GB2580738A

GB2580738A - Improvements in or relating to well abandonment

Info

Publication number: GB2580738A
Application number: GB1913717.3A
Authority: GB
Inventors: Kristian Kristiansen Lars; Linklater James
Original assignee: Ardyne Holdings Ltd
Current assignee: Ardyne Holdings Ltd
Priority date: 2018-09-25
Filing date: 2019-09-24
Publication date: 2020-07-29
Anticipated expiration: 2039-09-24
Also published as: WO2020065291A1; GB201913717D0; GB201815603D0; GB2580738B

Abstract

A method to break a sealing contact between a casing and material in the annulus behind the casing 12 in a wellbore 10, comprising running a cement bond breaker tool 30 into the casing, operating the bond breaker to act against the casings inner surface, running a cutter tool 34 into the casing and penetrating the casing with the cutter tool to form an aperture 60 in the casing. The bond breaker may be a shock wave generator 31 or casing expander used to elastically deform the casing. The cutter tool may take the form of a perforating tool, punching tool, casing cutter, section mill, abrasive cutter or pipe cutter and act to perforate or form a circumferential slot resulting in a cut casing section. The aperture may be used to circulate fluid to look for fluid return at the surface, to wash the annulus removing material or to pump plugging material into the annulus. The cutting and bond breaker tool may be run in on the same string enabling simultaneous operation. The string may include a jack, spear, anchor, jetting tool, washing tool or bridge plug.

Description

IMPROVEMENTS IN OR RELATING TO WELL ABANDONMENT

The present invention relates to methods and apparatus for well s abandonment and in particular, though not exclusively, to a method and apparatus in well abandonment for breaking the sealing contact between the casing and material in the annulus behind the casing such as the cement bond between casing and a surrounding cement sheath.

ao In the course of constructing an oil or gas well, a hole is drilled to a pre-determined depth. The drilling string is then removed and a metal tubular or casing is run into the well. When the casing reaches the bottom of the well, cement is pumped down the casing and displaced up the annulus between the casing and the original wellbore. The function of the cement is to secure the casing in position and ensure that the annulus is sealed by creating a cement bond between the casing and the wall of the bore hole. This process of drilling, running casing and cementing is repeated with successively smaller drilled holes and casing sizes until the well reaches its target depth.

To produce from the well, the casing and cement bond are perforated at the target depth to expose the formation at the borehole wall. Oil or gas can be produced from the formation or fracking fluids can be pumped in to enhance production.

On reaching the end of its commercial life, the well is abandoned according to strict regulations in order to prevent fluids escaping from the well on a permanent basis. In meeting the regulations it has become good practise to create the cement plug over a predetermined length of the well. If the cement bond is found to be of sufficient quality the cement plug can be created in the casing. If not, there are two techniques available.

U59010425 discloses a perf, wash and cement technique. The method comprises: conducting a perforation tool into a casing to said longitudinal section; forming holes in the casing along the longitudinal section; by s means of a washing tool conducted into the casing on a tubular work string, pumping a washing fluid through the tubular work string and out into the casing via the washing tool; by means of a directional means associated with the washing tool, conducting the washing fluid out into the annulus via at least one hole at a first location within the longitudinal section, after which the washing fluid will flow via the annulus and onward into the casing via at least one hole formed in at least one second location within the longitudinal section; pumping a fluidized plugging material out into the casing at the longitudinal section; and placing the plugging material in the casing and in the annulus along the longitudinal section so as to plug the casing and the annulus. This technique can work well over short sections of casing and in arrangements where the annulus is full of only settled solids and loose debris typically found above the cement sheath.

The second technique is to remove the casing and then create a cement plug across to the well bore wall.

At locations above the cement sheath, the casing can typically be cut and pulled. However, the presence of drilling fluid sediments, cement, sand or other debris behind the casing can prevent the casing from being pulled. W02018/069685 describes a cut and pull system which tests for circulation in the annulus to determine if the casing can be pulled. If not, time is saved by making successively higher cuts and testing for circulation before a spear is engaged and the casing pulled.

In order to pull casing which may be stuck due to the presence of settled debris above the cement sheath or for short lengths of cemented casing, jacking systems have been used such as described in US 8365826. The TITAN® system available from Ardyne Technologies Limited, Aberdeen UK, provides such a jacking system in combination with a cut and pull system.

Agitation has also been described for assisting in casing removal. Use of the AgitatorTM tool from National Oilwell Varco, USA as described in US 7077205 is a flow pulsing tool which may be used in conjunction with an extension and retraction means, such as a shock tool, to vary the tensile load applied to a cut casing section.

US 9045958 describes a casing retrieval method which involves applying a cyclically varying fluid pressure to the interior of a section of cut bore-lining tubular while applying a pulling force.

However, using these techniques to assist when the cut section of casing is pulled will not be successful when a cement bond exists between the casing and a surrounding metal sheath. In such cases, the casing has to be milled away to expose the cement in the annulus and once, this is removed the cement plug can be formed. Milling is a time intensive and expensive process.

It is an object of the present invention to provide a method in well abandonment to break the sealing contact between the casing and 25 material in the annulus behind the casing such as the cement bond between casing and a surrounding cement sheath.

It is an object of an embodiment of the present invention to provide apparatus in well abandonment to break the sealing contact between the 30 casing and material in the annulus behind the casing such as the cement bond between casing and a surrounding cement sheath.

According to a first aspect of the present invention there is provided a method in well abandonment to break the sealing contact between the casing and material in the annulus behind the casing in a well bore, comprising the steps: s (a) running a cement bond breaker tool into casing in a well bore; (b) operating the cement bond breaker tool to act against an inner surface of the casing; (c) running a cutting tool into the casing; and (d) penetrating the casing with the cutting tool to form an aperture so in the casing.

In this way, the action of the cement bond breaker tool against the inner surface of the casing will cause the cement bond or other sealing contact between the outer surface of the casing and material in the annulus between the casing and a well bore wall or other surrounding casing, to be broken.

