NO345811B1

NO345811B1 - A method of performing abrasive perforation and washing in a well

Info

Publication number: NO345811B1
Application number: NO20180973A
Authority: NO
Inventors: Morten Myhre; Arne Gunnar Larsen; Arnold Østvold; Markus Iuell
Original assignee: Hydra Systems As
Priority date: 2018-07-10
Filing date: 2018-07-10
Publication date: 2021-08-16
Also published as: NO20180973A1

Description

A METHOD OF PERFORMING ABRASIVE PERFORATION AND WASHING IN A WELL

Technical field

The invention concerns a method of performing abrasive perforation and washing along a longitudinal section of a subterranean well. The well may be any type of well, for example a petroleum well (oil and/or gas well), production well, injection well, water well or hydrothermal well. The well may also be vertical or deviated. More particularly, the present method concerns use of abrasive liquid jets in a combined operation of gaining access to and removing solid material in an annulus surrounding a pipe body (e.g. casing or similar) in a well.

Advantageously, the invention may be used in context of plugging and abandoning (P&A) a well. The invention may also be suitable for other types of plugging operations in a well, such as zone isolation, sidetracking or remedial repairs in the well. Further, the invention is suitable for rig-less applications and may therefore be particularly advantageous in offshore settings where operational costs are especially high. Yet further, although not limited thereto, the invention is particularly suitable in relatively shallow well applications.

Technical background

When plugging and abandoning a well, pressure barriers are typically formed at different levels of the well to prevent pressurized fluids from discharging from a surface thereof, but also to prevent such fluids from flowing between permeable zones of the well. At deeper levels, a pressure barrier is normally formed in relation to a singular pipe body (e.g. casing or liner). At shallower levels, however, such a pressure barrier is normally formed in relation to a pipe assembly comprising two or more sizes of pipe bodies, i.e. a “pipe-in-pipe” assembly. Generally, a mechanical plug and/or cement plug is also positioned within the singular pipe body, or within an innermost pipe body of the pipe assembly. The one or more annuli surrounding the one or more pipe bodies typically also contain, at least along a section thereof, a substantially solid plugging (and bonding) material, usually cement. The internal mechanical plug or cement plug and the solid annular plugging material collectively form a cross-sectional pressure barrier in the well. For various reasons, however, the sealing capacity (hence quality) of the annular plugging material may be insufficient or has become degraded over time, whereby the annular plugging material cannot properly withstand ambient fluid pressures within the particular annulus or annuli and thus may allow fluid throughput. This plugging insufficiency may be observed as pressure build-up in one or more annuli of the well. Such a situation is generally not desirable or allowable, especially in context of plugging and abandoning a well.

Insufficient sealing capacity may result from the manner in which the fluidized plugging material (e.g. cement slurry) was displaced into the well when initially installing, typically many years earlier, a particular pipe body size in the well. In so doing, a volume of fluidized plugging material would, as is common in the art, be pumped down and up around the pipe body so as to displace upward into the surrounding annulus and thus form, upon setting, the solid annular plugging material. Displacement in this manner would allow a lead section of the fluidized plugging material to encounter various wellbore constituents along its flow path, such as wellbore fluids, particles and residues. This, in turn, would allow especially the lead section of fluidized material to become contaminated so as to potentially exhibit increased permeability and reduced sealing capacity once set in the annulus. Owing to its furthest displacement up into the annulus, this also implies that the lead section of reduced sealing capacity would be located at an upper part of the annulus, implying further that a pipe assembly located at a shallower level in a well is more likely to have one or more annuli containing inferior plugging material.

Notwithstanding the above, the fluidized plugging material may also experience socalled “channelling” effects when being displaced into and along an annulus. Once set, this may cause channels to be formed in the solid plugging material so as to increase the permeability and thus reduce the sealing capacity thereof. Such channelling may take place at any level within the annulus.

During the lifetime of a well, other well events may also influence the fluids and pressures present in the various annuli of the well. Such events may also influence the sealing capacity of the annular plugging material therein. As such, subterranean subsidence, tectonic events (e.g. faulting) and chemical and/or mechanical deterioration of pipe bodies (e.g. casings) and downhole equipment may alter the integrity and/or configuration of pipe bodies and annular plugging material in the well. This, in turn, may lead to fluid communication with shallow gas layers and/or nearby wellbores and may thus influence the fluids and pressures in the various annuli of the well.

Accordingly, there appears to be a need in the industry, e.g. the petroleum industry, for a simple, cost-efficient and versatile solution capable of removing solid annular material considered or proven to have insufficient sealing capacity from an annulus in a well. As such, there would also be a need in the industry for a solution capable of replacing the inferior material removed from the annulus with another material of sufficient sealing capacity (hence quality), and also allowing the replacement material to fill both the annulus and a pipe body defining the annulus inwardly thereof.

Although apparently required especially for relatively shallow well applications (as explained above), for example for applications at vertical depths of 1000 meters or less into the subsurface, the solution should preferably also be viable for deeper well applications so as to provide technical flexibility to the solution.

