WO2019151870A1

WO2019151870A1 - A method, system and plug for providing a cross-sectional seal in a subterranean well

Info

Publication number: WO2019151870A1
Application number: PCT/NO2019/050015
Authority: WO
Inventors: Morten Myhre; Arne Gunnar Larsen; Arnold ØSTVOLD
Original assignee: Hydra Systems As
Priority date: 2018-01-30
Filing date: 2019-01-23
Publication date: 2019-08-08
Also published as: NO20180152A1; NO345012B1

Abstract

A method, system and plug for providing a cross-sectional seal (40´´) in a well (2) comprising a pipe body (4) and an annulus (6), the method comprising: (A) lowering a pipe expansion device (14, 20) into the pipe body (4) to a selected location; (B) with the pipe expansion device (14, 20), expanding a section (L) of the pipe body (4) until contact with a wellbore wall (8), thus forming an expanded pipe section (18) closing the annulus (6); (C) lowering a fusible solid material (40) into the expanded pipe section (18); (D) lowering a heating tool (32) into the expanded pipe section (18); (E) activating the heating tool (32) and melting the fusible solid material (40) and allowing a molten mass (40´) thereof to fill a cross-sectional portion of the expanded pipe section (18); and (F) deactivating the heating tool (32) and allowing the molten mass (40´) to solidify and form the cross-sectional seal (40´´). (Figure 9)

Description

A METHOD, SYSTEM AND PLUG FOR PROVIDING A CROSS-SECTIONAL SEAL IN A

SUBTERRANEAN WELL

Technical field

The present invention concerns a method and system of forming a cross-sectional sealing plug in a subterranean well, for example a production well, injection well, water well or hydrothermal well, and the well may be vertical or deviated. The invention also concerns a cross-sectional sealing plug in such a well.

The invention is particularly suitable for temporary or permanent plugging and abandonment (P&A) of a well, however the invention may also be suitable for other plugging purposes, such as zone isolation, sidetracking or remedial repairs. Further, the invention is suitable for rig-less applications, hence may be particularly

advantageous in offshore settings.

Technical background

The background of the invention is the constant drive in the industry, e.g. the petroleum industry, for simpler and more cost-efficient solutions for plugging subterranean wells. This drive is particularly relevant to offshore settings where operational costs are very high. Considering also that the costs of plugging and abandoning wells represent non-recoverable expenses, the drive for simple and cost- efficient solutions is very strong. Relevant prior art and disadvantages thereof

Proper plugging and pressure-containment in a well generally requires one or more cross-sectional (rock-to-rock) and sealing barriers (plugs) to be formed in the well. So-called "section milling" represents an old and well-known method of providing such rock-to-rock well barriers. In the section milling method, a section of well lining, e.g. casing, liner or tubing, is milled away and removed from the well, thereby gaining access to the surrounding wellbore wall. The, the wellbore wall is under-reamed so as to extend and cut into new and fresh formation. Finally, a sealing agent, typically cement slurry, is filled into the under-reamed section and is allowed to set so as to form a proper rock-to-rock barrier in the well. This method is time-consuming, cumbersome and costly and also involves a number of environmental issues. For these reasons, the section milling method has experienced diminishing interest and use in the industry lately. As noted, the industry is currently looking for cheaper and simper plugging solutions.

Rather recently, i.e. since about year 2010, the so-called Perf-Wash-Cement - PWC® - method has gained increasing interest and use in the industry. When employing the PWC® method, a section of casing (or liner or tubing) is not removed. Instead, the casing section is perforated to gain access to an annulus surrounding the casing. A washing/flushing tool is then used to direct a washing fluid into the annulus via perforations formed in the casing section, thereby washing and cleaning the annulus. Subsequently, a fluidized plugging material is introduced into the casing and thus into the surrounding annulus via the perforations in the casing. With the PWC®-method, the plugging time (per plug) has been reduced significantly, and up to about 75-80 per cent that of the section milling method. Although being a great success in the industry, some parties have nonetheless held that a disadvantage of the PWC®- method may be insufficient cleaning in the annulus, causing potential insufficient plugging and sealing in the annulus. Various variants of the PWC®-method have been disclosed in, for example, WO 2012/096580 Al, WO 2013/133719 A1 and WO

2016/200269 Al.

Further, WO 2013/085621 Al, WO 2014/148913 Al and WO 2017/087331 Al disclose some other methods, systems and apparatuses for plugging wells. All of these publications teach to expand one or more pipe bodies, e.g. casing or tubing, within a well so as to fully or partially contact a surrounding wellbore wall or other pipe body, thereby forming an expanded pipe section, in the form of a bulge, flare or similar, in the well. These publications all teach to pump a fluidized plugging material, generally a cementitious material (e.g. cement slurry), down to the expanded pipe section via a suitable work string (e.g. a drill string or coiled tubing) and then allow the plugging material to set. This pumping and displacement of fluidized plugging material into the well normally represents a rather elaborate and costly well operation requiring use of various tools, equipment and materials to carry out the operation. Examples in this respect include assembling and operating a work string and associated equipment for conveying the fluidized plugging material into the well; preparing and handling the fluidized plugging material and associated fluids (e.g. spacer fluid) at the surface of the well; installing and operating associated pumping equipment at the surface. A drilling rig may also be required in this context. Pumping and displacing the fluidized plugging material within the well also carries a risk of the plugging material becoming mixed with fluids and materials already present in the well, thereby becoming contaminated and potentially causing insufficient or poor sealing in the well.

Importantly, there is no mentioning or indication in any of these publications about placing and melting a fusible solid material within such an expanded pipe section of a well in order to form a cross-sectional sealing plug in the well.

