NO314153B1 - Milling device for underground borehole casing - Google Patents

Description

The present invention relates to a milling device for underground borehole casing.

The present invention thus mainly relates to the completion of underground wells and, in a preferred embodiment thereof, it particularly relates to a device for milling a side wall window in a main borehole casing in preparation for the subsequent extension of a lateral borehole from the main borehole.

It is well known in the art when drilling underground wells to form a main borehole in the earth and then form one or more boreholes located laterally from this. Essentially, the mainbore is drilled and cemented first, and then a tool known as a guide wedge is placed in the mainbore casing over an anchor structure locked in place in the mainbore casing. The guide wedge is particularly designed to deflect a drill bit in the desired direction to form a lateral borehole. The drill bit is then lowered into the main borehole hanging down from a drill pipe and is deflected radially outward by the guide wedge to drill a window in the main borehole casing and cement. Directional drilling techniques can then be used to direct further drilling in the lateral borehole as desired.

The lateral borehole is then lined by inserting a tubular casing from the main borehole, through the window previously cut in the main borehole casing and cement, and then into the lateral borehole. In a normal lateral wellbore casing operation, the casing protrudes somewhat upwards into the main borehole casing and through the window when the casing operation is finished. In this way, an overlap is achieved where the lateral borehole casing is occupied in the main borehole's casing above the window.

A majority of guide wedges/anchor structures have previously been proposed for use when cutting out the sidewall window in the main borehole casing to enable the subsequent addition of a lateral borehole to this. However, each of these constructions has one or more disadvantages which cause inconvenient or uneconomical use. Some of these disadvantages include inaccurate positioning and orientation of the window opening to be cut, complexity in positioning and releasing the parts of the window-forming device, unwanted torque-induced rotational shifts of the device, and danger of leaving parts of the device in the well, requiring a subsequent fishing operation.

From the foregoing it can be seen that it would be relatively desirable to provide an improved device and method for forming a sidewall window opening in a main borehole casing that is convenient and economical in use, that provides accurate location and orientation of the opening to be cut, that has reliable placement and release characteristics, which are not complex in placement and release, and which reduce the danger of leaving parts of the device in the well. It is therefore the purpose of the present invention to provide such an improved device with associated method for forming a side wall window opening in a ferrule.

According to the invention, a milling device is therefore proposed for underground borehole casing, with the features stated in the characteristic in claim 1.

Further features of the milling device are indicated in the independent patent claims.

In carrying out the principles of the present invention, in accordance with the preferred embodiment thereof, a specially designed tubular anchor assembly with an extended milling guide projecting upwards from its upper end is used together with a pipe-supported milling bit to mill out a sidewall window in the casing in a substantially vertical main borehole to allow the subsequent connection of a lateral borehole thereto. To enable efficiency during the milling operation and retrieval from the casing of the anchor assembly, a specially designed tubular retrieval structure is also fitted.

According to a milling method, a tubular anchor construction is used with an upper end from which the extended milling guide protrudes longitudinally. Along its length, the upwardly projecting milling guide has a milling crown deflecting surface which is angled in relation to the longitudinal axis of the tubular anchor construction. The tubular anchor structure is coaxially and releasably locked in the casing, somewhat below the sidewall part of the casing which is to be milled out to form the desired window.

A length of milling pipe is provided with a lower end to which a milling bit is attached, a radially outwardly located outer side projection located above the milling bit, and a tubular retrieval structure that is coaxially and releasably attached to the milling pipe above its outer side projection.

At least a portion of the casing sidewall window is milled out by lowering the milling bit end of the milling pipe through a tubular fish neck located on a tubular upper end portion of the milling guide, rotating the milling pipe and laterally deflecting the rotating milling bit into shearing engagement with the casing sidewall by bringing the rotating milling bit for contact with the milling guide's deflecting surface. The milling tube is then pushed further downward to cause the retrieval assembly to enter and lock into the fish neck.

Then, the tubular anchor structure is pulled by pulling the cutter pipe up and out of the casing and sequentially (1) causing the cutter pipe to be pulled out of the retrieval structure and moved upward through the retrieval structure, and (2) causing the cutter pipe's outer side projection upwardly to impinge on an inner portion of the retrieval structure and accordingly, an upward force is created in the tubular anchor structure which releases the anchor structure from the casing and allows it to be pulled out of the casing with the retrieval structure, fish neck and milling guide.

The tubular anchor structure and associated milling guide and retrieval structure can be used to progressively mill out the casing's sidewall window using, for example, first and second differently configured milling crowns used for first and second milling pipe insertion. In the first of these insertions, the milling tube is releasably positioned coaxially in the tubular upper end portion of the milling guide, with the interior of the milling tube in communication with the interior of the pressure chamber of the setting piston in the anchor structure via a passage from the milling tube through the milling guide. When the anchor assembly is correctly positioned in the fairing tube, pressurized fluid is forced through the mill tube and into the anchor assembly's pressure chamber to cause movement of the seating piston and consequently cause the sliding element parts of the anchor breast assembly to grip the fairing tube and releasably lock the anchor assembly therein. At the last milling tube insertion (illustratively the second insertion) the retrieval structure is used to release and remove the anchor structure and its upwardly pulling milling guide.

The tubular anchor assembly is configured to give it a desired thin sidewall and significantly improved retrievability. In a preferred embodiment, the armature assembly includes a tubular inner spindle, upper and lower tubular sliding element carriers coaxially circumscribing the tubular inner spindle in radially outwardly spaced relation thereto, and circumferentially spaced, spaced series of upper and lower serrated sliding elements positioned between the upper and lower sliding element carriers and the inner spindle. The sliders are radially movable through slider windows in their associated carriers between inwardly retracted release positions and outwardly extended seat or fairing tube gripping positions.

