A downhole tool (1) for manipulating a target, includes a housing (2). The housing includes an inner surface (5) configured for mounting to a tubular carrier; and an outer surface (10). At least one chamber (20) is provided between the inner surface (5) and the outer surface (10) and contains at least one propellant source (22) and an ignition system. One or more outlets (12) lead from the chamber (20) to the outer surface (10), for combustion products from the at least one propellant source. The downhole tool may be employed for perforating and may be included in a hydraulic fracturing assembly. A method of hydraulic fracturing in a wellbore using the tool is provided.

RELATED APPLICATIONS

The present invention is a U.S. National Stage under 35 USC 371 patent application, claiming priority to Serial No. PCT/EP2020/082134, filed on 13 Nov. 2020; which claims priority from 1916511.7 filed 13 Nov. 2019; the entirety of which are incorporated herein by reference.

FIELD

The present invention relates to the field of downhole tools and associated methods that employ combustion products from a propellant to manipulate a target. The present invention finds application in the oil and gas industry and is particularly suitable for the perforation of tubulars, cement casings and rock formations

BACKGROUND

In the oil and gas industry downhole tools may be employed to perforate or sever tubulars or other structures present in a well.

A typical example of such activity is in hydraulic fracturing operations (‘fracking’).

In an exemplary method, a well is drilled and lined with a tubular casing. The casing may be cemented into place with a more or less continuous layer of cement provided as a seal between the casing and the surrounding formation. To provide access to the formation, a number of ‘perforating guns’ may be deployed downhole. The perforating guns employ means such as shaped charge explosives to punch holes through the casing, any associated cement layer and into the formation. The perforating guns are then removed and a number of ‘fracking sleeves’ (or ‘frac sleeves’) are deployed, fitted to a tubular (such as coiled tubing). The fracking sleeves provide fluid communication, via opening ports, from the interior of the tubular to the annulus between the tubular and the casing.

Fracking liquids including proppant solids are then pumped down the coiled tubing and out through the ports in the fracking sleeves, to pressurise the annulus. (Packers are used to isolate the annulus along sections of the well.)

The hydraulic pressure of the fracking liquids fractures the formation via the holes in the casing previously made by the perforating guns. After withdrawal of the fracking sleeve and packer arrangements the well produces hydrocarbons (e.g. methane) from the hydraulically fractured rock formation.

Although a number of tools and methods have been developed for perforating or severing structures downhole there remains the need for improved tools and methods.

SUMMARY

According to a first aspect of the invention there is provided a downhole tool for manipulating a target, wherein the tool comprises a housing, the housing comprising:

an inner surface configured for mounting to a tubular carrier in use;

an outer surface;

at least one chamber provided between the inner surface and the outer surface and containing at least one propellant source;

an ignition system for igniting propellant at the at least one propellant source; and

one or more outlets leading from the chamber to the outer surface, for combustion products from the at least one propellant source.

In use, the combustion products emanating from an outlet or outlets can, for example, manipulate a target, such as a tubular, by, for example, ablation, cutting, displacement, removal, heating, abrasion, or erosion and/or consuming.

The inner surface may take the form of the surface of a bore passing through the tool from a first end to a second end. The inner surface or bore may be sized to fit about a tubular such as a coiled tubing carrying one or more frac sleeves i.e. the tubular carrier may comprise a coiled tubing. The inner surface mounts onto the tubular carrier and is configured to allow the passage of fluid through the tubular carrier.

Alternatively the inner surface of the tool may form a portion of the wall of a tubular carrier such as a coiled tubing.

In a convenient form the tool has an inner surface comprising a generally cylindrical bore passing through from a first end to a second end of the housing. The tool may be generally cylindrical. The outer surface of the tool may be generally cylindrical.

The outlet or outlets lead from the at least one chamber to the outer surface of the housing. The chamber or chambers is/are provided between the inner and outer surfaces of the housing. A chamber may have one or more outlets for combustion products emanating from a propellant source or sources contained within the chamber. The outlets release combustion products from a respective chamber. The outlets may be shaped to control the combustion products direction and/or focus.