Yet further, US 6828531 Bl, US 2006/144591 A1 and US 2008/047708 A1 disclose some alternative methods and apparatuses for plugging in wells. All of these publications teach to position and melt a fusible solid material, for example a metal alloy in pellet form, in situ within a pipe body (e.g. casing or similar). The molten mass thereof is then allowed to flow into perforations or cracks in the casing and nearby structures so as to form a durable sealant therein upon solidification. The molten alloy may also solidify within the pipe body itself and form a sealing plug therein. US 6828531 Bl and US 2008/047708 A1 each disclose a heating tool, in the form of an electrical heater, for melting the alloy in situ. US 2006/144591 Al, however, discloses a heating tool comprising an igniter and an exothermic reactant material, such as thermite or thermate, for melting the alloy in situ. These

publications also teach to include the fusible solid material with the heating tool and, further, to lower the heating tool into the well on a pipe string or an electrical cable structure from which electric power may be supplied to the heating tool. Importantly, there is no mentioning or indication in any of these publications about forming an expanded pipe section, in the form of a bulge, flare or similar, in the pipe body before melting and solidifying a fusible solid material within the expanded pipe section so as to form a cross-sectional sealing plug in the well. Therefore, these publications do not teach to constrict and essentially close an annular area outside the pipe body by forming said expanded pipe section and then simply melting and solidifying the fusible solid material within at least a cross-sectional portion of the expanded pipe section.

WO 2017/203248 Al also discloses a plugging tool comprising a tubular heater body with an internal cavity for receiving a chemical heat source, such as a thermite formulation, and a quantity of eutectic bismuth-based alloy (fusible solid material) provided around the heater body. A surface operated ignition device is also included in the tool for remotely initiating an exothermic reaction in the chemical heat source and thus melting the alloy in situ within a well. In view of these observations, new and/or improved solutions would be advantageous for making well plugging operations even more expedient and cost-efficient.

Summary

The primary object of the present invention is to remedy or reduce at least one disadvantage of the prior art, or at least to provide a useful alternative to the prior art.

A further object is to provide new solutions for making well plugging operations more expedient and cost-efficient than those currently afforded by prior art well plugging technologies.

Another object of the invention is to provide solutions operable with relatively light- weighted structures, equipment and/or transportation means, such as water-borne light-weighted vessels (e.g. boats) or mobile light-weighted surface vehicles (e.g. trucks).

It is also an object of the invention to allow for use of substantially coilable

conveyance structures, such as coiled tubing, electrical cables and/or hydraulic supply conduits, to access subterranean wells and carry out plugging operations therein.

It is therefore also an object of the invention to provide substantially rig-less solutions.

As will become clear in the following, the present invention and various embodiments thereof serve to meet these objects of the invention, hence to provide expedient and cost-efficient well plugging solutions.

The objects are achieved by virtue of steps and features disclosed in the following description and subsequent claims.

In a first aspect, the present invention comprises a method of forming a cross- sectional sealing plug in a subterranean well comprising at least one pipe body, including an innermost pipe body, and at least one outwardly surrounding and corresponding annulus, the method comprising the following combination of steps:

(A) lowering a pipe expansion device into the innermost pipe body to a first location in the well;

(B) with the pipe expansion device, expanding a first section of the at least one pipe body until an outside thereof contacts a surrounding wellbore wall, thereby forming an expanded pipe section capable of closing the at least one annulus (i.e. fully or partially); (C) lowering a fusible solid material into the expanded pipe section;

(D) lowering a heating tool into the expanded pipe section;

(E) activating the heating tool and melting the fusible solid material so as to form a molten mass thereof, and allowing the molten mass to fill at least a cross-sectional portion of the expanded pipe section; and

(F) deactivating the heating tool and allowing the molten mass to solidify so as to form said cross-sectional sealing plug in the well.

The formation of the expanded pipe section constricts and essentially closes the at least one annulus surrounding the at least pipe body, after which the fusible solid material is simply melted and solidified within the expanded pipe section so as to fill and seal off at least a cross-sectional portion thereof. Steps (A)-(F) of the method may prove sufficient to complete the plugging operation without requiring any further actions. As will become evident in the following, the steps of the method may also be carried out using substantially coilable conveyance structures (e.g. coiled tubing, electrical cables and/or hydraulic supply conduits), as already noted. The method therefore represents a very simple and cost-efficient solution of forming a cross- sectional plug in a well.

Preferably, but not necessarily, the expanded pipe section is formed at a well location where the surrounding wellbore wall comprises substantially impermeable (e.g. low- permeability) rocks, thereby avoiding potential bypassing of pressurized formation fluids via the surrounding rocks.

Further, the amount of fusible solid material lowered into the expanded pipe section in step (C) must correspond to the in situ volume of molten mass required for forming the sealing plug. Moreover, the molten mass should have a specific gravity being larger, and preferably substantially larger, than the specific gravity of the ambient liquids in the well. This ensures proper displacement of the ambient fluids when filling the molten material within the expanded pipe section.

In context of the present method, it is to be understood that said at least one outwardly surrounding annulus might contain predominantly fluids (generally implying liquids). Depending on the type and age of the well, said at least one annulus might also contain various contaminants in a solid, semi-solid or liquid state, or a mixture thereof. These contaminants may therefore comprise various particles, debris, deposits and/or well fluids, for example filter cake, formation particles, drill cuttings, drilling additives, e.g. barite, cement particles and/or residues and old drilling fluids (or similar), that have settled out or remain in the annulus from previous well operations.

It is also to be understood that openings might develop along and around the circumference of the at least one pipe body when being expanded in step (B). The molten mass of the fusible solid material is likely to flow into and fill these openings, thereby sealing the openings along and around said cross-sectional portion of the expanded pipe section. Moreover, contaminants of the above-mentioned type may also be present in the one or more surrounding annuli. Considering that the expansion forces may be great during the pipe expansion in step (B), these contaminants may therefore be squeezed into the openings so as to act as secondary sealants in and around the openings. It is therefore highly likely that the one or more squeezed annuli are properly sealed against and, further, that pressure sealing of the one or more annuli does not represent a problem. Further, step (E) of the method may comprise filling molten mass into at least the entire expanded pipe section, possibly also further up within the innermost pipe body.

Yet further, the well may comprise only the innermost pipe body and an outwardly surrounding annulus.

Alternatively, the well may comprise two or more progressively larger pipe bodies arranged in a pipe-in-pipe constellation, and two or more outwardly surrounding and corresponding annuli.

