WO2018115053A1

WO2018115053A1 - Method and system for sealing an annular cement sheath surrounding a wellbore tubular

Info

Publication number: WO2018115053A1
Application number: PCT/EP2017/083700
Authority: WO
Inventors: Jasper Jacob Willem TAAL; Frank Ruckert
Original assignee: Shell Internationale Research Maatschappij B.V.; Shell Oil Company
Priority date: 2016-12-22
Filing date: 2017-12-20
Publication date: 2018-06-28

Abstract

Micro-annuli and/or other cavities in an annular cement sheath surrounding a wellbore tubular are sealed by drilling a plurality of sealant injection channels through the wall of the tubular and into the annular cement sheath, to a controllable depth of penetration for each sealant injection channel, and subsequently positioning a sealant injection device at the selected position. The sealant injection device has expandable seals which are expanded against the inner surface of the wellbore tubular, such that an upper expandable seal is located above and the lower expandable seal is located below the drilled sealant injection channels. A sealant generation composition is then injected via the sealant injection channels into the cement sheath.

Description

METHOD AND SYSTEM FOR SEALING AN ANNULAR CEMENT SHEATH SURROUNDING A WELLBORE TUBULAR

FIELD OF THE INVENTION

The present invention is relates to sealing of cavities, such as micro-annuli and/or other cavities, in an annular cement sheath surrounding a tubular in a subterranean wellbore.

BACKGROUND OF THE INVENTION

Subterranean wells for the production of

hydrocarbons, such as oil and/or gas, commonly contain a tubular, such as a casing, liner, tubing. Commonly the tubing is surrounded by a cement sheath, which fills an annular space surrounding the tubular. The cement sheath structurally reinforces the tubing with respect to its surroundings, which can be the drilled wellbore itself, or alternatively an outer tubular, such as an outer casing, that is arranged in the wellbore. In addition to mechanically supporting the tubular, the cement sheath typically also serves to prevent fluid communication in or along the annulus surrounding the inner tubular.

A cement sheath can have imperfections, as a result of which fluid communication in and along the annulus is still possible. This can for example be detected as so-called "sustained casing pressure". Leak paths in the cement can be formed in various ways, e.g. when the pumped cement slurry does not completely fill the annulus during initial cementing, or as a result of shrinking during setting of the cement. Also, set cement is a brittle material that can crack if it gets deformed by external and internal stress loads. Such processes, alone or in combination, can cause the formation of micro-annuli, cracks, voids and/or channels resulting in leak paths for fluid in or along the annulus . Any of such structures or pathways allowing fluid flow in or along the cement sheath shall be referred to as "micro-annuli and/or other cavities" herein. Sometimes, information can be available about the likely type and/or location of a leak path, e.g. whether micro-annuli are expected near the inner or outer surface of the cement sheath, or whether

excessive stress may have caused cracks, or whether there were problems during the initial cementing operation .

The presence of leak paths in a cemented annulus is particularly problematic when a well is to be

abandoned, in which instance it is desired to seal fluid communication to surface and between subsurface layers .

It has been attempted in the past to seal flow paths by intervention into the annulus. A known method is disclosed in SPE paper No. 159216 by M Zwanenburg et al . , 2012. Therein, abrasive jets are used for cutting holes into casing (s) at two depth levels. After placing a retainer plug between the two depth levels, a sealant material is squeezed behind the casing to stop the Sustained Casing Pressure or gas percolation in the annulus. The known method however creates large voids in the cement sheath, the dimensions and depth of which in practice depend on many factors and cannot be known with any certainty to the operators. Abrasive jetting was shown to easily cut through two substantially concentric casings. Abrasive jets were found to take the way of least resistance, and wash away large regions of cement in some areas and leaving other areas largely intact . There is a need for an improved method and system for sealing micro-annuli and/or other cavities in an annular cement sheath surrounding a tubular of a subterranean wellbore, permitting better control of the injection of sealant.

SUMMARY OF THE INVENTION

In one aspect, the present invention provides a method for sealing cavities in an annular cement sheath surrounding a tubular in a subterranean wellbore, the method comprising:

- drilling, at a selected position in the wellbore, a plurality of sealant injection channels through the wall of the tubular and into the annular cement sheath, to a controllable depth of penetration for each sealant injection channel;

- positioning a sealant injection device at the selected position, which device is connected to a sealant injection conduit and equipped with an upper expandable seal and a lower expandable seal;

- expanding the upper expandable seal and the lower expandable seal against the inner surface of the tubular such that the upper expandable seal is located above and the lower expandable seal is located below the drilled plurality of sealant injection channels; and

- injecting a sealant generation composition via the sealant injection channels into the cement sheath.

