AU2003203949B2 - Method for forming a window in a tubular and apparatus for use in said method - Google Patents

Description

P/00/011 Regulation 3.2

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT Invention Title: Method for forming a window in a tubular and apparatus for use in said method The following statement is a full description of this invention, including the best method of performing it known to us: Freehills Carter Smith Beadle Melbourne\00428751 I Printed 30 April 2003(12:27) page 2 Freehills Carter Smith Beadle Melbourne\00428751 i Printed 30 April 2003 (12:27) page 2 M&C Folio No P52578AU METHOD FOR FORMING A WINDOW IN A TUBULAR AND APPARATUS FOR USE IN SAID METHOD This invention relates to a method for forming a window in a tubular and an apparatus for use in said method.

Conventionally, when it is desired to form a window in a tubular, for example a length of casing, a whipstock is lowered down the tubular and set in position. A mill is then lowered down the tubular on a work string and rotated. The whipstock has a long tapered concave so that part of the weight of the work string biases the mill against the tubular to enable the mill to cut into the tubular and form the desired window.

Whilst whipstocks work well in long straight tubulars they have two problems. Firstly, standard whipstocks cannot be used where the tubular passes around a tight radius.

Secondly, it is normally necessary to provide the tapered surface of the whipstock with a sacrificial layer of material, for example brass, which is eroded by the mill and which has to be replaced each time the whipstock is used.

One solution to forming a window in a tubular which passes around a tight radius is to position the mill in the desired position and rotate it until the mill eventually cuts through the tubular. This relies on sufficient radial pressure being provided by the work string and can be a long and tedious process.

According to a first aspect of the present invention there is provided a method for milling an opening in a tubular in a wellbore, the method comprising: installing a mill guide in the tubular at a desired milling location, the mill guide comprising a hollow straight cylindrical bodyhaving an axial bore therethrough, an upper end with an upper end opening and a lower end with a lower end opening, the lower end having a first inside surface and a second inside surface extending along straight lines parallel to one another and to the axis of the bore and diametrically opposite one another, the first inside surface being shorter than the second inside surface, inserting a mill through the tubular and the bore of the mill guide so that the mill is in contact with the second inside M&C Folio No P52578AU surface and is directed by said contact against the tubular at the desired milling location adjacent the lower end opening, and milling an opening in the tubular.

According to a second aspect of the present invention there is provided a method for milling an opening in a tubular in a wellbore, the method comprising: installing a mill guide in the tubular at a desired milling location, the tubular having a whipstock installed therein, the whipstock having a concave member with a slanted portion for diverting a mill in a desired direction, and the mill guide comprising: a hollow cylindrical body having a bore therethrough, an upper end with an upper end opening and a lower end with a lower end opening, the lower end having a diverting portion shaped to correspond to the shape of the concave member of the whipstock, the lower end of the mill guide being movable to contact the concave member and protect it, inserting a mill through the tubular and bore of the mill guide so that the mill contacts the tubular at the desired milling location while the mill contacts and is directed toward the tubular by the mill guide, and milling an opening in the tubular.

According to a third aspect of the present invention there is provided a mill guide for use within a tubular in a wellbore, the mill guide comprising: a hollow straight cylindrical body having an axial bore therethrough, an upper end with an upper end opening and a lower end with a lower end opening, the lower end having a first inside surface and a second inside surface extending along straight lines parallel to one another and to the axis of the bore and diametrically opposite one another, the first inside surface being shorter than the second inside surface so that a mill inserted through the bore and disposed at the lower end is free on one side thereof to mill the tubular whilst simultaneously being in contact with the second inside surface on the side opposite said one side.

According to a fourth aspect of the present invention there is provided a mill guide for use within a tubular in a wellbore in association with a whipstock having a concave member with a slanted portion for diverting the mill to mill the tubular on one side thereof, the mill guide comprising: a hollow cylindrical body having a bore therethrough, an upper end with an upper end opening and a lower end with a lower end M&C Folio No P52578AU opening, the lower end having a diverting portion shaped to correspond to the shape of the slanted portion of the whipstock and positioned to overlie the slanted portion so that the mill contacts the diverting portion whilst milling the tubular on said one side and the slanted portion is protected.