Preferably, in step (b) the cement bond breaker tool causes temporary deformation of the casing. In this way, as the casing is deforms the seal 20 and cement bond is broken. Preferably, such deformation is within the elastic limit of the casing material.

The cement bond breaker tool may be a shock wave generation device, which generates at least one electrical discharge in order to propagate at 25 least one shock wave toward and against the inner surface of the casing.

Preferably a plurality of series of shock waves is generated.

Preferably a series of at least ten shock waves, and maybe twenty shock 30 waves, are generated for breaking the cement bond/seal.

Advantageously, each series of shock waves is generated repeatedly at different locations along the casing, for example different depths of a casing. In this way, the cement bond/seal can be broken along large sections of casing.

Preferably, the at least one shock wave propagates radially. In this way, maximum efficiency is achieved for breaking the cement bond/seal.

Alternatively, the at least one shock wave propagates in a predetermined so direction toward the inner surface of the casing. The string upon which the device is located may then be rotated to provide circumferential coverage. This arrangement allows the device to be mounted an a through tubing string.

Preferably, the at least one shock wave is generated in a transmitting fluid, such as e.g. water or oil.

Preferably, the at least one shock wave is generated in a transmitting liquid. Preferably, the transmitting liquid is at least partially delimited by a 20 membrane and the at least one shock wave is propagated through said membrane toward the casing.

The cement bond breaker tool may include an element, the element arranged to move radially outwardly with a radial component on operation and contact the inner surface of the casing. Such a cement bond breaker tool may be considered as an expander tool, arranged to cause temporary expansion of the casing, by a mechanical action.

The cement bond breaker tool may include upper and lower seals located 30 on a cylindrical body, the body having a port therethrough between the seals, and by application of the seals to the inner surface of the casing, fluid entering a chamber created between the body and the inner surface of the casing between the seals from the throughbore at the port, will increase pressure in the chamber and thereby expand the casing between the seals. Such a cement bond breaker tool may be considered as an expander tool, arranged to cause temporary expansion of the casing, by s hydraulic action.

The aperture can be formed in any way, for example by slicing, punching, milling, grinding, melting, dissolving or ablation to penetrate the casing.

so In an embodiment, in step (d) the cutting tool penetrates the casing by making perforations in the casing and the aperture is a perforation. There may be more than one aperture. This will facilitate a perf wash and cement procedure.

In an alternative embodiment, in step (d) the cutting tool penetrates the casing by cutting the casing and the aperture is a slot formed circumferentially around the casing to provide a cut section of casing. This will facilitate a cut and pull procedure.

The method may include the step of removing the cut section of casing for the well. In this way, a cut and pull procedure is performed.

The method may include the step of engaging a spear to the cut section of casing in order to pull the section of casing from the well bore. In an 25 embodiment a jack is used to assist in removing the cut section of casing from the well bore.

Steps (a) and (c) may be combined so that the cement bond breaker tool and the cutting tool are run on the same trip into the well.

Step (b) may be performed after step (d). In this way, the cement bond breaker tool is only required if it is found that a sealing contact exists in the annulus.

s The method may include the step of circulating fluid through the aperture and looking for a return at surface. This can be used to determine if the action of the cement bond breaker tool has effectively broken the cement bond/sealing contact.

so The method may include the step of circulating a washing fluid through the aperture to remove material in the annulus.

The method may include the step of pumping a fluidised plugging material through the aperture so as to fill the annulus. Preferably the fluidised plugging material is cement. This will create a new cement bond in the annulus.

Preferably the method is performed on a single trip into the well bore. In this way, time and costs are saved.

According to a second aspect of the present invention there is provided apparatus in well abandonment to break the sealing contact between the casing and material in the annulus behind the casing in a well bore, comprising a string for running in the casing, the string including a cutting tool and a cement bond breaker tool, the cement bond breaker tool being configured to be selectively operated to act against an inner surface of the casing.

Preferably, the cement bond breaker tool is a shock wave generation 30 device wherein the shock wave generation device comprises a discharge unit configured for generating at least one electrical discharge that propagates at least one shock wave toward and against an inner surface of the casing.

Preferably, the discharge unit comprises a first electrode and a second s electrode for generating a high voltage arc, preferentially in a shock wave transmitting liquid.

Preferably, the discharge unit is configured for generating at least one electrical discharge that propagates at least one shock wave radially.

Alternatively, the discharge unit is configured for generating at least one electrical discharge that propagates at least one shock wave in a predetermined direction.

Preferably, the shock wave generation device is as disclosed in US 15 2016/0348475 and incorporated herein by reference.

Preferably, the shock wave generation device comprises at least one metallic wire mounted between the first electrode and the second electrode for creating a pressure wave. When a current circulates between the first electrode and the second electrode, the at least one metallic wire heats until vaporization, generating therefore a pressure wave that propagates into fluid.

Preferably, the shock wave generation device further comprises a power conversion unit, a power storage unit and a control unit.

The cement bond breaker tool may be a casing expander tool. The casing expander tool may operate mechanically or hydraulically. In an embodiment, the casing expander tool includes one or more elements, the one or more elements arranged to move outwardly with a radial component on operation to contact the inner surface of the casing. Preferably, the casing expander tool is as disclosed in US6702030 and incorporated herein by reference. In this reference, the elements are rollers are moved outwardly with a radial component against the inner surface of pipe to cause expansion. While this is provided to give plastic deformation, for the present invention the tool is controlled to provide s deformation within the elastic limit only.

In an alternative embodiment, the casing expander includes upper and lower seals located on a cylindrical body, the body having a port therethrough between the seals, and by application of the seals to the so inner surface of the casing, fluid entering a chamber created between the body and the inner surface of the casing between the seals from the throughbore at the port, will increase pressure in the chamber and thereby expand the casing between the seals. Preferably, the casing expander tool is as disclosed in GB2398312 and incorporated herein by reference. In this reference, the tool is used to expand a liner against an outer casing, while this is provided to give plastic deformation to the liner, for the present invention the tool is controlled to provide deformation within the elastic limit only.

The cutting tool may be selected from a group comprising: a perforating tool, a punch tool, a casing cutter, a section mill, an abrasive cutting tool and a pipe cutter.