In another aspect, the present invention provides a system for sealing cavities in an annular cement sheath surrounding a tubular of a subterranean wellbore, the system comprising:

- a drilling device, which is adapted for drilling a plurality of sealant injection channels through the wall of the tubular and at least part of the annular cement sheath, the drilling device equipped to

monitoring a parameter relating to a depth of

penetration;

- a sealant injection device, which is connected or connectable to an injection conduit and equipped with an upper expandable seal and a lower expandable seal configured to expand against an inner surface of the tubular such that the upper expandable seal is located above and the lower expandable seal is located below the drilled plurality of sealant injection channels; and

- an injector for injecting a sealant generation composition through the sealant injection channels into the cement sheath.

The cavities may comprise micro-annuli .

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the invention shall be described by way of example and with reference to the drawings depicted in the accompanying drawings, wherein

Figure 1 shows schematically how sealant injection channels are drilled through a wellbore tubular and surrounding cement sheath;

Figure 2 is a schematic cross-sectional view of the assembly shown in Figure 1, showing how the sealant injection channels penetrate the tubular and

surrounding cement sheath;

Figure 3 shows schematically how a sealant

generating composition is injected via the channels into micro-annuli and other cavities in the cement sheath; and

Figure 4 is a cross-sectional view of the assembly shown in Figure 3.

Like reference numerals are used in the Figures to denote the same or similar objects. Objects and other features depicted in the figures and/or described in this specification, abstract and/or claims may be combined in different ways by a person skilled in the art .

DETAILED DESCRIPTION OF THE INVENTION

The following examples of certain aspects of some embodiments are given to facilitate a better

understanding of the present invention. In no way should these examples be read to limit, or define, the scope of the invention.

Figure 1 schematically shows an embodiment of the drilling step of the method for sealing micro-annuli and/or other cavities in an annular cement sheath surrounding a tubular of a subterranean wellbore 1, such as a hydrocarbon production well in an earth formation 2. The subterranean wellbore may be located on-shore below land, or off-shore below the sea floor.

The embodiment shows how sealant injection channels 5 can be drilled through a wellbore tubular 7, e.g. a production tubing, liner or wellbore casing, and surrounding annular cement sheath 8. In the embodiment as shown, an outer wellbore tubular 10, e.g. an outer wellbore casing, surrounds the cement sheath 8. It shall be understood that the invention also is

beneficial in situations where there is no such outer tubular 10. It is also possible that the cement sheath is surrounded by more than one further tubulars, e.g. several of increasing diameter, and further annuli may be present that may also be filled with a cement sheath.

A drilling device 12 is positioned at a selected depth in the wellbore 1 (or tubular 7), by a carrier device 13. Via the carrier device, the drilling device 12 is suitably connected or connectable to coiled tubing 14, and suitably lowered into the wellbore by coiled tubing. The drilling device 12 is adapted to drill holes into and through the tubular 7. It can be a rectangular drilling device as shown, adapted to convert a rotary drilling motion concentric with the liner axis into a drilling motion substantially perpendicular to the liner wall. The drilling device 12 can be powered from a downhole power source, or from surface, such as via or through the coiled tubing.

Suitably means 16 are provided to releasably fixate the drilling device against the inner tubing during drilling .

The drilling device is adapted so that it can change the drilling direction, e.g. assuming different angular positions about the longitudinal axis of the wellbore 1 or inner tubular 2, e.g. using an indexing head. In this manner a number of sealant injection channels 5 can be drilled.

The sealant injection channels 5 may be

circumferentially spaced. They may penetrate the inner tubular substantially perpendicularly to the inner surface. They may substantially lie in one plane, preferably a perpendicular to the wellbore tubular, although it shall be understood that any of these are not essential.

Rotary drilling by the drilling device 12 causes the sealant injection channels to have substantially uniform diameter along their depth. This diameter corresponds to the diameter of the drill that is used. The depth of penetration is also controlled, as indicated by the arrow 17, and as a result well-defined injection channels 5 are created.

