TOOL FOR MAKING AN OPENING IN A TUBULAR IN A WELLBORE

Abstract: A tool for forming a window in a casing (C), with a starting mill (520) having a nose which comprises cutting apparatus (525) covered by a protective layer (527). The protective layer acts as a bearing as the mill (520) travels down the whipstock (505) and helps urge the milling material (522) into the casing to form the window. The protective layer (527) is eroded as the mill (520) travels down the whipstock and the cutting apparatus (525) is exposed to allow the cutting apparatus (525) to cut through the casing and into the formation beyond.

Description: TOOL FOR MAKING AN OPENING IN A TUBULAR IN A ELLBORE This invention relates to a tool for making an opening in a tubular in a wellbore. During the construction of oil and gas wells a hole is bored in the ground. The hole is then lined with a string of casing which is often cemented in place by an annulus of cement. In order to extend the catchment area of a well it is becoming increasingly common to provide laterals. This involves forming a window in the casing and then drilling a new hole in the formation surrounding the window. The new hole is often provided with its own liner which itself may be provided with a lateral at a later date. At the present time laterals are formed by inserting a whipstock in the casing and using this to bias a rotating mill against the casing to form a window therein. The edges of the window are then usually enlarged and shaped by another mill. Typically, the window will be formed by a tool string which has a starting mill and a water melon mill. After the window has been formed the starting mill and the water melon mill are brought to the surface and replaced by a formation drill for cutting into the formation. The formation drill is then lowered and the lateral drilled. One of the difficulties encountered when forming a window is ensuring that the starting mill cuts through the casing and does not simply demolish the whipstock. One solution to this problem has been to provide the starting mill with a smooth conical nose section which engages and rotates on the concave of the whipstock whilst biasing the cutting elements of the mill away from the concave and urging them into engagement with the wall of the casing. Whilst this works very effectively milling must cease when the tip of the smooth conical nose reaches the intersection between the concave and the casing. It has been suggested that this problem can be overcome by detaching the smooth conical nose from the mill after the mill has penetrated the casing, at which point serious damage to the whipstock is unlikely. The present invention is concerned with a different approach to this problem. According to the present invention there is provi- ded a tool for making an opening in a tubular in a well- bore, which tool comprises a mill having a body portion and a nose portion, characterised in that the nose portion includes cutting apparatus at least a portion of which has thereon a material to be worn away thereby exposing the cutting apparatus for cutting the tubular. Other features of the invention are set out in Claim 2 et seq. For a better understanding of the present invention reference will now be made, by way of example, to the accompanying drawings, in which: - Fig. 1 is a side view in cross-section, showing a first embodiment of a tool in accordance with the present invention incorporated in a tool string in a length of casing; Fig. 2 is an enlarged view of part of the tool string of Fig. 1; Fig. 3 shows a window milled in the casing and a lateral extending therefrom; Fig. 4 is a side view of the tool shown in Fig. 1 prior to application of its protective layer; Fig. 5 is an end view of the tool of Fig. 4; Fig. 6 is an enlargement of part of the tool as shown in Fig. 5; Fig. 7 is an end view of the tool of Fig. 1; Fig. 8 is a side view in cross-section of one part of the tool shown in Fig. 7; Fig. 9 is an enlargement of part of the tool shown in Fig. 8; Fig. 10 is a side view of a sacrificial element which forms part of the tool string shown in Fig. 1; Fig. 11 is a front view of the sacrificial element of Fig. 10; Fig. 12 is a top view of the sacrificial element of Fig. 10; Fig. 13 is a cross-section view along line XIII- XIII of Fig. 11; Fig. 14 is a fragmentary perspective view of an alternative sacrificial element; Fig. 15 is a side view of a second embodiment of a tool in accordance with the present invention; Fig. 16 is a side view of a third embodiment of a tool according to the present invention; Fig. 17 is a side view of a fourth embodiment of a mill according to the present invention; Fig. 18 is a side view of a blade with a taper member; Fig. 