Prior art

Relatively recently, since about year 2010, the so-called Perf-Wash-Cement - PWC® -method has gained increasing interest and use in the industry. When employing the PWC® method, a section of e.g. casing (or liner) is perforated to gain access to an annulus surrounding the casing. The perforation is typically carried out using explosive charges lowered into the well on a pipe string or a wireline cable. Subsequently, a washing or flushing tool is used to direct a washing fluid into the annulus via perforations formed in the casing section, thereby washing and cleaning away contaminants (e.g. various wellbore fluids, particles and residues) that may be present in the surrounding annulus. A fluidized plugging material, typically cement slurry, is then introduced into the casing and thus into the surrounding annulus via the perforations in the casing.

WO 2012/096580 A1 discloses the PWC® method in general and more specific terms. This publication describes embodiments of a washing tool generally referred to as the HydraWash™ washing tool in the oil and gas industry. Various variants of the PWC®-method have also been disclosed in e.g. WO 2012/096580 A1, WO 2013/133719 A1 and WO 2016/200269 A1. None of these publications explicitly concern removal of substantially solid plugging material in an annulus surrounding a pipe body (e.g. casing or liner) in a well, nor do they disclose to use abrasive liquid jets in a combined operation of gaining access to and removing solid material in said annulus, as disclosed herein.

US 6828531 B1, US 2006/144591 A1, US 2008/047708 A1 and WO 2017/203248 A1 disclose some alternative methods and apparatuses for performing plugging in wells, as detailed further in the following summary of the invention.

US 2012/0279706 A1 discloses a method of closing a well using a cutting tool with a movable nozzle head to cut out several openings, or windows, across a longitudinal portion of a casing in the well. Preferably, a fluid jet discharging from a cutting nozzle in the nozzle head is used to cut out these openings. A cleaning fluid discharging from cleaning nozzles in the nozzle head is then used to clean away cement in an annulus outside the casing via said casing openings. A curable mass, such as cement, is then filled into the casing and further into the annulus via the casing openings, thereby forming a cross-sectional plug in the well.

Further, NO 20171650 A1 discloses a system and method of cleaning an annular area in a well having an inner pipe body and an outer pipe body defining an inner annulus containing a clean fluid, and an outer annulus containing contaminants to be removed therefrom. A washing tool with spaced apart flow guides is used to force a washing fluid through holes formed in the inner pipe body so as to generate flushing jets passing onwards through said clean fluid and holes formed in the outer pipe body, thereby allowing said flushing jets to enter and clean away contaminants in the outer annulus. A fluidized plugging material, such as cement, may then be placed in the cleaned section of the well so as to form a cross-sectional plug therein.

Summary

The primary object of the present invention is to provide a simple, cost-efficient and versatile solution capable of removing solid annular material considered or proven to have insufficient sealing capacity from one or more annuli in a subterranean well.

A further object is to replace the inferior sealing material removed from said annulus with another material of sufficient sealing capacity (hence quality), and also allowing the replacement material to fill both the annulus and a pipe body defining the annulus inwardly thereof.

It is also an object to suggest a variety of potentially suitable replacement materials.

Another object is to provide a solution particularly suitable in relatively shallow well applications, although not restricted thereto.

Yet another object is to provide a solution suitable for rig-less applications, which may be particularly advantageous in offshore settings.

A further object of the present invention is to provide a useful addition or alternative to the above-mentioned prior art variants of the PWC® method.

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

The present invention concerns a method of performing abrasive perforation and washing along a longitudinal section of a subterranean well comprising a pipe body and an annulus located between the pipe body and a surrounding well body, the annulus containing solid material to be removed therefrom, characterized in that the method comprises the following steps:

(A) using a jetting tool formed with a plurality of outwardly directed outlets distributed around the jetting tool, the outlets configured to discharge jets upon operation of the jetting tool;

(B) connecting the jetting tool to a lower portion of a flow-through string and, with the string, lowering the jetting tool into the pipe body and positioning the plurality of outlets within the longitudinal section of the well;

C) pumping an abrasive liquid down the string to the jetting tool and further out through the plurality of outlets so as to discharge as abrasive liquid jets directed outwardly onto an inner surface of the pipe body, the abrasive liquid comprising a carrier liquid admixed with an abrasive agent;

(D) whilst pumping and keeping the jetting tool static at the longitudinal section of the well, allowing the abrasive liquid jets to cut holes through the pipe body within the longitudinal section; and

(E) whilst continuing pumping and keeping the jetting tool static at the longitudinal section of the well, allowing the abrasive liquid jets to flow through the holes and further out into the annulus so as to impact, dislodge and wash away at least some of the solid material therein (e.g. in the vicinity of the holes), thereby performing consecutive abrasive perforation and washing with the jetting tool within the longitudinal section of the well.

An uppermost and lowermost hole thus cut through the pipe body define the extent of the longitudinal section.

In one embodiment, the surrounding well body is another and larger pipe body. In this particular embodiment, the annulus is therefore defined between two pipe bodies of different sizes, i.e. between an innermost pipe and an outermost pipe body, so as to define a “pipe-in-pipe” assembly or “nested casings”. It is envisaged that the present method will receive most application in such “pipe-in-pipe” assemblies.

Advantageously, when using abrasive liquid jets to wash away solid material in the annulus in step (E), the jets simultaneously engage and vigorously “polish” or “sandblast” the annular surfaces of the two pipe bodies, thereby effectively removing any deposits (e.g. rust, oil film and wax) on these surfaces. Therefore, if subsequently introducing a fluidized plugging material in the annulus, as discussed in a further embodiment below, the polished surfaces allow for tight and sealing contact with the fluidized plugging material and thus facilitate the formation of a proper pressure barrier.