In accordance with a feature of the present invention, the sliders are flexibly biased toward their radially retracted release positions by means of a compact clamping device comprising circumferentially spaced series of arcuate elongated spring elements deposited in the annular space between the slider carriers and the inner spindle and interlaced with those along series of sliding elements located around the circumference. The spring elements have central parts attached along the longitudinal axis to the corresponding sliding element carriers, and outer end parts of the springs enter outer side depressions in the sliding elements and engage slidingly in the sliding elements.

According to a further feature of the present invention which advantageously reduces the overall side wall thickness of the tubular anchor assembly, radial inner side portions of the slide elements are slidably carried in axially spaced upper and lower circumferentially spaced series of axially spaced pockets formed in the outer side surface of the inner spindle.

The upper and lower sliding members are preferably in an opposite relationship, with a tubular wedge member coaxially and slidably circumscribing the inner spindle between the opposing serrated and stepped ends of the upper and lower sliding members. A stepped upper end portion of the gusset has a continuous, fixed annular configuration, while a circumferentially spaced series of axial sidewall slots extend up through the lower end of the gusset. The slits form a circumferentially spaced series of collar finger portions on the wedge member, the lower ends of which collar fingers have a stepped configuration.

The inner spindle, the upper and lower sliding elements and the collar-shaped wedge element are relatively movable in axial directions between (1) a set position where the outer ends of the collar finger parts outwardly lie above and are radially supported by areas where pockets are not formed in the inner spindle, with the opposite ends of the wedge member tapering into contact with the inclined ends of the upper and lower slide members, and (2) a release position where the outer ends of the collar finger portions overlie the second series of inner spindle cavities and can be radially deflected into them, influenced of an axially directed engaging force between the outer ends of the collar finger parts and the inclined ends of the other sliding elements. In this way, the release of the tubular anchor assembly from the fairing pipe is generally carried out.

In a preferred embodiment thereof, the retrieval structure includes a tubular body with an upper and a lower end, and a peripherally spaced series of axially located side wall slits formed in the body and with respective upper and lower ends separated axially inwardly from the upper and lower ends of the body . In between, the slits form a circumferentially separated series of axially situated collar fingers which are elastically bendable radially inwards and outwards in relation to the rest of the body. Each of the collar flanges has a radially outwardly located outer side protrusion and a radially inwardly located inner side protrusion.

The internal collar fmger protrusions have lower surfaces that slope upwardly and radially outwardly at a first angle relative to a reference plane transverse to the longitudinal axis of the body of the retrieval structure; the outer collar finger protrusions have upper surfaces that slope downwardly and radially outwardly at a second angle relative to a reference plane transverse to the longitudinal axis of the retrieval structure body; and the outer collar finger protrusions have lower surfaces that slope upward and radially outward at a third angle relative to a reference plane transverse to the longitudinal axis of

the body of the retrieval structure.

The first angle is smaller than the second angle, which in turn is smaller than the third angle. Preferably, the first angle is about 10 degrees, the second angle is about 20 degrees and the third angle is about 45 degrees.

Near the upper end of the fish neck at the top of the milling guide is an annular side surface recess having an annular upper end shoulder with a slope parallel to the slopes of the upper ends of the outer retrieval structure collar finger projections, and an annular lower end shoulder with a slope parallel to the slopes of the lower ends of the outer retrieval constriction collar flange protrusions. Because of these oblique angles, the retrieval structure's outer collar finger projection can enter the fish neck's recess when the retrieval structure is introduced into the fish neck, but is locked in the recess with regard to upward removal from it. Consequently, the retrieval collar design is a "one-way" design that allows for release and removal of the anchor assembly from the casing.

The milling tube preferably has a projecting annular flange with an upper surface having a sloping angle corresponding to the sloping angles at the lower ends of the inner collar finger projections on the tubular retrieval structure. This milling tube flange acts as a pick-up abutment surface that upwardly abuts the inner collar finger protrusions, during upward movement of the milling tube after it is disconnected from the tubular retrieval structure, to transmit a release force to the anchor assembly, via the retrieval structure, the fish neck and the milling guide, and then upwardly carry the retrieval structure and the fitted fish neck, milling guide and anchor assembly out of the casing with the rest of the milling pipe.

Figs IA and IB are very schematic longitudinal sections through part of an underground well and show a particularly designed milling guide and anchor device according to the invention, for forming a side wall window in the well's casing;

fig. 2 is a highly schematic longitudinal section through an underground well section showing an upper portion of a lateral wellbore casing installed after the formation of the casing window;

fig. 3A-3E are sections through successive sections of the milling guide and anchor assembly of the invention, with the components of the milling guide and anchor assembly in their original insertion orientations;

fig. 4A and 4B, 5A and 5B, and 6A and 6B show respective reduced-scale half-sections of downward longitudinally successive parts of the anchor part of the assembly and show sequentially the setting of the anchor part in the well casing,

fig. 7 is a half-section of a tubular upper end part of the milling guide and shows its reception of a particularly designed double-ended collar construction according to the invention;

fig. 8 is an enlarged section through a portion of one of the collar construction finger members, taken along line 8-8 of FIG. 7;

Fig. 9 is a half-section through an upper part of the milling guide and shows a locking engagement between the collar structure and the milling tube during a retrieval operation for milling guide and anchor assembly, and

fig. 10 is an enlarged cross-section through an anchor part of the assembly, along the line 10-10 in fig. 3D.

Schematically illustrated in fig. 1A-2 is a first drilled or "main" borehole 10 which runs essentially vertically into the earth. The main borehole 10 is lined with a mainly tubular and vertically oriented metal casing 12. Cement 14 fills an annular space between the casing 12 and the earth.

As a result of a milling operation, to be described below, the main borehole 10 has a sidewall window 16 in the casing 12 (see Figs. 1B and 2). A lateral borehole 18 extends from the window 16 and includes a tubular bearing construction 20 with cement 14 in the annular space between the bearing 20 and the earth. The liner 20 has an upper part 20a which goes up coaxially into the main borehole casing 12, and has an open upper end 20b at a distance from the casing window 16. The upper casing part 20a limits, together with the inner side wall of the casing 12, an annular space which is also filled with cement 14.