In order to prevent the molten mass from potentially flowing deeper into the innermost pipe body and thus escaping the expanded pipe section, it may become necessary to retain the molten mass in the expanded pipe section. The method may therefore comprise disposing a blocking device within the innermost pipe body, and below the first location in the well.

In one embodiment, the method comprises disposing, before step (A), a blocking device within the innermost pipe body, and below the first location at which the at least one pipe body is to be expanded. In an alternative embodiment, the method comprises disposing, between steps (B) and (C), a blocking device within the innermost pipe body, and below the expanded pipe section. In both of these embodiments, the blocking device may be a mechanical plug anchored to the innermost pipe body. The mechanical may be of any suitable type known in the art.

Further, the blocking device may comprise at least one thermo-protective element or cushion for protecting the blocking device against the molten mass. The thermo- protective element/cushion may be of any suitable material known in the art, for example a cushion of sand or glass, or some other thermo-resistant structure.

In one embodiment, the method comprises performing steps (C) and (D) in one trip into the well. This requires both the fusible solid material and the heating tool to be introduced simultaneously into the well.

In an alternative embodiment, the method comprises performing steps (A)-(F) in one trip into the well.

In a first embodiment of the method, the pipe expansion device comprises at least one explosive charge; and

- wherein the method comprises detonating, in step (B), the at least one explosive charge within the innermost pipe body and expanding the at least one pipe body so as to form said expanded pipe section at the first location.

As such, the at least one explosive charge may comprises an explosive, nitrated organic compound, for example the explosive compound C4, which is commonly known in the industry.

In this first embodiment, step (A) of the method may comprise lowering the at least one explosive charge into the innermost pipe body using one of a flow-through string (e.g. a drill string or coiled tubing) and a cable structure (e.g. an electrical cable structure in the form of a wireline or braided cable). In a second embodiment of the method, the pipe expansion device comprises a mechanical expansion tool; and

- wherein the method comprises activating, in step (B), the mechanical expansion tool and mechanically engaging and forcing the at least one pipe body outwards so as to form said expanded pipe section at the first location. In one variant, the mechanical expansion tool is a swage tool comprising a motor drivingly connected to radially movable arms. The motor may be an electric or a hydraulic motor of suitable type. A swage tool of this type is discussed in WO

2013/085621 A1 mentioned under prior art above.

In an alternative variant, the mechanical expansion tool is a hydraulically activated expansion tool. This implies that a hydraulic fluid, for example drilling mud, must be supplied to the expansion tool in order to operate and drive hydraulically activated expansion elements in the tool.

In yet an alternative variant, the mechanical expansion tool is one of a solid cone pipe expansion tool, roller cone pipe expansion tool, and axial rotating pipe expansion tool. This implies that a pulling force or rotating axial force must be applied to the expansion tool in order to operate and drive mechanically activated expansion elements in the tool.

These alternative variants are discussed in WO 2017/087331 A1 mentioned under prior art above.

Further, the fusible solid material of the method may be selected from a group of materials comprising :

- a metal;

- an alloy;

- elemental sulphur;

- a thermosetting plastic; and

- a thermoplastic.

The melting point of these materials would have to be lower, and preferably substantially lower, than the melting point of said at least one pipe body, which is commonly made of an iron alloy, typically some type of steel. The melting point of pure iron is 1538 °C. The suitability of the above group of materials depends on the particular temperature at said first location in the well. As such, elemental sulphur (S) and thermoplastics have the lowest melting points. The melting point of elemental sulphur is 115 °C, whereas the melting points of thermoplastics typically are in the 70-150 °C range. Thermosetting plastics, however, generally melt and cure at temperatures in the ISO- 350 °C range, typically above 200 °C, and remain solidified at lower temperatures thereafter. Suitable and stable metals could be tin (Sn) having a melting point at 232 °C, and lead (Pb) having a melting point at 327 °C. Alloys have a wide range of melting temperatures ranging from approximately 50-1000 °C. The most applicable alloys in the present invention, however, are envisaged to have melting points in the 50-600 °C range.

Further, the alloy may be a metal-based alloy, which advantageously may be a eutectic metal alloy for ensuring homogeneous melting of the constituent metal elements in the alloy. Preferably, the metal alloy has a melting point in the 100-400 °C range.

In one embodiment, the metal alloy comprises tin (Sn) and lead (Pb), or some other type of suitable soldering or brazing material.

In an alternative embodiment, the metal alloy is a bismuth-based alloy. The melting point of pure bismuth (Bi) is 271 °C. Further, the bismuth-based alloy may comprise chiefly bismuth (Bi) and one or more elements selected from a group comprising lead (Pb), tin (Sd), cadmium (Cd), antimony (Sb), and silver (Ag). Other elements may also be suitable in this alloy.

Bismuth-based alloys having melting points of 385 °C or less appear to be most suitable in the present invention. As used in the present invention, bismuth-based alloys are advantageous in that they exhibit very useful physical properties. When in a molten state, such a bismuth-based alloy exhibits low viscosity, similar to that of water, and the specific gravity thereof is approximately 10. Therefore, the molten bismuth-based alloy will displace any lighter ambient liquids present in the expanded pipe section so as to flow readily into and fill any void spaces in and around the expanded pipe section. When solidifying, the bismuth-based alloy expands

approximately 10 per cent by volume (like ice), thereby ensuring tight bonding and sealing in the void spaces filled, including any openings developed along and around the circumference of the expanded pipe section. The bismuth-based alloy is also corrosion-resistant and therefore ensures long term durability of the cross-sectional sealing plug in the well.

It is conceivable that other fusible solid materials may be suitable in the present invention and, therefore, that other melting point ranges and physical properties may apply. In a third embodiment of the method, the fusible solid material is embodied as a particulate material; and

- wherein the method comprises conveying, in step (C), the particulate material into the expanded pipe section. Advantageously, the particulate material may be in the form of pellets or similar having a suitable size and specific gravity to be conveyed into the well and used therein. The particulate material may be dropped into the expanded pipe section from the surface of the well. Alternatively, the particulate material may be placed inside a dump bailer or similar subsequently being lowered to the expanded pipe section where the particulate material is dumped.

