Technical Field

The invention relates to hydrocarbon well intervention methods, a method of sealing an annulus in a wellbore, and in particular a method of blocking water inflow into a hydrocarbon producing well.

Background

Annulus packers are used in the oil and gas industry as a component of the well casing. For example, running annulus packers in a wellbore is a typical step in well completion. In general, their primary function is to permanently seal the annular gap defined between the external casing/wellbore wall and the production tubing of the wellbore. This seal acts to maintain high pressure in producing regions of the well, which is important for maintaining economical productivity of the wellbore. The seal also prevents the transport of fluids within the annular gap from passing further downstream in the wellbore. Within the producing region of the well, a slotted liner may be present to enable production fluids to enter the production tubing.

During operation, annulus packers are exposed to dynamic temperature and pressure conditions. Conditions fluctuate over short time scales (within individual extraction campaigns) and long-time scales (over the different life stages of the wellbore). These dynamic conditions may be unpredictable, leading to pressure differences across the packer, which may cause leak paths to develop within the annulus packer. For example, under excessive high pressure, the annulus packer’s rubber may be displaced upwards and generate a leak path. Furthermore, such failure mechanisms may be exacerbated at elevated temperature as the stiffness of the packer reduces. Annulus packers are also exposed to corrosive fluids, such as oilfield brine, water, dissolved carbon dioxide, and hydrogen sulphide. All of which may further contain abrasive suspended solids. Corrosion mechanisms such as erosion-corrosion, stress corrosion cracking and crevice corrosion are prevalent. The generation of leak paths in annulus packers is a problem in the oil/gas industry. In most cases, these annulus packers are set permanently, and milling is required for their removal and replacement. Milling is a slow process. During removal, production of the wellbore may be reduced or stopped completely, as such; it is economical to repair leaks as quickly as possible.

The source of fluid of the leak may be any sub-surface reservoir of fluid. Generally speaking, these reservoirs of fluid are mobile over large length scales (compared to the wellbore). It may be practically difficult to predict and/or track the exact location of these mobile reservoirs. In a particular scenario, the source of fluid may be water. In this way, water may be present (via leak paths or otherwise) within the annular region defined between the production tubing/liner and the external casing/formation of the wellbore. The water may be under high pressure and the tubulars are therefore exposed to corrosive environments. These conditions may worsen already present leak paths, and exacerbate the problem. In some examples, the leak path may extend to groundwater reservoirs, and may lead to contamination. In some examples, the producing region of the wellbore may be lower in pressure than the source of fluid. In this scenario, leaking fluid may mix with production fluids. In general, the leaking fluid may need to pass through a leak path in an annulus packer to mix with the production fluid. This mixing process dilutes the production fluid, and requires expensive downstream separation processes. The mixing may also lead to further problems such as: increased corrosion rate in the production tubing, reducing the lifetime of the tubing; salt deposition, leading to scaling down the flow line; possible gas hydrate formation and/or hydrocarbon solid deposition, causing unwanted plugs. As such, it is important to seal or limit leakage in annulus packers as quickly as possible.

Therefore, leak paths are unacceptable defects for ensuring optimal productivity of wellbores. In some examples, such leaks may, as a last resort, need the deployment of killing fluid to cease production of the well entirely, before the tubing string and/or packer assembly are removed and reinstalled in the wellbore. This process interrupts production for prolonged periods.

To present, document US3381748 discloses a method for repairing leaks in a production packer, wherein a low density sealant fluid containing particles of an insoluble polymer is forced through the tubing string between two piston-like members until the lowermost member emerges from the lower end of the tubing and at least part of the sealant is displaced into the wellbore beneath the packer. Document US4663450 discloses providing a fixation of a packer by explosively bonding the packer to the borehole casing.

Document RU2498044 discloses a method for sealing a leak in tubing string using an explosive charge and a plastic material.

Summary

The present invention aims to solve or at least partially solve the above-described problems, and, further, to provide a simple, cost-effective, efficient method for sealing an annulus in a wellbore without compromising access to, and production of the wellbore.

In accordance with a first aspect of the present invention there is provided a method of sealing a section of an annulus in a wellbore, the wellbore comprising a formation and a tubular provided within the formation, and the tubular and formation defining an annulus between the tubular and the formation, the method comprising: perforating a section of the tubular downstream of a source of fluid to generate an array of holes in the tubular; providing a source within the tubular section radially adjacent to said array of holes, wherein the source comprises an expansion force source and a sealing material; and activating the expansion force source to propel the sealing material through said array of holes.

The method further comprising one or more of the following optional features.

The process of propelling the sealing material through the array of holes may further comprise sealing the annulus along the circumference of the annulus and sealing the array of holes with said sealing material.

The sealing material may be an elastomer. The source of fluid may comprise water. The tubular may be a production liner.

The process may further comprise deforming a section of the tubular and expanding said section against the formation. The array of holes in the tubular may comprise one or more rows. Each row in the array of holes may define a path on the tubular section with a component of said path in a circumferential direction of said tubular, a component of said path in a longitudinal direction of said tubular, and wherein the ratio between each component along the path is constant. In this way, each row in the array of holes may follow a spiral path on the tubular.

Each hole in the array of holes in the tubular section may comprise a first continuity along the circumferential direction of the tubular and a second continuity along the longitudinal direction of the tubular, and wherein the first continuity and second continuity define a hole path along a direction between said first and second continuities. In this way, each hole has a length in the circumferential and longitudinal direction of the liner, and these lengths define a hole path.

In some examples, the first continuity of the holes may be greater in length than the second continuity. In this example, the holes are elongated in the circumferential direction.

In some examples, the first and/or second continuity of each hole in the array of holes may be provided by overlapping holes in the tubular with a component of the overlap in the respective continuity direction. For example, holes may overlap along the longitudinal and/or circumferential direction of the tubular.

In some examples, the total component of the hole path along the first continuity may comprise a length that is larger than the circumference of the tubular.

The spacing of the array of holes in the tubular along the circumferential direction and/or the longitudinal direction may be configured in size, such that, after the sealing material is deformed through said array of holes, the sealing material may recoil along the circumferential direction and/or longitudinal direction by at least half the length of the spacing in each direction, to form a seal.

In some examples, the tubular section may comprise a perforated section, perforating the tubular section may comprise enlarging the perforations in the perforated section along the circumferential and/or longitudinal direction of the perforated section to generate the array of holes. In this way, the holes within the perforated section may be adapted to the method.

In some examples, perforating the tubular section may comprise drilling, and this process may comprise deploying one or more drills in the tubular section, or, in the annulus defined between the tubular and the formation or external casing of the wellbore.

In some examples, the expansion force source may comprise an explosive charge, and/or a mechanical/hydraulic device. In these examples, activating the expansion force source comprises activating the explosive source, and/or mechanical/hydraulic device.

In some examples, perforating the tubular section may further comprise activating a further expansion force source in the tubular section of the production tubing before the step of activating the expansion force source to propel the sealing material through said array of holes, and/or wherein said activating a further expansion force source comprises explosion welding the tubular section to the external casing or formation of the wellbore. In this way, the perforations in the tubular may be generated using an expansion force source.

The sealing material may be an expandable elastomer. The expandable elastomer may expand in response to the source of fluid. In some examples, the source of fluid may be water.