For a better understanding of the present invention reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1A is a schematic side view, partially in cross-section, showing a mill attempting to cut a window in a length of casing using one prior art method; Figure 1B is a schematic side view, partially in cross-section, showing a mill attempting to cut a window in a different length of casing using the same prior art method; Figure 2A is a side view, in cross-section, showing a first embodiment of an apparatus in accordance with the present invention anchored in a length of casing; Figure 2B is a section taken on line 2B-2B of Figure 2A; Figure 3 is a view similar to Figure 2A but showing the apparatus in use; Figure 4 is a side view, in cross-section, showing a second embodiment of an apparatus in accordance with the present invention in use; Figure 5A is a perspective view of a whipstock assembly for use with an embodiment of the present invention; Figure 5B is a cross-section, on an enlarged scale, of a connection apparatus which forms part of the whipstock assembly shown in Figure Figure 5C is a section taken on line 5C-5C of Figure M&C Folio No P52578AU Figure 5D is a side view of one component of the connection apparatus shown in Figure Figure 6A is a side view of a first example of a mill for use with an embodiment of the present invention; Figure 6B is a bottom plan view of the mill shown in Figure 6A; Figure 6C is a view similar to Figure 6A but with part cut away; Figure 6D is a view taken on line 6D-6D of Figure 6C; Figure 7A is a side view of a second example of a mill for use with an embodiment of the present invention with part cut away; and Figure 7B is a bottom plan view of the mill shown in Figure 7A.

Referring to Figure 1A of the drawings there is shown a length of casing C. A mill M is mounted on the bottom of a drill string P and abuts the casing C at a point T.

When the drill, string P is rotated the mill M will rub against the inside of the casing C.

However, it will be appreciated that because of the inherent flexibility of the drill string P the mill M is not biased significantly against the casing C and the formation of a window in an acceptable period of time is most unlikely.

Referring now to Figure 1B of the drawings there is shown a length of casing S. A mill L is mounted on the bottom of the drill string R and abuts the casing S at a point N in a curved portion V of the casing S. When the drill string R is rotated the mill L will rub against the inside of the casing S. Because of the curvature of the casing S the force exerted by the mill L on the casing S will be greater than that of the mill M against the casing C in Figure 1A. However, forming a window could still take a very long time.

M&C Folio No P52578AU Referring now to Figures 2A, 2B and 3 there is shown a first embodiment of an apparatus in accordance with the present invention which is generally identified by the reference numeral The apparatus 10 comprises a hollow cylindrical body 9 having a bore 8 which extends therethrough from an open top end 7 to an open bottom end 6.

The apparatus 10 is positioned in a length of casing 5 and retained therein by an anchor 4.

The lower section 3 of the apparatus 10 is shaped so that the open bottom end 6 overlies the curved portion 1 of the casing 5 as shown.

In use, the apparatus 10 is conveniently lowered down the casing 5 on a work string or on coiled tubing and the anchor 4 can conveniently be mechanically actuated.

Once the apparatus 10 is in position a mill 11 is lowered down the casing 5 on a drill string 12. The mill 11 enters the apparatus 10 through the open top end 7, passes downwardly through the bore 8 and comes to rest on the curved portion of the casing As shown in Figure 3 the mill 11 is trapped between the side 30 of the apparatus 10 and the casing 5 and consequently part of the weight of the drill string 12 biases the mill 11 against the casing When the mill 11 is rotated it cuts into the casing 5 forming a window therein as shown in Figure 3. The mill 11 is provided with an elongate body 13 which remains in contact with the side 30 of the apparatus 10 whilst at least the initial portion,; preferably at least a quarter, of the axial length of the first window is formed.

It will be appreciated that as the window is cut the mill 11 rotates against the section If desired the section 30 may be provided with a sacrificial bearing layer which can be replaced after the apparatus 10 is retrieved. Alternatively, the section 30 may be thickened or hardened if desired.

M&C Folio No P52578AU Various modifications to the apparatus described are envisaged, for example the shape of the lower section 3 of the apparatus 10 (and hence the shape of the open bottom end 6) could be varied to facilitate the formation of the window in the general shape desired.

Turning now to Figure 4, there is shown a second embodiment of an apparatus in accordance with the present invention. The apparatus, which is generally identified by the reference numeral 15, has a hollow cylindrical body 16 with a bore 19 therethrough which extends from an open top end 17 to an open bottom end 18 which is generally perpendicular to the plane of the open top end 17. The apparatus 15 has a slanted side wall 21 which terminates at the bottom of the apparatus In Figure 4 the apparatus 15 is shown resting on the concave 24 of the whipstock In use, a mill 25 is lowered through the apparatus 15 on a drill string 26 and is deflected into contact with the wall of the casing 22 by the slanted side wall 21 which acts as a sacrificial bearing for the concave 24 of the whipstock 20. The weight of the drill string 26 acting downwardly on the mill 25 biases the mill 25 into engagement with the wall of the casing 22 and subsequent rotation of the mill 25 forms the window 27.

In this embodiment the whipstock 20 supports the apparatus 15 which can thus be made of comparatively light material. However, the whipstock 20 could conceivably be dispensed with if the apparatus 15 were made sufficiently strong.