The present origin is directed towards the formation of side wall window opening 16 in the fairing tube 12 as shown in fig. 2. As will be described in more detail below, the window 16 is formed by using a particularly designed pull-out anchor assembly 22 (see fig. IA and IB) which exhibits principles from the present invention. The anchor assembly 22 has a hollow tubular configuration and an extended milling guide element 24 which extends up from the upper end of the anchor assembly 22 laterally offset relative to its longitudinal axis. The milling guide element 24 has an offset lower end part 26 with, as representatively illustrated in fig. IA and IB, a downward and left-sloping guide surface 28.

Figs. IA and IB, in highly schematic form, sequentially illustrate the use of the milling guide member 24, and its associated tubular anchor assembly 22, to form the ferrule window 16 shown in Figs. 2. With reference to fig. IA, the lower end of a tubular fish neck 74 is coaxially located relative to a tubular upper end portion 24a of the milling guide element 24. In a manner as subsequently described, the upper milling guide element end portion 24a is coaxially received and placed on a lower end of a tubular milling pipe 30 with a substantially flat first milling crown 32 placed on its lower end. When the milling guide element's end part 24a is installed on the milling pipe 30, the lower end of the milling crown 32 will be close to the open lower end of the milling guide element's end part 24a, as schematically shown in fig. IA.

With the tubular fish neck 74, milling guide 24 and anchor assembly 22 placed on the lower end of milling pipe 30, as shown in fig. IA, the milling pipe 30 is lowered into the fairing pipe 12 until, as indicated in fig. IA, the milling guide element 24 has been given a predetermined vertical position and rotational orientation in the guide tube 12 in relation to the desired position of the guide tube window 16 (see Fig. 2) which is to be formed. During this introduction, the total milling and anchor construction can be rotationally oriented in the casing 12 by using e.g. a conventional gyroscope.

After the anchor assembly 22 and its associated milling guide element 24 are vertical and rotationally oriented in the casing 12, the anchor assembly 22 is set hydraulically, in a manner to be described below, by using pressurized fluid in the milling pipe 30. The setting part of the anchor assembly 22 includes an annular elastomer waste barrier seal member 36 coaxially carried by anchor assembly 22 downwardly near its upper end 38, a circumferential series of upper sliding members 40 below seal member 36; and a circumferential series of lower sliding elements 42 below the upper sliding elements 40. The setting process moves the sealing element 36, and the sliding elements 40 and 42, radially outward into gripping contact with the opposite inner side wall of the casing 12, which locks the anchor assembly 22 (and thereby the milling guide element 24 and also the tubular fish neck 74 in the casing 12.

With the anchor assembly 22 set in the casing 12, the milling pipe 30 is forced down in a vertical direction to break it loose from the tubular end part 24 of the milling guide element 24. The milling pipe 30 is then rotationally driven (here in a clockwise direction as seen from above) and further lowered through the fish neck 74 and the upper milling guide element end part 24 into the fairing pipe 12, as indicated by the arrow 44 in fig. IA, parallel to the vertical fairing tube axis 46. When the rotating milling bit 32 meets the inclined milling guide element surface 28, the bit is deflected laterally to the left, as indicated by arrow 48 in FIG. IA, to engage with the ferrule 12 to thereby form an incipient window opening 16a therein. After the formation of this initial fairing window opening 16a, the rotation of the milling pipe 30 is stopped, and the milling pipe 30 and the milling bit 32 are pulled up through the upper milling guide member end portion 24a and attached fish neck 74 and out of the fairing pipe 12, leaving the anchor assembly 22, the milling guide member 24 and the tubular fish neck 74 in place in the casing 12.

The first milling crown 32 is then replaced with a second milling crown 52 (see Fig. 1B) on the lower end of the extracted milling tube 30. This second crown 52 has a substantially conical front end part 52a. In addition, a specially designed tubular retrieval collar construction 54 is placed on the extracted milling tube 30, somewhat above the second milling bit 52. As schematically shown in fig. IB, the extracted milling tube 30 is then lowered into the ferrule 12 and through the tubular fish neck 74 until the milling crown 52 exits the upper milling guide element end part 24a. The milling tube 30 is then rotated and lowered further, as indicated by arrow 56 in fig. IB. As the rotating cutter bit 52 contacts the inclined cutter guide surface 28, the bit 52 is deflected to the left, as indicated by arrow 58, to engage the casing 12 and will enlarge the previously milled casing sidewall opening 16a (see Fig. 1A) thereby forming the desired ferrule window opening 16 shown in both fig. 1B and fig. 2.

After this second casing stage is completed, the rotation of the milling pipe 30 is stopped, and the milling pipe 30 is then pushed further downward to push

the retrieval collar structure 54 into the open upper end 74a of the tubular fish neck 74. In a manner described in more detail below, this causes the collar structure 54 to lock itself into the interior of the fish neck 74. The milling tube 30 is then pulled upwards. In a manner that will also be described in more detail below, this separates the milling tube 30 from the locked collar structure 54 and allows the milling tube 30 to be pulled up through the interior of the fish neck 74 and the collar structure 54. A shoulder portion (not shown in Fig. IB) on the upward moved milling tubes 30 then lock onto the collar structure 54 and transmit the upward milling tube extraction force to an inner portion of the anchor assembly 22 via the collar structure 54 and the milling guide member 24, in a manner that releases the anchor assembly 22 from the guide tube 12 by pulling out the anchor assembly seal and sliding members 36,40 and 42 .

The freed anchor assembly 22, together with the fish neck 74 and milling guide member 24, is then withdrawn from the casing 12 of the milling pipe 30 with the locked collar assembly 54 and milling bit 52. It should be noted that during the use of the specially designed retrieval collar assembly 54, the anchor assembly 22 is recovered, along with the milling guide element 24 and the fish neck 74 placed thereon in connection with the second milling step (or the first milling step if only a milling bit is used to form the desired fairing pipe window 16), and does not require a subsequent separate anchor/milling guide construction retrieval step. After recovery of the anchor assembly, milling guide member 24 and fish neck 74 as just described, the lateral borehole bushing 20 can be installed in the casing 12 in a suitable conventional manner as shown in fig. 2.