A cross-section in a plane at A is illustrated in Figure 2 (not showing the drilling device and carrier device) . The channels 5 extend through the inner tubular 7 and the cement sheath 8. It shall be

understood that the channels could also merely extend some distance into but not fully through the cement sheath 8, or only just through the inner liner 7, if it was desired to inject sealant specifically in these areas, for example so as to treat micro-annuli on one or the other side of the annulus .

When it is desired to treat the cement sheath specifically, in case there is an outer liner 10, it is preferred that the sealant injection channels do not extend through the outer liner 10 as shown. This prevents sealant from leaking away into the surrounding earth formation 2. In case there are more tubulars surrounding the inner tubular, forming an assembly of consecutive casings it can be desired to penetrate outward through more than one, but not all of the tubulars. The sealant injection channels can be drilled such that they do not extend through a selected one of the one or more further tubular (s) .

The drilling device 12 is adapted so that it can drill to a controllable depth, i.e. it can drill to any desired depth, and/or drilling can be stopped when a desired depth is reached. The desired depth can be predetermined, or it can be determined during drilling. It can for example be dependent on a live monitoring of a parameter from the drilling operation, e.g. when a void is reached, or when a change in material such as from cement to metal is detected, or another

measurement result. The drilling device can be suitably equipped to accomplish that by measuring a parameter relating to depth of penetration it is determined whether the material being drilled is cement. For instance, a sensor may be provided, such as for example with a rate-of-penetration measurement means, depth measurement means control, imaging or sensing means, drill cutting analyzer means, or detectors for a change in material being drilled that can distinguish cement from the liner material (typically steel) .

The number of channels 5 being drilled may depend on a number of factors, such as the diameter of the tubing 7, any prior knowledge about micro-annuli, channels and voids in cement sheath, the constitution of the sealant composition (e.g. viscosity) . Suitably, between 2 and 50 channels are drilled, in particular between 3 and 30, such as between 4 and 20. They may be spaced at about equal angular distances. The diameter may be 5 cm or less, preferably 3 cm or less, more preferably for example about 2.5 cm (1 inch) . The diameter is suitably larger than 3 mm, such as 5 mm or more, or 1 cm or more.

After the sealant injection channels 5 have been drilled, the drilling device 12 can be moved with the carrier device 13 from its position, either pushed to a different downhole position or pulled to surface.

Then, with reference to Figure 3, a sealant injection device 20 is positioned at the depth where sealant injection channels 5 have been drilled.

The sealant injection device is connected to a sealant injection conduit 22 and is equipped with upper and lower expandable seals 25,26, e.g. elastomeric seals or inflatable seals. These are expanded against the inner surface of the liner 7 as shown, such that the upper expandable seal 25 is located above and the lower expandable seal 26 is located below the drilled sealant injection channels 5. This way an enclosed annular space 28 is created between the upper and lower expandable seals 25,26, the tubing 7 and the outer surface of the injection device 20. A flow channel 30 in fluid communication with the injection conduit 22 extends through the sealant injection device 20 and debouches into the enclosed space 28.

A sealant generation composition can now be injected into the cement sheath via the injection conduit 22, flow channel 30 and enclosed space 28 into the sealant injection channels 5, typically applying sufficient pressure to the injection conduit 22. The sealant composition flows into micro-annuli and/or other cavities accessible from the sealant injection channels 5. From the enclosed space 28 the sealant composition may be distributed over multiple of the circumferentially spaced injection ports 5, thereby injecting the sealant composition into the cement sheath simultaneously through multiple of the

circumferentially spaced ports 5.

Figures 3 and 4 schematically indicate in this example that sealant composition has been flowing into a large part of the interface 32 between the cement sheath 8 and the outer tubular 10, and into a smaller part of the interface 33 between the inner tubular 7 and the cement sheath 8, indicative of the extent of micro-annuli or other channels at these interfaces. Cleary the distribution of sealant composition depends on the flow paths in the cement sheath 8.

After a suitable amount of sealant generation composition has been injected, the composition can be allowed to set, to form a solid or non-flowable material, sealing the micro-annuli and/or other cavities in which it is located. In some situations, especially when there is not an outer tubular 10, the sealant generation composition can (also) flow into cracks in the surrounding formation and extended periods and volumes of injection may be needed.

Injection can be repeated after a period of setting, or the sealant injection device 20 can be removed.