19 is a side view of another blade with a taper member; Fig. 20 is a bottom view of a mill body; Fig. 21 is a bottom view of another mill body. As shown in Fig. 1 a tool string 500 comprises an upper water melon mill 501 which is connected to a lower water melon mill 503 by a flexible sub 502. The lower water melon mill 503 is connected to a tool 520 in accordance with the present invention by a flexible sub 504. The tool 520 is releasably connected to a sacrificial element 510 which is connected to a whipstock 505. The whipstock 505 is anchored in a casing string C in a wellbore, by an anchor A. As shown in Fig. 2, the tool 520 has side blades 521 dressed with matrix milling material 522. The exterior surfaces of the side blades 521 are smooth (e.g. ground smooth with a grinder). The matrix milling material 522 may be any known mill dressing material applied in any known manner. Matrix milling material 523 covers lower ends 524 of the side blades 521. Blades 525 (see Fig. 4) on the nose 526 of the tool 520 form a cutting apparatus which is initially laterally protected with a protective layer of a relatively soft material 527 (e.g. but not limited to bearing material such as brass) and the leading face of which is preferably partially or wholly covered with matrix milling material 523. The protective layer forms a bearing which engages the concave of the whipstock as will be explained hereinafter. Fluid under pressure, pumped from the surface, exits through ports 528 at the lower ends 524 of the side blades 521. To initially isolate, cover, and/or protect the blades 525 or apparatus 555, instead of separate and distinct members or bodies 527, a cylindrical member (closed off or open at the bottom, a ring, or a hollow cap may be used, either secured immovably to the body, blades, or apparatus or rotatably secured thereto. The material 523 acts like a bearing or bearing material may be used in its place so that the side portion of tool acts as a bearing. Two fingers 511 extend upwardly from a body 512 of the sacrificial element 510. The fingers 511 are re- leasably connected to the mill 520 by shear bolts. Knobs 513 project from the body 512. From top to bottom the knobs 513 project increasingly from the body 512 to correspond to a taper of the whipstock 505. Alternatively a series of grooves (up-and-down or side-to-side ) may be used instead of the knobs 513. It is within the scope of this invention to employ at least one recess, a series of recesses, or a series of recesses at angles to each other to reduce the amount of material in the sacrificial element 510. The sacrificial element 510 may be welded or bolted to the whipstock 505. In one aspect the sacrificial element 510 is made of millable material or bearing material (e.g. bearing bronze). In milling down the body 512 of the sacrificial element 510, the mill 520 mills the body 512 more easily than if material were present between the knobs 513. Instead of an integral solid remainder of the body 512 left after the mill-drill tool 520 has passed, small pieces of the body 512 (knobs or knobs with portions of the body 512) are left rather than a floppy piece which might impede operations or large pieces which may be difficult to mill or to circulate. Small pieces or chunks may fall down and/or fall away following milling and are more easily circulated away from the milling location and/or out of the hole. Fig. 14 shows an alternative sacrificial element 680 with a body 681 and fingers 682 projecting from a ring 683. One or more of the fingers 682 are releasably connectable to a tool in a manner similar to that as described for the sacrificial element 510. The sacrificial element 680 is made of steel, plastic, metal mill- able or drillable material, or bearing material in certain embodiments, or any of the materials out of which the sacrificial element 510 is made. A knob structure (see knobs 513 of the sacrificial element 510) may be provided for the sacrificial element 680. As is the sacrificial element 510, the sacrificial element 680 is securable to a whipstock and the body 681 (shown partially) may extend for any desired and suitable length along such a whipstock and the body 681 may have any desired taper to correspond to the whipstock on one side and to direct cutting apparatus on the other side. The ring 683 is sized, in one aspect, so the nose or projecting lower end of the tool may extend into the ring and, in one aspect, contact the ring for stability. The ring also strengthens the sacrificial element 680. Fig. 15 shows a tool 550 (similar to the mill-drill 520 with like parts bearing the same reference numerals). A cutting apparatus 555, shown schematically by a dotted line, is initially covered