The term ‘propellant source’ used herein means a location of propellant material provided for ignition. Thus, a propellant source within the chamber or chambers may comprise or be a charge (portion) of a propellant composition, or components for a propellant composition, placed at a location within the chamber. Alternatively, a propellant source may be an opening into the chamber from a supply system that feeds propellant composition, or the components for a propellant composition, for ignition. Feeding the tool with propellant allows the tool to be used continuously after ignition. The propellant may be fed into the housing in the form of a solid, liquid, paste, foam, gel or gas composition or a combination of these.

Chambers including a charge of propellant as propellant source are convenient. For example chambers may include blocks of solid propellant, that may be shaped to fit the chamber geometry. In some examples an outlet may be placed to exit more or less centrally from an associated chamber. Two or more propellant sources may be placed so as to direct their combustion products towards each other (i.e. the charges are opposed to each other). The flows of combustion products interact as they collide and then exit via the outlet. Without wishing to be bound by theory, tests have shown that the flow of combustion products from each propellant source in a tool where the propellant charges are opposed to each other appear to interact within the chamber—one against the other. This may produce results that may be more consistent and/or effective than those of arrangements using only one propellant source in the chamber. The combustion products may include gases, solid and/or liquid particles and in some cases plasma.

Propellants are generally classified as explosives for transportation purposes. Thus a propellant is a generally explosive material which has a low rate of combustion and once ignited burns or otherwise decomposes (i.e. deflagrates) to produce propellant gas. This gas is highly pressurised, the pressure driving the gas and other combustion products away from the propellant, forming a stream of combustion products. A propellant can burn smoothly and at a uniform rate after ignition without depending on interaction with the atmosphere and produces propellant gas and/or heat on combustion; and may also produce additional combustion products. The use of a propellant rather than a conventional explosive charge, such as a shaped charge arrangement, may provide a more controlled and/or sustained attack on a target.

The housing defines one or more chambers and the propellant source or sources are located within the chamber or chambers. Ignited propellant can develop a pressure of combustion products within its respective chamber, which can then exit the tool via one or more respective outlets. An outlet may comprise one or more apertures, which can each act as nozzles for jets of combustion products emanating from a respective chamber.

The outlets may be closed before the propellant is ignited, and open following ignition. This may be achieved in a number of ways. The outlets may be sealed, for example with a fusible material, such as a relatively low melting point metal. The combustion products generated following ignition of the propellant melt or decompose the seal. Alternatively the pressure generated within a chamber following ignition of the propellant may move a part, such as a piston, to uncover the outlet.

The tool may take the form of a downhole perforator, typically with a plurality of outlets spaced apart circumferentially and/or axially about the outer surface of the housing. An elongate generally cylindrical tool may comprise a first array of axially spaced apart outlets along the outer surface and a second array of axially spaced outlets diametrically opposite the first. The first array may be axially spaced apart on the outer surface along a line parallel with the longitudinal axis of the tool and the second along the diametrically opposite line. An array of outlets may comprise at least two, typically three or more outlets.

Alternatively a generally cylindrical perforator tool may have two or more arrays of outlets, each array comprising circumferentially spaced apart outlets with each array axially spaced from the next along the length of the housing. This arrangement can allow simpler manufacture, as each array of outlets may be provided on a circumferential ring that forms part of the generally cylindrical outer surface of the tool. In such an arrangement the outlets of one array may be circumferentially staggered with respect to the outlets of the next array along the length of the housing.

In a convenient arrangement a generally cylindrical perforating tool may include one or more circumferential rings. Each circumferential ring may include one or more outlets. The outer surface of the ring may provide a part of the outer surface of the housing of the tool. The outlet or outlets in the ring is/are in fluid communication with one or more chambers containing one or more propellant sources. In such a tool the chamber or chambers may be provided within one or more cylindrical sleeves. Thus the housing may comprise one or more cylindrical sleeves, and one or more circumferential rings providing a generally cylindrical housing with a bore therethrough.

Where the chamber or chambers are provided within cylindrical sleeves, the cylindrical sleeves, in particular the outer surface of the cylindrical sleeves, may be of metal, to provide durability. In such examples, during manufacture, the inner surface of the cylindrical sleeve may be formed as a layer after insertion of propellant source, ignition system components etc. within the chamber or chambers. For example the inner surface may be formed of a thermosetting resin or other polymer, such as a phenolic resin. Similarly, a cavity within a cylindrical sleeve that is used to form chambers may be divided into two or more chambers by the use of blocks of a thermosetting resin or other polymer.