The method described herein does not require a drilling rig for these operations, and thus allows very economic operation. In particular, drilling of the injection channels and/or sealant injection can be conducted using coiled tubing, wireline, in particular wireline adapted for data communication (also referred to as "e-line") or high pressure line, or a combination of above.

In some embodiments the sealant generation

composition comprises substantially no particles larger than 10 μηι, in order to allow smooth flow into micro- annuli and narrow cracks. In some embodiments the sealant generation composition is substantially free of solids .

In some embodiments the sealant generation

composition comprises a fumed silica. It can be substantially formed of fumed silica. Fumed silica can form a thixotropic sealant or sealant component .

In some embodiments the sealant generation

composition comprises a resin-type sealant. A suitable solids-free epoxy resin is for example disclosed in the paper "Resin system facilitates shut-off of difficult gas well" by J. A Urdaneta et al . , World Oil, February 2015, p. 101-104. In this paper, the resin is

introduced via conventional perforations produced by perforating guns that do not allow control over the depth and size of perforations.

In some embodiments, the sealant generation composition can be a single component composition, which sets after a certain time dependent on

environmental factors such as temperature, pressure and other fluids and materials.

In some embodiments the sealant generating

composition can comprise separate components which are transported to the sealant injection device though separate conduits. This option is indicated in Figure 3 by the optional umbilical 35 which constitutes a further injection conduit for a second component of a sealant generation composition. It debouches into the enclosed space 28 where it mixes with a first component of the sealant generation composition that is received via injection conduit 22 and flow channel 30, before the mixed sealant is introduced via the sealant injection channels 5 into the cement sheath 8, suitably while maintaining an elevated pressure in the enclosed space. After injection it is suitably allowed to cure.

A two-component sealant generation composition can provide significant operational flexibility, in that it can be processed while avoiding premature curing.

In some embodiments the sealant generation

composition can comprise a heat curable resin

composition comprising a curable resin, a filler, a swelling agent, a nitroxide crosslinking retarding agent, and an organic peroxide curing initiator. The retarding agent serves to delay curing of the resin to permit pumping the composition into the wellbore. The curing initiator serves to initiate the reaction.

Suitably, one component of at two-component sealant generation composition comprises the curing initiator, and this can be the component introduced via umbilical 35. The other component suitably comprises the curable resin, filler, swelling agent, and nitroxide crosslinking retarding agent, and is suitably

introduced via injection conduit 22.

In some embodiments the heat curable resin can comprise polydimethylsiloxane (PDMS) ,

polymethylhydrosiloxane (PHMS) , vinylneodecanoate and/or polyvinylneodecanoate .

In some embodiments an ambient elevated downhole temperature in the wellbore is between 20 and 150 C and the organic peroxide curing initiator comprises one or more of 1 , 1-di- (tertbutylperoxy) -3 , 3 , 5- trimethylcyclohexane (TMCH, pure) from United

Initiators; Bis ( 4 -tertbutylcyclohexyl ) - peroxydicarbonate (BCHPC, pure) from United Initiators was used as an initiator; Bis (2,4- dichloorbenzoyl ) peroxide (Luperox DCBP, 50%) from

Arkema B.V. TMCH, BCHPC and/or DCBP release radicals at different ranges of elevated temperatures between 20 and 150 C.

In some embodiments, the nitroxide crosslinking retarding agent comprises 2,2,6,6-

Tetramethylpiperdinyloxyl (C19H18NO) known as TEMPO and/or 4-Acryloyoxy-2, 2, 6, 6-tetramethylpiperdine-N- oxyl, known as AOTEMPO.

In some embodiments, the nitroxide crosslinking retarding agent is configured to absorb at least part of the released radicals and thereby delay curing of the resin during at least one hour and the organic peroxide curing initiator/nitroxide crosslinking retarding agent molratio is less than 1.

In some embodiments, the organic peroxide curing initiator/nitroxide crosslinking retarding agent molar ratio is between 0.1 and 1 and is configured to absorb at least part of the released radicals and thereby delay curing of the resin during a period of 1 to 5 hours .