Preferably, the apparatus includes a casing spear. Preferably, the apparatus also includes a packer. The apparatus may also include a jack. Preferably, the casing spear comprises an anchor, the anchor being used to grip the inside surface of the casing. Preferably, the packer is a tension-set packer.

The apparatus may include a washing tool, to circulate fluids from the string to the annulus.

The apparatus may include a bridge plug.

The string may be a tubing string to allow the fluid to pass therethrough. The string may be a drill string. The string may be coiled tubing.

s Alternatively, the string may be wireline or slickline. Wireline and slickline can allow the use of electrical control of the shock wave generation device from surface.

In the description that follows, the drawings are not necessarily to scale. Certain features of the invention may be shown exaggerated in scale or in somewhat schematic form, and some details of conventional elements may not be shown in the interest of clarity and conciseness. It is to be fully recognized that the different teachings of the embodiments discussed below may be employed separately or in any suitable combination to produce the desired results.

Accordingly, the drawings and descriptions are to be regarded as illustrative in nature, and not as restrictive. Furthermore, the terminology and phraseology used herein is solely used for descriptive purposes and should not be construed as limiting in scope. Language such as "including," "comprising," "having," "containing," or "involving," and variations thereof, is intended to be broad and encompass the subject matter listed thereafter, equivalents, and additional subject matter not recited, and is not intended to exclude other additives, components, integers or steps. Likewise, the term "comprising" is considered synonymous with the terms "including" or "containing" for applicable legal purposes.

All numerical values in this disclosure are understood as being modified 30 by "about". All singular forms of elements, or any other components described herein including (without limitations) components of the apparatus are understood to include plural forms thereof.

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings of which: Figures 1(a) and 1(b) are schematic illustrations of apparatus being used in a method for well abandonment to break the sealing contact between the casing and material in the annulus behind the casing in a well bore according to an embodiment of the present invention; and Figures 2(a) to (g) are schematic illustrations of apparatus showing steps in a casing cut and pull procedure according to further embodiments of the present invention; Figures 3(a) to (g) are schematic illustrations of apparatus showing steps in a perf wash and cement procedure according to further embodiments of the present invention; Figure 4 is an illustration of apparatus being used in a method for well 20 abandonment to break the sealing contact between the casing and material in the annulus behind the casing in a well bore according to an embodiment of the present invention; and Figure 5 is a schematic illustration of apparatus being used in a method 25 for well abandonment to break the sealing contact between the casing and material in the annulus behind the casing in a well bore according to an embodiment of the present invention.

Reference is initially made to Figures 1(a) and 1(b) of the drawings which 30 illustrate a method for well abandonment to break the sealing contact between the casing and material in the annulus behind the casing in a well bore, carried out on a single trip, according to an embodiment of the present invention.

In Figure 1(a) there is shown a cased well bore, generally indicated by s reference numeral 10, in which casing 12 lines the bore 14. Material 16 is located in the annulus 18 between the outer surface 20 of the casing 12 and the wall 22 of the bore 14. Material 16 may be cement which formed the cement sheath when the well 10 was completed. Alternatively, the material may be drilling fluid sediments, cement, sand or other debris ao which sits above the cement sheath or in uncemented sections of the annulus 18. The material 14 can fill the annulus and effectively bond to the outer surface 20 thereby creating a seal across the annulus 18. For a cement sheath, the seal is referred to as a cement bond. If it can be shown that the cement bond is of good quality along a sufficient length of casing, say 100m to 200m, well abandonment can be achieved by merely depositing cement into the casing bore 24 over the length of casing to create the required cement plug. However, as the cement sheath has been in place for the life of the well 10, it is likely that cracks, fissures and fractures 26 exist together with sections 28 in which the cement has come away from the surface 20 of the casing 12. In well abandonment, legislation now dictates that this does not provide an adequate seal to prevent the potential leakage of fluids from the well 10. Operators are left with two options, either remove the casing and deposit a cement plug in the bore 14 or perforate the casing 12 and pump cement up the annulus 18 to form a new cement bond, before filing the casing bore 24 with cement also. However, the presence of material 16 in the annulus 18 causes difficulties as sufficient bonding may exists so that the casing 12 is stuck and cannot be pulled or cleaning the annulus 18 does not effectively remove cement bonded to the outer surface 20, leaving the possibility of an inadequate cement bond being formed when new cement is pumped into the annulus 18.

The present invention therefore provides a cement bond breaker tool 30 run into the well 10 on a string 32. A cutting tool 34 is also provided n the string 30 so as to provide access to the annulus 18. The cement bond breaker tool 30 is configured to operate so as to act on the inner surface 58 of metallic casing 12.

In a preferred embodiment, as shown in Figures 1(a) and 1(b), the cement bond breaker tool 30 is a shock wave generation device 31. The shock wave generation device 31 is a source of electrohydraulic energy and the device 31 is configured for generating a series of electrical discharges that propagate a series of shock waves. The shock wave generation device 31 is coupled to the string 32 which is operable to raise and lower said shock wave generation device 31 and to supply power from the surface to said shock wave generation device 31. A voltage source (not shown) located external of the well 10 and an electrical circuit (not shown) mounted within the string 32 allow connecting said voltage source to the shock wave generation device 31. Electrical power is supplied by the low voltage source at a steady and relatively low power from the surface through the string 32 to the downhole shock wave generation device 31. Alternatively, power may be supplied at the device 31.

In this example, and as already described in U.S. Pat. No. 4,345,650 issued to Wesley, U.S. Pat. No. 6,227,293 issued to Huffman or US 2016/0348475 to Parker incorporated hereby by reference, the shock wave generation device 31 comprises a power conversion unit 36, a power storage unit 38, a control unit 40 and a discharge unit 42. The power conversion unit 36 comprises suitable circuitry for charging of the capacitors in the power storage unit 38. Timing of the discharge of the energy in the power from the power storage unit 38 through the discharge unit 42 is controlled by the control unit 38. In a preferred embodiment, the control unit 38 is a switch, which discharges when the voltage reaches a predefined threshold.