If desired the apparatus 15 could be removably attached to the whipstock 20 and, if desired, could be lowered into position with the whipstock 20 before use.

It should also be appreciated that, whilst an anchor similar to the anchor 4 is highly desirable, it may not be essential in all applications, for example where the apparatus is attached to a whipstock.

M&C Folio No P52578AU If a window is formed with the use of a whipstock then eventually it becomes necessary to remove the whipstock and the anchor to which it is attached. At one extreme this can be effected by simply drilling out both the whipstock and the anchor. However, whipstocks are relatively expensive to construct and recovery of the whipstock is desirable.

Referring now to Figure 5A there is shown a whipstock assembly which is generally identified by the reference numeral 200.

The whipstock assembly 200 comprises a whipstock 202 having a concave 204, an anchor 208 and a connection apparatus 206.

The whipstock 202 and the anchor 208 are of essentially conventional construction, the anchor 208 being described in US A 5 341 873, co-owned with the present invention.

As shown in Figure 5B, the connection apparatus 206 comprises an upper member 222 and a (lower) fishing member 216 which are connected by a shear pin 210 designed to fail at about 43,200kg (950001bs) and which extends through a hole 212 in the neck 214 of the fishing member 216 and the holes 226 in the lower portion of the upper member 222.

The top of the upper member 222 is provided with a recess 228 which receives a stub which projects downwardly from the bottom of the whipstock 202. The whipstock 202 is then welded to the upper member 222 circumjacent the stub.

The lower end of the fishing member 216 is provided with a stub 218 which is welded to the anchor 208.

It will be noted that the fishing member 216 is provided with a fluid relief channel 211 which extends along the fishing member 216 and opens into the cavity 224 which is formed in the upper member 222. The upper member 222 is also provided with a fluid relief channel 230 which communicates with the cavity 224.

M&C Folio No P52578AU In use, when it is desired to remove the whipstock assembly 200 a fishing tool having a hook is lowered until it reaches the concave 204. The hook is then manipulated until it enters the rectangular slot in the concave 204. The fishing tool is then lifted. This causes the shear pin 210 to fail and the whipstock 202 can then be recovered, separation of the upper member 222 from the fishing member 216 being facilitated by the fluid relief channel 230.

Once the whipstock 202 and the upper member 222 have been recovered another fishing tool can be lowered to clamp onto the fishing member 216 for retrieval of the anchor 208. If desired the fluid relief channel 211 may be connected to a mechanism to release the anchor 208 although the anchor 208 could be provided with a variety of mechanical or hydraulic release devices.

Once the anchor 208 is released it can be lifted to the surface and recovered.

(As used herein the term "fishing member" refers to any member which can be gripped for removal of the anchor and is not limited to members having flanges and/or collars which are particularly adapted to be retrieved by grapples.) Mills tend to be judged by the speed at which they cut. When cutting a window it is not unusual for the performance of most mills to suddenly drop and later recover. This has been attributed to various reasons including "coring". Coring occurs when the centre of the mill is over the wall of the casing and the relative speed between the mill and the wall is minimal (theoretically nil).

Referring now to Figures 6A to 6D there is shown a mill which is generally identified by the reference numeral 400. The mill 400 comprises a body 402 having an upper threaded end 404 and a plurality of (optional) blades 408 on the lower end 412 thereof.

The leading faces of the blades 408 and the bottom of the mill 400 are covered with cutting and/or grinding material, for example milling inserts with or without chipbreakers and/or tungsten carbide chips.

M&C Folio No P52578AU A first fluid flow bore 406 (Figure 6C) extends from the top of the body 402 and divides into a single second fluid flow bore which is effectively an extension of the first fluid flow bore 406 (but of smaller diameter than the first fluid flow bore 406), and a plurality of inclined flow bores 16 which are inclined downwardly and outwardly from the first fluid flow bore 406 and are of smaller diameter than both the first fluid flow bore 406 and the second fluid flow bore.

The second fluid flow bore opens on the rotational axis of the mill 400 and is provided internally with cutting and/or grinding material similar to the bottom of the mill 400.

In use, drilling mud is pumped down the first fluid flow bore 406 whilst the mill 400 is rotated. It has been found that the presence of the cutting and/or grinding material on the inside of the second fluid flow bore produces a significant increase in drilling efficiency. It is suspected that by applying cutting and/or grinding material to the inside of the inclined fluid flow bores 16 a further small increase in efficiency may be obtained.

