NO346193B1

NO346193B1 - Toolstring assembly and method for releasing and removing a stuck casing

Info

Publication number: NO346193B1
Application number: NO20190740A
Authority: NO
Inventors: Kimmo Aleksanteri Mikalsen Stangeland
Original assignee: Archer Oiltools As
Priority date: 2019-06-17
Filing date: 2019-06-17
Publication date: 2022-04-11
Also published as: GB2600286A; NO20190740A1; GB2600286B; WO2020256563A1

Description

Title of the invention:

Toolstring assembly and method for releasing and removing a stuck casing.

Applicant: Archer Oiltools AS, Norway.

Inventor : Kimmo Aleksanteri Mikalsen Stangeland, employee of Archer Oiltools AS, Norway.

The present invention is a toolstring assembly and a method for retrieving a casing from a petroleum well. More specifically, the present invention is a toolstring arranged for releasing a stuck casing from a well, severing the casing and pulling the severed casing out of the well.

Problem to be solved

Casing may be retrieved from a well due to several reasons; the casing may be removed before redrilling of a portion of the well, or the casing changed due to the need for lateral drilling from a level in the well, or for plugging and abandonment of a part of the well below a cut point.

A significant problem related to retrieval of casing is often what is recognized as stuck casing. The annulus may during operation of the well have settled with particle debris from the borehole wall or from particles and low-viscosity liquids settled from the annulus fluid itself, to a degree such that the casing sticks in such settled annulus material from below a point which is called a free casing depth. It is not uncommon that stuck casing must be severed one short section at a time using a drill pipe conveyed cutting tool combined with a casing spear and pulled out under high vertical pulling force, section by section. Such an operation requires many runs and is time consuming and due to the rig time day rates for sea operations it is highly undesirable to pull a severed casing in several runs.

Background art

In the background art several patent publications relate to releasing and pulling casing.

NO20140029 by the applicant, relates to a method for pulling casing or liner in a petroleum well, comprising the steps of:

a) perforating, using a multi-perforation gun, almost the entire section of casing to be removed in the well, and then

b) washing one or more annuli outside the entire perforated section in order to remove debris, particles or cement or other binding means which would otherwise hold the casing section stuck,

c) cutting the casing in or below the perforated section to release it from the beyond remaining portion of casing,

d) pulling the released, washed-out portion of casing out of the well.

D2 US1779652 describes a drill pipe conveyed perforating tool with a knife which is forced against the casing wall and perforates one hole at a time out through one or more surrounding pipes such as production pipe or casing, in order to let in oil or water.

D3 WO2019078728 Hydra Systems describes a method for plugging a well with double casing, the method comprising

- setting a bridge plug in the casing, below the plug to be cement formed,

- to perforate using a perforation gun with many shots fired simultaneously,

- to wash out the first and second annulus by means of a wash tool with swab cups, and by using a very high fluid velocity for the flushing,

- to fill the casing with cement and allowing the cement to penetrate to the first and second casing, - and leave the well plugged wall to wall in its full diameter.

The purpose of D3 is not to pull casing, but to plug the well.

D4 WO2018203062 describes a method and apparatus for single trip casing cutting and pulling for abandoning a well, or slot recovery. The casing is perforated by use of a punch tool at a maximum depth, and fluid is circulated through the perforation to determine whether there is a return a the surface. If there is a return at the surface, the casing is cut and pulled. If there is no return at the surface, one makes perforations at shallower and shallower depths until a return is detected, and the casing is cut. The casing is then pulled.

Brief summary of the invention

The invention is a casing retrieval drill pipe string (0) conveyed toolstring assembly (1) for a well comprising one or more casings (130, 120, 118), said toolstring assembly (1)

c h a r a c t e r i z e d b y,

comprising, from top to bottom:

- a casing spear tool (30) arranged for engaging an inner wall of said casing (130) and lifting part of said casing (130) out when severed;

- a casing cutter tool (40) arranged for cutting and severing said casing (130) at a casing cutting target depth (CCTD)

- a casing perforation punching tool (50) arranged for perforating said casing (130)

- a wash tool (60) arranged for washing said casing's (130) annulus (132) through perforations made by said punching tool (50),

said wash tool (60) comprising:

- a wash tool central bore

- a wash fluid outlet

- upper and lower swab cups straddling said wash fluid outlet

- tool annulus fluid bypass channels straddling said swab cups,

- said casing perforation punching tool (50) arranged for hydraulic activation by pressure set up in said drill pipe string.

