Patent Description:
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.

<CIT> relates to a propellant tool for use in a hydrocarbon bearing formation.

The present invention provides a downhole perforator tool, a hydraulic fracturing tool utilising the perforator tool and a method of hydraulic fracturing in a wellbore as set out in the appended claims.

In use, 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 of the tool 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 is a downhole perforator tool, 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:.

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:.

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.

<FIG> shows a downhole tool <NUM> in schematic perspective with some parts cut away to allow viewing of the interior. The tool <NUM> is a perforator tool and is cylindrical in form. Cylindrical housing <NUM> has a cylindrical bore <NUM>, the surface <NUM> of the bore (see <FIG>) provides an inner surface of the housing, running from a first end <NUM> through to a second end <NUM>.

The outer surface <NUM> of the housing <NUM> includes outlets <NUM>. The outer surface <NUM> includes cover plates <NUM> in this example, through which the outlets <NUM> emerge. Three outlets <NUM> are visible and constitute an array of outlets that are spaced axially on the outer surface <NUM> along a line parallel to the longitudinal axis of the tool. Not visible in this view is a corresponding array of outlets <NUM> diametrically opposite those that are in view.

Protectors <NUM> are fitted to the first <NUM> and second <NUM> ends of the housing <NUM>. The protectors <NUM> are cylindrical and have a larger diameter than that of the housing <NUM>. Ends <NUM> of the protectors <NUM> are conical, narrowing in the direction away from the housing <NUM>. The protectors have passages <NUM> therethrough to allow fluid communication (see <FIG>). Each outlet <NUM> has an associated chamber <NUM> between the inner surface <NUM> and the outer surface <NUM>, one chamber <NUM> is visible by the cut away on the figure.

As shown at the cut away, the chamber <NUM> has the corresponding outlet <NUM> placed centrally. Charges <NUM> of solid propellant are placed in chamber <NUM> to either side of the outlet <NUM>. Magnified view <FIG> shows that the outlets <NUM> comprise two apertures <NUM> constituting nozzles for the emanation of combustion products from the propellant charges <NUM>, following their ignition. The apertures <NUM> are shown sealed with a fusible metal (e.g. zinc) that will be melted or even combusted when the propellant is ignited.

The tool <NUM> also includes a control module <NUM> that can receive wired or wireless communications from the surface and includes the electronics for an ignition system for propellant.

<FIG> show cross sections of the tool <NUM> of <FIG>. <FIG> shows a section at diametrically opposed outlets <NUM>, <FIG> shows the arrangement of propellant charges <NUM> within chambers <NUM>. Details of outlets <NUM> are shown in <FIG> shows the interior of an outlet <NUM> with shaped projections <NUM> (also visible in cross section <FIG>) for directing flows of combustion products (as suggested by arrows C) towards apertures <NUM>. <FIG> shows the outer surface of outlet <NUM>. The outlet <NUM> projects slightly above the surface <NUM> as a cover plate <NUM> surrounds it (see <FIG> and <FIG>).

<FIG> shows a section of a tubular carrier <NUM> to which tools similar to those depicted in <FIG> can be fitted. In this example tubular <NUM> has a protector <NUM> fitted. A tool such as that shown in <FIG> but without protectors <NUM> fitted to the housing can be slid onto tubular carrier <NUM> until an end is adjacent protector <NUM>. A further protector <NUM> can then be fitted onto tubular <NUM> adjacent the other end of the tool.

Part of an alternative tool <NUM> is shown fitted to a tubular carrier <NUM> in <FIG>. The housing includes circumferential rings <NUM>, each having three outlets <NUM> about the circumference of the corresponding ring <NUM>. The outlets <NUM> of one array <NUM> are staggered circumferentially with respect to the outlets <NUM> on the next array along the length of the tool.

<FIG> shows a circumferential ring <NUM> for the tool of <FIG>. Outlets <NUM> are spaced at <NUM> degrees around the ring <NUM>. Each outlet <NUM> has an inlet passage <NUM> for communication with a chamber containing a propellant source. Each outlet <NUM> has two apertures <NUM> on the outer surface of ring <NUM> for emanation of combustion products.

<FIG> shows in perspective view with cut away part of the tool of <FIG>. In this example outer surface <NUM> of housing <NUM> comprises the outer surface of circumferential ring <NUM> and cylindrical sleeves <NUM>, of metal. Inner surface <NUM> formed about bore <NUM> is formed of a resin, such as a phenolic resin. This arrangement allows access to chambers <NUM> during manufacture of the tool, to allow placement of propellant charges <NUM> in chambers <NUM>. In this example blocks of a phenolic resin <NUM> are placed within the cavity defined by the inner surface <NUM> of the tool <NUM> and the inner surface of sleeves <NUM> to divide it into chambers <NUM>. Thus each chamber <NUM> provides combustion products from propellant charges <NUM> to its respective outlet <NUM>.

<FIG> show cross section views of the tool <NUM> of <FIG>. In <FIG> the cross section is shown at a circumferential ring <NUM> allowing a view of outlets <NUM> and the inlet passages <NUM>, through which propellant charges <NUM> in chambers <NUM> can be seen.

Claim 1:
A downhole perforator tool (<NUM>) comprising a housing (<NUM>), the housing (<NUM>) comprising:
an inner surface (<NUM>) configured for mounting to a tubular carrier in use;
an outer surface (<NUM>);
at least one chamber (<NUM>) provided between the inner surface (<NUM>) and the outer surface (<NUM>) and containing at least one propellant source (<NUM>);
an ignition system for igniting propellant at the at least one propellant source (<NUM>); and
one or more outlets (<NUM>) leading from the chamber (<NUM>) to the outer surface (<NUM>), for combustion products from the at least one propellant source (<NUM>);
wherein the housing (<NUM>) comprises one or more cylindrical sleeves (<NUM>) including the at least one chamber (<NUM>), and one or more circumferential rings (<NUM>) including the one or more outlets (<NUM>), to provide a generally cylindrical housing with a bore (<NUM>) therethrough;
wherein the outer surface of the cylindrical sleeve or sleeves (<NUM>) is of metal and the inner surface of a thermosetting resin or other polymer;
wherein each outlet (<NUM>) comprises one of more apertures (<NUM>) which act as nozzles for jets of combustion products from the at least one propellant source (<NUM>);
whereby the jets of combustion products can produce access holes into a rock formation.