In one variant of the third embodiment, the heating tool comprises an electrical heater equipped with at least one heating element; and

- wherein the method comprises placing, in step (D), the electrical heater in thermal communication with the particulate material in the expanded pipe section and activating, in step (E), the at least one heating element and melting the particulate material.

The electrical heater may be a resistance or induction type heater, and said heating element may be in the form of a heater coil or similar. Such a heater is discussed in US 6828531 A1 mentioned under prior art above.

Further, the electrical heater may be configured to receive electric power from an electrical cable (e.g. an electrical wireline cable) connected to the electrical heater and extending to the surface of the well.

In an alternative variant of the third embodiment, the heating tool comprises a chemical heater that includes (hence carries) an exothermic reactant material and an ignition device; and

- wherein the method comprises placing, in step (D), the chemical heater in thermal communication with the particulate material in the expanded pipe section and using, in step (E), the ignition device to selectively initiate an exothermic chemical reaction in the reactant material and melting the particulate material.

The ignition device may be e.g. a chemical, electrical or pyrotechnic ignition device. The ignition device may receive control signals and/or power via a suitable cable, e.g. an electrical cable, extending to the surface of the well.

As an example, the British company BiSN Tec Ltd. is marketing a chemical reaction heater capable of being run into a well on any standard wire equipment and, further, that the power required for starting the reaction is 240 volts and 60 mA (milliamperes for approximately 15 seconds. Such a chemical reaction heater is discussed in WO 2017/203248 A1 mentioned under prior art above. Alternatively, the chemical heater may include equipment and devices, such as chemicals, pyrotechnic compounds, triggering mechanisms, timers, batteries and control devices, for controlling and operating the ignition device in situ and thus selectively initiate the exothermic chemical reaction in situ. Further, the exothermic reactant material used in the chemical heater may be selected from a group of materials comprising :

- a thermite composition;

- an ammonium chloride and sodium nitrite composition; and

- a hydrocarbon-based fuel and an oxidizer. The thermite composition may be a formulation comprising e.g. iron oxide and aluminium, whereas the hydrocarbon-based fuel and oxidizer may comprise e.g. diesel and air/oxygen.

Thermite formulations are known in various arts and are capable of reaching very high exothermic reaction temperatures, e.g. in order of 3200 °C, in their pure and undiluted form. Such temperatures could potentially cause undesirable meltdown of pipe bodies and other well elements if used in the present invention.

It may therefore prove advantageous for the thermite reactant material to be diluted to lower at least one of its reaction temperature and its reaction velocity. For example, the thermite reactant material may be diluted with a eutectic material, a metal oxide (e.g. aluminium oxide, calcium oxide or other metal oxide) and/or with silica. Further, the thermite reactant material may be diluted by between 5 and 75 per cent by mass.

An exothermic reaction temperature range of 500-1000 °C appears suitable for melting the fusible solid material in the present invention, which is embodied as a particulate material in the third embodiment of the method. In a fourth embodiment of the method, the heating tool includes (hence carries) the fusible solid material, wherein the heating tool is in thermal communication with the fusible solid material, and wherein the fusible solid material is embodied as at least one of:

- a particulate material;

- at least one sheath or collar;

- at least one solid block; and

- a wire structure; and

- wherein the method comprises activating, in step (E), the heater tool and melting the fusible solid material included with the heater tool. The particulate material may be in the form of pellets or similar disposed in or on the heating tool. Further, the at least one sheath or collar may surround the heating tool, whereas the at least one solid block may be attached to or carried by the heating tool. Yet further, wire structure may be coiled or wrapped on or around the heating tool, alternatively on or around a part of the heating tool.

In one variant of the fourth embodiment, the heating tool comprises an electrical heater (resistance or induction type heater) equipped with at least one heating element (e.g. in the form of coils or similar) for melting the fusible solid material in step (E). As noted above, the electrical heater may be a resistance or induction type heater, and said heating element may be in the form of a heater coil or similar.

In one embodiment, the at least one heating element is contained within a housing of the electrical heater, and wherein the fusible solid material is disposed outside the housing and in thermal communication with the housing. In an alternative embodiment, the fusible solid material is contained within a housing of the electrical heater, and wherein the at least one heating element is disposed outside the housing and in thermal communication with the housing.

In an alternative variant of the fourth embodiment, the heating tool comprises a chemical heater that includes (hence carries) an exothermic reactant material for melting the fusible solid material in step (E), and an ignition device for selectively initiating an exothermic chemical reaction in the reactant material. As noted above, the ignition device may be a chemical, electrical or pyrotechnic ignition device.

In one embodiment, the exothermic reactant material is contained within a heater body of the chemical heater, and wherein the fusible solid material is disposed outside of the heater body. In an alternative embodiment, the fusible solid material is contained within a heater body of the chemical heater, and wherein the exothermic reactant material is disposed outside of the heater body. Further, the exothermic reactant material may be selected from a group of materials comprising :

- a thermite composition;

- an ammonium chloride and sodium nitrite composition; and

- a hydrocarbon-based fuel and an oxidizer.

As noted above, the thermite composition may be a formulation comprising e.g. iron oxide and aluminium, whereas the hydrocarbon-based fuel and oxidizer may comprise e.g. diesel and air/oxygen. The thermite reactant material may also be diluted by between 5 and 75 per cent by mass, for example to reach reaction temperatures in the range of 500-1000 °C, as specified above.

Additional to any of the preceding embodiments, the method may further comprise the following steps:

(G) lowering a perforation tool into the innermost pipe body to a second location above the cross-sectional sealing plug formed at the first location in steps (A)-(F); (H) with the perforation tool, forming at least one hole in the at least one pipe body at the second location; and

(I) placing a fluidized plugging material in the innermost pipe body at the second location, also allowing the fluidized plugging material to displace into the at least one outwardly surrounding annulus via the at least one hole formed in step (H), the fluidized plugging material forming, upon setting, a secondary cross-sectional plug along a second section of the at least one pipe body.

The addition of a secondary cross-sectional plug above the solidified plug at the first location of the well provides additional sealing of the well. Advantageously, the upper part of the underlying expanded pipe section also provides annular support to the fluidized plugging material when being displaced into the at least one outwardly surrounding annulus in step (I), thereby preventing the plugging material from escaping downwards in said annulus.