In some examples, the process of activating the expansion force source may comprise detonating the explosive charge, or, deflagrating the explosive charge.

In some examples, providing the source in the tubular section may comprise hanging the expansion force source on a wireline, a coiled tubing or a workstring.

In some examples, the wireline, coiled tubing or workstring may be detached from the expansion force source after activating the expansion force source. In some examples, the source may further comprise a housing radially disposed between the expansion force source and the sealing material

Preferably, the thickness of the housing may be configured in size to provide mechanical integrity to the source, therein maintaining production of the wellbore during providing of said source into the tubular.

In some examples, the source may comprise a plurality of sub-sources, and each sub source may comprise an expansion force source. In these examples, the expansion force sources may be activated concurrently to form the seal. In other examples, the expansion force sources may be activated sequentially. In these examples, the source may also comprise a plurality of sub-sources, and the steps for providing and activating a first source are performed before the steps for providing and activating a second source. Preferably, the first source may comprise an explosive charge and the second source may comprise an explosive charge, an elastomer and/or housing. The first source, or what is left thereof, may be retrieved to the surface by wireline before the second source is lowered to the site where the seal is formed.

In all examples, a predetermined length of seal may be placed along the longitudinal direction of the tubular section by overlapping a plurality of seals in said direction. In this example, overlapping more than one seal comprises activating each expansion force source longitudinally adjacent to the seal generated by a previous expansion force source.

In some examples, the sealing material may act as a choke.

In some examples, the source of fluid may pass through a leaking annulus-packer and the seal is preferably disposed downstream of the leaking annulus-packer. In this way, the source of fluid in the leaking annulus-packer may be blocked.

In some examples, the explosive charge may comprise one or more, of the following, in any combination: trinitrotoluene (TNT), RDX or ammonium nitrate/fuel oil (ANFO). In some examples, the method of sealing the annulus may substitute an annulus packer. In this way, the deployment of annulus packers may be replaced with the described method.

Thus, the embodiments of this disclosure provide the above-described advantages. Brief Description of Drawings

Some embodiments of the disclosure will now be described by way of example only and with reference to accompanying drawings, in which:

Figure 1 shows a schematic cross section of a wellbore.

Figure 2 shows an exemplary method for sealing a leaking annulus.

Figure 3a-e shows exemplary array of holes.

Figure 4a-f show exemplary cross sections of sources.

Figure 5 shows an exemplary method for sealing a leaking annulus.

Figure 6 shows a method diagram for sealing a leaking annulus.

Figure 7 shows an exemplary method for sealing a leaking annulus.

Figure 8 shows a method diagram for sealing a leaking annulus.

Detailed Description of the Preferred Embodiments

In general terms, this disclosure relates to a method of sealing a section of an annulus in a wellbore, the wellbore comprising a formation and a tubular provided within the formation, and the tubular and formation defining an annulus between the tubular and the formation, the method comprising: perforating a section of the tubular downstream of a source of fluid to generate an array of holes in the tubular; providing a source within the tubular section radially adjacent to said array of holes, wherein the source comprises an expansion force source and a sealing material; and activating the expansion force source to propel the sealing material through said array of holes. A seal is thereby formed within the annulus, preferably in circumferential direction.

Some examples of the solution provided by this disclosure are given in the accompanying figures.

Figure 1 shows a schematic cross section of a wellbore 100. The wellbore 100 comprises production tubing 102, an external casing of the wellbore 103 and an annulus packer 105. In some examples, the annulus packer 105 may be a permanent packer. In other examples, the annulus packer 105 may be temporary. The production tubing 102 comprises a liner 102, which defines a bore within the production tubing 101 used to transport production fluids out from the wellbore 100. The annulus packer 105 fills an annulus defined between the external casing/formation 103 and the liner/production tubing 102. In some examples, this annulus may comprise a leaking annulus 104. In these examples, the annulus packer 105 may include a leak path 106 to generate the leaking annulus. As such, the annulus packer 105 may be a leaking annulus packer. The location of the source of the leak is not shown in the Figure, but it is appreciated that the source of the leak is located in a region below the leak path 104, 106. In a more general case, the source of the leak is located in a region of higher pressure than that shown in Figure 1. Therefore, fluid 504 from the source of the leak may be transported through the leak path of the annulus packer 106 along the leaking annulus 104, down the pressure gradient. In good working order, the annulus packer seals the annulus above the region of the formation where inflow of water takes place. The seal separates annulus at the formation section with inflow from the annulus at the formation section which produces hydrocarbons. The tubing at the production section includes slots to allow the production fluids to enter the bore. When there is a leak, a seal is provided downstream of the source of the leak in order to block the leaking fluid from entering the production tubing 102. In some examples, the fluid 504 may pass further up (downstream) the wellbore 100 in the leaking annulus 104 and contaminate groundwater supplies, if left unnoticed. In some examples, the fluid 504 may be water. In other examples, the fluid 504 may comprise oil and/or gases, such as methane. In other examples, the fluid 504 may comprise salts dissolved into water and/or sediment submerged in the water. For example, brine or muddy brine. In some examples, the fluid may comprise any combination of these fluids. It is appreciated that the skilled person would anticipate any type of fluid 504 that is typically present in an operating wellbore.

In a particular example, the location of the source of the leak may be below (upstream) a production zone of the wellbore. The production zone is a region that is producing oil and/or gas in quantities deemed to be economically viable. In these cases, the liner section of the production tubing 102 may be perforated 501. The location of said perforations may therefore be located above (downstream) the leaking region. Generally speaking, perforated liners 501 are designed to allow fluid to pass from the outside of the production tubing into the inner hole of the production tubing. They are also designed to minimise sediment from passing into the production tubing. In effect, they function at least partly as a sieve. Sometimes an additional sand screen is used to keep sand and sediment out of the bore. Perforated liners 501 may not be suitable for the method as disclosed herein. In examples where the liner is already perforated 501 , and a leaking annulus 104 and/or leaking annulus packer is disposed between said perforated region and the source of the leaking fluid, then the leaking fluid 504 may be transported up the leaking annulus 104 through the leak path 104, 106 and enter into the production tubing via said perforations. This leads to mixing of the production fluids that may lead to at least the following problems: a reduction in operating pressure within the production tubing 102, reducing the productivity of the well; increasing corrosion rate in the production tubing 102, reducing the lifetime of the tubing; salt deposition, leading to scaling further down the flow line; and possible gas hydrate formation and/or hydrocarbon solid deposition, causing unwanted plugs. At least some of these problems are at least partially solved by the present invention.