The discharge unit 42 comprises a first electrode 44 and a second s electrode 46 configured for triggering an electrical discharge. The discharge unit 42 may be configured to propagate shock waves radially or in a predetermined direction. Upon discharge of the capacitors in the power storage section through the first electrodes 44 and the second electrode 46, electrohydraulic shock waves 50 are produced. The discharge unit 42 comprises a plurality of capacitors (not represented) for storage of electrical energy configured for generating one or a plurality of electrical discharges. Other designs of discharge unit 42 are disclosed in U.S. Pat. No. 6,227,293 issued to Huffman which is included hereby reference. According to the electrohydraulic effect, an electrical discharge is discharged in a very short time (few micro seconds).

In this example, the discharge unit 42 further comprises a membrane 48 delimiting a chamber 52 which is filled with a shock wave transmitting liquid 54, allowing transmitting shock waves through the membrane 48 toward the metallic casing 12. In another embodiment, the discharge unit 42 may not comprise a membrane 48. Such membrane 48 isolates the discharge unit 42 from the casing bore 24 while maintaining acoustic coupling with said casing bore 24, improving the propagation of shockwaves while preventing external fluids 56 from the well 10 from damaging the discharge unit 42. In a preferred embodiment, the membrane 48 is flexible in order to an efficient propagation of shock waves in many directions and prevent shock waves to bounce on it, allowing therefore an efficient conduction of the shock wave toward the inner surface 58 the metallic casing 12. To this end, the membrane 48 may be made of fluorine rubber or fluoro elastomer with a relative elongation of at least 150%, preferably at least 200% and being operable between -35° C. and 250° C. In Figure 1(a), the cutting tool 34 is a punch tool known to those skilled in the art.

s In use, the shock wave generation device 31 is first positioned inside the casing 12 at a location where it is desired to break the sealing contact between the casing 12 and the material 16 in the annulus 18. An optimized position of the shock wave generation device 31 is defined by the alignment of the location with the space between the first electrode 44 and the second electrode 46. As shown in Figure 1(a), at least one shock wave 50, preferably a series of shock waves, is generated into the transmitting liquid 54 by the discharge unit 42 of the shock wave generation device 30. Thus at least one shock wave 50 propagates through the membrane 48 toward the inner surface 58 of the casing 12.

The at least one propagated shock wave 50 acts on the inside surface 58 of the casing 12. The shock wave 50 travels through the casing 12 and the casing 12 will experience some electrohydraulic deformation, causing it to temporarily elastically deform and then return to its original shape after the shock wave 50 has passed therethrough. The process will cause the material 16 to be dislodged from the outer surface 20 of the casing 12. Additionally, the shock wave 50 may cause cracks, fissures 26 or disassociation of the material 16 in the annulus 18. This is as illustrated in Figure 1(b) were it can be seen that the sections 28 without a cement bond now exist along the length of the outer surface 20 of the casing 12.

Larger fractures 26 are seen at the location opposite the electrodes 44,46 but peripheral cracks have also been made to the material 16 radially outwards of the main shock wave 50 location. The sealing contact between the casing 12 and the material 16 has been broken.

The shock wave generation device 31 is then moved, to another position inside the casing 12 in order to extend the break in sealing contact along a desired length of casing 12. The shock generation device 31 can be raised or lowered in the well 10 to achieve this.

A series of shock waves preferably comprises at least ten shock waves, s for example propagated at a periodic interval of time, e.g. every 5 to 20 seconds. A plurality of series may be advantageously repeated at different heights in well 10 to break the sealing contact between the casing 12 and the material 16.

While a single shock wave generation device 31 is shown in Figure 1 it will be appreciated that a plurality of devices 31 may be located around a central bore, to provide a through passage for fluid when the device 31 is used with a tubular string such as a drill string or coiled tubing. Power and control of the devices 31 may then be provided at the discharge units 42. Control can be made from surface by any known telemetry method.

As shown in Figure 1(b), the casing 12 has also been cut to form an aperture 60 by the cutting tool 34. This is as known in the art and may be performed before or after the cement bond breaker tool 30 has been operated. In an embodiment, cement bond breaker tool 30 is operated as the string 32 is run in the well 10 with the cutting tool 34 being operated at a location below the last location at which the cement bond breaker tool 30 was operated. When the cement bond breaker tool 30 is a shock wave generation device 31, the shock waves 50 are generated as the string 32 is run in the well 10 with the cutting tool 34 being operated at a location below the last location a shock wave 50 was created. In an alternative embodiment, the cutting tool 34 is operated to create the aperture 60 prior to the cement bond breaker tool 30 being used above the location of the aperture 60. This embodiment allows a circulation test to be performed to determine if the cement bond breaker tool 30 is required.

A circulation test, as described in W02018069685 and incorporated herein by reference, can be performed as soon as the aperture 60 is formed. A circulation test is performed by pumping fluid into the aperture 60 from the casing bore 24, the fluid typically being delivered through the tubing s string 32, seeing if it can circulate by travelling up the annulus 18 to surface. If a fluid return at surface is seen then it can be assumed that the sealing contact is broken as a path exists through the material 16. If the aperture 60 is a full circumferential cut of the casing 12, then an attempt can be made to pull the cut section of casing from the well as it may not be stuck.

This can be considered as one step in a cut and pull procedure as illustrated in Figures 2(a) to 2(g) according to an embodiment of the present invention. Like parts to those of Figures 1(a) and 1(b) have been given the same reference numerals to aid clarity. Referring initially to Figure 2(a) of the drawings there is illustrated a well 10 in which a string 32 is run. The drill string 32 has mounted thereon in order from a first end 62: a drill 64 for dressing a cement plug 66 already located in the casing 12; a cutting tool 34, being a casing cutter; an anchor mechanism 68; a packer assembly 70; and a cement bond breaker tool 30.