In another embodiment, the surrounding well body is a wellbore formed through subterranean rocks. Therefore, in this particular embodiment, the annulus is defined between the pipe body and the wellbore defining the well. As in the preceding embodiment, the abrasive liquid jets will engage and vigorously “polish” the annular surface of the pipe body and may thus facilitate tight and sealing contact with a potential fluidized plugging material introduced in the annulus thereafter.

The flow-through string may be a pipe string, typically in the form of a jointed pipe string assembled consecutively from individual pipe joints (e.g. a drill string), or in the form of a coiled tubing deployed from a reel.

Alternatively, the flow-through string may be a coilable hose. Such a hose may be a hose of suitable size and quality and deployed to and from a corresponding reel.

The longitudinal section of the well may be relatively short considering that one or more cross-sectional barriers of substantial length, e.g. 30-50 m, typically have been formed at one or more deeper levels in the well before initiating the present method, the deeper barriers generally retaining pressures from deeper reservoirs. Therefore, although not limited thereto, the longitudinal section may have a length within a range of 0.5-10 m, possibly within a range of 0.5-5 m, or even within a range of 0.5-2 m.

Further, the jetting tool may comprise a centralizing device for centralizing the jetting tool in the pipe body during operation of the jetting tool (e.g. spring-loaded arms and/or a centralizing collar, possibly with bypass channels, etc.).

Yet further, the jetting tool may comprise an anchoring device for selective anchoring of the jetting tool to an inside of the pipe body during operation of the jetting tool (e.g. radially movable gripping dogs for selective activation and deactivation thereof).

In one embodiment, the carrier liquid comprises water. Advantageously, the water may be taken from nearby surroundings of the well, hence may comprise e.g. freshwater or saline seawater.

In another embodiment, the carrier liquid comprises drilling mud. Such drilling mud is commonly used in context of well operations and may therefore be readily available at the wellsite.

Advantageously, the abrasive agent may comprise sand-sized particles. For example, garnet sand having a specific gravity of approximately 4.2 is suitable for admixing to the carrier fluid.

Although not limited thereto, the abrasive agent may be admixed to the carrier liquid within a range of 5-120 kg/m<3>, more particularly within a range of 12-85 kg/m<3>, and even more particularly within a range of 45-70 kg/m<3>, e.g. ca. 60 kg/m<3>.

The amount of abrasive agent admixed to the carrier liquid represents one of several factors, including jet velocity and jet angle, affecting the cutting and washing ability of the abrasive liquid jets when operational in the well. It is therefore difficult to specify particular amounts of abrasive agent to be used in a specific well setting and/or pipe constellation. In a pipe-in pipe assembly, it may be imperative to cut through the innermost pipe body only, and not through the outermost pipe body. In this case, a smaller amount of abrasive agent may be advantageous for extending the required cutting time and thus better controlling the cutting and washing action in the annulus, e.g. by providing a gentler and less forceful action therein. On the other side, a higher amount of abrasive agent may be required should the pump rate and/or discharge velocity of the abrasive liquid jets be restricted due to operational constraints. In a singular pipe body having only one external annulus, however, a more aggressive cutting and washing action may be warranted given that the annulus is outwardly defined by the wellbore rather than a pipe body and therefore only requires for the solid material to be removed from the annulus.

Further, the plurality of outlets may be in the form of nozzles which, advantageously, may be embodied as releasable nozzle inserts for allowing easy replacement thereof with other nozzles of same or different types or sizes.

Yet further, the diameter of the plurality of outlets may be within a range of 2-7 mm, and more particularly within a range of 3-6 mm, as measured at the discharge point of an outlet.

For the purpose of performing abrasive perforation and washing, the applicant has carried out successful experiments using a jetting tool furnished with several outlets having an outlet diameter of 3.2 mm. The abrasive liquid jets of the jetting tool were used to cut holes through a first pipe body and then to dislodge and wash away solid cement located within a surrounding annulus confined outwardly by a second pipe body. The cross-sectional area of each hole formed in the first pipe body was approximately 1 cm<2>, which was significantly larger than the cross-sectional area of each abrasive liquid jet. The enlarged cross-sectional area of each hole allowed the abrasive liquid jet to enter the annulus in one direction so as to impact and dislodge solid cement in the annulus, simultaneously allowing the particles of dislodged cement, which were entrained in the abrasive liquid, to exit the hole in the opposite direction and thus wash away dislodged particles from the annulus. By so doing, a circulatory flow pattern was established despite keeping the jetting tool in a fixed, static position during operation thereof.

The plurality of outlets may also comprise at least one set of circumferentially aligned outlets. This allows the jetting tool to deliver a more concentrated dislodging and washing action with respect to the solid material present within the corresponding circumferential volume of the annulus.

In one embodiment, the set of circumferentially aligned outlets is formed in a collar on the jetting tool. This may be useful for positioning the outlets closer to the inner surface of the pipe body and/or to control the distance between the outlets and the inner surface thereof. Such a collar may also serve as a centralizing device for the jetting tool. Possibly also, the collar may be provided with bypass areas or bypass ports for facilitating flow past the collar when required. In the noted experiments, the outlets were aligned at an 18° circumferential spacing along a collar integral to the jetting tool and protruding outwardly therefrom.