Figure 2 illustrates in an exemplary implementation of the method of the present invention. S202, comprises perforating a tubular downstream of a source of fluid to generate an array of holes 300 in the tubular. In an example, the tubular may be a liner section 102 of the wellbore 100. The location of the array of holes 300 is positioned such that at least a portion of the array of holes 300 is downstream (above in Figure 2) from the location of the source of the leaking annulus 104. The source of the leak may be any sub-surface reservoir of fluid. Generally speaking, these reservoirs of fluid are mobile over large length scales. It may be practically difficult to predict and/or track the exact location of these reservoirs. These reservoirs are very large and under high pressure. It may be preferable to mitigate the damage of leaks, or prevent leaks generated by these reservoirs via sealing of the leaking annulus and/or leak path. In some examples, the lowermost hole in the array of holes may be positioned downstream (above in Figure 2) from the location of the source of the leak. In some examples, an annulus packer 105 may be disposed within between the source of the leak and the tubular section. In these examples, the annulus packer 105 may develop a leak path 104, 106 and the source may travel through the leak path 104, 106 to generate the leak into the tubular section. Preferably, in these examples, the array of holes 300 is generated downstream from the top-most part of the leak in the leaking annulus packer. It is appreciated that a portion of the production tubing/liner 102 may not be vertical in orientation. For example, the production tubing/liner 102 may be disposed horizontally. In these examples, the array of holes 300 may not necessarily be located above the source of the leak and/or the annulus packer 105. In most general terms, the array of holes 300 may be disposed downstream of the source of the leak. The source of the leak is found by tracking the leak upstream until termination. The array of holes may be generated further downstream than the leaking annulus packer. Alternatively, the array of holes may generated upstream from the point of mixing of the production fluids and the leaking fluid. In some examples, a perforated section of the tubular may already exist. The array of holes 300 generated in a liner section 102 may comprise altering said perforated region 501 , or perforating the liner elsewhere. The geometry, size and arrangement of the array of holes 300 is described in further detail in following sections.

Step S204 comprises providing a source 400 within the tubular section radially adjacent to the array of holes 300. In an example, the tubular section may be a liner section of the production tubing 102. In S204, the source 400 and at least a portion of one hole in the array of holes may be contained in the same plane defined by the opening of the liner/production tubing 101. In some examples, the plane may contain either: the hole longitudinally closest or furthest from the source of the leak, or anywhere in between. In this way, the centre of mass of the source may overlap along the longitudinal direction of the production tubing/liner with the section of the liner containing the array of holes. The source 400 comprises an expansion force source 407 and a sealing material 408. The sealing material is an elastomer 408, but other suitable materials may also be used instead. The elastomer 408 is disposed around the expansion force source 407. The expansion force source 407 is configured to generate an expansion force radially away from the centre of mass of said expansion force source. In other examples, the source 400 is positioned longitudinally above the array of holes 300. In these examples, the centre of mass of the source does not overlap along the longitudinal direction of the production tubing/liner with the section of liner containing the array of holes 300. The source 400 may alternatively be disposed longitudinally below the array of holes 300. In these examples, the flow of the production fluids within the production tubing may preferentially deflect the elastomer downstream and through said array of holes. Generally speaking, the elastomer may be any material that is capable of forming a seal.

S206 comprises activating the expansion force source 407 to propel the sealing material 408 through the array of holes 300 to form a seal 503. The sealing material is an elastomer 408. In S206, the elastomer 407 is propelled at high velocity radially away from the centre of mass of the expansion force source. A portion of the elastomer may be directed towards the liner section of the production tubing 102 containing the array of holes 300. This portion of elastomer is forced through the holes in the array of holes in an extrusion process. It may be preferable when the expansion force source 407 is positioned radially adjacent to the array of holes 300, because, in this arrangement, the portion of elastomer that extrudes through the holes may be essentially perpendicular with the longitudinal axis of the production tubing/liner section. In this case, the cross section of the hole along the direction of travel of the elastomer may be maximised. In this case, the elastomer 408 extrudes the shortest distance. This geometry may be preferable to maximise the total volume of elastomer that is extruded through said holes, since less energy is required to extrude the elastomer 408 through the hole compared to alternative arrangements.

Activating the expansion force source 407 may generate a front of high pressure. The front travelling radially away from the centre of mass of the explosive charge. This high- pressure front may propel the elastomer 408 radially away from the centre of mass of said expansion force source. In some examples, the high-pressure front may also deform the liner section 102. This may be either directly or indirectly. In the former, the high-pressure front itself generates the deformation in the liner section. In the latter, the high pressure front transfers its energy to other objects, which in turn cause deformation in the liner section 102. For example, the high-pressure front may transfer energy to the elastomer 408 and the propelled elastomer 408 may deform the liner section 102. In some examples, other components of the source 400, 407 may be used to deform the liner section 102.

Activating the expansion force source 407 may also increase the temperature locally in the region of the liner section. As such, the high-pressure front may also be associated with a high temperature front. In some examples, the high-pressure front travels more rapidly than the high temperature front, and therefore the fronts are spatially separated. The high temperature front may reduce the viscosity of the elastomer. By reducing the viscosity of the elastomer, resistance to deformation and internal frictional losses are reduced, thereby making extrusion more efficient. The total volume of extruded elastomer may increase at higher temperatures for the same explosive quantity of the expansion force source. In some examples, the elastomer 408 may be pre-heated to reduce its viscosity prior to activating the expansion force source 407. The combination of the high temperature front and high-pressure front may cause the liner section 102 to deform and explosion weld with the external casing of the wellbore 103 to generate a partial seal 503, 704. This explosion weld may generate a leak-proof seal 503, 704.

As mentioned previously, in some examples, the expansion force source 407 may also be positioned above or below the longitudinal centre of the array of holes. In these examples, a portion of the elastomer may be propelled through the holes in the array of holes 300 with a component of velocity in the longitudinal direction. The leaking annulus 104 may be positioned longitudinally below or above the array of holes 300 respectively. In this way, the expansion force source 407 may be disposed in line-of- sight of the leaking annulus 104. In this arrangement, the elastomer 408 may be extruded preferentially in the direction towards the leaking annulus 104 to form the seal 503, 704. In some of these examples, the extruded elastomer may form an annular seal 503, 704.

In step S204, the source 400 may hang on a hanging device 502, such as: a wireline, a coiled tubing or a workstring. Preferably, the source 400 may be attached to said hanging devices 502 via the expansion force source 407. It is appreciated that all methods to hang and position the source 400 within the wellbore 100 would be anticipated by the skilled person. In S204, preferably, during providing of the source 400, the centre of mass of the source is positioned at the radial centre of the production tubing hole 101. In these cases, the exact location of the leak path 104, 106 may not be known, and positioning the source 400 in the centre of the production tubing hole may act to produce a uniform circumferential seal. In other examples, the location of the leak path may be more accurately determined, and the position of the source within the liner section 102 optimised to deliver the best chance of generating a seal 503, 704 at said location of leak path. In these examples, the position of the source may be off- centre in the production-tubing hole 101. In some examples, it may be advantageous to position the source 400 closer to the location of the leak or further away from the location of the leak path. The exact position may be optimised and may comprise optimisation of at least the following parameters: the size and type of the source and/or the expansion force source; the composition of the expansion force source; the flow- rate and direction of the production fluids in the production tubing 102; the diameter of the production tubing; the material of the external casing and its mechanical properties; the material of the annulus packer and its mechanical properties, and the size and extent of the leak path 104, 106.

It is appreciated that the order of the steps in Figure 2 are not limited to being carried out in the order as described above. For example, the step of perforating the liner section of the production tubing 102 (2202) may be carried out as a result of the step of activating the expansion force source 407 (S206). In this step, said activating of the expansion force source 407 may also cause explosion welding of the liner section to the external casing of the wellbore 503, 704.