In fig. 3A-3E are downward longitudinally subsequent parts of the total anchor, milling guide and fish neck assembly 22,24,74 of the present invention illustrated in cross-section in greater detail, and on a larger scale, with the milling tube 30 located coaxially through the interior of the fish neck 74 The tubular anchor assembly 22 is shown in FIG. 3C-3E in the fairing tube 12, with the various replaceable components of the armature assembly 22 (as later described below) in their original insertion positions.

The tubular fish neck 74 (see Fig. 3A) has, near its upper end 74a, an annular inner side surface recess 76 with a downwardly and radially outwardly sloping upper annular end ledge surface 78, and a downwardly and radially inwardly sloping lower annular end ledge surface 80. Near its lower end, the fish neck 74 has an annular stop flange part 81. The lower end of the fish neck 74 is threaded, as at 82, externally onto the tubular upper end part 24a of the milling guide element 24. A tubular lower end part 24b of the milling guide element 24 is screwed onto it at 86 inner main spindle 88 (see Fig. 3C). In order to prevent relative rotation between the lower milling guide end portion 24b and the upper end of the inner main spindle 88, an anti-rotation shank 89 (see Fig. 3C) located in axially opposed slots 89a, 89b is formed in the milling guide end portion 24b and the upper end part of the main spindle 88.

Immediately below the lower end portion 24a of the milling guide member 24 is an annular, projecting outer shoulder portion 90 of the main spindle 88. The aforementioned annular elastomeric sealing element surrounds the inner spindle 88 and abuts upward and downward against the opposing annular side surfaces of the annular spindle shoulder 90. the components of the armature assembly 22 in their insertion orientation shown in FIG. 3C-3E is the lower end of the sealing member 36 (see Fig. 3C) upwardly separated from the upper end 96 by a tubular upper slide member carrier 98 (see Fig. 3D) which outwardly and slidably surrounds the main spindle 88.

Referring now to fig. 3D, a lower end portion of the upper sliding member carrier 98 has a circumferentially spaced separate series of upper and lower

sliding element window openings 100,102 which outwardly overlie a series of axially located pocket areas 104 (see also Fig. 10) formed in and circumferentially separated around the outer side surface of the inner main spindle 88. The upper sliding elements 40 are circumferentially separated around the inner spindle 88, is slidably engaged in the pocket areas 104 and has upper and lower parts 40a, 40b which are engaged in respective sliding element windows 100,102. Each of the upper sliding elements 40 has a recessed area 40a between its upper and lower parts 40a and 40b. Lower slide member parts 40b have gripper teeth 106. The teeth 106 spiral downward in a clockwise direction

from above (ie in the same rotating direction as the rotation of the milling tube 30 during the milling operations).

As shown in fig. 10, the upper sliders 40 are resiliently biased radially outward, in a manner that pushes their upper and lower portions 40a, 40b out through their respective slider windows 100,102, by means of a unique and highly compact spring system comprising a circumferentially spaced series of elongated arcuate metal spring plate elements 108 deposited in the annular space between the main spindle 88 and the upper sliding element carrier 98, as illustrated in fig. 10. The springs 108 are placed so that their convexly curved side surfaces are directed radially outwards and in the longitudinal direction central parts of these are placed between neighboring pairs of upper sliding elements 40 located along the circumference and are anchored to the inner side surface of the upper sliding element carrier 98 with screws 110 .

As shown, at each upper sliding surface 40, end portions of circumferentially spaced pairs of springs 108 enter the recessed sliding member areas 40c and slideably abut against the radially thinned sliding member portions between the sliding member portions 40a and 40b. When the anchor assembly 22 is seated in the casing 12, the sliders 40 are forced radially outwardly into biting engagement with the casing 12. This radially outward settling motion of the upper sliders 40 is elastically resisted by the springs 108 as their outer ends slide along their associated sliders and is temporarily moved towards the right orientation by the outwardly moving sliding elements 40. When the radially outwardly directed settling force is removed from the sliding elements 40, the spring ends return to their in fig. 10 marked curved orientations, thereby pulling the sliding elements 40 radially towards theirs in fig. 10 signed orientations.

An annular wedge element 112 (see Fig. 3D) surrounds the main spindle 88 below the upper sliding elements 40. The wedge element 112 has a circumferentially continuous upper end part 114 which lies below the lower end of the upper sliding element carrier 98 and is releasably anchored to it by two longitudinal circumferentially spaced break pins 116. A circumferentially spaced series of inclined, substantially "flat" areas 118 are formed on the upper wedge end 114, corresponding to inclined inner "flat" areas 120 on the lower end of the upper slide members 40. When the opposite flat areas 118,120 cooperate when setting the sliding elements 40, they serve to prevent unwanted relative rotation between the wedge element 112 and the sliding elements 40.

A circumferential series of axial slots extends up through the wedge element 112 to its upper end part 114, thereby forming on the wedge element 112 a circumferential series of downwardly projecting collar finger parts 124. The collar fingers 124 are, as illustrated in fig. 3D, radially tapered relative to the upper wedge end portion 114, and having radially offset lower end portions 126. With the components of the armature assembly 22 in their insertion orientation shown in FIG. 3A-3D, these lower collar finger end portions 126, as shown in FIG. 3B, over a circumferential series of axial pocket regions 128 in the outer side surface of the main spindle 88.