by a material 557 which may be eroded by contact with a tubular and/or formation. In one aspect, as with the tool 520, the material is not worn away until the material 557 is trapped between the concave and the tubular. By using bearing material as the material 557 movement of the nose down and against the sacrificial element (e.g. sacrificial element 510) is facilitated whilst inhibiting damage thereto. The cutting apparatus 555 may be any suitable known formation drilling apparatus. The matrix material may incorporate known milling inserts or cutting elements, with or without chipbreakers, in any known pattern or array. Fig. 2 shows the tool string 500 in a cased well- bore C with various positions of the tool 520 shown in dotted lines. Initially (as shown) the tool 520 has not been released from the fingers 511. Following release from the fingers 511 and downward movement, the lower ends 524 of the side blades 521 mill away a portion of the sacrificial element 510 including the fingers 511. The outer surface of the material 527 then engages the concave of the whipstock. The material 527 rotates on the sacrificial element 511 whilst biasing the mill towards the wall of the casing. The outer blade surfaces have moved to contact at point A an inner surface S of the casing C. A distance d is, preferably, of sufficient extent that the lower blade surface along the distance d is wider than the casing thickness t. Although the mill is biased towards the casing the blades mill down the sacrificial element 510, leaving "chunks" thereof behind as the tool 520 moves onto the whipstock 505 and blades reach the outer surface of the casing at point B. The outer blade surfaces which contact the whipstock are, preferably, smooth to facilitate movement of the mill- drill tool 520 down the whipstock 505 and to minimize milling of the whipstock 505 itself. The tool 520 continues downwardly (e.g. rotated all the while by a surface rotary or by a downhole motor in the string at some point above the tool ) , milling away the sacrificial element 510, moving down the whipstock 505, milling through the casing C, to a point C at which outer surface of the material 527 of the nose 526 contacts the inner surface of the casing C. At this point the mater- ial 527 begins to be eroded exposing the cutting apparatus 525. The tool 520 continues to mill down the casing to a point D at which the nose 526 begins to exit the casing C and the tool 520 begins to cut the formation outside the casing C. The tool moves down the whipstock 505 forming the beginning of a lateral. A lateral L thus formed is shown in Fig. 27C. Such a lateral may be any desired length. When a full gauge body is used for the tool 520, the resulting window and lateral wellbore are full gauge, i.e. a desired diameter and no further milling is required as opposed to certain prior art systems using a tool which is less than full gauge, e.g. an under gauge lead mill, producing a "rathole" of a smaller diameter than the diameter of the bore above the rathole which must be milled further to enlarge it to the desired diameter often requiring one or more additional trips into the wellbore or requiring the drilling of an excessively long rathole. By using a system as described herein, a completed lateral of a desired diameter can be achieved which extends only a relatively short distance from the casing; i.e., the extent to which the lateral's initial opening extends into the formation can be relatively small which facilitates the production of a lateral at a desired angle to the primary wellbore. With certain prior art systems which do not use a full gauge tool body and which do employ narrower mills, e.g. under gauge lead mills, when the desired window is completed the lateral wellbore ( including the portion of the formation of narrow diameter into which the starting mill has moved) may be ten, fifteen, twenty or more feet long. It is relatively difficult to produce a lateral wellbore turned at a desired angle from such a relative- ly long initial lateral wellbore. With the system described with reference to the drawings a uniform diameter relatively short full gauge initial lateral can be produced in the formation in a single trip. In one aspect such an initial lateral wellbore is five feet long or less, three feet long or less, two feet long or less, or about one and a half feet long. It is also within the scope of this invention to use multiple blade sets, i.e. one or more additional sets of blades above the tool 520 e.g. as described below. The sacrificial element 510 may be made of plastic, fiberglass, composite, fiber-reinforced plastic, cement, ceramic, metal (steel, mild steel, zinc, aluminium, zinc alloy, aluminium