Also here there is a restriction RE, making it difficult to use the well tool device <NUM>. Here, both the first constituent <NUM> and the second constituent <NUM> are lowered to the desired location as particles.

As in one of the alternatives of the first example above, the first constituent <NUM> and the second constituent <NUM> may be mixed to a pyrotechnic mixture <NUM> topside and then lowered by means of the container <NUM> before the pyrotechnic mixture <NUM> is released from the container.

Alternatively, also mentioned as one of the alternatives of the first example above, the first constituent <NUM> and the second constituent <NUM> are lowered to the desired location alternatingly, allowing the constituents to settle as sediment before a new layer is added. Hence, also here, a layered or multilayered structure of the pyrotechnic mixture <NUM> is achieved.

It should be noted that example <NUM> may be used in wells WE without any restriction RE.

It is now referred to <FIG>. Here it is shown an inner casing IC in which a part of the casing IC has been removed. The removed part of the inner casing IC is indicated as a perforation PE in <FIG>. However, any method for removing a part of the casing can be used, for example milling, perforation, melting, eroding (for example by high pressure water with eroding particles), water jet cutting, mechanical punching, hydraulic punching, corrosion by acids etc..

The inner casing IC is partially cemented to the cap rock CR, as indicated by the cement CM. Above the cement CM, there is an annulus AN between the inner casing IC and the cap rock CR.

In <FIG> it is shown a guiding device GD lowered into the well. The guiding device GD comprises a guiding surface, for example a cone or similar, which are held stationary in the area below the removed part of the inner casing IC as shown in <FIG>. Above the guiding device GD, a container (not shown in <FIG>) similar to the container <NUM> of <FIG> is releasing the first constituent <NUM> and the second constituent <NUM>, both constituents as particles. The particles are guided by the guiding device GD into the annulus AN via the removed part of the inner casing IC, where it will move down towards the cement CE due to gravity.

In addition to allow the first and second particles to settle as sediment, the particles may undergo a sintering process.

It is now referred to <FIG>, where the guiding device GD has been removed and a heater HT has been lowered into the inner casing IC by wireline <NUM>. Here, the first and second constituents are sintered by means of heat from the heating tool HT. The first and second constituents are heated to a temperature of ca <NUM> - <NUM>, which is a temperature considerably lower than the temperature of ca. <NUM> needed to initiate the thermite heat generation process.

The sintering process will prevent that the particulate constituent <NUM> and the second, particulate constituent <NUM> become unintentionally flushed out from the annulus again.

In an alternative to the above, it is possible that only one of the first constituent <NUM> and the second constituent <NUM> is be delivered to the annulus AN. Preferably, the first constituent <NUM> is delivered to the annulus AN.

In <FIG>, it is shown that the well tool device <NUM> is lowered inside the inner casing IC. The well tool device <NUM> may here comprise a desired amount of the first constituent <NUM> and the second constituent <NUM>, taken the amount of the first and/or second constituent <NUM>, <NUM> already present in the annulus AN into the consideration.

It should be noted that the annulus AN may be filled with the first constituent <NUM> already during the construction of the well. Here, the first constituent <NUM> is brought to the annulus outside predetermined sections of the casing, while cement is brought to the annulus outside other sections of the casing. Here, the step of removing a part of the casing (i.e. by perforation or other methods) is not necessary, as the annulus AN is available from the topside during the construction of the well. As an example, the first constituent <NUM> may be circulated to the desired location of the annulus, similar to how the cement is brought to the annulus.

The first constituent <NUM> to also here allowed to solidify in the annulus, thereby providing zonal isolation between the casing and the formation wall or between the casing and the further casing.

The first constituent <NUM> may also here be solidified by a sintering process by means of a heater or is allowed to solidify by allowing the first constituent <NUM> to settle as sediment.

It should be noted that during the production phase of the well, the first constituent <NUM> will not be considered to represent a danger with respect to unintentional ignition, as only small amounts of metal to react with is present and as the ignition temperature needed is very high.

The first constituent <NUM> will be present in the annulus AN until a plugging and abandonment operation is to be performed. Here, the second constituent <NUM> of the pyrotechnic mixture <NUM> is lowered to the area of the solidified first constituent <NUM>, and the pyrotechnic mixture <NUM> is ignited to start the heat generating exothermic reduction-oxidation process.

Even though the examples and drawings above only show the well WE to comprise one casing, the same examples may be used for wells WE having two or more casings radially outside of each other. In some situations, there may be a need to seal of the annulus between two casings and/or between a casing and the formation. Sealing of an annulus between two casings and/or between a casing and a formation is known from for example <CIT> (in the name of CannSeal AS).

In the above examples, we have referred to the formation as a cap rock CR. It should be noted that the examples may be used for other formations in the well.

In the above examples, one alternative has been to mix the first constituent <NUM> with the second constituent <NUM> into a pyrotechnic mixture <NUM> topside, and then lower the pyrotechnic mixture <NUM> into the desired position. Due to the different densities of the first constituent <NUM> relative to the second constituent <NUM>, it may be difficult to predict how the distribution of the respective constituents will be when the pyrotechnic mixture <NUM> has settled as sediment in the well WE.

Therefore, in one alternative embodiment, the first and second constituents <NUM>, <NUM> are formed as a core-shell composition with alternating materials in the core and in the shell. The process of forming such a core-shell composition is described in <NPL>.

It should be noted that the pyrotechnic mixture <NUM> may comprise 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.

Claim 1:
Method for providing a permanent barrier in a well (WE), wherein the method comprises the steps of:
a) lowering a first, particulate constituent (<NUM>) of a pyrotechnic mixture (<NUM>) to a desired location in the well (WE); wherein the first particulate constituent is a metal oxide;
b) waiting a first predetermined period of time (TP1) to allow the first, particulate constituent (<NUM>) to settle as sediment at the desired location;
c) lowering a second constituent (<NUM>) of the pyrotechnic mixture (<NUM>) to the desired location in the well (WE); wherein the second constituent (<NUM>) is a metal;
d) igniting the pyrotechnic mixture (<NUM>) to start a heat generating exothermic reduction-oxidation process; wherein the step of lowering the second constituent (<NUM>) comprises:
c1) lowering the second constituent (<NUM>) as a second, particulate constituent (<NUM>) to the desired location in the well (WE);
c2) waiting a second predetermined period of time (TP2) to allow the second, particulate constituent (<NUM>) to settle as sediment; and
wherein the steps a) and b) are performed before steps c1) and c2).