The lower collar finger end portions 126 have sloped flat outer side surface areas 130

r

and lies below an upper end portion of a tubular lower sliding element carrier 132 which slidably surrounds the main spindle 88. Five circumferentially spaced break pins 134 releasably anchor the upper end of the lower sliding element carrier 132 to underlying lower collar finger end portions 126. The circumferentially distributed lower sliding elements 42 is in opposite relationship with the upper sliding elements 40, slidably carried in the spindle pockets 128, and has upper and lower parts 42a, 42b which are occupied respectively in upper and lower sliding element windows 136, 138 formed in the lower sliding element carrier 132 and lying above the spindle pockets 128. Each of the lower sliding elements 42 has a recessed area 42c deposited between its upper and lower parts 42a and 42b. At the upper end of each of the lower slide members 42 is a flat sloping inner side surface area 139 which faces a corresponding flat area 130 on one of the collar fingers 124 of the wedge member.

Upper sliding element part 42a has gripping teeth 40 on its outer side surface. The teeth 140 spiral downwards in a clockwise direction as seen from above, and thereby have an opposite spin to the upper sliding element gripping teeth 106. The lower gripping elements 42 are elastically pressed radially outwards by springs 108, in a manner identical to that described for the upper sliding elements 40 in connection with fig. 10. Accordingly, when the upper and lower sliding elements 40,42 are placed in gripping engagement with the casing 12, as described in more detail below, these very strongly resist a rotation of the anchor assembly 22 relative to the casing 12 in both directions about the vertical axis 46.

As shown in fig. 3D is the inner main spindle 88 with three sets of torque pins 142,144 and 146 rotationally locked to the upper and lower slider carriers 98 and 132 in a manner that allows relative axial shift between the spindle 88 and the slider carriers 98 and 132. The torque pins 146 pass through the upper slider carrier 98 and is slidably engaged in axially elongated slots 148 in the inner spindle. The torque pins 144 pass through the upper sliding element carrier 98 and are slidably engaged in axially elongated slots 150 in the upper sliding element carrier 98 and in significantly longer axially elongated slots 152 in the inner spindle 88. The torque pins 146 pass through the upper sliding element carrier 132 and are slidably engaged in spindle slots 152 and in shorter axially extended slots 154 in the lower sliding element carrier 132.

With continued reference to fig. 3D, an annular, downwardly directed outer ledge 156 is formed on a lower end portion of the lower sliding member carrier 132, below its lower sliding member windows 138. This lower end portion of the lower sliding member carrier 132 is outwardly overlapped by an upper end portion of a tubular piston retaining member 158 which circumscribes the main spindle 88 in a radially outwardly spaced relationship therewith. At its upper end, the holding element 158 is screwed at 159, on the lower sliding element carrier 132 directly above the landing 156. A tubular piston element 160 (see Figs. 3D and 3E) is coaxially and slidably carried in the annular space between the spindle 88 and the piston holder 158, and is slidably sealed against the opposing side surfaces of the spindle 88 and the piston holder 158 by means of the indicated O-rings 162 and 164.

The tubular piston 160 has an upper end 166 (see Fig. 3D) downwardly separated from the annular lower sliding member support landing 156, and a lower end 168 (see Fig. 3E). As indicated in fig. 3D, an upper end portion of the piston holder 158 is releasably anchored to the underlying upper end portion of the piston 160 with break pins 170. Referring now to FIG. 3E, there is separated downwardly from the lower piston end 168 a tubular sliding element spindle 172 which is slidably received in an annular space between the main spindle 88 and the piston holding element 158 and slidably sealed against the opposite side surfaces by means of the indicated O-rings 174,176.

The upper end 178 of the sliding element spindle 172 is separated downwardly from the lower end 168 of the tubular piston 160 and thereby forms an annular pressure chamber 180 between the main spindle 88 and the piston holding element 158. A lower end part of the sliding element spindle 172 is located downwardly past the lower end 182 of the retaining member 158 and is releasably anchored to the main spindle 88 by a circumferentially spaced series of breaker pins 184. A longitudinally located series of rack teeth 186 is formed on the outer side surface of the slide member spindle 172 and is operatively engaged with corresponding teeth on an annular rack slide member 188 enclosed in an annular inner side surface pocket 190 formed in a lower end portion of the piston retaining member 158. Conventionally, the rack sliding member 188 allows the piston retaining member 158 to move upward along the sliding member spindle 172, but not downward along it. The rack sliding element 188 is pressed upwards in the pocket 190 by spring elements 192 in this.

Referring now to fig. 3B-3E, with the total anchor, cutter guide and fish neck assembly 22,24,74 in their previously described inlet orientations, a lower end portion of the cutter tube 30 (see FIG. 1B) is releasably seated in the tubular upper cutter guide portion 24a with breakable dowel elements 60 The set pins 60a shown are hollow and communicate with the interior of the milling tube 30 with the upper end of an elongated fluid supply port 62 which is recessed in a vertically located recess 64 formed in the outer side surface of the milling guide member 24 opposite the inclined side surface 28. As illustrated in fig. 3C, the lower end of the pipe 62 is in communication with interconnected internal passages 66,68 formed in the lower end of the milling guide element 24. The passage 68 is connected by a threaded connection 69 to the upper end of a second fluid supply pipe 70 which is centrally located downward through the anchor assembly 22. As illustrated in fig. 3E, the lower end of the tube 70 is attached to the inner spindle 88 with a threaded connection 72 and communicates with the pressure chamber 180.

As shown in fig. 3A, a diametrically enlarged annular outer flange 198 is formed on the milling tube 30, located immediately below an annular outer side surface recess 200 formed in the milling tube 30. A downwardly directed annular upwardly and radially outwardly sloping ledge 202 is formed at the upper side of the annular recess 200; an upwardly directed annular, downwardly and radially outwardly sloping ledge 204 is formed at the upper side of the flange 198; and a downwardly directed annular, upwardly and radially outwardly sloping ledge 206 is formed at the lower side of the flange 198.

Referring now to fig. 7 and 8, the retrieval collar 54 has a tubular body 222 with open upper and lower ends 224,226. A circumferentially spaced series of axial slits 228 are formed in the body 222, with the upper ends of the slits 228 downwardly separated from the upper end 224 of the collar body 222, and the lower ends of the slits 228 upwardly separated from the lower end 226 of the collar body 222. The slits 228 in between form a circumferentially separated series of axial double-ended collar finger parts 230 which are flexibly displaceable radially inward and outward relative to the rest of the retrieval collar body 222.