The method of the invention is a method for retrieving a casing (130) from a well (100), comprising the steps of:

- assembling a casing retrieval toolstring assembly (1) comprising

- a casing cutter tool (40) arranged for cutting and severing said casing (130) at a casing cutting target depth (CCTD),

- a casing perforation punching tool (50) arranged for hydraulic activation by pressure set up in a drill pipe string (0) for perforating said casing (130),

- running said casing retrieval toolstring assembly (1) into a well on said drill pipe string (0) until said casing wall perforation punching tool (50) is just below said casing (130) hanger depth,

- set said punching tool (50) to a punching mode,

- make said punching tool (50) punch a reference circulation hole (P0) for preparing a return circulation path from the casing annulus (131) just below said casing (130) hanger (131) depth,

the method c h a r a c t e r i z e d b y the following steps:

- run-in-hole said toolstring assembly (1) with said punching tool (50) to a first, expected, estimated free casing depth (EFCD) in said casing (130), where said casing (130) annulus (132) is freely fluid communicating upwardly to said reference circulation hole (P0);

- repeat the following steps until no fluid communication back from a test circulation hole (P1, P2, P3.... ) up to said reference circulation hole (P0) is confirmed:

- make an additional test circulation hole (P1, P2, P3, ..);

- for each additional test circulation hole (P1, P2, P3, ..) made, pull up for said perforation wash tool (60) to cover said additional test circulation hole (P1, P2, P3, ...) and exert a fluid pressure via said wash tool (60) through said additional test circulation hole (P1, P2, P3, ..) to test for fluid communication back through said reference circulation hole (P0),

- when no fluid communication from the latter of said additional test circulation holes (P1, P2, P3, ..) up to said reference circulation hole (P0) is confirmed, assume an Actual Free Casing Depth (AFCD) to reside between said present, additional test circulation hole (P1, P2, P3, ...) and the preceding test circulation hole (P1, P2, P3, ...),

- pulling said punch tool (50) back to the preceding test circulation hole (P1, P2, P3, ...) wherein communication was established,

- using said perforation punch tool (50), sequentially punch perforations for washing through said casing throughout said casing down to Casing Cutting Target Depth (CCTD),

- pull slowly out said washing tool (60) along said perforated sections below Actual Free Casing Depth (AFCD) and wash the debris filled annulus (134) about said casing (130) until satisfactory return of flushed out annulus material,

- run said toolstring assembly (1) down until said casing cutter tool (40) is at the casing cutter target depth (CCTD),

- circulate in a cutter activation ball, set said casing spear (30) to stabilize said cutter tool (30) at CCTD, activate said cutter tool (30) and rotate until it severs said casing (130) at CCTD, - using said casing spear tool (30), exert axial pull on said drill pipe string (0) to test for free casing while at CCTD,

- release said spear (30) from said CCTD depth and pull up to near a top of said severed, free casing (130'),

- pull said severed casing (130') out of hole.

Embodiments of the invention are defined in the dependent claims. Pipe dimensions such as the upwardly increasing series of 95/8'' (245mm) , 133/8'' (340 mm), 185/8 '' (473 mm) given in the claims and used in the illustrations are commonly used dimensions and may be used in various well settings, and are given as an example to facilitate the reading of the application for the person skilled in the art.

Brief Figure Captions

The invention is illustrated in the attached patent drawings. The below figure captions are kept brief and a more thorough description of each step is found under the heading "Embodiments of the invention".

Fig.1 illustrates a well with a 95/8'' (245mm) casing pipe (130) which casing pipe (130) shall be pulled from a so called casing cutting target depth CCTD further down. The casing is free in its annulus from a not precisely known free casing depth (FCD) and upwardly, but is surrounded by debris or other sticking material in the annulus down to a casing cutting target depth (CCTD). Figure 1 shows a wear bushing in 185/8'' (473 mm) csg (118), ID 121/2'', allows working in 95/8'' csg. (111) and a 185/8'' (473 mm) csg (118). The figure further shows an 185/8" (473mm) casing shoe (121), and a 133/8" (340 mm) csg (120), and a cmt: 133/8" (340 mm) csg sealed annulus no fluid comm. to surf. (cmt), and a 95/8'' (245mm) csg hanger / seal. Figur 1 further shows a 95/8'' (245mm) casing (13), a borehole (100), a wall (101), an annulus of 95/8'' (245mm) casing (132), and non-bound portion of (the) annulus 130 [132] (133). Figure also shows the EFCD range estim by well operator (EFCD) and the FCD free csg depth (FCD). Then the figure shows debris impermeable in 95/8'' (245mm) csg annulus (debirs) and the bound portion of the annulus (134), and the CCTD target depth (CCTD), tool rathole, cmt, plug and the casing cut target depth (CCTD).