Figure 3a-e show exemplary array of holes 300 arrangements. Each hole 306 in the array of holes 300 comprises a first continuity 307 along the circumferential direction of the liner, and a second continuity 308 along the longitudinal direction of the liner. The continuity 307, 308 in each direction is a length of the hole 306 in that direction. For example, a hole circular in section has a first continuity 307 and second continuity 308 that are equal in length. In other examples, the first continuity 307 and the second continuity 308 may differ in length. It may be preferable if the first continuity 307 is greater in length than the second continuity 308, such that each hole is elongated in the circumferential direction. The array of holes 300 comprises a spacing along the circumferential direction (w) and the longitudinal direction (h), wherein the spacing defines the gap between adjacent holes 306. Preferably, the spacing in each direction (w, h) may be constant across the array. The first and second continuity 307, 308 define a hole path 309 along a direction between said first and second continuities 307, 308. As such, the hole 306 may be positioned at any angle on the liner section relative to the longitudinal axis. The angle may vary from -180 to 180 degrees.

In Figures 3a-b, each row of holes in the array of holes 300 may define a path on the liner section 310 with a component of the path in the circumferential direction of the liner section, and a component of the path in the longitudinal direction of the liner. Preferably, the ratio between each component may be constant across the length of the defined path. In some examples, the row of holes in the array of holes 300 may only comprise a single hole 306. In Figure 3a, each hole comprises a circular section. In some examples, the holes in the array of holes 301 may be elongated. Preferably, the elongated direction is in the circumferential direction of the liner. In Figure 3b, an array of holes 302 is shown in which each row in the array of holes 302 is positioned equivalently to that of Figure 3a, but wherein the holes are elongated in the circumferential direction of the liner. In this example, each hole is rectangular in section.

In Figure 3c, the array of holes 303 comprises one hole. In this example, the first continuity 307 of the hole is larger than the second continuity 308 of the hole: the hole is elongated. In this example, the total component of the hole path 309 along the first continuity 307 comprises a length that is greater than the circumferential length of the liner. In this case, the hole is elongated and defines a pitch. In some examples, multiple rows of holes may be present, and the pitch may be the spacing between each individual hole along the longitudinal direction (h). Preferably, the pitch of each row of hole may be the same as the other spirals. However, the second continuity 308 of each hole path 309 may not be the same. For example, the difference in pitch may provide a means to control the ratio of the volume fraction of hole 306 compared to liner 102 along the longitudinal axis of the production tubing in the section of the production tubing comprising the array of holes 300. In some examples, each row in the array of holes may be fabricated as a single hole, making the fabrication process a simple one- step procedure. However, in some examples, the hole path may be generated by overlapping a number of holes along that path 310.

In Figure 3d, the holes in the array of holes 304 are elongated in the second continuity 308 direction. In this example, the spacing of the holes in the circumferential direction (w), and the spacing of the holes in the longitudinal direction (h) of the liner may be configured to allow an annular seal to form between said extruded elastomer and the leaking annulus.

In Figure 3e, the array of holes 305 comprises an array of holes 305 with a single hole and a single row. In this example, the hole is annular in shape, such that the length of the hole is the length of the circumference of the liner. In this example, the hole divides the liner section into two parts. This array of holes 305 is generated by activating the expansion force source 407 in the liner section of the production tubing 102.

Any elongated hole in the preceding figures may be generated in a number of ways. In some examples, the elongated holes may be formed by overlapping holes in the first and/or second continuity direction 307, 308. In some examples, the holes 306 being overlapped may already be elongated in the first and/or second continuity direction

307, 308. The number of overlapping holes may be sufficiently large that the total components of the hole path 309 in the first continuity 307 may be larger in length than the circumference of the liner section. In these examples, the length of the holes in the second continuity direction 308 may not be constant along the path of said generated hole. Likewise, in examples where the holes overlap in the second continuity direction

308, the length of the holes in the first continuity direction 307 may not be constant along the second continuity length 308. For example, if the holes in Figure 3a overlap along the hole path 310, the magnitude of the first continuity and second continuity will vary along the hole path.

In some examples, the liner section may already be perforated 501. The perforations in said perforated liner section 501 may then be enlarged, such that the arrays of holes 300 as described in Figure 3 are generated. In particular, the holes may be enlarged along the circumferential and/or longitudinal directions of the perforated liner to generate the array of holes. In other examples, the perforated region may not be modified, and a separate region of the production tubing, comprising a non-perforated liner section is perforated to form the array of holes 300.

For all the examples of the array of holes 300 as described above, there may be an optimisation process between the relative fraction of holes and the relative fraction of the remaining liner section. The optimisation process being between at least two opposing conditions. The first condition being to increase the relative fraction of holes in the liner section 102. The first condition may be optimised such that sufficient volume of elastomer 408 is extruded through the array of holes 300 to form a seal 503, 704. In some examples, the volume of elastomer required may be a volume that can form an annular seal 503, 704. The second condition being to decrease the relative fraction of holes. The second condition may be optimised such that the production tubing 102 remains mechanically integral and does not fail under its own weight. The optimisation between these two conditions may not just be achieved by varying the relative fraction of the holes, but also may be achieved by adopting a different shape and/or arrangement of holes. For example, hexagonal shaped holes may be suitable for ensuring better mechanical integrity for a given relative fraction of holes. Furthermore, there may be a minimum threshold size of each hole and/or area of each hole in the array of holes. For example, the length of each hole in the array of holes along the first and second continuity directions 307, 308 may need to be larger than a threshold value. The threshold value may vary depending on the situation and the nature of the sealing material. Generally speaking, it may be determined by predicting the maximum strain that may be transferred to the elastomer 408 for a given expansion force source 407. For example, in some examples, the expansion force 407 may not be energetic enough to propel the elastomer 408 to extrude through a hole 306 that is too small in size/area.

The spacing between the holes (w, h) in the array of holes 300 may be configured to form an annular seal 503, 704 in the leaking annulus 104. During the extrusion process, the elastomer 408 may deform elastically and/or plastically. The elastomer 408 may deform via compression in a plane on the liner section 102 containing the hole 306 in the array of holes 300, and deform via tension in a direction normal to said plane. The elastomer 408, after passing through each hole 306, may then elastically recoil along any directions contained in the aforementioned planes. The direction of the recoil is in the opposite direction to the deformation induced by the extrusion process. As such, the elastomer 408 may recoil and expand in the circumferential direction and/or longitudinal direction of the liner section after the extrusion process. In particular, it may be preferable if the elastomer 408 elastically recoils by at least half the length of the spacing in that direction. For example, the elastomer 408 may recoil by at least half the spacing in the longitudinal spacing of the array of holes. In this case, extrusion of said elastomer may avoid the development of voids in the annulus region. That is to say, the spacing in the array of holes is configured such that this statement is held true. In another example, the array of holes 300 may comprise an array of holes with circular section. After extrusion, the elastomer 408 may then elastically expands radially in the direction away from the centre of the circular hole after passing through said circular hole. The spacing of the holes (w, h) may be configured such that the elastic recoil of the elastomer in said radial direction is smaller than twice the magnitude of said recoil. In this way, the elastomer may be able to recoil and ‘reconnect’ with the other portions of the elastomer that have been extruded through adjacent holes 306 in the array of holes 300.