Additionally, or alternatively, the plurality of outlets may comprise several sets of circumferentially aligned outlets, and wherein the several sets are spaced apart along the jetting tool. This allows the jetting tool to simultaneously cut several sets of spaced apart holes in the pipe body and also remove solid material from the corresponding volume of the annulus.

In order to e.g. adjust the cutting time and/or control the cutting and washing action in the annulus (as noted above), the outlet axes of the plurality of outlets may also be directed at an angle relative to a perpendicular axis extending from a longitudinal axis of the jetting tool, whereby corresponding abrasive liquid jets are also directed, in steps (C)-(E), at an angle relative to the perpendicular axis. In this context, 0° may also be a potentially viable angle.

Therefore, in one embodiment, the angle of at least one of the outlet axes has a longitudinal (i.e. axial) component, i.e. an angular component parallel to the longitudinal axis of the jetting tool. Further, although not limited thereto, the longitudinal component may be angled within ± 60° of the perpendicular axis, and more particularly within ± 45° of the perpendicular axis.

Additionally, or alternatively, the angle of at least one of the outlet axes may have a tangential (or transverse) component, i.e. an angular component perpendicular to both the longitudinal axis and said perpendicular axis extending therefrom. Further, although not limited thereto, the tangential component may be angled within ± 45° of the perpendicular axis, and more particularly within ± 20° of the perpendicular axis.

In the noted experiments, the angle of the outlet axes had a longitudinal component angled at 45° and a tangential component angled at 10.4° relative to the perpendicular axis. This angular configuration of the outlet axes allowed the resulting abrasive liquid jets to cut efficiently through the pipe body and impact the cement in the annulus. Subsequently, the angled jets generated a very turbulent and efficient dislodging and washing action in the annulus, which caused the remaining cement to be efficiently removed from the annulus.

Advantageously, abrasive liquid jets discharging along outlet axes having angular components (as defined in the preceding embodiments) may be used for extending the required cutting time and thus better controlling the cutting and washing action in the annulus, e.g. by providing a gentler and less forceful action therein. This may be particularly advantageous in a pipe-in pipe assembly comprising an innermost pipe body placed eccentrically within an outermost pipe body. In such a case, the radial space on one side of the annulus is larger than the radial space on the opposite side of the annulus, which results in variable thickness of solid material from one side to the opposite side of the annulus. Using angled jets may allow the thickest section of solid material to be removed from the one side of the annulus before angled jets on the opposite side thereof, which may already have removed the thinnest section of solid material, have cut through the outermost pipe body, thereby cutting through the innermost pipe body only, and not through the outermost pipe body.

Further, the angles of the outlet axes may be variously angled relative to the perpendicular axis. By way of example, reactive forces generated by abrasive liquid jets directed in one direction may thus be counteracted by abrasive liquid jets directed in the opposite direction so as to maintain the jetting tool stationary (i.e. immobile) during its operation at a specific well position. As such, both longitudinal and rotational movement of the jetting tool may be prevented through proper balancing of the directions of the jets involved. For example, jets discharging in one direction from a first tool collar may be counteracted by jets discharging in an opposite direction from a spaced apart second tool collar. Proper balancing of angular variations along a circumference of such a collar are also conceivable to prevent rotation of the jetting tool during operation. These and other angular configurations of the outlet axes along and around the jetting tool will be obvious to the skilled well practitioner once familiarized with the present method and may be readily adapted to well specific desires and requirements.

In a specific embodiment (as alluded to above), all outlet axes of the plurality of outlets are angled at 0° relative to the perpendicular axis, whereby all corresponding abrasive liquid jets coincide with the perpendicular axis, hence are directed perpendicularly (i.e. completely radially) out from the longitudinal axis of the jetting tool. This specific embodiment provides for very efficient cutting of holes through the pipe body as well as very efficient impacting, dislodging and washing away of solid material in the annulus. In many well applications, however, a more extended and gentler operation is desirable at the expense of extreme efficiency, as already discussed above.

In order to e.g. adjust the cutting time and/or control the cutting and washing action in the annulus (as noted above), the method may also comprise pumping, in steps (C)-(E), the abrasive liquid out through the plurality of outlets at a discharge velocity within a range of 100-200 m/s, more particularly within a range of 120-180 m/s, and even more particularly within a range of 130-170 m/s. In the noted experiments, discharge velocities of 131 m/s and 168 m/s were used successfully. Other discharge velocities may also prove suitable, and the method is therefore not limited to these particular velocity ranges.

Yet further, in one embodiment, the plurality of outlets span the entire longitudinal section, thereby impacting, dislodging and washing away, in step (E), the solid material along the entire longitudinal section. As observed in the noted experiments, particles of dislodged solid material (entrained in the abrasive liquid) may exit the annulus whilst simultaneously allowing the abrasive liquid jets to enter the annulus via the holes formed in the pipe body. This allows a circulatory and turbulent flow pattern, which is capable of efficiently removing the dislodged particles from the annulus, to be maintained. This is possible despite keeping the jetting tool static during operation at the longitudinal section of the well.