As best shown in fig. 8, the longitudinal middle sections 230a of the fingers 230 are radially displaced to form on each finger 230 a radial protrusion 232 and a radially inwardly directed protrusion 234. The protrusion 232 has an upper end surface 236 which slopes downward and radially outward at an angle A in relation to a reference plane situated across the longitudinal axis of the collar body 222, and a lower end surface 238 which slopes upwards and radially outwards at an angle B in relation to a reference plane situated across the longitudinal axis of the collar body 222. The protrusion 234 has a lower end surface 240 which slopes upwards and radially outwards at an angle C in relation to a reference plane situated across the longitudinal axis of the collar body 222, and an upper end surface 242 which slopes downwards and radially outwards at an angle C in relation to a reference plane located across the 222 longitudinal axis of the collar body.

Relative to a reference plane transverse to the longitudinal axis of the collar body 222, the slope of the end surface 240 is less than the slope of the end surface 236, which, in turn, is less than the slope of the end surface 238. The end surface 242 is substantially parallel to the end surface 238. Preferably, the angle C about 10 degrees, angle A is about 20 degrees and angle B is about 45 degrees.

When the connected milling tubes 30, the fish neck 74, the milling guide 24 and the anchor assembly 22 are guided down the fairing pipe 12 to their predetermined vertical and rotational orientation according to IA, the anchor assembly 22 is hydraulically set into the fairing pipe 12 by forcing pressurized fluid downward through it interior of milling tube 30 and, via tube 62, passages 66 and 68 and tube 70 (see Figs. 3B-3E), into the annular pressure chamber 180 (see Fig. 3E).

Referring now to fig. 4A-6B, which sequentially illustrate the operation of the tubular armature assembly 22, when hydraulic set pressure in the chamber 180 first reaches the predetermined level where the resulting upward compressive force on the lower piston end 168 causes the pins 170 (see Fig. 4B) to break. This in turn causes the pressure in the chamber 180 to drive the piston 160 upwardly from its inlet position along the main spindle 88. The upper end 166 of the piston 160 abuts the annular ledge 156 on the lower sliding member carrier 132 (see Fig. 4A) and forces the mating members, viz. the lower slide member carrier 132, the slide members 40 and 42, the wedge member 112, the upper slide member carrier 98 and the piston holder 158, upward to their positions shown in FIG. 4A and 4B where the upper end 96 of the upper sliding element carrier 98 upwardly abuts the annular elastomeric sealing element 36, axially compresses this, and radially outwardly deforms this into sealing engagement with the inner side wall of the casing 12.

Then, as illustrated in fig. 5A and 5B, a further increase in pressure in the chamber 180 drives the piston 160 further upward along the main spindle 88 until the pins 116 are broken, allowing the upwardly moving piston to drive the upper end 114 of the key member 112 into forced key engagement (via the opposing key and the slide member surface 118,120) with the upper sliding elements 40, thereby radially driving the upper sliding elements 40, against the elastic forces from the associated springs 108, outwards into settling engagement with the casing 12 as shown in fig. 5A. At this point, the lower ends 126 of the wedge element collar fingers 124 are moved upwardly past the spindle pockets 128 and are radially supported by an underlying pocket-free outer side surface portion of the main spindle 88.

Finally, as illustrated in fig. 6A and 6B, a further increase in the pressure in the chamber 180 will break the pins 134 and cause the piston 160 to move further up along the main spindle 88 in a manner that brings the opposing wedge and lower sliding element surfaces 130,139 into forced wedge engagement, whereby the lower sliding elements 42, against the elastically displacing forces from their associated springs 108 are pushed outwards into seating engagement with the suspension tubes 12 as shown in fig. 6A.

With the anchor assembly 22 set in the casing 12 in this manner, the milling tube 30 is released from the tubular upper milling guide end portion 24a (see Fig. 3B) by moving the milling tube 30 up and down to break the pins 60, 60a. The freed milling tube 30 is then lowered and rotated to perform the first milling operation as previously described in connection with fig. IA.

The milling pipe 30 is then removed upwards from the casing 12, leaving the anchor assembly 22, the milling guide 24 and the fish neck 74 firmly placed in the casing, and is prepared for the second milling step as previously described in connection with fig. IB. In particular (as shown in Fig. 7), the extraction collar structure 54 is placed coaxially on the milling tube 30 with breakable mounting screws 244, and the first milling bit 32 (see Fig. IA) is replaced with the second milling bit 32 (see Fig. IB). The milling pipe 30 is then lowered back into the fairing pipe 12, and the second milling step as previously described in connection with fig. IB, is performed.

Referring now to fig. 7, after this second milling step is performed, the milling tube is pushed downward to cause the retrieval collar structure 54 to enter the upper end 224 of the fish neck 74. As the collar structure 54 enters the fish neck 74, the outer collar finger projections 232 are deflected radially inward by an upper inner end surface portion of the fish neck 74 and will then flexibly move radially outward and into the inner fish neck recess 76. The downward insertion movement of the collar structure 54 through the fish neck 74 is automatically limited by the inner fish neck flange 89 which acts as a bearing surface for the lower end 226 of the collar structure 54.

While the relatively shallow lower shoulder surface angle B of the outer collar projections 232 allows the projections 232 to deflect inwardly thereby allowing them to enter the fish neck recess 76, the substantially steeper sloping upper shoulder surface angles A prevent the outer collar finger projections 232 from exiting the recess 76 when the collar structure is pulled up in relation to the anchor assembly 22. As indicated in fig. 7, the upper herringbone inner ledge 78 is substantially parallel to the upper end surfaces 236 of the outer collar finger projections, and the lower herringbone inner ledge 80 is substantially parallel to the lower end surfaces 238 of the outer collar finger projections.