Further, the fluidized plugging material may comprise a cementitious material, e.g. cement slurry or some other suitable cement-based material. Other types of fluidized plugging material may also be applicable, e.g. liquid resins materials or similar.

Alternatively, the fluidized plugging material may comprise a second molten mass of fusible solid material formed between steps (H) and (I). A fusible solid material and heating tool (as described above) may be used to provide said second molten mass of fusible solid material. The method may also comprise the following steps between steps (H) and (I) :

- with a washing tool attached to a flow-through work string, lowering the washing tool into the innermost pipe body to the second location above the cross- sectional sealing plug formed at the first location in steps (A)-(F);

- pumping a washing fluid down through the work string and out into the innermost pipe body via the washing tool; and

- directing the washing fluid further out into the at least one outwardly surrounding annulus via the at least one hole formed in step (H), thereby cleaning both the innermost pipe body and said at least one annulus before placing the fluidized plugging material therein in step (I).

This cleaning embodiment may prove necessary or advantageous if the at least one annulus contains significant amounts of contaminants, as discussed above. Should a second molten mass of fusible solid material be used in context of this embodiment, said cleaning operation is carried out before melting the fusible solid material. Additional to any of the preceding embodiments, the method may also comprise repeating at least steps (A)-(F) of the method at one or more locations above said first location in the well, thereby forming one or more additional cross-sectional sealing plugs from fusible solid material along the well.

Further, each such additional plug may be supplied with a secondary cross-sectional plug made from a fluidized plugging material, as specified in step (I) of the method.

In a second aspect, the present invention comprises a system for forming a cross- sectional sealing plug in a subterranean well comprising at least one pipe body, including an innermost pipe body, and at least one outwardly surrounding and corresponding annulus, the system comprising :

- a pipe expansion device structured for lowering into the innermost pipe body to a selected location in the well, said pipe expansion device also structured for allowing it to expand a section of the at least one pipe body until an outside thereof contacts a surrounding wellbore wall, thereby forming an expanded pipe section capable of closing the at least one surrounding annulus (i.e. fully or partially);

- a fusible solid material structured for lowering into the expanded pipe section; and

- a heating tool structured for lowering into the expanded pipe section, said heating tool also structured for allowing it to be activated and melting the fusible solid material so as to form a molten mass thereof capable of filling at least a cross-sectional portion of the expanded pipe section, and said heating tool also structured for allowing it to be deactivated and thus allowing the molten mass to solidify so as to form said cross- sectional sealing plug in the well.

From this definition of the system, it is clear that many of the features and comments provided above in relation to the claimed method, also are inherent and thus applicable to the claimed system. For the sake of expedience, such comments will not be reiterated in the following, and reference is therefore made to the comments made in relation to the method above.

Further, a blocking device may be disposed within the innermost pipe body, and below the selected location in the well.

In a first embodiment of the system, the pipe expansion device comprises at least one explosive charge.

In a second embodiment of the system, the pipe expansion device comprises a mechanical expansion tool.

Further, the fusible solid material of the system may be selected from a group of materials comprising :

- a metal;

- an alloy;

- elemental sulphur;

- a thermosetting plastic; and

- a thermoplastic. Yet further, the alloy may be a metal-based alloy, which advantageously may be a eutectic metal alloy for ensuring homogeneous melting of the constituent metal elements in the alloy.

In one embodiment, the metal alloy comprises tin (Sn) and lead (Pb), or some other type of suitable soldering or brazing material. In an alternative and advantageous embodiment, the metal alloy is a bismuth-based alloy. Further, the bismuth-based alloy may comprise chiefly bismuth (Bi) and one or more elements selected from a group comprising lead (Pb), tin (Sd), cadmium (Cd), antimony (Sb), and silver (Ag). Other elements may also be suitable in this alloy.

In a third embodiment of the system, the heating tool comprises an electrical heater (resistance or induction type heater) equipped with at least one heating element (e.g. in the form of coils or similar) for melting the fusible solid material. The electrical heater may be configured to receive electric power from an electrical cable (e.g. electrical wireline cable) connected to the electrical heater and extending to the surface of the well.

In a fourth embodiment of the system, the heating tool comprises a chemical heater that includes (hence carries) an exothermic reactant material for melting the fusible solid material, and an ignition device (e.g. chemical, electrical or pyrotechnic ignition device) for selectively initiating an exothermic chemical reaction in the reactant material and melting the fusible solid material.

Further, the exothermic reactant material used in the chemical heater may be selected from a group of materials comprising :

- a thermite composition;

- an ammonium chloride and sodium nitrite composition; and

- a hydrocarbon-based fuel and an oxidizer.

The thermite composition may be a formulation comprising e.g. iron oxide and aluminium, whereas the hydrocarbon-based fuel and oxidizer may comprise e.g. diesel and air/oxygen.

Advantageously, the thermite reactant material may be diluted to lower at least one of its reaction temperature and its reaction velocity. For example, the thermite reactant material may be diluted with a eutectic material, a metal oxide (e.g. aluminium oxide, calcium oxide or other metal oxide) and/or with silica. Further, the thermite reactant material may be diluted by between 5 and 75 per cent by mass.

In a fifth embodiment of the system, the heating tool includes (hence carries) the fusible solid material, wherein the heating tool is in thermal communication with the fusible solid material, and wherein the fusible solid material is embodied as at least one of:

- a particulate material;

- at least one sheath or collar;

- at least one solid block; and

- a wire structure. The particulate material may be in the form of pellets or similar disposed in or on the heating tool. Further, the at least one sheath or collar may surround the heating tool, whereas the at least one solid block may be attached to or carried by the heating tool. Yet further, wire structure may be coiled or wrapped on or around the heating tool, alternatively on or around a part of the heating tool. In one variant of the fifth embodiment, the heating tool comprises an electrical heater equipped with at least one heating element for melting the fusible solid material.

In one embodiment, the at least one heating element is contained within a housing of the heating tool, and wherein the fusible solid material is disposed outside the housing and in thermal communication with the housing.