Perforating tools as described herein may find use in connecting a wellbore to a production reservoir. They may also find particular use in methods of hydraulic fracturing such as are described in more detail hereafter.

The tools of the invention may further comprise a control module. The control module may include items such as electronic control of the ignition system; and a sensor or sensors for monitoring downhole positioning and/or conditions such as pressure and temperature. Signalling between the control module and the surface may be by wire or wireless connection.

The tools include an ignition system for igniting the propellant. The ignition mechanism may include an ignition device at each of the propellant sources. The ignition devices may be controlled to ignite propellant at the respective propellant source simultaneously or substantially simultaneously. For example, a control signal (by wire or wireless) from a control module may cause activation of the ignition device to ignite the propellant at each propellant source. However, it has been found that ignition at one propellant source in a chamber of a tool will tend to rapidly cause ignition at the other or further propellant sources contained within the same chamber. Therefore, only one ignition device may be provided within each chamber.

The propellant ignition mechanism may be any suitable arrangement for the propellant employed, such as those used in the oil and gas industry or the space industry to ignite combustible or explosive materials. Examples include but are not limited to: electric or other direct heating; non-explosive and explosive chemical ignition (such as propellants or other pyrotechnics); spark plug or other electric discharge; and the like.

To aid in protecting the outer surface of the tool from damage during deployment downhole, the tool may be provided with a protector or protectors, typically one at either end. The protectors may have a larger diameter than the housing. For example in a cylindrical tool of the invention the protectors may be generally cylindrical and be fitted to the first and second ends. Where the inner surface of the tool is in the form of a bore, the protectors may be provided with a bore for the passage of a tubular carrier. A protector may have a conical or generally conical end, narrowing in the direction away from the housing. This can aid in deploying the tool downhole, especially when passing through a restricted diameter section of the well bore.

A protector may have one or more passages therethrough, to allow fluid in the annulus to pass.

Protectors may be fitted to the tool. Alternatively protectors may be fitted to a tubular carrier and the tool fitted adjacent e.g. in contact with the protector on the tubular carrier. Thus the protector or protectors may be provided as part of an assembly including the tool and a tubular carrier.

The present invention also provides a method of hydraulic fracturing in a wellbore, the method comprising the steps of:

a) deploying a tubular carrier downhole in a rock formation, wherein the tubular carrier mounts at least one downhole perforator tool as described herein and includes at least one frac sleeve and two or more packers for isolating sections of the annulus;

b) operating the downhole perforator to produce access holes into the rock formation;

c) setting the packers to isolate a section of the annulus including the access holes and the at least one frac sleeve; and

d) pumping fracking fluid through the tubular carrier and out of the at least one frac sleeve into the annulus, to fracture the rock formation via the access holes.

After the fracturing step is completed the method may continue by unsetting the packers, to release sealing contact, and removing the tubular carrier. The well may then produce hydrocarbon product from the rock formation via the wellbore.

Where the tool includes more than one downhole tool and associated frac sleeve or sleeves, together with associated packers, then the method may include repetition of steps b) and c). (Making use of further downhole perforator/frac sleeve and packer arrangements already fitted to the tubular carrier.) In this way one deployment of one tubular carrier may allow multiple perforation and fracking steps to be carried out in a wellbore.

It will be appreciated that steps b) and c) above may be carried out in the order b) and then c), or c) and then b), as desired. As an alternative all the perforation action may be carried out before setting the packers, or all the setting of packers may be done before perforating.

As a yet further alternative the tubular carrier may be left in situ and product produced from the well bore via the annulus and/or via the inside of the tubular carrier.

The present invention also provides a hydraulic fracturing assembly comprising:

a) a tubular carrier comprising one or more frac sleeves and two or more packers; and

b) a downhole perforator tool, wherein the tool comprises a housing, the housing comprising:

an inner surface mounted to the tubular carrier;

an outer surface;

at least one chamber provided between the inner surface and the outer surface and containing at least one propellant source;

an ignition system for igniting propellant at the at least one propellant source; and

one or more outlets leading from the chamber to the outer surface, for combustion products from the at least one propellant source.

The frac sleeves employed in the hydraulic fracturing methods and assemblies described herein may be of the conventional types, such as sliding sleeves that may be ball operated.