In another embodiment, the plurality of outlets span a portion of the longitudinal section, thereby impacting, dislodging and washing away, in step (E), the solid material along the portion of the longitudinal section;

- the method further comprising a step (F) of moving the jetting tool to at least one remaining portion of the longitudinal section and repeating steps (C)-(E) for each remaining portion, thereby impacting, dislodging and washing away, in the repeated step (E), the solid material along each remaining portion of the longitudinal section.

The latter embodiment involves stepwise movement of the jetting tool along the longitudinal section, where abrasive perforation and washing is carried out at the or each remaining portion of the longitudinal section. This may serve to further facilitate the dislodging and removal of particles of solid material from the annulus via previously formed holes in the pipe body. Depending on the direction of moving the jetting tool, particles removed from the annulus may discharge via holes formed above or below the jetting tool.

For both of the preceding embodiments, it may be advantageous or necessary to allow the removed particles of solid material to sink and be deposited at a deeper level in the pipe body. This would be especially applicable if using the jetting tool in a relatively large-sized pipe body (e.g. a 20” or 13 3/8” casing) located, normally, at a relatively shallow level in a well (e.g. less than 1000 m vertical depth). In such larger pipe bodies, the flow velocity and thus lifting capacity of a transport liquid flowing upward in the pipe body would typically be insufficient for lifting the dislodged particles to the surface of the well. For a smaller and typically deeper pipe body (e.g. a 9 5/82 or 7” casing), however, the flow velocity and lifting capacity of said transport liquid would typically be sufficient for lifting the dislodged particles to the surface of the well, hence is a viable and possibly preferable option for removing such dislodged particles.

In accordance with one object of the invention, the method may further comprise a step (G) of placing a fluidized plugging material in the pipe body along at least the longitudinal section, and also allowing the fluidized plugging material to flow into the annulus via the holes in the pipe body so as to form, once set, a plug filling both the pipe body and the annulus along at least the longitudinal section. By so doing, the solid material dislodged and washed away from the annulus in step (E) is replaced with a fluidized plugging material filling both the annulus and the interior of the pipe body so as to form a pressure sealing barrier once set therein.

As noted above, the abrasive liquid jets used in step (E) have already polished (or sandblasted) the annular surface(s) of the pipe body/bodies so as to allow for tight and sealing contact with the fluidized plugging material. Further, the walls defining the holes formed in the pipe body represent anchoring points for the fluidized plugging material once set in the well, thereby properly anchoring the resulting plug filling both the pipe body and the annulus along at least the longitudinal section.

Before step (G), the method may further comprise positioning a plug base in the pipe body below the longitudinal section. The purpose of the plug base is to support the fluidized plugging material in the pipe body, if required. The plug base may be in the form of e.g. a so-called viscous pill, a mechanical plug and/or a cement plug of suitable length.

In one embodiment, step (G) of the method comprises transporting the fluidized plugging material into the pipe body from a surface of the well and down to the longitudinal section. The transporting may thus involve pumping the fluidized plugging material into the pipe body via a suitable flow-through string, e.g. a jointed pipe string, a coiled tubing, or a coilable hose extending to the surface of the well, as mentioned above. Alternatively, the transporting may involve dumping the fluidized plugging material at the longitudinal section after having lowered e.g. a dump bailer (or similar) containing the fluidized plugging material into the pipe string.

Further, the fluidized plugging material may comprise a cementitious material, as is common in the art. Additionally, or alternatively, the fluidized plugging material may also comprise a resinous material, as is also relatively common in the art.

In another embodiment, step (G) of the method comprises transporting a fusible solid material and a heating device into the pipe body from a surface of the well and down to the longitudinal section and, with the heating device, melting the fusible solid material in situ so as to form a molten mass thereof constituting the fluidized plugging material. This embodiment is in accordance with another object of the invention, which is to suggest a variety of potentially suitable materials for replacing the solid material removed from the annulus in step (E).

The transporting in this particular embodiment may involve lowering or dumping the fusible solid material into the pipe body from a surface of the well and down to the longitudinal section. Advantageously, the fusible solid material is in the form of a particulate material, e.g. pellets or similar, having a suitable size and specific gravity to be conveyed into the pipe body. The particulate material may be dropped from the surface of the well so as to fall freely within the pipe body onto the longitudinal section. Alternatively, the particulate material may be placed inside a dump bailer or similar, which is then lowered into the pipe body onto the longitudinal section where the particulate material is dumped.

Moreover, the heating device may be lowered into the pipe body simultaneous with or subsequent to the transporting of the fusible solid material into the pipe body. The lowering may be carried out using e.g. a cable structure, such as an electrical cable structure in the form of a wireline or braided cable. The heating device may be in the form of an electrical heater or a chemical heater, both of which may be positioned within or, alternatively, may be configured to carry the fusible solid material on or within the heating device. Electric power for initiating and/or operating the heating device may be conveyed from the surface of the well via an electrical cable, e.g. an electrical wireline cable.

More particularly, the fusible solid material may be selected from a group of materials comprising:

- a metal;

- an alloy;

- elemental sulphur;

- a thermosetting plastic; and

- a thermoplastic.

Advantageously, the alloy may be a metal-based alloy. More particularly, the metalbased alloy may comprise bismuth. If used in the fluidized plugging material, bismuth possesses the favourable property of expanding somewhat volumetrically upon solidifying from a molten state, thereby establishing a particularly tight and sealing contact with the annular surface(s) previously polished by the abrasive liquid jets (as discussed above).