Referring now to Figures 7A and 7B there is shown a mill which is generally identified by the reference numeral 420. The mill 420 is generally similar to the mill 400 and comprises a body 422 having an upper threaded end 424. However, the mill 420 does not have any blades. The bottom of the mill and the lower part of the side thereof are covered with grinding material in the form of tungsten carbide chips which are brazed thereto.

A first fluid flow bore 426 extends from the top of the body 422 and divides into a single second fluid flow bore 438 which is effectively:an extension of the first fluid flow bore 426 (but smaller in diameter), and a plurality of inclined flow bores 428 that are of smaller diameter than both the first fluid flow bore 426 and the second fluid flow bore 438.

The second fluid flow bore 438 is provided internally with grinding material as shown.

P04752238.

9a Reference to any prior art in the specification is not, and should not be taken as, an U acknowledgment, or any form of suggestion, that this prior art forms part of the common general knowledge in Australia or any other jurisdiction or that this prior art could reasonably be expected to be ascertained, understood and regarded as relevant by a person skilled in the art.

Claims (16)

1. A method for milling an opening in a tubular in a wellbore, the method comprising: installing a mill guide in the tubular at a desired milling location, the mill guide comprising a hollow straight cylindrical body having an axial bore therethrough, an upper end with an upper end opening and a lower end with a lower end opening, the lower end having a first inside surface and a second inside surface extending along straight lines parallel to one another and to Mc, the axis of the bore and diametrically opposite one another, the first inside surface being shorter C than the second inside surface, N inserting a mill through the tubular and the bore of the mill guide so that the mill is in contact with the second inside surface and is directed by said contact against the tubular at the desired milling location adjacent the lower end opening, and milling an opening in the tubular.

2. A method for milling an opening in a tubular in a wellbore, the method comprising: installing a mill guide in the tubular at a desired milling location, the tubular having a whipstock installed therein, the whipstock having a concave member with a slanted portion for diverting a mill in a desired direction, and the mill guide comprising: a hollow cylindrical body having a bore therethrough, an upper end with an upper end opening and a lower end with a lower end opening, the lower end having a diverting portion shaped to correspond to the shape of the concave member of the whipstock, the lower end of the mill guide being movable to contact the concave member and protect it, inserting a mill through the tubular and bore of the mill guide so that the mill contacts the tubular at the desired milling location while the mill contacts and is directed toward the tubular by the mill guide, and milling an opening in the tubular.

3. A method according to claim 2, further comprising installing the whipstock in the tubular prior to installing the mill guide. P04752238 11 S

4 A method according to claim 1, 2 or 3, wherein said tubular is a length of casing.

A method according to any preceding claim, including the step of anchoring the mill guide in said tubular prior to introducing said mill therein.

6. A method according to any preceding claim, including the step of removing the mill from the tubular after forming the window. C

7. A method according to any preceding claim, including the step of removing the mill N, guide from the tubular after forming the window. S

8. A method according to claim 6 or 7, including the step of removing the mill and the mill guide from the tubular together. l0

9. A mill guide for use within a tubular in a wellbore, the mill guide comprising: a hollow straight cylindrical body having an axial bore therethrough, an upper end with an upper end opening and a lower end with a lower end opening, the lower end having a first inside surface and a second inside surface extending along straight lines parallel to one another and to the axis of the bore and diametrically opposite one another, the first inside surface being shorter than the second inside surface so that a mill inserted through the bore and disposed at the lower end is free on one side thereof to mill the tubular whilst simultaneously being in contact with the second inside surface on the side opposite said one side.

A mill guide according to claim 9, wherein the lower end is shaped to correspond to an interior shaped portion of the tubular.

11. A mill guide according to claim 9 or 10, wherein said second inside surface is provided with a sacrificial bearing layer.

12. A mill guide according to claim 9 or 10, wherein said second inside surface is thickened or hardened.

13. A mill guide for use within a tubular in a wellbore in association with a whipstock having a concave member with a slanted portion for diverting the mill to mill the tubular on one side thereof, the mill guide comprising: 004752238 12 a hollow cylindrical body having a bore therethrough, an upper end with an upper end opening and a lower end with a lower end opening, the lower end having a diverting portion shaped to correspond to the shape of the slanted portion of the whipstock and positioned to overlie the slanted portion so that the mill contacts the diverting portion whilst milling the tubular on said one side and the slanted portion is protected.

14. A mill guide according to any one of claims 9 to 13, further comprising an anchor for anchoring the mill guide in the tubular.

A method for milling an opening in a tubular in a wellbore comprising the steps substantially as hereinbefore described with reference to the drawings.

16. A mill guide substantially as hereinbefore described with reference to the drawings. Dated 15 December 2005 Freehills Patent Trade Mark Attorneys Patent Trade Mark Attorneys for the Applicant Weatherford/Lamb Inc