The materials obtained by such delayed radical initiated polydimethylsiloxane (PDMS) ,

Polymethylhydrosiloxane (PMHS) and other polymer crosslinking, meets the requirements needed for use in sealing application. The delay enables pumping and placement of the liquid polymer mixture before it becomes solid. The effect of 2,2,6,6- tetramethylpiperidinyloxyl (TEMPO nitroxide) on the curing of PDMS was examined. TEMPO delays the

crosslinking reaction of PDMS using a number of peroxides with different decomposition temperatures. As a result a temperature range of 40°C to 100°C can be covered. The reaction mixtures have a low viscosity for several hours before the crosslinking reaction occurs. In actual well conditions barite and salt can be added to the silicone mixture. Addition of barite and salt has no significant influence on the effect of TEMPO. At a certain concentration, depending on the peroxide and the temperature used, TEMPO will have a significant effect on the crosslink density of the final product. An alternative material could be

poly (vinylneodecanoate ) . TEMPO can also delay the polymerization of vinylneodecanoate.

An ideal polymerization would have the following kinetic properties: the reaction mixture is mixed at room temperature for one hour, then during pumping and placement it would have a low viscosity for

approximately eight hours. The temperature in the wellbore can vary between 20°C to 120°C. After pumping and placement it would take three hours for the polymer to be fully hardened. The polymer material should generally have the following properties: a viscosity of maximum 1500 mPa-s at 20°C and a density of 1000 kg/m3 up to 3000 kg/m3. Furthermore, it requires a certain flexibility. It needs to have an elongation before break of minimum 50% but also must be able to withstand an absolute pressure up to 1000 bar. The final product should be resistant to water, seawater and

hydrocarbons .

For such application it is desired to have a delayed polymerization where the mixture could be pumped for several hours before polymer curing occurs. Polymer curing may be accomplished by addition

polymerization, which is a chain process involving several steps. First active centers are formed, either catalytically or by thermal activation. These active centers are formed when an initiator, for example a peroxide, decomposes into free radicals (r») . The radicals can react with double (or triple) bonds or can undergo hydrogen abstraction to form a carbon-centered radical R» . Polymer chains are formed by the successive addition of monomer molecules (M) to the radicals. In chain transfer the active site is transferred to a monomer or solvent molecule, initiating the growth of a new chain. Chain termination can occur by combination. This is when a growing chain combines with another growing chain or radical. Termination can also occur by disproportionation . In case of disproportionation a free radical removes a hydrogen from an active chain. A carbon-carbon double bond is formed and the

polymerization reaction stops . Disproportionation can also occur when the radical reacts with an impurity.

During the pumping and placement of the reaction mixture into the wellbore, the temperature will rise 1°C every 40 meters deeper into the ground. The peroxide could partially decompose, causing premature crosslinking, or scorching. Scorching can be prevented by selecting a suitable initiator. Different types of initiators are used for radical polymerization. Oxygen and carbon centered radicals are often used due to their reactivity, thus organic peroxides and azo compounds are common initiators. An important

characteristic of an initiator for a polymerization is its rate of decomposition at a certain temperature expressed by its half-life (t ½) . The relation between the temperature and the rate of decomposition of an initiator may be expressed by an Arrhenius equation.

Another way to prevent scorch is by using an inhibitor. Inhibitors are widely used as radical scavengers to prevent polymerization during monomer storage. Inhibitors convert initiating and propagating radicals to non-radical species or radicals with low reactivity. Strong inhibitors react with every radical they encounter. The chain no longer propagates until the inhibitor is consumed. Weak inhibitors (retarders) on the other hand react with a portion of the radicals. The inhibitor can terminate the reaction when a radical abstracts a hydrogen atom from the inhibitor molecule. The inhibitor radical that is formed is less reactive. The inhibitor can also quench the propagation by adding to the chain to form a relatively stable species.

Different types of inhibitors are available for the inhibition or retardation of radical polymerization. A common inhibitor that can add to a growing chain is oxygen. When a growing chain reacts with molecular oxygen, a much less reactive peroxyl radical (R02») is formed .

Antioxidants are commonly used as curing

inhibitors. Addition of the antioxidant terminates the propagating chain by forming highly resonance stabilized tertiary radicals that have very limited reactivity. Phenol- and amine-type inhibitors work best in the presence of oxygen. They react with the peroxyl radicals and stop chain propagation. In a wellbore little to no molecular oxygen is present, which makes this type of inhibitor less suitable for downhole application. Another downside of using antioxidants for scorch control is that there is a loss in crosslink density because of the radical quenching of the polymer radicals as well as the initiator radicals.