Step S202 may comprise perforating the tubular in a drilling process. In an example, the tubular may be a liner. The drilling process may comprise using one or more drills. The drill may either be deployed with the production tubing 101 , or in an annulus defined between the liner and an external casing of the wellbore 104. In these examples, drilling either occurs on the interior side of the liner section, or, from the exterior side of the liner section. Perforating the liner section 102 may comprise any form of drilling, and the method is not limited to only mechanical drilling. For example, holes may be generated using high-pressure fluid, such as in a jet cutter process. The cutting fluid may comprise water, and any abrasive substance.

There may be preparation stages before activating the expansion force source 407. For example, the holes 306 in the array of holes 300 may be smoothed to remove burrs and rough edges. Sandblasting may be suitable for this method. The holes may also be coated with a lubricant. In particular, the lubricant may be water-based. In some examples, the exterior side of the liner section of the production tubing 102 may be polished, and/or cleaned. Pickling of the external casing 103 may also be carried out to remove surface oxides, which may encourage explosion welding.

Figures 4a, 4b, 4c, 4d, 4e and 4f show particular examples of the source 400. In Figure 4a, the source 401 comprises an expansion force source 407 that is an explosive charge. In Figure 4b, the source 402 comprises an expansion force source 407 that is a explosive charge and an elastomer 408. In Figure 4c, the source 403 comprises an expansion force source 407 that is an explosive charge, elastomer 408 and a housing 409 radially disposed between the explosive charge and the elastomer 408. In Figure 4d, the source 404 comprises an expansion force source 407 that is an explosive charge and a housing 409, which surrounds the explosive charge. In Figure 4e, the source 405 comprises an expansion force source 407 that is an expandable source. In Figure 4f, the source 406 comprises an expansion force source 407 that is a series of concentric layers of explosive charges and elastomers 408.

In Figure 4a, the source 401 comprises an explosive charge. Activating the expansion charge 407 generates the expansion force in the form of an explosive discharge. As such, the expansion force source 407 comprises an explosive charge. The explosive discharge may produce a large expansion force, wherein the expansion force may be directed radially away from the centre of mass of said explosive charge. The explosive charge may comprise combustible material or the release of pressurised gas. Any type of explosive charge may be used: primary, secondary or tertiary. Preferably, the explosive charge may be either secondary or tertiary, such that, the explosive charge may be deployed safely. The explosive charge may also be either a low or high explosive. In the former, the explosive charge may generally be less powerful and the rate of decomposition is propagated by a flame front. The flame front travelling at a speed less than the speed of sound. In this discharge, a high-pressure front may also be generated. In some examples, the flame front and high-pressure front may travel at the same speed. In other examples, they may spatially separate after activation. In low explosives, activation of the expansion of the source is known as deflagration. In the latter, the explosive charge may generally be more powerful and the rate of decomposition may be propagated by a shock wave, travelling at a speed greater than the speed of sound. In this discharge, a flame front may still be present. The flame front travelling at a slower speed than the shock wave, and therefore spatially separating from the shock wave after activation. In high explosives, activation of the expansion of the source is known as detonation. In both cases, the activation of said explosive charge generates the expansion force. Generally speaking, high explosives may be better suited for this method. In a high explosive discharge, the momentum produced by the expansion of the high explosive charge source may be larger, and as such, greater deformation may be induced into the liner section of the production tubing 102. In the activation of the explosive charge, the expansion force source 407 rapidly expands changing from solid to hot gas. Examples of low explosives that may be used in any example for activating the expansion force source 407 may be as follows: petroleum based products, such as propane, gunpowder and gasoline. Examples of high explosives may comprise: trinitrotoluene (TNT), RDX and ammonium nitrate/fuel oil (ANFO). Many types of explosives may be used for the disclosed methods as will be appreciated by the skilled person. All explosive charges described herewith may refer to any form of explosive charge as previously described.

In Figure 4a, after detonation/deflagration of the explosive charge, the resulting explosive discharge transfers a large momentum to the liner section 102 over a short period. At the same time, a portion of the chemical energy associated with the detonation/deflagration of the explosive charge contributes to a rapid temperature increase. The local increase in temperature accompanied by the significantly large forces on the liner section 102 may cause the liner section to deform and expand. The explosive quantity of the explosive charge may be predetermined such that the liner section 102 may not rupture/fail. Preferably, the liner section 102 deforms and expands without failure. In some examples, the liner section of the production tubing 102 may deform and expand to form a weld with the external casing 503, 704. Explosion welding is a solid-state welding process. This type of bonding is advantageous, as the microstructure of the components in the weld are not significantly affected. As such, tailor engineered microstructures of the external casing 103 and production-tubing 102 may be maintained after the welding process. In this way, both the weld and the components welded may not require additional processing steps to reach mechanical integrity. Furthermore, the explosion welding process is a highly non-equilibrium process. As such, two dissimilar materials, which thermodynamically do not readily mix and form a bond, can. In this example, the production tubing 102 may not be perforated with the array of holes 300.

Instead of an external casing, the tubular may be surrounded by a formation. In that case, the tubular would not weld with the formation but instead form a sealing connection against the formation. Either way, the tight fit or welded connection closes the annulus in circumferential direction and in combination with the sealing material and effective seal is formed which closes the leak path into the well bore.

In Figure 4b, the source 402 comprise an explosive charge and an elastomer 408. The expansion force source 407 comprises an explosive charge. Preferably, the explosive charge may be the high explosive of the secondary or tertiary type. In this example, the elastomer 408 may be radially disposed around the explosive charge. In some examples, the elastomer 408 may surround the explosive charge. The elastomer 408 may be any form of polymer, but preferably, the polymer may be insoluble in water and/or resistant to sublimation at high temperatures. In particular, the elastomer 408 may be configured to soften during the explosive discharge, rather than sublime. It may be advantageous if the polymer has a negative thermal expansion coefficient, such that the polymer expands after cooling. In some examples, the elastomer 408 may comprise an expandable elastomer. In general, the elastomer 408 may expand in response to certain stimuli. Preferably, the stimuli may be leaking fluid 504. The leaking fluid 504 may be any of: oil/gas, water or brine. It is appreciated that any fluid 504 that may be expected to be present in a wellbore may be the leaking fluid 504, and an expandable elastomer suited for any particular leaking fluid 504 may be used. All elastomers 408 described herewith may refer to any form of elastomer 408 as previously described. After detonating the explosive charge, the elastomer 408 expands in the direction of the expansion force.

Generally speaking, the elevated temperatures of activating the expansion force source

407 leads to an induced shock wave/high pressure front travelling radially away from the centre of the explosion may cause the elastomer 408 to become less viscous. The elastomer 408 may be exposed to temperatures above its glass transition temperature. At these elevated temperatures, the propelled elastomer may extrude more easily through said array of holes 300 and fill any crevices, such as the leak path of the annulus packer 106, or the leaking annulus 104 more effectively. At these temperatures, the elastomer 408 may deform under its own weight. In this case, weight alone may provide the stimulus for the elastomer 408 to fill any crevices/voids. Capillary action may also comprise a driving force for the elastomer 408 to fill the voids/crevices. Compared to lower temperatures, the elastomer 408 may be able to pass deeper into the crevices, and increase the longitudinal length of the seal 503, 704. In some cases, the expansion force source 407 may also act to propel the elastomer

408 into these crevices, therein increasing the probability of a high quality seal. The elastomer 408 may also greater lower corrosion rates. In an example, the elastomer 408 may comprise a large ionic resistance. As such, the dissolution of the liner section may be kinetically limited by the large resistance of the elastomer seal. In this way, the elastomer 408 may also generate a seal that is corrosion resistant.