In an alternative embodiment, the fusible solid material is contained within a housing of the heating tool, and wherein the at least one heating element is disposed outside the housing and in thermal communication with the housing.

Further, the electrical heater may be configured to receive electric power from an electrical cable connected to the electrical heater and extending to the surface of the well.

In an alternative variant of the fifth embodiment, the heating tool comprises a chemical heater that includes (hence carries) an exothermic reactant material for melting the fusible solid material, and an ignition device for selectively initiating an exothermic chemical reaction in the reactant material.

In one embodiment, the exothermic reactant material is contained within a heater body of the chemical heater, and wherein the fusible solid material is disposed outside of the heater body.

In an alternative embodiment, the fusible solid material is contained within a heater body of the chemical heater, and wherein the exothermic reactant material is disposed outside of the heater body.

Further, the exothermic reactant material may be selected from a group of materials comprising :

- a thermite composition;

- an ammonium chloride and sodium nitrite composition; and

- a hydrocarbon-based fuel and an oxidizer.

Yet further, the thermite reactant material may be diluted to lower at least one of its reaction temperature and its reaction velocity, as described above.

In a third aspect, the present invention comprises a cross-sectional sealing plug in a subterranean well comprising at least one pipe body, including an innermost pipe body, and at least one outwardly surrounding and corresponding annulus, the sealing plug comprising : - an expanded section of the at least one pipe body having an outside in contact with a surrounding wellbore wall so as to close the at least one surrounding annulus; and

- a fusible solid material melted and solidified within the innermost pipe body so as to fill at least a cross-sectional portion of the expanded pipe section and thus form said cross-sectional sealing plug in the well.

From this definition of the sealing plug, it is clear that many of the features and comments provided above in relation to the claimed method and system, also are inherent and thus applicable to the claimed sealing plug. For the sake of expedience, such comments will not be reiterated in the following, and reference is therefore made to the comments made in relation to the method and the system above.

Further, the solidified plug material may fill at least the entire expanded pipe section.

Yet further, the fusible solid material may be selected from a group of materials comprising :

- a metal;

- an alloy;

- elemental sulphur;

- a thermosetting plastic; and

- a thermoplastic.

The alloy may be a metal-based alloy, which advantageously may be a eutectic metal alloy for ensuring homogeneous melting of the constituent metal elements in the alloy.

In an alternative and advantageous embodiment, the metal alloy is a bismuth-based alloy. Further, the bismuth-based alloy may comprise chiefly bismuth (Bi) and one or more elements selected from a group comprising lead (Pb), tin (Sd), cadmium (Cd), antimony (Sb), and silver (Ag). Other elements may also be suitable in this alloy.

Brief description of the drawings

Exemplary embodiments of the invention are described and depicted in the

accompanying drawings, where: Figure 1 shows, in side view, a well to be plugged and abandoned according to the present invention; Figure 2 shows, in side view, the well after having lowered an explosive charge to a selected (e.g. first) location in a pipe body of the well;

Figure 3 shows, in side view, the well upon detonating the explosive charge and thus expanding a longitudinal (e.g. first) section of the pipe body at the selected location;

Figure 4 shows, in side view, an alternative expansion embodiment in which a mechanical expansion tool, in the form of a swage tool, has been lowered to the selected location in the pipe body;

Figure 5 shows, in side view, the swage tool activated and in the process of

expanding said longitudinal section of the pipe body at the selected location;

Figure 6 shows, in side view, the pipe body after being expanded so as to form an expanded pipe section having, in this case, longitudinal cracks formed therein, and after having placed a mechanical plug below the expanded pipe section;

Figure 7 shows, in side view, the well after having lowered a chemical heater carrying a fusible solid metal alloy into the expanded pipe section;

Figure 8 shows, in side view, a cross-section through the chemical heater, thereby showing constituents of the chemical heater; Figure 9 shows, in side view, the chemical heater activated and in the process of melting the fusible solid metal alloy so as to form a molten thereof being filled into the expanded pipe section; and

Figure 10 shows, in side view, the well after having deactivated and retracted the chemical heater, and after the molten mass has solidified so as to form a cross-sectional sealing plug within the expanded pipe section of the well.

The figures are schematic and merely show steps, details and equipment being essential to the understanding of the invention. Further, the figures are distorted with respect to relative dimensions of elements and details shown in the figures. The figures are also somewhat simplified with respect to the shape and richness of detail of such elements and details. Elements not being central to the invention may also have been omitted from the figures. Further, equal, equivalent or corresponding details shown in the figures will be given substantially the same reference numerals. Detailed description of an embodiment of the invention

Figure 1 shows a well 2 to be plugged and abandoned in accordance with the present invention. The well 2 comprises a pipe body 4 (e.g. a casing, liner or tubing) and an outwardly surrounding annulus 6 defined between the pipe body 4 and a wellbore wall 8 comprising low-permeability rocks 10. In this embodiment, the annulus 6 contains contaminants 12 in the form of various particles, debris, deposits and/or well fluids, as discussed above.

Figure 2 shows the well 2 after having lowered an explosive charge 14 to a selected location in the pipe body 4. In this embodiment, a coilable cable 16 is used to do so. The coilable cable 16 could be in the form of a flow-through string, for example coiled tubing or some other hydraulic conduit, or in the form of a cable structure, for example an electrical cable in the form of a wireline, braided cable or similar. The person skilled in the art would know of such coilable structures, hence would select the most appropriate structure. Depending on detonation mechanism employed, detonation may be initiated using hydraulic pressure or an electric signal, as would also be known to the person skilled in the art.

Figure 3 shows the well 2 upon detonating the explosive charge 14 and thus expanding a longitudinal section L of the pipe body 4 until an outside thereof is forced into the surrounding wellbore wall 8, thereby forming an expanded pipe section 18 along the longitudinal section L. The explosive expansion forces are shown with outwardly directed arrows in Figure 3. Essentially, the expanded pipe section 18 constricts and closes the annulus 6 located external to the expanded pipe section 18, thereby sealing the annulus 6 in this region. Figure 3 also shows a free end of the coilable cable 16 located immediately above the expanded pipe section 18. Figure 4 shows, in an alternative expansion embodiment, a mechanical expansion tool in the form of a swage tool 20 for expanding the pipe body 4 along its longitudinal section L. The swage tool 20 is shown after being lowered on a suitable coilable cable 16 ^' (as discussed above) to the selected location in the pipe body 4. The swage tool 20 comprising a motor (not shown) located within a motor housing 22 and drivingly connected, via a threaded spindle 24, to radially movable arms 26.