The cutting tool 34, anchor mechanism 68 and packer assembly 70 may be formed integrally on a single tool body or may be constructed separately and joined together by box and pin sections as is known in the art. Two parts may also be integrally formed and joined to the third part. Such an assembly is the TRIDENT® system offered by Ardyne, Aberdeen UK. In an alternative arrangement, the assembly may be the TITAN® system offered by Ardyne, Aberdeen UK which includes a downhole power tool to operate as a hydraulic jack.

In use, the drill string 32 with components mounted thereon is run-in the wellbore 10 and casing 12 until it reaches the cement plug 66. At this point a wellbore integrity test can be performed using the anchor mechanism 68 and the packer assembly 70, if desired. With the casing cutter 34, anchor mechanism 68 and packer assembly 70 all held in inactive positions, fluid can be pumped at a fluid pressure below a pre-set s threshold through a bore of the drill string 32 to hydraulically activate the drill 64. This does not actuate the casing cutter 34, anchor mechanism 68 or the packer assembly 70. The drill 64 is used to dress the cement plug 66. In an alternative arrangement the drill 64 could be replaced with a bridge plug which is located in the casing 12 when a cement plug 66 is not present.

The drill string 32 is then pulled up to locate knives 72 of the casing cutter 34 at a desired location to cut the casing 12. At this position, the anchor mechanism 68 is hydraulically actuated to grip the casing surface 58 to secure the axial position of the casing cutter 34 in the wellbore.

The fluid circulation rate through bore is increased above the pre-set threshold rate. This causes actuation of the anchor mechanism 68 with slips 74 extending outward to engage the surface 58 of casing 12. The slips provide friction to maintain the position of the casing cutter 34 within the casing 12. The string 32 is then anchored to the casing 12 by reversibly setting the anchor mechanism 68. To set the anchor mechanism 68 an upward tension or pulling force is applied to the drill string 32 causing the slips 74 to be wedged or locked between a surface of a cone of the anchor mechanism 68 and the casing 12 of the wellbore.

At this point the string 32 will remain at this location even if the fluid pressure in the bore is stopped or reduced below the pre-set threshold.

Once the anchor mechanism 68 has engaged the casing 12 and is set, as illustrated in Figure 2(b), the casing cutter 34 can be actuated. Note that the casing 14 is held in tension when the casing cutter 34 is operated. Casing cutter 34 can be operated by a drop ball or other mechanism. Fluid from the bore is diverted through the casing cutter 34 to extend the knives 72 from a retracted storage position to an extended operational position. During the cutting operation the anchor mechanism 68 remains substantially stationary relative to the casing cutter 34, with rotation of the casing cutting 34 being made possible via a bearing with the rotation s being undertaken by virtue of rotation of the drill string 32. During cutting fluid is also diverted out of the casing cutter 34 into the annulus 76 between the string 32 and the casing 12, and a venturi flow path provides induces localised recirculation of fluid around the casing cutter 34 to ensure that the casing cuttings are removed from the cutting site. This is as illustrated in Figure 2(c) with arrows showing the direction of fluid flow.

It is noted that upward flow travels in the annulus 76 passed the packer assembly 70 without any obstructions in the annulus 76 at the location of the packer assembly 70.

If a kick occurs in the wellbore 10 for any reason, the packer assembly 70 can be rapidly set to seal the wellbore by simply applying greater tension to the drill string 32 to set the packer.

When the casing cutter 34 has finished cutting the casing, the cutting 20 mechanism is deactivated. The rotation the tool string 32 is stopped to stop the rotation of the cutting mechanism 68. By reducing fluid pressure the knives 72 are moved back to the retracted position.

To perform a circulation test the packer assembly 70 is first set to seal the casing 12. To set the packer an upward tension or pulling force is applied to the drill string 32. The axial position of the string 32 in the wellbore is maintained by the anchor mechanism 68 gripping the casing. Ports are opened allowing fluid communication between the bore and the annulus 76 below the packer assembly 70. This is as illustrated in Figure 2(d).

The annulus 76 is now sealed off and pressurised fluid pumped through the drill string 32 will enter the annulus 76 and travel through the cut aperture 60 in the casing 12. Fluid will be forced upwards between the casing 12 and the bore wall 22 towards the surface. A recording of s pressure in the annulus behind the casing at surface indicates a positive circulation test and that the annulus behind the casing is free of debris and/or the seal is broken on the cement bond which may cause the casing 12 to stick when removed. The casing 12 can now be removed.

If the circulation test is negative and a return is not seen at surface, the shock wave technique can be applied. The technique may also be applied in the absence of a circulation test or in addition to a positive circulation test.

On completion of the circulation test, the packer 70 returns to its original uncompressed state and moves away from the well casing 12. The anchor mechanism 68 is also released to pull the slips 74 away from the casing 12.

The string 32 is pulled to locate the cement bond breaker tool 30 in the casing 12 at a point above the aperture 60. The cement bond breaker tool 30 then is operated to act against the inner surface 58 of the casing 12. In the preferred embodiment, this is by emitting one or a series of shock waves 50 as described herein with reference to Figures 1(a) and 1(b). The action of the cement bond breaker tool 30 breaks any seal between the outer surface 20 of the casing 12 and the material 16 within the annulus 18 at the location. Fractures and pathways will be created in the material 16. This is as illustrated in Figure 2(e). The string 32 is raised and the cement bond breaker tool 30 activated at intervals up the casing 12 until the anchor mechanism 68 is located at an upper end of the cut section of casing 78. The number of activations of the cement bond breaker tool 30 along the casing 12 can be as selected by an operator. At the upper end of the cut section of casing 78 the anchor mechanism 68 is activated to grip the casing section 78 as described above and as illustrated in Figure 2(f).

By pulling the drill string 32 from the wellbore 10, the cut section of casing 78 is removed from the wellbore 10. The wellbore 10 now contains the casing stub 80 and cement plug 66 as shown in Figure 2(g). A cement plug can now be deployed which will fill the bore 14 extending to the wall 22 to complete abandonment of the well.

If desired, after one or more operations of the cement bond breaker tool 30, the method can repeat the circulation test, to determine if the cement bond breaker tool 30 has broken the seal/cement bond between the casing 12 and the wall 22.