In Figure 4c, the source 403 comprises the explosive charge, housing 409 and elastomer 408. In this case, the expansion force source 407 comprises the explosive charge. Preferably, the explosive charge comprises the high explosive of the secondary or tertiary type. Preferably, the housing 409 may be disposed radially between the explosive charge and the elastomer 408. When the explosive charge of the expansion force source 407 is activated, the elastomer 408 expands in the direction of the expansion force. In this example, both the elastomer 408 and the housing 409 may be propelled by the expansion force radially towards the liner section of the production tubing 102 and/or the array of holes 300 in said liner section from the centre of mass of the explosive charge. As described above, the elastomer 408 may extrude through the array of holes 300 and fill the leaking annulus 104, 106. Further, the housing 409 may be propelled towards said array of holes 300. The housing 409 may explosion weld with the liner section. In these examples, the housing 409 may act to seal off the elastomer 408 such that the elastomer 408 may be unable to viscoelastically deform and retract from the seal region. In some examples, the housing 409 may prevent flow within the production tubing 102 from wearing the elastomer 408 away from the seal region. In general, the housing 409 may comprise a steel. In some examples, the housing 409 may be a stainless steel. As such, the corrosion resistance of the liner section 102 may be further improved in the vicinity to the leak. Generally speaking, the housing 409 may be sufficiently rigid, that it prevents the elastomer 408 from viscoelastically recoiling from the leaking annulus 104, 106 after forming the seal. Furthermore, the thickness of the housing may be configured in size to provide mechanical integrity to the source 400 during positioning. For example, the thickness may be sufficient that the source 400 maintains its shape, and/or does not break when deployed in the wellbore 100. In some examples, the production of the wellbore may not be stopped. As such, the source 400 may be exposed to stresses derived from the flow of said production fluids. There may be an optimization process here between the flow rate of production fluids in the production tubing 102, the thickness of the housing and the explosive quantity of the expansion force source. For example, the thickness of the housing may be thick enough to withstand the flow stresses from the production fluids, but not too thick that the expansion force source 407 required to expand said housing 409 is too large. In some examples, the production of the wellbore may be reduced during providing of said source 400 for this optimization. In other examples, the thickness of the housing may be configured in size to provide mechanical integrity to the source without reducing the production of the wellbore. As such, the production of the wellbore may be maintained during providing of said source 400 and/or activating the expansion force source 408. The explosive quantity of the expansion force source may be correspondingly changed to the thickness of the housing. For these examples, the housing 409 may be sufficiently dense such that the source 400 sinks in the production fluid flow. In some examples, the production flow rate, thickness of the housing and quantity of explosive may need to be adjusted such that the source sinks.

In some examples, the elastomer 408 may be radially disposed between the housing 409 and the explosive charge. In these examples, the housing 409 may generate explosive welds with the liner section and/or external casing of the wellbore 503, 704, and the elastomer 408 may fill any holes/voids generated in said process. In some examples, the elastomer 408 may be radially disposed on both sides of the housing 409.

In Figure 4d, the source 404 comprises an explosive charge and housing 409. The expansion force source 407 comprises an explosive charge. Preferably, the high explosive of the secondary or tertiary type, and may be radially surrounded by housing 409. Preferably, the housing 409 may comprise a material that is readily ductile at the high strain rates of the explosion. For example, the housing 409 may be a form of steel. In some examples, the housing 409 may be a stainless steel. After activating the explosive charge, the explosive discharge produces the large expansion force onto the housing 409, which in turn induces a stress within the housing 409, such that the housing expands in the direction of the expansion force. Preferably, the thickness and/or strength of the housing and the explosive quantity of the explosive charge may be configured such that the housing 409 may not rupture. During said expansion of the housing 409, in some examples, the elevated temperature and large momentum of the housing may form an explosion weld. In this case, the explosion weld comprises a weld between the housing 409 and the external casing of the wellbore 103. In some examples, welds may also form between the housing 409 and the liner section 102. Preferably, in these examples, the liner section may not be perforated. In some examples, using a housing 409 such as stainless steel produces an explosion weld that is more corrosion resistant.

In Figure 4e, the source 405 comprises the housing 409 as described in Figure 4d, but the housing 409 also comprises a top and bottom portion. In this example, the housing 409 comprises an expandable material. This expandable material may be selected such that rupture does not occur during expansion of the source 405. In these examples, the expansion force source 407 may comprise a number of different methods to produce expansion of the source 405. For example, the housing 409 may be expanded by a hydraulic device. Activating the expansion force source 407 may comprise pressurising the housing 409 with gas and/or liquid. The hydrostatic pressure within the housing may cause expansion of said housing 409. In these examples, there may be no explosion, as such. The fluid used for pressurising the housing 409 may be air or nitrogen gas, the liquid may be water. In some examples, cryogenic fluids and/or solids such as liquid nitrogen or dry ice may be used as expansion force sources 407 within the housing 409. In another example, the expansion force source 407 may comprise the explosive charge. Preferably, the explosive charge may be either a high or low explosive. Furthermore, in some examples, it may be preferable to expand the source using a mechanical device. For example, it may be preferable to use a piston pump or any other form of positive displacement pump to produce pressurised gas in the source. In some examples, generating the expansion force may comprise a mixture of these methods. For example, the pressurised gas may be combustible. At a threshold pressure, the pressurised gas may ignite to generate the explosive discharge. In these examples, activating the expansion force source 407 comprises activating the explosive source, and/or mechanical/hydraulic device.

Generally speaking, it may be preferable, if the source 400 is axially symmetric around the longitudinal axis of the production tubing. In this example, the source 400 expands in the radial direction of the production tubing towards the external casing of the wellbore 103, such that it may be contiguous with the liner section of the production tubing 102. In some examples, expanding the source 400 may be partially reversible, such that the housing 409 recoils after activating the expansion force source 407, and may then be removed from the production tubing 102 more easily. In some examples, the housing 409 may expand plastically and form explosive welds with the external casing 103. In some examples, the housing 409 may also be radially surrounded with an elastomer 408, and the method for sealing the leaking annulus 104, 106 may comprise essentially the same process as previously described. The top and bottom portions of the housing 409 may be advantageous in localising damage to within the production tubing 102 in the radial direction of the production tubing. For example, the top and bottom portions may protect regions of the production tubing 102 longitudinally distal to the location of said source 405. In some examples, the circumferential bond between the sides of the housing 409 and top and bottom portions of the housing may be deliberately weak. In these examples, preferential rupture may occur along this seam. This may act to direct a larger portion of the explosion energy radially towards the liner section 102, and therefore provide more explosion welds and/or extrusion of elastomer 408 to form a better seal.