Fig.2 illustrates a casing retrieval toolstring assembly (1) according to the invention for use in the method for retrieving a casing from the well. Figure 2 shows a toolstring with 12 dogs, 121/2'' WBRT retrieval tool 10 optional, figure further shows DP (0, 20) space out and the LH+pull. Figure 2 shows further a casing spear, a ball for cutting tool, a cutting tool 83/8", the 21/2'' ID ball seat, and a punch tool L=6-10 m. The figure also shows a bypass sect, an upper cup (62U), a was port and a wash tool 8 3/8'' for 95/8'' (245mm) csg and a lower cup (62L). Figur 2 shows the ball for wash tool and the Ball seat 2'' for wash tool.

Fig.3 illustrates the use of the toolstring of the invention making a punched reference perforation (P0) for reference return communication below the hanger (131) of the casing (130). Figur 3 shows a 133/8'' (340 mm) csg (120), a 95/8'' (245mm) casing hanger (131) and the punch tool (50). The figure shows a punch perf tool and further a make P0 as return path from 95/8'' (245mm) casing annulus and a csg (130). The figure shows also a wash tool and a ball to allow setting pressure in punching tool (ball). Fig.4 is an illustration of the invention wherein a first test punch perforation (P1) is made at the clientprovided estimated free casing depth (EFCD). Figure 4 shows a 95/8'' (245mm) casing hanger (131), a P0 reference return, a DP space out (20), a cut tool (40) and a P1 FCD test range. The figure shows further a EFCD, a perf tool (50), a punch P1 and a wash tool (60). Figure also shows a ball (65) in seat.

Fig.5 is an illustration of the further step of Fig.4, showing the punch tool (50) pulled slightly up so as for the wash tool (60) swab cups to straddle the recently formed punch perforation (P1) in order to set the annulus outside the casing (130) under pressure, and test for return through the reference perforation (P0) made below the casing hanger (131). The figure 5 shows a 95/8'' (245mm) hanger (131), a DP space out (20) and a punch tool (50).

Fig.6 is an illustration of the subsequent step of perforating a second test perforation punch hole (P2) below (P1) as a consequence of the test result of free communication between the first test perforation punch hole (P1) and the reference perforation hole (P0). The figure 6 shows a 131: 93/8'' casing hanger (131), a DP space out (20), a punch / perf tool (50) and a wash tool (60).

Fig.7 is an illustration of the test of communication between the newly formed test perforation hole (P2) and the reference perforation hole (P0). In the illustrated embodiment and situation, there is no communication from the second perforation punch hole (P2) and the reference perforation hole (P0), and we assume from this that the actual free casing depth (AFCD) is below (P1) and above (P2). The figure 7 shows a 93/8'' casing hanger (131), a punch perf tool (50) and a wash tool (60).

Fig.8 illustrates the subsequent step after determining, in the embodiment shown in Fig.7, the actual free casing depth AFCD, i.e. the actual free casing depth (AFCD) range extending between (P1) and (P2) in this case. Now continuous perforation shall be prepared befor washing free the stuck caasing (130). Figure 8 shows a DP space out (20) and a cutter tool (50).

Fig.9 illustrates the subsequent step after perforating from throughout and below the actual free casing depth (AFCD) range down to the casing cutter target depth (CCTD). Wash upwardly pulling slowly out to the upper level of actual free casing depth (AFCD), then return downwardly with the wash tool.

Fig.10 illustrates that the casing cutter tool is placed at the casing cutter target depth (CCTD) and the spear tool (30) is preferably set in the casing (130) to stabilize the cutter tool at the (CCTD). This concludes the end of the actual operation made in one run. The figure 10 shows a spear tool (30) and a cutter tool (50).

Fig.11 illustrates the desired result which may be achieved by the invention; the severed-off casing (130') on its way out of the well, leaving a free space above the casing cutter target depth (CCTD).

Embodiments of the invention

An objective of the invention is to identify the actual “free casing point” by regular punching moving down- or upwards from estimated casing stuck point in 50 or 100m intervals until AFCD is found, then subsequently continuously punching from the actual free casing point (AFCD) where below the casing is stuck, and down to target casing cut depth, cut casing at target casing cut depth, pull wear bushing seal assembly, confirm casing cut and free to pull out of hole and then pull casing up to surface - all in one run.

The well and the problem to be solved

Fig.1 illustrates a well with a 185/8 '' (473 mm) casing extending down to a depth whereafter a 133/8'' (340 mm) casing (120) extends further down to a 95/8'' (245mm) casing hanger and seal (131) near the lower end of the 133/8'' (340 mm) casing (120). The 95/8'' (245mm) casing pipe (130) may be a liner not extending to the surface. Anyway, this casing pipe (130) shall be pulled from a so called casing cutting target depth CCTD further down. As explained in the introduction, there is an estimated free casing depth (EFCD) provided by the well owner, and a real, free casing depth (FCD) distinguishing between a non-bound annulus (133) about the casing (130) and a bound portion of annulus (134) surrounding the casing (130), said bound portion of annulus (134) extending at least down to the casing cutting target depth (CCTD), please see Fig.1.