With the "one-way" collar structure 54 thus locked in place in an upper end portion of the fish neck 74, the mill pipe 30 is pushed further down into the casing 12 to break the collar retaining pins 244 thereby releasing the mill pipe 30 from the collar structure 54. It now freed milling tubes 30 are then pulled upwards relative to the collar structure 54, thereby raising the second milling crown 52 (see Fig. 1B) back into a lower end portion of the anchor structure 22, while at the same time the annular milling tube's outer side surface recess 200 (see Fig. 3A) also is moved upwards towards the inner collar finger projections 234 (see fig. 7-9).

As the milling tube's annular ledge 204 upwards meets the downwardly directed annular surfaces 240 of the inner collar finger projections 234, further upward movement of the milling tube relative to the collar structure 54 is stopped, and the upwardly directed retrieval force exerted on the milling tube 30 is transferred to the inner spindle 88 via the collar structure 54, the fish neck 76 and the milling guide member 24. This upward force, now transmitted to the main spindle 88, breaks the pins 184 (see lower part of Fig. 6B), thereby allowing the fish neck 76, the milling guide member 24 and the main spindle 88 to be pulled upwards relative to the rest of the anchor assembly 22, thereby bringing the main spindle 88 back to its original inlet position as shown in fig. 3C-3E.

Furthermore, this allows the upper and lower slide members 40,42 to retract, and the annular seal member 36 to return to its axially uncompressed inlet configuration, thereby freeing the anchor structure 22 and allowing it to be withdrawn from the casing 12 together with the mill pipe 30, the collar structure 54, the fish neck 74 and the milling guide element 24. Advantageously, this allows removal of the anchor structure 22 in conjunction with the second milling step rather than requiring a subsequent separate descent into the casing to secure and then withdraw the anchor assembly.

After the pins 184 are broken, it forms the upward movement of the main spindle 88

in the armature assembly 22 the following release sequence via interaction between the torque pins 142,144,146 and their associated slots 148,150,152 and 154 shown in fig. 3D. First, the upwardly moving inner spindle 88 picks up the torque pins 142, thereby upwardly moving the upper sliding torque carrier 98 and moving the upper sliding members 40 of the upper end 114 of the wedge 112, thereby allowing the upper sliding members to retract. The torque pins 144 are then picked up and moved upwards by the spindle 88 to thereby move the wedge 112 upwards by the lower sliding elements 44 to allow these to be retracted. Finally, the torque pins 146 are picked up to thereby pick up the lower sliding element carrier 132 and eliminate any further relative movement among the sliding elements and wedge members of the assembly 22.

The uniquely configured anchor assembly 22 with the projecting milling guide portion 24, and the retrieval collar structure 54, provides a number of desirable advantages over conventional down-hole milling equipment and associated methods. E.g. which can be seen in fig. 3C-3E, compared to conventionally configured tubular anchor devices (such as packers), the anchor assembly 22 has a relatively thin overall sidewall, with a maximum of three metal element thicknesses along its entire length. Because this is significantly thinner than conventionally constructed down-hole anchor devices, the anchor assembly 22, for a given outer diameter, provides a significantly larger inner diameter which correspondingly provides easier passage through it for various tools and other structures.

In the present invention, this reduced wall thickness property is partially provided by placing the previously described main spindle pockets 104, 128 (see Fig. 3D) in which radially inner side parts of the upper and lower sliding elements 40, 42 are recessed and slidably supported to thereby place the outer sides of the sliding elements further inward into their inlet positions. These pockets 104 and 128, together with specially designed collared wedge elements 112, also enable the release of the opposite upper and lower sliding elements 40,42 corresponding to pulling up of the main spindle 88 in relation to the rest of the anchor assembly 22, as previously described.

In particular, as the main spindle 88 is pulled up relative to the rest of the previously set anchor assembly 22, the upper sliding elements 40 exert (via the provided stepped wedge and sliding element surfaces 118,120) a downwardly directed force on the upper end of the wedge element 112. Because of the collar-arranged configuration of the lower part of the wedge element 112, downwards releasing movement of the wedge element 112 is permitted due to a simultaneous radial inward bending of the collar fingers 124 in the underlying spindle pockets 128, the wedge element 112 being forced to move downwards along the main spindle 88.

The particularly configured and positioned slide-displacing spring elements 108 shown in fig. 10, also contributes to the desirable reduction in overall wall thickness of the armature assembly 22. The shape of these springs, and how they operatively engage their associated sliding elements, allows them to perform their intended displacement function in the narrow annular space between the main spindle 88 and their associated sliding element carrier ( carries 98 or 132).

In addition to these and other desirable configuration features, the anchor assembly 22 also has significantly improved stability and retrievability. E.g. because the gripping teeth of the upper and lower sliding members 40, 42 spiral in opposite directions about the vertical casing axis 46, the positioned anchor assembly 22 is capable of strongly resisting torque generated rotary displacement in any direction relative to the casing 12. Furthermore, as previously described, by using the specially designed one-way tubular collar structure 54, the anchor assembly 22 can be released and retrieved in connection with a milling operation as opposed to having to retrieve the anchor assembly in a subsequent separate retrieval operation that requires an additional down-hole movement .

Additionally, if the intended anchor assembly retrieval technique fails, the design of the anchor assembly 22 allows it to be partially milled out, to allow a secondary retrieval process to be performed, without the anchor assembly falling further down the casing 12 and necessitating a fish-out process. In particular, if the anchor assembly 22 becomes stuck in the casing pipe 12 so that it cannot be pulled out on the milling pipe 30, the upward force on the milling pipe 30 can simply be increased to the point where an annular radially thinned safety breaking part 24c is internally formed in the lower milling guide end part 24a ( see fig. 3C) breaks into pieces, in which case the fish neck 74 and the part of the milling guide 24 located above the threaded connection will be pulled up onto the milling pipe 30, leaving the anchor assembly 22 still seated in the casing 12. A suitable milling device can then be lowered in the casing 12 and is used to mill away the upper part of the remaining anchor assembly 22 to just below the upper sliding elements 40.