Figure 5 shows the swage tool 20 activated by allowing the motor to move the arms 26 along the spindle 24 and mechanically expand the arms 26 outwards against the pipe body 4. By so doing, the pipe body 4 is forced into the surrounding wellbore wall 8 so as to form said expanded pipe section 18. The mechanical expansion forces are shown with outwardly directed arrows in Figure 5. After expansion, the motor is allowed to move the arms 26 in the opposite direction along the spindle 24 so as to retract the arms 26. Then the swage tool may be removed from the well 2.

Figure 6 shows the pipe body 4 after being expanded so as to form said expanded pipe section 18. In this embodiment, longitudinal cracks 28 have been formed in the expanded pipe section 18 during expansion of the pipe body 4. Besides being sealed by contact with the surrounding wellbore wall 8, contaminants 12 present in the annulus 6 outside the expanded pipe section 18 will be squeezed into these cracks 28 during said expansion, thereby acting as secondary sealants in and around the cracks 28. Figure 6 also shows a mechanical plug 30 placed below the expanded pipe section 18.

Figure 7 shows the well 2 after having lowered a chemical heater 32 to the expanded pipe section 18. In this embodiment, the chemical heater 32 carries a fusible solid metal alloy on an outside thereof. A coilable cable 16 ^{' '} of suitable type is used do lower the chemical heater 32 into the pipe body 4 (as discussed above). A suitable deployment tool (not shown) may be connected between the coilable cable 16 ^{' '} and the chemical heater 32.

Figure 8 shows a cross-section through the chemical heater 32. Essentially, the chemical heater 32 comprises a heater body in the form of a heat-resistant housing 34 connected to an overlying connection piece 36, which in turn is connected to the coilable cable 16 ^{' '} . In this embodiment, the heat-resistant housing 34 contains pellets of a diluted thermite composition 38. Further, the fusible metal alloy is a eutectic bismuth-based alloy embodied as a collar 40 surrounding the heat-resistant housing 34 (as discussed above). The top of the housing 34 also includes an electrical ignition device 42 for selectively igniting the thermite composition 38 and receiving power from an electric wire 44 included in or attached to the coilable cable 16 ^{' '} . An upper portion of the chemical heater 32 is shown extending some distance above the expanded pipe section 18 so as to provide a sufficient amount of metal alloy for filling, when molten, at least a portion (or more) of the expanded pipe section 18. Figure 9 shows the chemical heater 32 after being activated using the electrical ignition device 42 to initiate an exothermic chemical reaction in the pellets of thermite composition 38 within the heat-resistant housing 34. The exothermic chemical reaction proceeds in a top-down fashion within the housing 34, thereby also melting the bismuth-based alloy in a top-down fashion. A molten mass 40 ^' of bismuth-based alloy flows like water into and fills the expanded pipe section 18, including said longitudinal cracks 28 therein. Figure 9 shows the molten mass 40 ^' being filled up to a level somewhat above the expanded pipe section 18.

Figure 10 shows the well 2 upon completion of the exothermic chemical reaction in the thermite composition 38, and after having retracted the chemical heater 32 from the well 2. Figure 10 also shows the molten mass 40 ^' of bismuth-based alloy after having solidified within the expanded pipe section 18 due to exposure to lower ambient temperatures in the expanded pipe section 18, thereby forming a cross-sectional sealing plug 40 ^{' '} therein. In this embodiment, the plug 40 ^{' '} also extends up to a level somewhat above the expanded pipe section 18. When solidifying, the bismuth- based alloy expands approximately 10 per cent by volume, thereby ensuring tight bonding and sealing in the expanded pipe section 18, including the cracks 28 therein.

Claims

C l a i m s

1. A method of forming a cross-sectional sealing plug (40 ^{' '}) in a subterranean well (2) comprising at least one pipe body (4), including an innermost pipe body, and at least one outwardly surrounding and corresponding annulus (6), the method comprising the following combination of steps:

(A) lowering a pipe expansion device (14, 20) into the innermost pipe body to a first location in the well (2);

(B) with the pipe expansion device (14, 20), expanding a first section (L) of the at least one pipe body (4) until an outside thereof contacts a surrounding wellbore wall (8), thereby forming an expanded pipe section (18) capable of closing the at least one annulus (6);

(C) lowering a fusible solid material (40) into the expanded pipe section (18);

(D) lowering a heating tool (32) into the expanded pipe section (18);

(E) activating the heating tool (32) and melting the fusible solid material

(40) so as to form a molten mass (40 ^') thereof, and allowing the molten mass (40 ^') to fill at least a cross-sectional portion of the expanded pipe section (18); and

(F) deactivating the heating tool (32) and allowing the molten mass (40 ^') to solidify so as to form said cross-sectional sealing plug (40 ^{' '}) in the well (2).

2. The method according to claim 1, the method comprising disposing a blocking device (30) within the innermost pipe body, and below the first location in the well (2).

3. The method according to claim 1 or 2, wherein the pipe expansion device

comprises at least one explosive charge (14); and

- wherein the method comprises detonating, in step (B), the at least one explosive charge (14) within the innermost pipe body and expanding the at least one pipe body (4) so as to form said expanded pipe section (18) at the first location. 4. The method according to claim 1 or 2, wherein the pipe expansion device

comprises a mechanical expansion tool (20); and

- wherein the method comprises activating, in step (B), the mechanical expansion tool (20) and mechanically engaging and forcing the at least one pipe body (4) outwards so as to form said expanded pipe section (18) at the first location.

5. The method according to any one of claims 1-4, wherein the fusible solid material (40) is selected from a group of materials comprising :

- a metal;

- an alloy;

- elemental sulphur;

- a thermosetting plastic; and

- a thermoplastic.