The toolstring assembly

Fig.2 illustrates a casing retrieval toolstring assembly (1) according to the invention for use in the method for retrieving a casing (130) from the well. The toolstring assembly (1) comprises from top to bottom a casing spear tool (30), a cutter tool (40), a casing perforation puncher tool, and an annulus wash tool (60). The invention is this casing retrieval drill pipe string (0) conveyed toolstring assembly (1) for a well comprising one or more casings (130, 120, 118), said toolstring assembly comprising

- wash tool (60) arranged for washing said casing's (130) annulus (132) through perforations made by said punching tool (50).

On the use of the toolstring assembly

The purpose of the toolstring assembly (1) is not evident from its assembly as such. Making perforations in order to wash the annulus is well known from e.g. NO20111641, Hydrawell, "Method for combined cleaning and plugging", but done in one shot, not sequentially, and is not used both for perforating for washing, but also for actively punching to search for free annulus communication. Further, Hydrawell's perforation tool is not used in the context of severing the casing, nor for retrieving the casing.

* one of the main purposes of the present invention's toolstring assembly (1) is to use the perforation puncher tool (50) to perforate the casing (130) in order to test for fluid communication upwardly, in order to establish which portions of casing (134) are backed by supposedly casing sticking material in the annulus,

* further in order for washing out debris and removing such casing sticking material from the annulus down to a required casing cutting target depth (CCTD) (a requirement set by other operational factors) and pulling out the severed casing (130') to retrieve it from the well.

An optional spaced-out wear bushing retrieval tool (10) may be arranged for retrieving a wear bushing before pulling the wear bushing (111) from the well in the same run as pulling out the severed casing (130').

Wash tool

In an embodiment of the invention wash tool (60) is arranged for washing said casing (130) annulus (132). The wash tool comprises a mandrel box and pin connectors at the ends, and with

- a wash tool central bore for conducting drill pipe string conducted fluids,

- a wash fluid outlet,

- upper and lower swab cups (62, 62U, 62L) straddling said wash fluid outlet,

- tool annulus fluid bypass channels straddling said swab cups, (so as for allowing to run the wash tool along blank pipe sections),

- a wash tool central bore ball seat arranged below said wash fluid outlet, and

- a wash tool drop ball (65) to be dropped from surface and landing sealing said seat.

There are two main purposes of the wash tool (60):

a) The drop ball (65) shall be dropped from surface and landing sealingly in said central bore ball seat to block the wash tool central bore to force drill pipe supplied wash fluid out through the wash fluid outlet. If no ball present, the fluid would go straight through the wash tool central bore and no central bore pressure is established for washing. The open ball seat is for allowing axial passage of well fluids during running in the toolstring assembly into the well in order for allowing circulation of fluids during run-in. b) The purpose of setting up pressure in the central bore is also for activating one or more tools above the wash tool, not only for washing as in the prior art. In an embodiment of the invention the punching tool (50) is pressure activated for extending its cutter arms or knives and forcing them through the casing (130) wall. This pressure is established by placing the wash tool (which resides below the punch tool in this embodiment) against a blank, unperforated casing portion and pumping high pressure at the drill pipe string. In an embodiment the punching tool is non-rotating when punching.

In an embodiment of the invention, said casing cutter tool (40) is provided with

- a central bore

- a ball seat in said central bore arranged for receiving a ball in said central bore for establishing a static or dynamic pressure and for activating:

- an actuating mechanism for extending

- said cutter arms to a cutting position.

In this embodiment of the cutting tool (40), it is designed for being rotated while the cutter arms knife ends, usually carbide reinforced, are forced against the inner surface of the casing (130) and arranged for cutting and severing said casing (130). In an embodiment of the invention the casing spear tool (30) may be swivel-mounted and engage its slips in the casing wall in order for holding the cutting tool at a constant elevation during the cutting process. In an alternative embodiment, the cutting tool may be explosive, severing the casing along a circular line at CCTD, the Casing Cutting Target Depth.

In the cutter tool (40), the central bore is for fluid communication to below punching tool (50) and wash tool (60).

Wear bushing retrieval tool

In an embodiment of the invention, the toolstring assembly (1) comprises a wear bushing retrieval tool (10) arranged for retrieving a wear bushing (111) in the well, and

- drill pipe space-out sections (0, 20) arranged below said retrieval tool (10) in order to create a required separation between the wear bushing retrieval tool (10) and the usually much deeper situated casing spear tool (30).