In Figure 4f, the source 406 comprises a plurality of concentric layers of elastomer 408 and explosive charges. In this case, the expansion force source 407 comprises an explosive charge. The explosive charge may be any type of explosive charge as described above. In this example, the explosive charges are distributed in layers between a plurality of elastomer layers 408. In some examples, the number of the plurality of layers may be increased. When the explosive charge layers are activated, the elastomer layers 408 expand radially away from the explosive charges. Preferably, the layers of explosive charge are such that the explosive power/quantity of the explosive charges decreases in the radial direction. Therefore, when the explosive charges are activated in the source 406, the net force on each elastomer layer 408 may be in the radial direction towards the external casing of the production tubing 103. The activation process may comprise either detonating all the explosive layers simultaneously, or, detonating the largest explosive layer (most central explosive layer) to activate detonation of the other explosive layers. The elastomer 408 may therefore be propelled with a greater expansion force source 407, producing a better seal 503, 704. In some embodiments, the elastomer 408 may be replaced with a plurality of housing layers 409. The housing layers 409 may therefore generate explosion welds with one another, as well as the external casing 103. In these examples, each housing layer 409 or elastomer layer 408 may be different. For example, the radially outermost housing layers 409 may be configured to form high quality explosion welds with the liner section 102. The radially inner layers of housing 409 may be configured to form high quality explosion welds that are corrosion resistant to said radially outer layers. The outermost layers of elastomer 408 may be expandable elastomers with especially low viscosity, such that they provide excellent seals. The innermost layers of elastomer 409 may comprise more viscous and tougher elastomers 409 that are more durable to the flow in the production tubing 102 after the seal 503, 704 is formed. In some examples, both elastomer layers 408 and housing layers 409 may be used.

For Figure 4b, 4c, 4e and 4f it is appreciated that it is preferable to use the elastomer 408. In these cases, it is preferable if the liner section of the production tubing 102 is perforated with an array of holes 300. It may be preferable to activate the expansion force source 407 adjacent to the array of holes 300 in the liner section with an elastomer 408 radially disposed on said expansion force source 407. In these cases, the array of holes 300 may provide mechanical weakness into the liner 102, and mean that a smaller explosive charge may be required to achieve the seal 503, 704. As such, this may provide a cost effective way to produce the seal 503, 704. In a first case, less explosive charge is required as only the energy required to deform/extrude the elastomer 408 through the array of holes 300 is required. Polymers are much less strong than metallic alloys. Therefore, much less energy is required to deform polymers than to deform the liner section of the producing tubing 102. In a second case, less damage may occur to regions of the wellbore 100 near the activation of the expansion force source 407. The use of an elastomer 408 may also reduce damage to other regions within the wellbore 100, as the elastomer 408 may dampen the explosion for other regions within the wellbore 100.

For all the examples described, the hanging device 502 may be used to activate the expansion force source 407. For example, the hanging device 502 may comprise the wireline, and an electrical signal may be used to activate the expansion force source 407.

In all the above examples, the source 400 may be removed from the wellbore 100 after activating the expansion force source 407. The source 400 may be removed using the hanging device 502 to which the source 400 is deployed. In some of the examples, the detonation of the expansion force source may essentially destroy the source. In this example, the wireline, coiled tubing or workstring may be detached from the expansion force source 407 after activating the expansion force source 407. For example, the source 400 may be hung on the expansion force source 407 and the wireline may be broken/severed during the explosion process. In yet more examples, a separate hanging device (not shown) may be deployed to retrieve the previous hanging device 502 and the source 400. In these cases, the previous hanging device 502 are too damaged to be retrieve in a safe manner.

The source 400 may comprise a plurality of sub-sources. In some examples, each sub source 400 may in turn comprise a plurality of expansion force sources 407. In some examples, these expansion force sources 407 may be different from one another, or the same. For example, it may be preferable to use a particular type of expansion force source to activate the other expansion force sources 407 in the sub-sources 400. The one or more expansion force sources 407 of each sub-source 400 may be activated concurrently/simultaneously to form the seal 503, 704.

In other examples, the source 400 may also comprise a plurality of sub-sources, but the method steps of providing and activating each of the plurality of sources may be carried out sequentially. For example, the plurality of sources may comprise a first source 701 and a second source 703. The first source 701 may be positioned and activated before the second source 703. In this example, it may be preferable if the first source 701 comprises an explosive charge, and the second source 703 comprises an explosive charge, an elastomer 408 and/or housing 409, and wherein the arrangement of the each source 701 , 703 is any as described previously 400. In this example, the technical purpose of the first source 701 and the second source 703 may be different.

In some examples, a predetermined length of the seal 503, 704 along the longitudinal axis of the liner section may be produced. In this case, multiple sources 400 may be expanded sequentially. In some examples, the predetermined length of seal 503, 704 may be produced by overlapping more than one seal 503, 704 in the longitudinal direction. Overlapping one or more seals 503, 704 may comprise activating each expansion force source 407 longitudinally adjacent to the seal 504, 704 generated by a previous expansion force source 407. Preferably, the first source 400, 701 in the sequential series may be positioned and activated immediately above the leaking annulus 104. The next source 400, 702 is detonated above the seal 503, 704 formed by the previous source 400, 701 , such that the seal 503, 704 formed by the subsequent detonation overlaps with the previous one. This procedure may be repeated until the length and quality of seal 503, 704 produced is sufficient. In other examples, the multiple sub-sources 400 may be activated concurrently/simultaneously. In these examples, each sub-source 400 may be disposed longitudinally adjacent to one another in a chain. A spacing between the sub-sources 400 may be predetermined. Each expansion force source 407 within the multiple sub-sources 400 may be activated, and therein the predetermined length of the seal 503, 704 may be produced in a single step. In these examples, the multiple sub-sources 400 are hung on the same hanging device 502. In some examples, the seal 503, 704 may not be perfect, but may leak a volume of fluid 504, which is below an allowable range set by regulation. In other examples, the length of the annular seal may be increased arbitrarily until the seal 503, 704 reaches a predetermined leakage rate. In some examples, the leakage rate may be measurably zero. In cases where the seal 503, 704 is not perfect, the seal may act effectively as a choke.

The leaking annulus 104 described above may not necessarily comprise a leaking annulus-packer 105, 106. The annulus may not be leaking. In some examples, the leak may not comprise an annulus.