US 6828531 B1, US 2006/144591 A1 and US 2008/047708 A1 disclose some alternative methods and apparatuses for performing plugging in wells. All of these publications teach to position and melt a fusible solid material, for example a metal alloy in pellet form, in situ within a pipe body, such as a casing or similar. US 6828531 B1 and US 2008/047708 A1 each disclose a heating tool, in the form of an electrical heater, for melting the alloy in situ. US 2006/144591 A1, however, discloses a heating tool comprising an igniter and an exothermic reactant material, such as thermite or thermate, for melting the alloy in situ.

WO 2017/203248 A1 also discloses a plugging tool comprising a tubular heater body with an internal cavity for receiving a chemical heat source, such as a thermite formulation, and a quantity of eutectic bismuth-based alloy (fusible solid material) provided around the heater body. A surface operated ignition device is also included in the tool for remotely initiating an exothermic reaction in the chemical heat source and thus melting the alloy in situ within a well.

Brief description of the drawings

An exemplary embodiment of the invention is described and depicted in the accompanying drawings, where:

Figure 1 shows, in side view, a jetting tool to be used in a method according to the present invention for performing abrasive perforation and washing in a well;

Figure 2 shows, in plan bottom view, the jetting tool of Fig. 1;

Figure 3 shows, in side view, a subterranean well comprising a first pipe body and a larger second pipe body, and after having lowered the jetting tool into the first pipe body to a lower portion of a longitudinal section of the well;

Figure 4 shows, in side view, the jetting tool in operation at the lower portion of the longitudinal section;

Figure 5 shows, in side view, the jetting tool in operation at an upper portion of the longitudinal section;

Figure 6 shows, in side view, the well whilst placing a fluidized plugging material along at least the longitudinal section of the well; and

Figure 7 shows, in side view, the fluidized plugging material after having set within at least the longitudinal section of the well so as to form a sealing plug therein.

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

Detailed description of the embodiment of the invention

Figures 1 and 2 show a tubular jetting tool 2 suitable for use in the present method. The jetting tool 2 comprises, as viewed from a lower end 4 to an upper end 6 thereof, a first nozzle collar 8, a second nozzle collar 10 and a centralizing collar 12 spaced apart along the jetting tool 2 and protruding outwardly from a central tubular element 14 thereof. All collars 8, 10, 12 are integral to the jetting tool 2. The centralizing collar 12 comprises a set of bypass grooves 16 spaced apart along the circumference thereof for allowing fluid flow past the centralizing collar 12. Similarly, each nozzle collar 8, 10 comprises a set of bypass grooves 18, 20 spaced apart along the circumference thereof for allowing fluid flow past each nozzle collar 8, 10. Each nozzle collar 8, 10 also comprises a set of circumferentially aligned nozzle outlets 22, 24 conveniently embodied as releasable nozzle inserts 22a, 24a spaced apart along the circumference thereof. The nozzle inserts 22a, 24a are screwed into the respective nozzle collars 8, 10 for allowing easy replacement thereof with nozzles of same or different types or sizes. Further, each set of nozzle outlets 22, 24 communicates with a corresponding set of supply bores 26, 28 in further communication with a central bore 30 through the jetting tool 2, as shown in Fig. 1. A ball seat 32 for receiving a (dropped) ball 34 is also located in the central tubular element 14 at the lower end 4 of the jetting tool 2, and below the first nozzle collar 8. Once seated in the ball seat 32, as shown in Fig. 1, the ball 34 closes off the lower end 4 and forces any liquid flow in the central bore 30 out through the supply bores 26, 28 so as to discharge as liquid jets from the sets of nozzle outlets 22, 24.

Given that the first and second nozzle collars 8, 10 collectively provide a centralizing and stabilizing effect to the jetting tool 2, the centralizing collar 12 is shown mostly for illustrative purposes in this embodiment. However, such a centralizing collar 12 is likely to be more useful, or may even be required, in an embodiment (not shown) in which the jetting tool is provided with one nozzle collar only, thereby allowing the centralizing collar and nozzle collar to collectively provide a centralizing and stabilizing effect to the jetting tool.

Although not shown in this particular embodiment, the centralizing collar 12 could also be replaced or supplied with some other type of centralizing and/or stabilizing device (e.g. spring-loaded arms) for centralizing and/or stabilizing the jetting tool 2 during operation thereof. Some type of anchoring device (e.g. radially movable gripping dogs) may also be desired or required for selective anchoring of the jetting tool to a surrounding pipe body during operation thereof.

Figures 1 and 2 also show an outlet axis A of a nozzle outlet 22 of the first nozzle collar 8 directed at an angle B relative to a perpendicular axis P extending from a longitudinal axis C of the jetting tool 2 and through (an apex of) the nozzle outlet 22. In this particular embodiment, the angle B of all outlet axes A has a longitudinal component BC, for example 45°, as shown for a specific nozzle outlet in Fig. 1. The longitudinal component BC is an angular component being parallel to the longitudinal axis C of the jetting tool 2. In this particular embodiment, the angle B of all outlet axes A also has a tangential component BT, for example 10°, as shown for a specific nozzle outlet in Fig. 2. The tangential component BT is an angular component perpendicular to both the longitudinal axis C and the perpendicular axis P extending therefrom. However, as noted above, the angle B of the outlet axes A may be variously angled relative to the perpendicular axis P, hence may exhibit quite different angular configurations than the angular configuration depicted in this particular embodiment.