6. The method according to claim 5, wherein the alloy is a metal-based alloy.

7. The method according to claim 6, wherein the metal alloy is a bismuth-based alloy.

8. The method according to any one of claims 1-7, wherein the fusible solid

material (40) is embodied as a particulate material; and

- wherein the method comprises conveying, in step (C), the particulate material into the expanded pipe section (18). 9. The method according to any one of claims 1-7, wherein the heating tool (32) includes the fusible solid material (40), wherein the heating tool (32) is in thermal communication with the fusible solid material (40), and wherein the fusible solid material (40) is embodied as at least one of:

- a particulate material;

- at least one sheath or collar;

- at least one solid block; and

- a wire structure; and

- wherein the method comprises activating, in step (E), the heater tool (32) and melting the fusible solid material (40) included with the heater tool (32). 10. The method according to claim 9, wherein the heating tool (32) comprises an electrical heater equipped with at least one heating element for melting the fusible solid material (40) in step (E).

11. The method according to claim 9, wherein the heating tool (32) comprises a chemical heater that includes an exothermic reactant material (38) for melting the fusible solid material (40) in step (E), and an ignition device (42) for selectively initiating an exothermic chemical reaction in the reactant material (38).

12. The method according to claim 11, wherein the exothermic reactant material (38) is contained within a heater body (34) of the chemical heater (32), and wherein the fusible solid material (40) is disposed outside of the heater body (34). 13. The method according to claim 11, wherein the fusible solid material (40) is contained within a heater body (34) of the chemical heater (32), and wherein the exothermic reactant material (38) is disposed outside of the heater body (34).

14. The method according to any one of claims 11, 12 or 13, wherein the exothermic reactant material (38) is selected from a group of materials comprising :

- a thermite composition;

- an ammonium chloride and sodium nitrite composition; and

- a hydrocarbon-based fuel and an oxidizer.

15. The method according to any one of claims 1-14, the method further comprising the following steps:

(G) lowering a perforation tool into the innermost pipe body to a second location above the cross-sectional sealing plug (40 ^{' '}) formed at the first location in steps (A)-(F);

(H) with the perforation tool, forming at least one hole in the at least one pipe body (4) at the second location; and

(I) placing a fluidized plugging material in the innermost pipe body at the second location, also allowing the fluidized plugging material to displace into the at least one outwardly surrounding annulus (6) via the at least one hole formed in step (H), the fluidized plugging material forming, upon setting, a secondary cross-sectional plug along a second section of the at least one pipe body (4).

16. The method according to claim 16, the method also comprising, between steps (H) and (I), the following steps:

- with a washing tool attached to a flow-through work string, lowering the washing tool into the innermost pipe body to the second location above the cross-sectional sealing plug (40 ^{' '}) formed at the first location in steps (A)-(F);

- directing the washing fluid further out into the at least one outwardly surrounding annulus (6) via the at least one hole formed in step (H), thereby cleaning both the innermost pipe body and said at least one annulus (6) before placing the fluidized plugging material therein in step (I).

17. The method according to any one of claims 1-16, comprising repeating at least steps (A)-(F) of the method at one or more locations above said first location in the well (2), thereby forming one or more additional cross-sectional sealing plugs (40 ^{' '}) from fusible solid material (40) along the well (2).

18. A system for forming a cross-sectional sealing plug (40 ^{' '}) in a subterranean well (2) comprising at least one pipe body (4), including an innermost pipe body, and at least one outwardly surrounding and corresponding annulus (6), the system comprising :

- a pipe expansion device (14, 20) structured for lowering into the innermost pipe body to a selected location in the well, said pipe expansion device (14, 20) also structured for allowing it to expand a section (L) of the at least one pipe body (4) until an outside thereof contacts a surrounding wellbore wall (8), thereby forming an expanded pipe section (18) capable of closing the at least one surrounding annulus (6);

- a fusible solid material (40) structured for lowering into the expanded pipe section (18); and

- a heating tool (32) structured for lowering into the expanded pipe section (18), said heating tool (32) also structured for allowing it to be activated and melting the fusible solid material (40) so as to form a molten mass (40 ^') thereof capable of filling at least a cross-sectional portion of the expanded pipe section (18), and said heating tool (32) also structured for allowing it to be deactivated and thus allowing the molten mass (40 ^') to solidify so as to form said cross-sectional sealing plug (40 ^{' '}) in the well (2).

19. The system according to claim 18, wherein the fusible solid material (40) is

selected from a group of materials comprising :

- a metal;

- an alloy;

- elemental sulphur;

- a thermosetting plastic; and

- a thermoplastic.

20. The system according to claim 19, wherein the alloy is a metal-based alloy.

21. The system according to claim 20, wherein the metal alloy is a bismuth-based alloy.

22. The system according to any one of claims 18-21, wherein the heating tool (32) includes the fusible solid material (40), wherein the heating tool (32) is in thermal communication with the fusible solid material (40), and wherein the fusible solid material (40) is embodied as at least one of:

- a particulate material;

- at least one sheath or collar;

- at least one solid block; and

- a wire structure.

23. The system according to claim 22, wherein the heating tool (32) comprises a chemical heater that includes an exothermic reactant material (38) for melting the fusible solid material (40), and an ignition device (42) for selectively initiating an exothermic chemical reaction in the reactant material (38). 24. The system according to claim 23, wherein the exothermic reactant material (38) is selected from a group of materials comprising :

- a thermite composition;

- an ammonium chloride and sodium nitrite composition; and

- a hydrocarbon-based fuel and an oxidizer. 25. A cross-sectional sealing plug (40 ^{' '}) in a subterranean well (2) comprising at least one pipe body (4), including an innermost pipe body, and at least one outwardly surrounding and corresponding annulus (6), the sealing plug (40 ^{' '}) comprising :

- an expanded section (18) of the at least one pipe body (4) having an outside in contact with a surrounding wellbore wall (8) so as to close the at least one surrounding annulus (6); and

- a fusible solid material (40) melted and solidified within the innermost pipe body so as to fill at least a cross-sectional portion of the expanded pipe section (18) and thus form said cross-sectional sealing plug (40 ^{' '}) in the well (2).