Figure 5 and 6 show an exemplary method 500 for carrying out S206. In this example, the source 400 comprises the explosive charge, the elastomer 408 and the housing 409. The housing 409 is radially disposed between the explosive charge and the elastomer 408. In some examples, the housing 409 may surround the elastomer 408. In such an example, the mechanical integrity of the source may be maximised. In the first stage of this Figure, the source 400 has already been positioned radially adjacent to the array of holes 300, 501 perforated in the liner section. As shown in the Figure, leaking fluid 504 from the leaking annulus 104, 106 may pass through the array of holes in the liner section of the production tubing 300 and enter the hole defined by the production tubing 101. S602 comprises activating the expansion force source 407, wherein activating the expansion force source 407 comprises detonating/deflagrating the explosive charge to generate an expansion force in the radial direction of the tubular towards the formation of the wellbore. In an example, the tubular is a liner section of the production tubing 102 and the expansion force is directed towards the external casing of the wellbore 103. In S602, the connection between the source 400 and the hanging device 502 may be broken. S604 comprises deforming the perforated tubular section 501 , housing 409 and elastomer 407 in at least the radial direction of the tubular towards the formation of the wellbore. In an example, the perforated tubular section is a perforated liner section 501 and the expansion force source is directed towards the external casing of the wellbore 103. It is appreciated that the housing 409 and elastomer 408 expand in radius, and as such, tensile deformation of the housing 409 and elastomer 408 is actually in the circumferential direction of each component 408, 409. The high-pressure front and/or high temperature front generated by the explosion may be sufficient in energy that the housing 409 explosion welds to the external casing 103 and/or liner section 102, 501. The housing 409 may mainly explosion weld to the liner section 102. The liner section 102 may explosion weld with the external casing of the wellbore 103. Preferably, the liner section 102 may be at least contiguous with said external casing 103 after activation. S606 comprises extruding the sealing material or elastomer 408 through the holes 306 in the array of holes 300 in the tubular or liner section 102 to form a seal 503. Preferably, the seal is in the leaking annulus 104, 106 and blocks the leak. In this step, the elastomer 408 may be propelled into the perforated liner section 300, 501 with sufficient velocity to extrude said elastomer 408 through the array of holes 300. In some examples, it may be preferable that the liner section 102 expands radially towards the external casing 103, as in this case, the total volume of the leaking annulus 104, 106 may be reduced. As such, the total volume of extruded elastomer required to form said seal 503 may be reduced. In some examples, the leaking annulus 104, 106 may comprise a leaking annulus packer 105, 106. In these examples, the leaking annulus packer 105 comprises the leak path 106. As described previously, the position of said source may be configured such that extruded elastomer may be propelled towards the leaking annulus packer 105, 106, and fill the leak path 106 to seal the leaking annulus 104, 106. The quantity of elastomer may be greater than the volume required to fill the leaking annulus 104, 106 to form the seal 503. Preferably, the explosive quantity of the expansion force source may be configured to produce a sufficient volume of extruded elastomer to fill the leaking annulus 104, 106. In some the leaking annulus 104, 106 comprises the leaking annulus packer 105, 106. Preferably, the seal 503 may be an annular seal, but it may not be necessary to form an annular seal to form a leak-proof seal 503. In such examples, the extruded elastomer may form a seal on top of the leak paths 106, and this is sufficient to block the leak. S608 comprises retracting the hanging device 502 from the wellbore 100. Preferably, the hanging device 502 may be a wireline, such that in S602, the connection between the hanging device 502 and said source 400 may be broken. After S608, production may be continued under normal production conditions, if production was reduced for said method steps.

Figure 7 and 8 show a preferred method for sealing a leaking annulus 104, 106. S802 comprises providing a first set of expansion force source 701 radially adjacent to the tubular or liner section 102, and wherein the expansion force source 407 may be hung on a first hanging device 502. As described previously, the liner section 102 may already comprise a perforated liner section 501 , 300, and the array of holes 300 may be generated by modifying the existing perforations in the perforated liner 501. S804 comprise activating the first set of expansion force source 701 , wherein the expansion force source 407 comprises an explosive charge to generate a circumferential opening in the tubular or liner section 702. In S804, detonating/deflagrating the explosive charge generates a large expansion force in the radial direction of the production tubing towards the external casing of the wellbore 103. Furthermore, the expansion force source 407 may be large enough to rupture and deform the liner section 102. Preferably, along with rupturing the liner section 102, the explosive discharge generates explosion welds between the liner section 102 and the external casing of the wellbore 103. In some examples, the liner section may be perforated 501 , and as such, the explosion weld may not seal the leaking annulus. However, in some examples, the liner 102 may not be perforated and the array of holes 300 may be generated using this explosive discharge. In those cases, explosion welding the liner section with the external casing 102 may form an annular explosion weld and therefore an annular seal. In S804, the explosive discharge may sever/break the connection with the first hanging device 502. The hanging device 502 may comprise the wireline. In S804, the circumferential opening may expose the external casing 103 or the formation of the wellbore. In S806, the first hanging device 502 may be retracted from the wellbore. S808 comprises providing the second set of expansion force source 703 radially adjacent to said circumferential opening 702, wherein the second set of expansion force 703 may be hung on a second hanging device 502, and wherein the expansion force source 407 comprises an explosive charge, a sealing material or an elastomer 408 and a housing 409, and activating the second set of expansion force source 703 to extrude said sealing material or elastomer 408 through the circumferential opening 702 to form an annular seal 704. Optionally, the second set of expansion force source 703 may be positioned at essentially the same location as the first set of expansion force source 701. In this step, the housing 409 may be radially disposed between the explosive charge and the elastomer 408, or optionally, the housing 409 may surround the elastomer 408. After the expansion force is generated, the elastomer 408 and the housing 409 are deformed in at least the radial direction, and propelled in the radial direction towards the external casing 103 and/or circumferential opening 702 generated by the first set of expansion force sources 407. In this case, the elastomer 408 may fill any voids in the explosion weld and/or circumferential opening 702 in the liner section of the production tubing 102. In the case that the liner contains an array of holes 300, the elastomer 408 may be extruded through said array of holes 300 and fill the annular portion between the production tubing 102 and the external casing 103 to form a seal 503, 704. Preferably, sufficient volume of elastomer is extruded such that the seal formed may be an annular seal 503, 704. The housing 409 may further explosion weld with the liner section 102 and/or external casing 103, and provide support to the elastomer seal, such that the elastomer seal may not be damaged by the production fluids during later operation. In S808, the connection between the second hanging device 502 and the second set of source 703 may be broken/severed. In an example, the second hanging device 502 may be the wireline. In S810, the second hanging device hanging 502 may be retracted from the wellbore.

An advantage of exposing the external casing or formation is that the sealing material can be formed against the casing or formation without intermediate tubular or tubular remains.

In some examples, the leaking annulus 104, 106 may comprise an annulus, and the method of sealing the annulus substitutes the annulus packer 105. In particular, during the well completion process, annulus packers 105 may be replaced with the current method for sealing annuli.

For all the disclosed methods for generating a seal, it may be preferable to form an annular seal.

Generally speaking, the method of sealing an annulus may be applicable to any annular section in a wellbore. The annular section being defined by a tubular section and the external casing and/or formation of the wellbore. In some examples, the annulus may be defined by an intermediate tubular in-between the formation and production tubing. The location or type of tubulars defining the annulus are not limited in this application. However, at least one of the tubulars is a tubular transporting production fluid. Any annulus that would be anticipated by the skilled person are appreciated.

The skilled person will understand that in the preceding description and appended claims, positional terms such as ‘above’, ‘along’, ‘side’, etc. are made with reference to conceptual illustrations, such as those shown in the appended drawings. These terms are used for ease of reference but are not intended to be of limiting nature. These terms are therefore to be understood as referring to an object when in an orientation as shown in the accompanying drawings. In general, terms such as ‘above’ and ‘below’ refer a vertical configuration. In general, these terms refer to downstream and upstream process respectively, unless otherwise stated.

Although the disclosure has been described in terms of preferred embodiments as set forth above, it should be understood that these embodiments are illustrative only and that the claims are not limited to those embodiments. Those skilled in the art will be able to make modifications and alternatives in view of the disclosure that are contemplated as falling within the scope of the appended claims. Each feature disclosed or illustrated in the present specification may be incorporated in any embodiments, whether alone or in any appropriate combination with any other feature disclosed or illustrated herein.