In the basic version of the invention, for a situation where is no wear bushing (111) arranged to protect the wellhead, there is no wear bushing retrieval tool (10) in the drill pipe string (0) between the drilling deck and the toolstring assembly (1) downhole. But in an embodiment of the invention there is a wear bushing retrieving tool (10) which is arranged on the same drill pipe string (much further up) so as for retrieving the wear bushing (111) in order to retrieve the 95/8'' (245mm) casing (130). The distance between the wear bushing retrieval tool and the spear tool (30) with the remainder of the toolstring assembly (1) corresponds to the expected distance down to an estimated free casing depth (EFCD). In an embodiment of the invention said retrieval tool (10) enabled for running through said wear bushing and arranged for engaging the wear bushing while being rotated in a predefined way, e.g. left-hand rotation, while being pulled upwardly into J-slots of the wear bushing, thus enabling engaging dogs into the J-slots and pulling out the wear bushing thus opening up for pulling out the severed casing (130').

Casing spear:

In an embodiment of the invention, the casing spear tool (30) is provided with

- spear slips arranged for engaging and holding the inner face of said casing (130),

- a central bore for the passage of fluids and one or more balls,

- a ball seat in a moveable, shear-out ball seat sleeve arranged for receiving a ball and for being sheared out and moved in order to release a slips actuating mechanism, said slips actuating mechanism arranged for engaging said slips with an inner wall of said casing (130), said slips arranged for being forced into holding and lifting engagement with said inner wall of said casing (130) by axially pulling said casing spear tool (30) via said drill pipe string (0).

in an embodiment of the invention, the spear tool (30) is provided with drag blocks arranged for dragging along the inner wall of the casing (130), in order for providing an initial force for starting activating the slips to engage with the inner wall of the casing (130), whereafter they provide their own activation "counterforce", and the drag blocks for providing a counterforce when the pull on the drill pipe string (0) is released and allowing to lower the tool relative to the casing wall. There may be a return spring mechanism for the release, or there may be a LH rotation release mechanism relative to the mandrel in order to release the slips in order for releasing the spear tool (30).

In an embodiment of the invention, said slips are arranged for releasing from said inner wall of said casing (130) by downward movement of said drill pipe string (0) relative to said wall of said casing (130).

In an embodiment of the invention, said slips are arranged for releasing subsequent to a left-hand (LH) rotation of the drill pipe string (0) relative to the casing spear tool in combination with said downward movement of said drill pipe string (0).

This enabling of the spear tool is important for allowing first an engagement of the slips down near the casing cutter target depth to cut, then release and allow for pulling up to a new slips engagement depth near the top of the severed-off casing portion (130) and pulling it out by its top portion to avoid buckling.

The activation / deactivation mechanism of the spear tool may be similar to the one in the Archer Oiltools retrievable plug, which may be considered as a drill pipe string conveyed tool, with a set of right hand threads / blank portion / left hand outward threads at the rotating mandrel arranged for being engaged by corresponding right-hand and left-hand inward threads on spring loaded ratchet-sliding engagement blocks of the barrel of the spear tool (30). This mechanism will only be enabled to be engaged when a shear sleeve ball seat as mentioned above is moved out of its blocking position, just like in the Archer Vault plug tool.

Swivelled spear tool

In an embodiment of the invention, in order for allowing the spear tool (30) to engage with the casing (130) in order to make a cut at a precisely held casing cutting depth (CCTD), said casing spear tool (30) comprises

- a rotatable mandrel with said central bore, said mandrel rotatable by said drill pipe string (0) and for transferring torque, in that

- said rotatable mandrel being torque coupled in its upper end to said drill pipe string (0), - said rotatable mandrel further being torque coupled in its lower end to the casing cutter tool (40),

- an upper swivel and a lower swivel allowing said mandrel to rotate relative to a barrel carrying said expanded slips.

This will allow the barrel with the slips to be non-rotating relative to the casing (130) while the below arranged casing cutter tool (40) is rotated by the rotatable mandrel. This will allow the barrel of the casing spear tool (30) to be static both axially and rotationally, remember that the slips are holding their grip on the inner wall of the casing while its pipe mandrel is allowed to rotate with the drill pipe string (0, 20) in order to rotate the cutter tool (40). In this manner the cutter tool knives are allowed to work at one single circumferential casing cutting target depth CCTD instead of working its way upwardly or downwardly while cutting. Firmly holding the cutter tool at a fixed depth relative to the casing will also avoid any drill pipe string heave or vertical vibration influence.

Casing perforation punching tool

In an embodiment of the invention, said casing perforation punching tool (50) comprises a hydraulically operated punch knife activation mechanism arranged for forcing out extendable knives for cutting slits through the casing (130) wall. In a further embodiment, said hydraulically operated punch knife activation mechanism is activated by drill pipe string pressure set up after said ball (65) has been landed in said ball seat in said wash tool (60). In this way, there is no need for explosive charges for perforating the casing wall; hydraulic pressure through the drill pipe string is sufficient to actuate the knives to perforate, dependent on the swab cups of the wash tool straddling a blank casing portion. Thus it may be important to start at the upper perforation position and run downwardly while making new perforations.