Figure 3 shows a subterranean well 36 comprising a first pipe body 38 and a surrounding second pipe body 40. An annulus 42 is located between the first pipe body 38 and the second pipe body 40 and contains solid material 44 (e.g. cement) of inferior sealing quality to be removed therefrom using the present method to do so. A further annulus 46 is also located between the second pipe body 40 and a surrounding wellbore 48 formed through subterranean rocks 50. The further annulus 46, however, contains solid material 52 (e.g. cement) of sufficient sealing quality and is not to be removed from the well 36 in context of performing the present method.

Figure 3 also shows the well 36 after having connected the upper end 6 of the jetting tool 2 to a lower portion of a flow-through string 54 (e.g. a drill string, coiled tubing or coilable hose) extending to a surface of the well 36, and after having lowered (with the string 54) the jetting tool 2 into the first pipe body 38 to a longitudinal section L of the well 36. The jetting tool 2 is shown in an inoperative position at a lower portion of the longitudinal section L, implying that the sets of nozzle outlets 22, 24 span only a portion of the longitudinal section L.

Figure 4 shows the jetting tool 2 in operation at the lower portion of the longitudinal section L whilst pumping an abrasive liquid 56 from the well surface to the jetting tool 2 via the flow-through string 54. Abrasive liquid jets 58 are shown discharging at high velocity, and at said angle B relative to the perpendicular axis P, from the respective nozzle outlets 22, 24 of the jetting tool 2 so as to be directed outwardly onto an inner surface 60 of the first pipe body 38. The abrasive liquid jets 58 are also shown after having abrasively cut corresponding holes 62 through the (pipe wall of the) first pipe body 38 at the lower portion of the longitudinal section L.

Figure 4 also shows the abrasive liquid jets 56 flowing, upon continued pumping of abrasive liquid from the well surface, through the newly formed holes 62 so as to vigorously impact, dislodge and wash away solid material 44 in vicinity of the holes 62. Particles 64 of dislodged solid material 44, which are entrained in the abrasive liquid 56, are removed from the annulus 42 via the holes 62 and are also shown in the process of sinking down inside the first pipe body 38 so as to be deposited at a deeper level therein. The flow path of dislodged particles 64 entrained in the abrasive liquid 56 and discharging from the annulus 42 via the holes 62 is indicated with curved arrows in Figures 4 and 5.

Figure 5 shows the cutting and cleaning process of Fig. 4 being repeated at a last remaining upper portion of the longitudinal section L, and after having moved the jetting tool 2 stepwise and consecutively repeated the process at successive portions along the longitudinal section L. By so doing, particles 64 of dislodged solid material 44 are removed from the annulus 42 along the entire longitudinal section L of the well 36. As the jetting tool 2 is moved upward within the longitudinal section L, such solid particles 64 are also allowed to be removed via previously formed holes 62, which facilitates the annular cleaning process.

Figure 6 shows the well 36 after having removed the jetting tool 2 from the first pipe body 38 and then having positioned a mechanical plug 66 (i.e. a plug base) in the pipe body 38 below the longitudinal section L. The figure also shows the well 36 whilst placing a fluidized plugging material 68 in the first pipe body 38 along at least the longitudinal section L, and also allowing (simultaneously) the fluidized plugging material 68 to flow into the annulus 42 via the holes 62 formed in the pipe body 38 along the longitudinal section L. In this embodiment, the fluidized plugging material 68 comprises a cementitious or resinous material being pumped into the first pipe body 38 via a suitable flow-through string 70 (e.g. a drill string, coiled tubing or coilable hose) extending to the surface of the well 36. This string 70 may be the same as, or differ from, the string 54 used to pump the abrasive liquid 56 into the well 36.

Additionally, or alternatively, although not shown in this particular embodiment, the fluidized plugging material 68 could be a molten mass formed in situ at the longitudinal section L by melting a fusible solid material, using a suitable heating device to do so, and placing the molten mass along at least a portion of the longitudinal section L, as described in further detail above.

Figure 7 shows the fluidized plugging material 68 after having set so as to form a sealing plug 68 ́ filling both first pipe body 38 and the annulus 42 along at least the longitudinal section L of the well 36.

In another variant of this embodiment, the nozzle outlets 22, 24 of the jetting tool 2 may be kept static at only one portion of the well 36 so as to abrasively cut and wash away solid material 44 only at this particular portion, e.g. as shown at a lower portion in Figure 4. This implies that there would be no subsequent and stepwise movement of the jetting tool 2 to repeat the cleaning process at one or more remaining portions of a longitudinal section L of the well 36, as shown in Figure 5. In this variant, the nozzle outlets 22, 24 would therefore span the entire longitudinal section (i.e. portion) being perforated and washed, after which a fluidized plugging material 68 could be introduced therein to form a sealing plug 68 ́, e.g. as shown in Figures 6 and 7. A molten mass might also be used to form a sealing plug 68 ́ in this variant.