The method may also include the step of jacking the cut section of casing 78 once the anchor mechanism 68 is set at the top of the casing section 78. The step and an arrangement for jacking is described in W02018083473 and incorporated herein by reference. This can assist where operation of the cement bond breaker tool 30 may have caused breakage of the seal/cement bond at intervals but left some intervals in which the casing section 78 may be stuck.

Use of the cement bond breaker tool 30 in combination with a hydraulic 25 jack can remove casing where a cement sheath is in place.

The method can be performed on a single trip into the wellbore.

For a perf wash and cement technique we now refer to a procedure as illustrated in Figures 3(a) to 3(g) according to an embodiment of the present invention. Like parts to those of Figures 1 and 2 have been given the same reference numerals to aid clarity. Referring initially to Figure 3(a) of the drawings there is illustrated a well 10 in which a string 32 is run. The drill string 32 has mounted thereon in order from a first end 62: a bridge plug 82, a cutting tool being a perforating tool 34, a cement bond breaker tool 30, and a washing or jetting tool 84.

The tools 34, 30, 84 may be formed integrally on a single tool body or may be constructed separately and joined together by box and pin sections as is known in the art. Other tools may be present. The tools may be arranged in any order. Where the bridge plug 82 is located higher on the string, tools arranged below may be sacrificial and deposited in the well 10.

Tool string 32 may be a drill string or coiled tubing having a central bore for the passage of fluid pumped from surface, as is known in the art.

The cutting tool or perforating tool 34 is a perforating gun which is known in the art. The perforating gun produces multiple holes 86 through the casing 12. However, the perforating tool 34 may be any tool which can create individual holes 86 in casing 12. A punch tool may be used but would require an anchor in the string if it was to be set by tension.

The jetting tool 84 provides a plurality of radial ports 88 through which fluid can pass out of the tool 84. The ports 88 may include nozzles 90 to increase the velocity of the ejected fluid. The outer diameter of the tool 84 is sized so that ports 88 lie close to the inner surface 58 of the casing 12. This is done to encourage the fluid to pass directly into the holes 86 in the casing 12. Alternatively, the jetting tool 84 may include diverter cups on either side of the ports 88. These cups can be used to direct the fluid towards the surface 58 of the casing 12, the nozzles 90 are then not required.

The cement bond breaker tool 30 is preferably the shock wave generation device 31 as described with reference to Figures 1(a) and 1(b).

In Figure 3(a), the bridge plug 82 is shown as being set in the casing 12 s to thereby seal the casing bore 24, as is known in the art.

Referring now to Figure 3(b), there is illustrated the perforating tool 34 positioned at a lower end 92 of a longitudinal section 94 selected over which a cement plug 66 is required. Guns have been actuated to create a spread of holes 86 through the wall 96 of the casing 12. The holes 86 are spaced circumferentially around the casing 12 and can extend along a portion of the casing 12. The holes 86 provide multiple pathways between the annulus 18, bounded by the casing 12 and the borehole wall 22, and the casing bore 24.

The string 32 is pulled to locate the cement bond breaker tool 30 in the casing 12 at a point above the holes 86 which have formed apertures 60. The cement bond breaker tool 30 is then operated to act on the inner surface 58 of the casing so as to break any seal between the outer surface 20 of the casing 12 and the material 16 within the annulus 18 at the location. Fractures and pathways will be created in the material 16 so that the material 16 is broken into pieces. In the preferred embodiment, the shock wave generation device 31 emits shock waves 50 towards and against the inner surface 58 of the casing 12 as described herein with reference to Figures 1(a) and 1(b). A series of shock waves 50 are generated so as to break any seal between the outer surface 20 of the casing 12 and the material 16 within the annulus 18 at the location. Fractures and pathways will be created in the material 16 so that the material 16 is broken into pieces. This is as illustrated in Figure 2(c). The string 32 is raised and the cement bond breaker tool 30 operated, as a series of shock waves 50 produced in the preferred embodiment, at short intervals up the casing 12 until the perforating tool 34 is located at an upper end 98 of the longitudinal section 94. The shock waves 50 may be produced continuously as the string 32 is pulled and, if desired, rotated in the well casing 12.

s The perforating tool 34 is then fired to create further holes 99 at the upper end 98 of the of the longitudinal section 94. This is as illustrated in Figure 3(d). The annulus 18 is now accessible from the casing bore 24 along the full length of the longitudinal section 94 via a path between the lower holes 86 and the upper holes 99. It will be appreciated that the perforation could be performed over the entire longitudinal section. Such perforations could be produced at one time with the shock wave generation device 30 being mounted above or below and then being moved over the longitudinal section 94 either before or after the perforations have been made.

At this stage, the string 32 is run to position the jetting tool 84 at the lower end 92 of the longitudinal section 94. The jetting tool 84 is now aligned with the holes 86 at the lower end 92 of the longitudinal section 94. Washing can now begin. A washing fluid, typically viscosified brine, is pumped through the string 32 from surface. The fluid will exit the jetting tool 84 through ports 88 and nozzles 90, if present. The ports 88 and nozzles 90 are arranged to be perpendicular to the axis of the string 32. In this way, fluid is passes directly from the jetting tool 84 through the perforated holes 86 i.e. apertures 60, in the casing 12. It can be seen that the portion of the jetting tool 84 which includes the ports 88/nozzles has a greater diameter than the drill pipe or coiled tubing forming the string 32. This increased diameter is selected so that there is a minimal gap between the nozzle 90 and the perforated hole 86. In this way, there is a reduced fluid velocity reduction on the fluid exiting the jetting tool 84.

Additionally, the reduced diameter of the string 32 above the jetting tool 84 allows fluid to travel back into the casing bore 24 in the annulus 76 between the string 32 and the casing 12. The jetting tool 84 does not require to be rotated during washing, but may be rotated if desired.

The washing fluid enters the annulus 18 between the casing 12 and the s borehole wall 22. Within the annulus 18 there is the material 16 present which may be in the form of fractured cement from the shock wave treatment and/or various particles, deposits, for example so-called filter cake, and fluids remaining from previous downhole operations, including remaining drill cuttings, cement residues, baryte deposits and/or drill fluid. This material 16 can block the annulus 18 and adhere to the walls of the casing 12 and borehole wall 22, thereby preventing cement from entirely filling the annulus 18 and adhering to the walls to create adequate cement bonding.