The perforator tool may be in accordance with any aspect of the tool for manipulating a target described herein.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG.1ashows a downhole tool1in schematic perspective with some parts cut away to allow viewing of the interior. The tool1is a perforator tool and is cylindrical in form. Cylindrical housing2has a cylindrical bore4, the surface5of the bore (see FIGS.1cand1d) provides an inner surface of the housing, running from a first end6through to a second end8.

The outer surface10of the housing2includes outlets12. The outer surface10includes cover plates13in this example, through which the outlets12emerge. Three outlets12are visible and constitute an array of outlets that are spaced axially on the outer surface10along a line parallel to the longitudinal axis of the tool. Not visible in this view is a corresponding array of outlets12diametrically opposite those that are in view.

Protectors14are fitted to the first6and second8ends of the housing2. The protectors14are cylindrical and have a larger diameter than that of the housing2. Ends16of the protectors14are conical, narrowing in the direction away from the housing2. The protectors have passages18therethrough to allow fluid communication (seeFIGS.1cand1d). Each outlet12has an associated chamber20between the inner surface5and the outer surface10, one chamber20is visible by the cut away on the figure.

As shown at the cut away, the chamber20has the corresponding outlet12placed centrally. Charges22of solid propellant are placed in chamber20to either side of the outlet12. Magnified viewFIG.1bshows that the outlets12comprise two apertures24constituting nozzles for the emanation of combustion products from the propellant charges22, following their ignition. The apertures24are shown sealed with a fusible metal (e.g. zinc) that will be melted or even combusted when the propellant is ignited.

The tool1also includes a control module25that can receive wired or wireless communications from the surface and includes the electronics for an ignition system for propellant.

FIGS.1cand1dshow cross sections of the tool1ofFIG.1a.FIG.1cshows a section at diametrically opposed outlets12,FIG.1dshows the arrangement of propellant charges22within chambers20. Details of outlets12are shown inFIGS.1eand1f.FIG.1eshows the interior of an outlet12with shaped projections26(also visible in cross sectionFIG.1c) for directing flows of combustion products (as suggested by arrows C) towards apertures24.FIG.1fshows the outer surface of outlet12. The outlet12projects slightly above the surface27as a cover plate13surrounds it (seeFIGS.1aand1c).

FIG.2shows a section of a tubular carrier28to which tools similar to those depicted inFIG.1can be fitted. In this example tubular28has a protector14fitted. A tool such as that shown inFIG.1but without protectors14fitted to the housing can be slid onto tubular carrier28until an end is adjacent protector14. A further protector14can then be fitted onto tubular28adjacent the other end of the tool.

Part of an alternative tool1is shown fitted to a tubular carrier28inFIG.3a. The housing includes circumferential rings30, each having three outlets12about the circumference of the corresponding ring30. The outlets12of one array30are staggered circumferentially with respect to the outlets12on the next array along the length of the tool.

FIG.3bshows a circumferential ring30for the tool ofFIG.3a. Outlets12are spaced at 120 degrees around the ring30. Each outlet12has an inlet passage32for communication with a chamber containing a propellant source. Each outlet12has two apertures24on the outer surface of ring30for emanation of combustion products.

FIG.3cshows in perspective view with cut away part of the tool ofFIG.3a. In this example outer surface10of housing2comprises the outer surface of circumferential ring30and cylindrical sleeves34, of metal. Inner surface5formed about bore4is formed of a resin, such as a phenolic resin. This arrangement allows access to chambers20during manufacture of the tool, to allow placement of propellant charges22in chambers20. In this example blocks of a phenolic resin36are placed within the cavity defined by the inner surface5of the tool1and the inner surface of sleeves34to divide it into chambers20. Thus each chamber20provides combustion products from propellant charges22to its respective outlet12.

FIGS.3dand3eshow cross section views of the tool1ofFIG.3a. InFIG.3dthe cross section is shown at a circumferential ring30allowing a view of outlets12and the inlet passages32, through which propellant charges22in chambers20can be seen.

InFIG.3ethe cross section is shown through a cylindrical sleeve34, and shows the arrangement of propellant charges22in chambers20around the circumference of the tool. Also visible in this view is an outer liner38of a phenolic resin provided about the whole inner surface of the cylindrical sleeve34.