In an embodiment of the invention, said casing perforation punching tool (50) may comprise a hydraulically actuated perforation gun arranged to shoot, one by one in a sequential and controlled mode, and punch one hole at a time, in said casing (130). A sequential shooting may be activated shot by shot by increasing the drill pipe string pressure for each triggering. The punching tool (50) may in a further alternative embodiment also be a flow-actuated drill arranged for drilling a lateral hole in the casing.

The method of the invention

Fig.1 illustrates a well with a 95/8'' (245mm) casing pipe (130) may be a liner not extending to the surface, which casing pipe (130) shall be pulled from a so called casing cutting target depth CCTD further down. As explained in the introduction, the casing is free in its annulus from a not precisely known free casing depth (FCD) and upwardly, but is surrounded by debris or other sticking material in the annulus down to a casing cutting target depth (CCTD) down to which the entire casing pipe (130) eventually shall be removed.

Fig.2 illustrates a casing retrieaval toolstring assembly (1) according to the invention for use in the method for retrieving a casing from the well. The toolstring assembly comprises from top to bottom an optional spaced-out wear bushing retrieval tool, a casing spear, a cutter tool, a perforation puncher tool, and an annulus wash tool.

Fig.3 illustrates the use of the toolstring of the invention making a punched reference perforation (P0) for reference return communication below the hanger (131) of the casing (130). A ball (65) is landed in the ball seat in the wash tool (60) below the punch tool (50) in order to allow for pressure buildup to make the punch.

Fig.4 is an illustration of the invention wherein a first test punch perforation (P1) is made at the clientprovided estimated free casing depth (EFCD).

Fig.5 is an illustration of the further step of Fig.4, showing the punch tool (50) pulled sligthly up so as for the wash tool (60) swab cups to straddle the recently formed punch perforation (P1) in order to set the annulus outside the casing (130) under pressure, and test for return through the reference perforation (P0) made below the casing hanger (131). Pressure is provided through the drill pipe string (0, 20). In the illustration it is indicated that the circulation is "OK", i.e. the free casing depth extends to at least the estimated free casing depth (EFCD) and most probably below this depth. We must go further down and test for the real actual free casing depth.

Fig.6 is an illustration of the subsequent step of perforating a second test perforation punch hole (P2) below (P1) as a consequence of the test result of free communication between the first test perforation punch hole (P1) and the reference perforation hole (P0). The possible range of the actual free casing depth (AFCD) is now between (P1) and (P2).

Fig.7 is an illustration of the test of communication between the newly formed test perforation hole (P2) and the reference perforation hole (P0) (Actually the first test perforation hole (P1) or both). In the illustrated embodiment and situation, there is no communication from the second perforation punch hole (P2) and the reference perforation hole (P0), and we assume from this that the actual free casing depth (AFCD) is below (P1) and above (P2). We have indicated by hatching a debris-filled annulus (134) about the casing (130), which is not free in this depth interval. It may be assumed to be a stuck casing which may not be pulled.

Refinements may be done in the punching and testing to pinpoint the real actual free casing depth (AFCD) with finer resolution by going up half the distance, make an intermediate punch hole "(P1-2)" but for simplicity we stop the illustration of the testing in Fig.7.

Fig.8 illustrates the subsequent step after determining, in the embodiment shown in Fig.7, the actual free casing depth AFCD, i.e. the actual free casing depth (AFCD) range extending between (P1) and (P2) in this case. Now continuous perforation shall be prepared befor washing free the stuck caasing (130). The punching tool (50) is here shown as having made perforations with relatively small intervals all the way from the upper bound (P1) of the actual free casing depth (AFCD) range and down to the casing cutter target depth (CCTD). Remember that in the illustrated embodiment of the invention using the wash tool requiring blank, unperforated casing to establish punching pressure, the perforations must be made downwardly from the top of the (AFCD) range. Pressure will be most probably established in this case also with the wash tool placed at the (P2) because there was initially no communication, unless there now is communication to the row of perforations made above. Remember that there must initially be planned a space for a rathole for the wash tool (60) and the perforation tool (50) below the lowest perforation, in order to allow for positioning the casing cutter tool (40) at the casing cutter target depth (CCTD).