Claims

C l a i m s

1. A method of performing abrasive perforation and washing along a longitudinal section (L) of a subterranean well (36) comprising a pipe body (38) and an annulus (42) located between the pipe body (38) and a surrounding well body (40; 48), the annulus (42) containing solid material (44) to be removed therefrom, c h a r a c t e r i z e d i n that the method comprises the following steps:

(A) using a jetting tool (2) formed with a plurality of outwardly directed outlets (22; 24) distributed around the jetting tool (2), the outlets (22; 24) configured to discharge jets upon operation of the jetting tool (2);

(B) connecting the jetting tool (2) to a lower portion of a flow-through string (54) and, with the string (54), lowering the jetting tool (2) into the pipe body (38) and positioning the plurality of outlets (22; 24) within the longitudinal section (L) of the well (36);

(C) pumping an abrasive liquid (56) down the string (54) to the jetting tool (2) and further out through the plurality of outlets (22; 24) so as to discharge as abrasive liquid jets (58) directed outwardly onto an inner surface (60) of the pipe body (38), the abrasive liquid (56) comprising a carrier liquid admixed with an abrasive agent;

(D) whilst pumping and keeping the jetting tool (2) static at the longitudinal section (L) of the well (36), allowing the abrasive liquid jets (58) to cut holes (62) through the pipe body (38) within the longitudinal section (L); and

(E) whilst continuing pumping and keeping the jetting tool (2) static at the longitudinal section (L) of the well (36), allowing the abrasive liquid jets (58) to flow through the holes (62) and further out into the annulus (42) so as to impact, dislodge and wash away at least some of the solid material (44) therein, thereby performing consecutive abrasive perforation and washing with the jetting tool (2) within the longitudinal section (L) of the well (36).

2. The method according to claim 1, wherein the diameter of the plurality of outlets (22; 24) is within a range of 2-7 mm.

3. The method according to claim 1 or 2, wherein the plurality of outlets comprises at least one set of circumferentially aligned outlets (22; 24).

4. The method according to claim 3, wherein the set of circumferentially aligned outlets (22; 24) is formed in a collar (8; 10) on the jetting tool (2).

5. The method according to claim 3 or 4, wherein the plurality of outlets comprises several sets of circumferentially aligned outlets (22; 24), and wherein the several sets are spaced apart along the jetting tool (2).

6. The method according to any one of claims 1-5, wherein outlet axes (A) of the plurality of outlets (22; 24) are directed at an angle (B) relative to a perpendicular axis (P) extending from a longitudinal axis (C) of the jetting tool (2), whereby corresponding abrasive liquid jets (58) are also directed, in steps (C)-(E), at an angle (B) relative to the perpendicular axis (P).

7. The method according to claim 6, wherein the angle (B) of at least one of the outlet axes (A) has a longitudinal component (BC).

8. The method according to claim 7, wherein the longitudinal component (BC) is angled within ± 60° of the perpendicular axis (P).

9. The method according to claim 6, 7 or 8, wherein the angle (B) of at least one of the outlet axes (A) has a tangential component (BT).

10. The method according to claim 9, wherein the tangential component (BT) is angled within ± 45° of the perpendicular axis (P).

11. The method according to any one of claims 6-10, wherein the angles (B) of the outlet axes (A) are variously angled relative to the perpendicular axis (P).

12. The method according to any one of claims 1-11, comprising pumping, in steps (C)-(E), the abrasive liquid (56) out through the plurality of outlets (22; 24) at a discharge velocity within a range of 100-200 m/s.

13. The method according to any one of claims 1-12, wherein the plurality of outlets (22; 24) span the entire longitudinal section (L), thereby impacting, dislodging and washing away, in step (E), the solid material (44) along the entire longitudinal section (L).

14. The method according to any one of claims 1-12, wherein the plurality of outlets (22; 24) span a portion of the longitudinal section (L), thereby impacting, dislodging and washing away, in step (E), the solid material (44) along the portion of the longitudinal section (L);

- the method further comprising a step (F) of moving the jetting tool (2) to at least one remaining portion of the longitudinal section (L) and repeating steps (C)-(E) for each remaining portion, thereby impacting, dislodging and washing away, in the repeated step (E), the solid material (44) along each remaining portion of the longitudinal section (L).

15. The method according to any one of claims 1-14, further comprising a step (G) of placing a fluidized plugging material (68) in the pipe body (38) along at least the longitudinal section (L), and also allowing the fluidized plugging material (68) to flow into the annulus (42) via the holes (62) in the pipe body (38) so as to form, once set, a plug (68 ́) filling both the pipe body (38) and the annulus (42) along at least the longitudinal section (L).

16. The method according to claim 15, wherein step (G) comprises transporting the fluidized plugging material (68) into the pipe body (38) from a surface of the well (36) and down to the longitudinal section (L).

17. The method according to claim 15, wherein step (G) comprises transporting a fusible solid material and a heating device into the pipe body (38) from a surface of the well (36) and down to the longitudinal section (L) and, with the heating device, melting the fusible solid material in situ so as to form a molten mass thereof constituting the fluidized plugging material (68).

18. The method according to claim 17, wherein the fusible solid material is selected from a group of materials comprising:

- a metal;

- an alloy;

- elemental sulphur;

- a thermosetting plastic; and

- a thermoplastic.

19. The method according to claim 18, wherein the alloy is a metal-based alloy.

20. The method according to claim 19, wherein the metal-based alloy comprises bismuth.