As can be seen in fig. 3D, the gripping teeth 140 on the lower sliders 42, in cross-section, are angled downward so that from a vertical standpoint, the lower sliders 42 serve primarily to prevent downward movement of the seated anchor assembly 22 through the casing 12. Accordingly, after the upper sliders 42 has been milled away, and the milling device has been removed from the casing 12, the remaining lower sliding elements 42 hold the remainder of the anchor assembly 22 in place and prevent it from falling further into the casing 12. Remains of the anchor assembly 22 can then be removed from the casing 12 by use of e.g., conventional spear device.

Claims (10)

1. Milling device for underground borehole casing, characterized by: a tubular anchor assembly having an upper end portion which is coaxially and releasably located in the casing, said tubular anchor assembly including: a tubular inner spindle with an outer side surface, a tubular sliding element carrier coaxially surrounding the inner spindle in a radially outwardly spaced relationship therewith, said sliding element carrier having a circumferentially spaced series of sidewall sliding element windows and outwardly adjacent an annular space between the inner spindle and the sliding element carrier, a circumferentially spaced series of sliders disposed in the annular space, with radially outer portions of the sliders received in the slider windows for movement therethrough between radially retracted and radially advanced positions, a thrust structure operative to elastically push the sliders to their radially retracted positions, and a set structure operative to force the sliding members from their radially retracted positions to their radially advanced positions; a milling guide member having a lower end portion connected to the upper end portion of the tubular anchor assembly, and a tubular upper end portion; and a tubular retrieval element coaxially placed on a milling tube and coaxially lockable in a tubular element coaxially placed on the upper end part of the milling guide element. 2. Milling device for underground borehole delivery pipe according to claim 1, characterized in that the outer side surface of the tubular inner spindle has a circumferentially separated series of elongated axially located pockets, and the sliding elements have radial inner parts engaged in the pockets for sliding movement along their length. 3. Milling device for underground borehole ventilation pipe according to claim 1, characterized in that the set structure includes a pressure chamber in the tubular anchor assembly, and the device further includes a pressurized fluid passage structure situated from the inner side of the tubular milling guide element's upper end part through the milling guide element and the tubular anchor assembly, and into the pressure chamber. 4. Milling device for underground borehole casing according to claim 1, characterized in that the set construction includes: a tubular wedge element coaxially slidable and circumscribing the inner spindle, which wedge element has a circumferentially spaced separated series of sidewall slits axially inward through one end thereof and defining a circumferentially spaced spaced series of collar finger portions on the tubular wedge member, said collar finger portions having outer ends axially opposite the end portions of said sliding members and stepwise engaging therewith to drive said sliding members from their radially retracted positions to their radially advanced positions. 5. Milling device for underground borehole bearing pipe according to claim 2, characterized in that: the set construction includes a tubular wedge element coaxially and slidably surrounding the inner spindle, which wedge element has a circumferentially spaced separated series of sidewall slots axially inward through one end thereof and defining a circumferentially spaced separate series of collar finger portions in the tubular wedge member, said collar finger portions having outer ends axially opposite to the end portions of the sliding members and stepwise engaging therewith to drive the sliding members from their radially retracted positions to their radially advanced positions, and that the inner spindle, the sliding members and the wedge member are relatively movable in axial directions between (1) a set position where the outer ends of the collar finger members outwardly overlie and are radially supported by areas of the inner spindle without pockets, and step-down meets the end members of the sliding member nts, and (2) a release position where the outer ends of the collar finger portions lie above the inner spindle pockets and can be radially deflected into them corresponding to an axially directed engaging force between the outer ends of the collar finger portions and the end portions of the slide members. 6. Milling device for underground borehole suspension pipe according to claim 1, characterized by: a circumferentially separated series of arc-shaped, elongated spring elements deposited in the annular space between the inner spindle and the sliding element carrier, which elastically displaces the sliding elements towards their retracted positions, which spring elements are intertwined with the sliding elements and has longitudinally centrally located parts attached to the sliding element carrier, where each sliding element engages with the end parts of the two spring elements on opposite sides of these along the circumference. 7. Milling device for underground borehole guide pipe according to claim 6, characterized in that the spring elements are concavely curved towards the inner spindle. 8. Milling device for underground borehole casing according to claim 7, characterized in that the sliding elements have radial outer sides where recesses are formed, and the end parts of the spring elements extend into the recesses. 9. Milling device for underground borehole casing according to claim 1, characterized in that the device further includes a release structure operative to shift the inner tubular mandrel upwardly relative to the tubular slider carrier to allow the sliders to be moved from their extended positions to their retracted positions to thereby release the anchor assembly from the casing, and the milling guide structure has a milling crown deflecting surface positioned and angled relative to the longitudinal axis of the tubular anchor assembly. 10. Milling device for underground borehole delivery pipe according to claim 9, characterized in that the device further includes: a milling pipe with a lower end and a radially projecting impact surface located above the lower end of the milling pipe, a part of the milling pipe above its lower end is coaxially placed on the tubular retrieval structure, and a milling bit positioned on the lower end of the milling pipe, and the milling pipe, with the tubular anchor assembly coaxially locked in the fairing pipe, are operative to perform a milling and anchor retrieval operation in the fairing pipe with the following sequence: (1) plunging through the fairing tube and the tubular upper end portion of the rotary driven milling guide assembly to cause the milling bit to engage and laterally deflect against a sidewall portion of the fairing tube at the milling guide deflecting surface; (2) further immersion for insertion and operative locking of the tubular retrieval structure in the tubular upper end portion of the milling guide structure, and (3) upwardly withdrawing from the guide tube to sequentially release the milling tube from the tubular retrieval structure, upwardly bringing the milling tube abutment surface into abutting relationship with the retrieval structure thereby forcing movement of the inner spindle relative to the tubular slide member carrier and activating the engagement structure, and withdrawing the released anchor structure , together with the milling guide structure, out of the fairing.