alloy), metal alloys, brass, bronze or metal matrix composites. Fig. 16 shows a mill 3300 according to the present invention with a body 3302 and a plurality of blades 3304. Associated with each blade 3304 is a taper member 3306 which is secured to the body 3302, or to the blade 3304, or to both, either with an adhesive such as epoxy, with connectors such as screws, bolts, or Velcro straps or pieces, or by a mating fit of parts such as tongue-and-groove. The taper members may be made of any suitable wood, plastic, composite, foam, metal, ceramic or cement . In certain embodiments the taper members are affixed to the mill so that upon contact of the lower point of the mill blades with the casing to be milled, the taper members break away so that milling is not impeded . Fig. 17 shows a mill 3330 according to the present invention with a body 3332 and a plurality of blades 3334. A taper device 3336 is secured around the mill 3330 or formed integrally thereon. The taper device 3336 extends around the entire circumference of the mill 3330 beneath the blades 3334 and facilitates movement of the mill 3330 through tubulars. The taper device 3336 may be a two-piece snap-on or bolt-on device and may be made of the same material as the taper member 3306. Fig. 18 shows a blade-taper member combination with a blade 3340 having a groove 3342 and a taper member 3344 with a tongue 3346. The tongue 3346 is received in the groove 3342 to facilitate securement of the taper member 3344 to the blade 3340. Optionally, an epoxy or other adhesive may be used to glue the taper member to the blade, to a mill body, or to both. The tongue and groove may be dovetail shaped. Fig. 19 shows a blade-taper member combination with a blade 3350 and a taper member 3352 with a recess 3354. The blade 3350 is received in and held in the recess 3354. Optionally an adhesive may be used to enhance securement of the taper member 3352 to the blade, to the mill, or to both. Fig. 20 shows a mill body 3370 (like the bodies of the mills shown in Fig. 5A, 10, and 11 of pending U.S. Application Ser. No. 08/642,118 filed 5/2/96), with a series of grooves 3372 therein which extend longitudinally on the mill body and are sized, configured, and disposed to receive and hold a taper member as shown in Fig. 16, Fig. 18, or Fig. 19. Such a mill body may be used instead of or in combination with any previously- described taper securement means. Fig. 21 shows a mill body 3380 (like the bodies of the mills mentioned in the previous paragraph), with a series of dovetail grooves 3382 therein which extend longitudinally on the mill body and are sized, confi- gured, and disposed to receive and hold a taper member as shown in Fig. 16, Fig. 18, or Fig. 19. Such a mill body may be used instead of or in combination with any previously-described taper securement means.

Claims: CLAIMS : - 1. A tool for making an opening in a tubular in a wellbore, which tool comprises a mill having a body portion and a nose portion, characterised in that the nose portion includes cutting apparatus (525) at least a portion of which has thereon a material to be worn away thereby exposing the cutting apparatus (525) for cutting the tubular. 2. A tool as claimed in Claim 1, further comprising a sacrificial element releasably secured to the mill and for directing the mill against an inner surface of the tubular. 3. A tool as claimed in Claim 2, further comprising a whipstock to which is secured the sacrificial element. 4. A tool as claimed in Claim 3, wherein the nose portion is sized and positioned so that the nose does not cut the whipstock. 5. A tool as claimed in Claim 3 or 4, wherein the sacrificial element has at least a portion projecting upwardly beyond the whipstock so that the milling system initiates milling of the tubular prior to reaching the top of the whipstock. 6. A tool as claimed in Claim 2, 3, 4 or 5, wherein the sacrificial element has at least one recess therein for reducing the amount of the sacrificial element remaining following milling of .the sacrificial element by the mill . 7. A tool as claimed in Claim 6, wherein said at least one recess is a plurality of spaced apart recesses. 8. A tool as claimed in Claim 7, wherein the plurality of spaced apart recesses includes recesses at angles to each other forming a plurality of projections projecting from the sacrificial element. 9. A tool as claimed in Claim 1, further comprising a whipstock.

Inventors: HAUGEN DAVID MICHAEL, MCCLUNG GUY LAMONT III, HAUGEN, DAVID, MICHAEL, MCCLUNG, GUY, LAMONT, III
Applicants: LUCAS BRIAN RONALD, WEATHERFORD LAMB, LUCAS, BRIAN, RONALD, WEATHERFORD/LAMB, INC.
Application year: 1998
Main classification: E21B29
IPC codes: E21B7, E21B10, E21B12, E21B29