Fig.9 illustrates the subsequent step after perforating from throughout and below the actual free casing depth (AFCD) range down to the casing cutter target depth (CCTD). It is rational to start washing with the wash tool situated at the lowest perforation above the casing cutter target depth (CCTD), and wash upwardly pulling slowly out. The pulling out speed while washing should be controlled while checking sufficient return fluid flow from the washing process, and is at the discretion of the tool operator at the site. When arriving at the upper level of actual free casing depth (AFCD), then return downwardly with the wash tool preferably continue washing down to the casing cutter target depth (CCTD).

Fig.10 illustrates that the casing cutter tool is placed at the casing cutter target depth (CCTD) and the spear tool (30) is preferably set in the casing (130) to stabilize the cutter tool at the (CCTD). Pressure is increased in the drill pipe string in order to activate the cutter tool, and, if required, the flow rate is increased. The cutter tool rotates and its knives cuts and severs the casing at (CCTD). A test lift using the spear tool (30) may be made in order to verify that the now severed casing (130) above the (CCTD) is actually cut-off and test lifted to check whether it is free in its annulus. If positive, then the spear tool (30) may be lifted up to just below the upper end of the now free severed-off casing (130'), and pull the severed-off free casing (130) out of hole. This concludes the end of the actual operation made in one run.

Fig.11 illustrates the desired result which may be achieved by the invention; the severed-off casing (130') on its way out of the well, leaving a free space above the casing cutter target depth (CCTD) which may enable abandonment of the well or further, subsequent operations of re-furbishing the well.

An embodiment of the present invention's method is described by the following steps:

* Receive a casing cut target depth (CCTD) provided by customer (P&A program).

* Run-in-hole with the toolstring assembly (1)with the perforation punching tool (50) to just below the 9 5/8” (245mm) casing (130) hanger's (131) depth, because there is in a subsea well, no b-annulus valve available for return circulation.

* set the perforation puncher tool (50) to perforation punch mode.

* Using the perforation puncher tool (50), punch a reference hole (0<th>) below the 95/8” (245mm) casing hanger (131) for subsequent return circulation from the free casing non-bound annulus (132, 133).

* Run-in-hole the toolstring assembly (1) with the casing perforation puncher tool (50) to an estimated free casing depth (EFCD). As an example, the estimated free casing depth (EFCD) provided by customer may be 2/3 down to the casing cutting target depth (CCTD). The estimated free casing depth (EFCD) is the depth where above this depth the casing (130, 133) ) is assumed to be free from any significant bond with material settled in the annulus (132) and could be retrieved to surface if cut free. Below this estimated free casing depth (EFCD) there is assumed to be a bond between the casing (130, 134) and material / settlement in the annulus eg. Barite, cement, clay, sand, etc.

Again using the perforation puncher tool (50), punch a first test hole at EFCD (1<st>) and attempt to circulate annulus between EFCD and the reference hole punched just below the casing shoe (131) (or bannulus surface valve).

a. If a test circulation is possible, it is confirmed that the casing (130) down to the estimated free casing depth (EFCD) is “free”, i.e. it could be pulled if severed at (EFCD). Move downwards 50 or 100m interval and perform a second (2<nd>) test punch. Repeat annulus test circulation upwards from this second (2<nd >) test punch. If free continue downwards in 50-100m intervals with new third, fourth, and so on, test perforation punching and test circulation until no circulation possible. In an embodiment of the invention the last (previous) confirmed circulation perforation is the actual free casing depth (AFCD). In a refined embodiment, move 1⁄2 interval upwards towards the last confirmed circulation perforation and punch and test. If free, that may be considered the actual free casing depth (AFCD) from which below the casing (130, 134) is considered stuck.

b. In case of the AFCD above EFCD, i. e. If no circulation possible between EFCD and the reference hole punched or b-annulus surface valve, then EFCD is not free. Move 50-100m upwards from the EFCD and repeat punch and circulation attempts until found free circulation. That’s considered the actual free casing depth point (AFCD).

Now having found the actual free casing depth (AFCD), the stuck casing portion (134) must be freed before pulling. The same toolstring assembly (1) may be used also for this part of continuously punch downwards from AFCD to CCTD to prepare stuck casing interval for Barricade operation (washing out the casing annulus behind the perforations in the casing) with 0.4-0.6 in entry hole diameter and 12 holes per foot punch density.

* keep the wash tool (60) in wash mode with ball (65) in the central bore ball seat,

* conduct washing of the annulus (134) about the non-free, bound casing and remove/degrade bond between casing (130) and material in annulus over entire section between the casing cutter target depth (CCTD) and the actual free casing depth (AFCD),

* move casing cutter tool (40) to casing cutter target depth (CCTD),

* circulate in a ball to land in ball seat in shear sleeve to activate the spear tool (30) and pressure up to activate casing cutter tool (40),

* rotate the drill pipe string (0, 20) to cut the casing (130) at CCTD,

* Release the spear tool (30) from the casing cutter target depth (CCTD),

* Move the wear bushing retrieval tool (spaced out) up to position and retrieve wear bushing seal assembly,

* Set the spear tool (30) in active mode again,

* Set the spear tool (30) in the severed-off casing (130') wall and attempt to pull the severed casing (130) up to confirm severed-off casing (130') free to pull-out-of-hole,

* Release the spear tool (30) and retract the spear tool (30) to just below casing hanger (131),

* Set the spear tool (30) and pull the severed casing (130') up to surface for being removed from the well.