The action of cement bond breaker tool 30 against the casing 12 will cause the materials 16 in the annulus 18 to break-up and dislodge from each other and the walls of the casing 12 and the borehole wall 22, breaking any seal therebetween and any of the original cement bonding which may have been in place. The washing fluid passed at pressure up the annulus 18, between the lower end 92 and the upper end 98 via the holes 86 and 99, respectively, forces the material 16 out of position and sweeps it upwards and preferably back though the perforation holes 99 into the casing bore 24. Thus the annulus 18 over the longitudinal section 94 is cleared of material 16 and the outer surface 20 of the casing 12 and borehole wall 22 are washed clean. This is as illustrated in Figure 3(e).

In the preferred embodiment a cement slurry is now passed down the string 32 and out through the jetting tool 84. This cement can be agitated so that it releases any gas to prevent pockets of empty space forming in the cement which could result in an incomplete cement plug. Agitation also encourages the cement slurry to enter the annulus 18 through the perforation holes 86 and better adhere to the inner surface 20 of the casing 12 and the borehole wall 22 to thereby provide a high quality cement bond. Cement slurry is pumped up the annulus 18 to exit into the casing bore 22 at holes 99. This ensures that the entire annulus 18 is s filled with cement over the longitudinal section.

The cement slurry is also released from the string 32 via the cutting tool 34. The cutting tool 34 can therefore be used as a cementing tool as well as a cutting tool. In the embodiment shown, see Figure 3(f), release of ports 97 on a base 95 of the cutting tool 34 which can be selectively opened to allow for the deposit of the cement slurry into the casing bore 24, if required. Pulsed cement slurry may also pass through the ports 88 and nozzles 90 of the jetting tool 84 at the same time. The string 32 is removed from well 10 and once set, a cement plug 66 is formed across the longitudinal section 94 extending down to the bridge plug 82 within the casing bore 24. This is as illustrated in Figure 3(g).

It should be noted that while we refer to a cement plug as being required, the plug can be formed of any fluidised plugging material. A cement slurry is typically used but the Applicants are aware of gels and other materials which may be used alone or in combination with cement to provide a fluidised material which sets hard and bonds to both the casing 12 and the borehole wall 22. A volume of the cement slurry is typically calculated for deposit to create the cement plug 66.

By passing the cement bond breaker tool 30 over the longitudinal section 94, perforations need only be made at an upper and lower position, particularly when the material 16 is that found above a cement sheath in the well. More perforations can be made along the longitudinal section if a cement sheath is present. In this way, the operation of the cement bond breaker tool 30 allows more material 16 to be flushed out of the annulus 18 and to provide a clean outer surface 20, free of cement and other debris so that a fresh cement bond can be formed by the cement plug 66. The entire method can also be performed as a single trip in the well bore 14.

s Those skilled in the art will recognise that cement bond breaker treatment can also be used for a perf wash cut and pull abandonment procedure by combining the relevant steps of the embodiments of Figures 2 and 3.

While the preferred embodiment of the cement bond breaker tool 30 is a so shock wave generation device 31, it will be realised that other tools capable of selective action on the inner surface 58 of the casing 12 could be used. Such tools 30 will provide temporary deformation of the casing 12 in discrete locations. Known tools which provide deformation to casing, liners and other tubulars are casing expanders. These are designed to plastically deform tubing to increase its diameter, typically to seal the tubing against an outer tubular in the well. In the present invention, such devices would be modified to only expand the tubular within its elastic limit so that following expansion the casing will return to its original diameter. Such temporary expansion, or expansion and contraction, compresses the casing against the cement or other material in the annulus and then, on contraction moves away from it so as to break any sealing contact and cause a passageway therebetween.

Figure 4 illustrates a cement bond breaker tool 30 in the form of a casing expander 33. Casing expander 33 has a cylindrical body 41 with connectors for location in the drill string 32. A plurality of rollers 43 are arranged circumferentially around the body 41 within a cage 45. The rollers 43 are held within the cage 45 away from the inner surface 58 of the casing 12 during run in. Fluid pressure through the bore of the string 34 and expander 33 cause opposing cones 47 to come together and force the rollers 43 outwards. Rotation of the string 32 causes rotation of the body 41 and the rollers 43 rotate around the longitudinal axis of the expander 33 and on their own axes while a radial component acting on the inner surface 58 of the casing 12. The casing 12 will be expanded at the location of the rollers 43. On decreasing fluid pressure through the expander 33, the cones 47 will separate and the rollers 43 return to the s contracted position. The expanded casing 12 which has been elastically deformed will also return to its original diameter. The expanded casing 12 will compress the cement and other material on the outer surface 20 of the casing 12. Once the rollers 43 are disengaged from the casing 12, the casing contracts inwards and so separates from the cement and other so material breaking any seal or bond between the two. This is as shown in Figures 1(a) and 1(b). The rollers 43 can be arranged on the body 41 so that they can be operated while the string is run-in or pulled out of the casing 12 so as to act of the casing as described hereinbefore with reference to Figures 2(a)-(g) and 3(a)-(g). This casing expander is as disclosed in US6702030 and incorporated herein by reference. It will be appreciated that the rollers 43 can be replaced with non-rolling elements which impact and press-into the casing 12. A greater number of elements is required to give an impact over a near full circumference of the expander 33, as the expander 33 itself cannot be rotated when operated.