Simple peroxide cures are essentially

stoichiometric reactions that yield at most one cross^¬ link per molecule of initiator. Crosslinking occurs only when two polymer radicals combine. The quenching effect on polymer radicals can therefore have a large effect on crosslink density.

Because of the properties of silicone rubber, it is a promising material for downhole application. Silicone rubber is a generic term used for a group of polymers with a backbone consisting of a silicone/oxygen chain. The silicone can be bonded to different side groups. The most common silicone rubber is polydimethylsiloxane (PDMS) and Polymethylhydrosiloxane (PMHS) where the silicone is bonded to two methyl substituents or one methyl and one hydrogen. PDMS rubber has relatively high temperature resistance, high chemical resistance, and good mechanical properties. PDMS chains are very flexible. This is because the polymer backbone consists of Si-0 bonds. There is less strain on Si-0 bonds compared to a C-C bond because of the larger length of the bond and a larger bond angle .

The linear silicone polymer chains can be

crosslinked to create a three dimensional elastic network (a rubber) . The substituents that are bonded to the silicone can have an effect on the properties of the rubber. For example if peroxides are used for the crosslinking of the silicone chains, the presence of some vinyl substituents (less than 1%) can increase the crosslinking efficiency. The resulting material will be more resistant to hot oil compared to PDMS without vinyl substituents. Silicone rubber acts as an

elastomer. This means that when relatively low forced are applied, the material can be largely deformed. When the force is released, it returns to its original shape. Although the rubber is elastic, it is not compressible. Silicone rubber in general has a very high chemical and thermal stability. The high stability is due to the strong bonds in the silicone chains. The silicone oxygen bonds are stronger than the bonds of other polymers like ethylene propylene rubber or epoxy. This property gives silicone rubber its stability against heat and UV radiation.

The long polymer chains in linear PDMS and PHMS can be crosslinked using organic peroxides. The peroxide radicals can react with polymer chains. This will generate polymer radicals. These polymer radicals can combine to form carbon-carbon bonds. The combination of the chains is an exothermic and irreversible reaction. The linear polymer chains combine to create a three dimensional elastic network.

Some peroxides, dicumylperoxide for example, are vinyl specific. This means they can only crosslink vinyl groups. Other peroxides, for example

benzoylperoxide, can crosslink both methyl and vinyl groups. This difference is proven by Dluzneski to be caused by the inability of alkoxy radicals to abstract a hydrogen from a methyl of the PDMS for thermodynamic reasons . The peroxide adds to the double bond, thereby generating polymer radicals .

Another possible alternative for cement could be poly (vinylneodecanoate ) . Poly (vinylneodecanoate ) offers advantages compared to silicone rubber. The thermal stability of poly (vinylneodecanoate ) is much higher than crosslinked silicone, which becomes unstable at temperatures higher than 120°C in the presence of water. A downside of using poly (vinylneodecanoate ) is that the polymerization reaction is exothermal. After the reaction is complete, the product will cool down and shrink. The shrinkage can cause ruptures in the final product and a loss in isolation efficiency.

During a crosslinking or polymerization reaction the viscosity can be used a measure of the degree of polymerization. Viscosity of a fluid is a measure of its resistance to gradual deformation by shear stress or tensile stress. The shear resistance in a fluid is caused by the friction between molecules when layers of fluid attempt to slide by one another. Dynamic (or absolute) viscosity is a measure of internal

resistance. The dynamic viscosity is measured by two horizontal plates that are placed at a given distance in a fluid. The plates are moved with respect to another at a unit velocity. Kinematic viscosity is the ratio of dynamic viscosity to density. Kinematic viscosity can be obtained by dividing the absolute viscosity of a fluid with the fluid mass density. The viscosity of a fluid is highly temperature dependent. It decreases with higher temperature. During a

polymerization the degree of polymerization can be calculated from intrinsic viscosity measurements. For most polymerizations the Mark-Houwink equation gives the relationship between molecular weight (degree of polymerization) and viscosity.

An ideal situation for this application would be to be able to control the polymerization or crosslinking reaction in such a way that the reaction mixture would have a low viscosity for several hours before the reaction proceeds and the mixture is cured. An unwanted scenario is for the retarder to delay the entire cure, leaving a limited amount of time for the mixture to be pumped into place, whilst delaying the total curing time. The time in which inhibitors and retarders are reacted away is called the induction period. In a typical polymerization the initial rate of monomer conversion is high. It gradually slows down until high conversions are reached. If a retarder is present, it will react with some of the initiator causing a lower initial monomer conversion. When the retarder is consumed, the conversion will increase to a high rate and then gradually decrease. If a strong inhibitor is present it will react with every radical it encounters. Therefore, the initial reaction rate will be very low. Only when a significant amount of inhibitor has been consumed, the reaction rate will increase. Due to the loss of initiator at the start of the reaction the polymerization will proceed quite slowly.