Components list of tool and well

Claims

Claims:

1. A casing retrieval drill pipe string (0) conveyed toolstring assembly (1) for a well comprising one or more casings (130, 120, 118), said toolstring assembly (1)

c h a r a c t e r i z e d b y,

comprising, from top to bottom:

said wash tool (60) comprising:

- a wash tool central bore

- a wash fluid outlet

- upper and lower swab cups (62, 62U, 62L) straddling said wash fluid outlet

- tool annulus fluid bypass channels straddling said swab cups (62),

2. The toolstring assembly (1) of claim 1, said casing (130) annulus (132) wash tool (60) comprising:

- a wash tool central bore ball seat arranged below said wash fluid outlet,

3. The toolstring assembly (1) of any of the above claims, said casing cutter tool (40) provided with a central bore,

- a ball seat in said central bore arranged for receiving a ball in said central bore for establishing a static or dynamic pressure and for activating an actuating mechanism,

- said actuating mechanism for extending cutter arms of said casing cutter tool (40) to a cutting position.

4. The toolstring assembly (1) of any of the above claims, said toolstring assembly (1) further comprising - a wear bushing retrieval tool (10) arranged for retrieving a wear bushing (111) in the well, and - drill pipe space-out sections (20) arranged below said retrieval tool (10).

5. The toolstring assembly (1) of any of the above claims, said casing spear tool (30) having

- spear slips arranged for engaging and holding the inner face of a casing,

- a central bore for the passage of fluids and one or more balls

- a ball seat in a moveable ball seat sleeve arranged for receiving a ball and for being sheared out and moved in order to release a slips actuating mechanism, said slips actuating mechanism arranged for engaging said slips with an inner wall of said casing (130), said slips arranged for being forced into lifting engagement with said inner wall of said casing (130) by axially pulling said casing spear tool (30) via said drill pipe string (0).

6. The toolstring assembly (1) of claim 5, said slips arranged for releasing from said inner wall of said casing (130) by downward movement of said drill pipe string (0) relative to said wall of said casing (130).

7. The toolstring assembly (1) of claim 6, said slips arranged for releasing subsequent to a left-hand (LH) rotation of the drill pipe string (0) relative to the casing spear tool in combination with said downward movement of said drill pipe string (0).

8. The toolstring assembly (1) of any of the preceding claims, said casing spear tool (30) comprising - a rotatable mandrel with said central bore, said mandrel rotatable by said drill pipe string (0) and for transferring torque, in that

- said rotatable mandrel torque coupled in its upper end to said drill pipe string (0),

- said rotatable mandrel torque coupled in its lower end to the casing cutter tool (40)

9. The toolstring assembly (1) of any of the preceding claims, said casing perforation punching tool (50) - comprising hydraulically operated punch knife activation mechanism arranged for forcing out extendable knives for cutting slits through the casing (130) wall.

10. The toolstring assembly (1) of claim 9, wherein said hydraulically operated punch knife activation mechanism is activated by drill pipe string pressure set up after said ball (65) has been landed in said ball seat in said wash tool (60).

11. The toolstring assembly (1) of any of the preceding claims, said casing perforation punching tool (50) - comprising a hydraulically actuated perforation gun arranged to shoot, one by one in a sequential and controlled mode, and punch one hole at a time, in said casing (130).

12. A method for retrieving a casing (130) from a well (100), comprising the steps of:

- assembling a casing retrieval toolstring assembly (1) comprising

- set said punching tool (50) to a punching mode,

the method c h a r a c t e r i z e d b y the following steps:

- make an additional test circulation hole (P1, P2, P3, ..);

- circulate in a cutter activation ball, set said casing spear (30) to stabilize said cutter tool (30) at CCTD, activate said cutter tool (30) and rotate until it severs said casing (130) at CCTD,

- using said casing spear tool (30), exert axial pull on said drill pipe string (0) to test for free casing while at CCTD,

- pull said severed casing (130') out of hole.

13. The method of claim 12, when no fluid communication up to said reference circulation hole (P0) is confirmed:

- pull up from halfway from the last confirmed communicating test perforation hole (P1, P2, P3, ...) and the first confirmed no-communication perforations (P1, P2, P3, ...) and make one or more intermediate test perforations to refine the definition of the actual Free Casing Depth (AFCD).