An alternative cement expander 35 is shown in Figure 5. In an alternative embodiment, the casing expander 35 includes upper and lower seals 51a,b located on a cylindrical body 53, the body 53 having a port 55 therethrough between the seals 51a,b, and by application of the seals 51a,b to the inner surface of the casing 58, fluid entering a chamber 57 created between the body 53 and the inner surface of the casing 58 between the seals 51a,b from the throughbore 59 at the port 55, will increase pressure in the chamber 57 and thereby expand the casing 12 between the seals 51a,b. The fluid pressure is selected so as to cause only elastic deformation of the casing 12 between the seals 51a,b. In this way when the fluid pressure is reduced, the casing 12 returns to its originally diameter having only been temporarily deformed to release the cement or other material adhering to the outer surface 20 of the casing 12 and thereby breaking any cement bonds present. The casing expander tool 35 is as disclosed in GB2398312 and incorporated herein by reference. The expander 35 can be operated repeatedly up or down the s casing 12 to undertake the methods described in Figures 2(a)-(g) and 3(a)-(g).

The principle advantage of the present invention is that it provides an apparatus and a method in well abandonment to break the sealing so contact between the casing and material in the annulus behind the casing such as the cement bond between casing and a surrounding cement sheath, to improve the installation of a cement plug.

A further advantage of the present invention is that it provides an apparatus and a method in well abandonment to break the sealing contact between the casing and material in the annulus behind the casing such as the cement bond between casing and a surrounding cement sheath, which can be done on the same trip as cutting and pulling casing or a perf wash and cement job.

It will be apparent to those skilled in the art that modifications may be made to the invention herein described without departing from the scope thereof. For example, the string may include a cement retainer. A plurality of cement bond breaker tools can be mounted along the string and/or around a central bore of the tubing. The apparatus and method could be run using wireline. Additionally, reference has been made to shallower and deeper, together with upper and lower positions in the well bore. It will be recognised that these are relative terms though a vertical well bore is illustrated the method and apparatus apply equally to deviated and horizontal well bores.

Claims

CLAIMS1. A method in well abandonment to break the sealing contact between the casing and material in the annulus behind the casing in s a well bore, comprising the steps: (a) running a cement bond breaker tool into casing in a well bore; (b) operating the cement bond breaker tool to act against an inner surface of the casing; (c) running a cutting tool into the casing; and (d) penetrating the casing with the cutting tool to form an aperture in the casing.
2. A method in well abandonment according to claim 1 wherein in step (b) the cement bond breaker tool causes temporary deformation of the casing.
3. A method in well abandonment according to claim 1 or claim 2 wherein the cement bond breaker tool is a shock wave generation device which generates at least one electrical discharge in order to propagate at least one shock wave toward and against the inner surface of the casing.
4. A method in well abandonment according to claim 3 wherein a plurality of series of shock waves is generated.
5. A method in well abandonment according to claim 4 wherein a series of at least ten shock waves are generated for breaking a cement bond/seal.
6. A method in well abandonment according to claim 4 wherein a series of at least twenty shock waves are generated for breaking a cement bond/seal.
7. A method in well abandonment according to any one of claims 4 to 6 wherein each series of shock waves is generated repeatedly at different locations along the casing.
8. A method in well abandonment according to any one of claims 3 to 7 wherein the at least one shock wave propagates in a predetermined direction toward the inner surface of the casing and the string upon which the device is located is rotated to provide circumferential coverage.
9. A method in well abandonment according to any preceding claim wherein, in step (d) the cutting tool penetrates the casing by making perforations in the casing and the aperture is a perforation.
10. A method in well abandonment according to any one of claims 1 to 8 wherein, in step (d) the cutting tool penetrates the casing by cutting the casing and the aperture is a slot formed circumferentially around the casing to provide a cut section of casing.
11. A method in well abandonment according to claim 10 wherein the method includes the steps of engaging a spear to the cut section of casing in order to pull the cut section of casing and removing the cut section of casing from the well.
12. A method in well abandonment according to claim 11 wherein a jack is used to assist in removing the cut section of casing from the well bore.
13. A method in well abandonment according to any preceding claim wherein steps (a) and (c) are combined so that the cement bond breaker tool and the cutting tool are run on the same trip into the well.
14. A method in well abandonment according to any preceding claim wherein the method includes the step of circulating fluid through the aperture and looking for a return at surface.
15. A method in well abandonment according to any preceding claim wherein the method includes the step of circulating a washing fluid through the aperture to remove material in the annulus.
16. A method in well abandonment according to any one of claims 1 to 9 wherein the method includes the step of pumping a fluidised plugging material through the aperture so as to fill the annulus.
17. A method in well abandonment according to any preceding claim wherein the method is performed on a single trip into the well bore.
18. Apparatus in well abandonment to break the sealing contact between the casing and material in the annulus behind the casing in a well bore, comprising a string for running in the casing, the string including a cutting tool and a cement bond breaker tool, the cement bond breaker tool being configured to be selectively operated in the well to act against an inner surface of the casing.
19. Apparatus in well abandonment according to claim 18 wherein the cement bond breaker tool is a shock wave generation device wherein the shock wave generation device comprises a discharge unit configured for generating at least one electrical discharge that propagates at least one shock wave toward and against an inner surface of the casing.
20. Apparatus in well abandonment according to claim 19 wherein the discharge unit comprises a first electrode and a second electrode for generating a high voltage arc in a shock wave transmitting liquid.
21. Apparatus in well abandonment according to claim 20 wherein the shock wave generation device comprises at least one metallic wire mounted between the first electrode and the second electrode for creating a pressure wave such that when a current circulates between the first electrode and the second electrode, the at least so one metallic wire heats until vaporization, generating therefore a pressure wave that propagates into fluid.Apparatus in well abandonment according to claim 18 wherein the cement bond breaker tool is a casing expander tool configured to operate selectively in the well and temporarily expand casing within its elastic limit.Apparatus in well abandonment according any one of claims 18 to 22 wherein the cutting tool is selected from a group comprising: a perforating tool, a punch tool, a casing cutter, a section mill, an abrasive cutting tool and a pipe cutter.Apparatus in well abandonment according to any one of claims 18 to 23 wherein the apparatus includes one or more tools selected from a group comprising: a casing spear, a packer, a jack, an anchor, a jetting tool, a washing tool and a bridge plug.Apparatus in well abandonment according to any one of claims 18 to 24 wherein the string is selected from a group comprising: a tubular string, a drill string, coiled tubing, wireline and slickline. 22. 23. 24. 25.