The method, system and/or any products according to present invention are well adapted to attain the ends and advantages mentioned as well as those that are inherent therein.

The present disclosure is not limited to the embodiments as described above and the appended claims. The particular embodiments disclosed above are

illustrative only, as the present invention may be modified, combined and/or practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein.

Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below.

It is therefore evident that the particular illustrative embodiments disclosed above may be altered, combined and/or modified and all such

variations are considered within the scope of the present invention as defined in the accompanying claims .

While any methods, systems and/or products

embodying the invention are described in terms of "comprising," "containing," or "including" various described features and/or steps, they can also "consist essentially of" or "consist of" the various described features and steps.

All numbers and ranges disclosed above may vary by some amount . Whenever a numerical range with a lower limit and an upper limit is disclosed, any number and any included range falling within the range is

specifically disclosed. In particular, every range of values (of the form, "from about a to about b," or, equivalently, "from approximately a to b," or,

equivalently, "from approximately a-b") disclosed herein is to be understood to set forth every number and range encompassed within the broader range of values .

Also, the terms in the claims have their plain, ordinary meaning unless otherwise explicitly and clearly defined by the patentee.

Moreover, the indefinite articles "a" or "an", as used in the claims, are defined herein to mean one or more than one of the element that it introduces . If there is any conflict in the usages of a word or term in this specification and one or more patent or other documents that may be cited herein by reference, the definitions that are consistent with this

specification should be adopted.

Claims

C L A I M S

1. A method for sealing cavities in an annular cement sheath surrounding a tubular in a subterranean

wellbore, the method comprising:

- injecting a sealant generation composition via the plurality of sealant injection channels into the cement sheath .

2. The method of claim 1, wherein the cement sheath is surrounded by one or more further tubular (s), and wherein the sealant injection channels are drilled such that they do not extend through a selected one of the one or more further tubular (s) .

3. The method of claim 1 or 2, wherein one or more of coiled tubing, wireline, e-line and high pressure line is/are used in one or more steps of the method.

4. The method of any one of the preceding claims, wherein the sealant generation composition

substantially comprises no particles larger than 10 μηι,

5. The method of any one of the preceding claims, wherein the sealant generation composition is

substantially free of solids.

6. The method of any one of the preceding claims, wherein the sealant generation composition comprises a resin-type sealant.

7. The method of any one of the preceding claims, wherein the sealant generating composition comprises fumed silica.

8. The method of any one of the preceding claims, wherein each of the upper expandable seal and the lower expandable seal, after expanding, form a seal against a full circumference of the inner surface of the tubular, thereby forming an enclosed space within the tubular between the upper expandable seal and the lower expandable seal, which enclosed space is in direct fluid communication with the drilled plurality of sealant injection channels.

9. The method according to claim 8, further comprising injecting the sealant generating composition into the enclosed space between the expanded seals and an outer surface of a sealant injection device and the inner surface of the tubular.

10. The method of claim 9, wherein the sealant

generating composition comprises separate components, said method further comprising:

- transporting the separate components to the sealant injection device though separate conduits;

- inducing the components to mix and generate a mixed sealant in the enclosed space;

- injecting the mixed sealant via the plurality of sealant injection channels into the cement sheath.

11. The method of any one of claims 8 to 10, wherein maintaining an elevated pressure in the enclosed space compared to in the annular cement sheath.

12. The method of any one of the preceding claims, wherein the injection is stopped and the sealant generation composition is allowed to cure.

13. The method of any one of the preceding claims, wherein the subterranean wellbore is a hydrocarbon production well being abandoned.

14. The method of any one of the preceding claims, wherein the cavities comprise micro-annuli .

15. A system for sealing cavities in an annular cement sheath surrounding a tubular in a subterranean

wellbore, the system comprising:

monitoring a parameter relating to a depth of

penetration;

16. The system according to claim 15, wherein the sealant injection device comprises a downhole pump in communication with the injector and adapted to creating additional injection pressure.