MILL FOR WELLBORE MILLING OPERATIONS

Abstract: A mill (M) for wellbore milling operations comprises a body (10) with a bore (100) therethrough, at least one milling surface on the body (10) and flow control apparatus within the body for selectively controlling fluid flow through the mill.

Description: Mill For Wellbore Milling Operations This invention relates to a mill for wellbore milling operations. In a typical sidetracking operation an anchor is first lowered down a casing and set at a desired posi¬ tion. A whipstock is then lowered down the casing and seated on the anchor. A starting mill is then lowered down the casing and is deflected radially against the wall of the casing by the whipstock whilst being simul- taneously rotated. This cuts a window in the casing. The starting mill is then withdrawn and a window mill or a water melon mill lowered down the casing and rotated to enlarge the initial window and smooth the edges thereof. The operation thus far described would involve four separate trips into the casing. This can be extremely expensive if the anchor is relatively deep. As a result many attempts have been made to reduce the number of trips required. In the preferred embodiment of the invention here¬ inafter described all the aforesaid operations can be effected in a single trip. According to one aspect of the present invention there is provided a mill for wellbore milling opera- tions, said mill comprising a body with a bore there¬ through for fluid flow through said mill, at least one milling surface on the body, and flow control apparatus within the body for selectively controlling fluid flow through the mill. Further features are set out in Claims 2 to 12. Another problem lies in determining whether a whipstock is properly seated and/or ensuring that the concave of the whipstock is properly disposed with respect to the casing. This is achieved by lowering the travelling block on the surface and noting whether there is an appropriate decrease in load. The problem with this operation is that the whipstock is typically atta¬ ched (directly or indirectly) to the tool string by a shear pin which may inadvertently shear when the travel- ling block is lowered. In order to help overcome this problem another aspect of the present invention provides a mill for wellbore milling operations, the mill comprising a body with at least one milling surface thereon, and force isolation apparatus on the body for isolating a shear- able member releasably connecting the mill to another member from a downward force on the mill. Further features are set out in Claims 14 to 18. The present invention also provides a method for installing a milling system in a wellbore lined with casing, the milling system having a mill releasably connected to a whipstock and an anchor connected to the whipstock, the mill comprising a body with a bore there¬ through for fluid flow through the mill, at least one milling surface on the body, and flow control apparatus within the body for selectively controlling fluid flow through the mill, the flow control apparatus including a first flow control device activatable by fluid at a first fluid pressure for permitting fluid at the first pressure to flow from the mill for actuating the anchor, the method comprising inserting the milling system into the casing, and flowing fluid at the first fluid pres¬ sure through the mill and through the first flow control device to the anchor to set the anchor in the casing. Preferably, said mill further comprises an amount of fluid confined within the bore prior to insertion of the mill into the wellbore, and leakage apparatus for controlled leakage of part of the amount of fluid from the mill. * * * The present invention also provides a whipstock which has an upper portion and a lower hollow portion. The lower hollow portion may be empty (initially) or it may be filled with cement, synthetic cement, or other millable material. The two portions may be releasably secured to each other, e.g. with one or more shear pins. The upper portion may have a concave portion or the concave portion may extend to and include part of the lower portion. In one aspect a raised portion on the lower portion is received in and held in a corresponding groove on the upper portion; or these interacting parts can be reversed with the raised portion on the upper portion and the groove on the lower portion. In either case more than one raised portion and groove may be ■ used. In other embodiments a solid whipstock core is releasably housed in an outer hollow member. For a better understanding of the present invention reference will now be made, by way of example, to the accompanying drawings, in which:- Fig. IA is a side view of one embodiment of a starting mill according to the present invention; Fig. IB is a cross-sectional view of the mill of Fig. IA; Fig. IC is an underneath plan view of the mill of Fig. IA; Figs. 2A is a side view of the main body of the starting mill of Fig. IA; Fig. 2B is a cross-sectional view of the body of Fig. IA; Fig. 2C is a cross-sectional view along line 2C-2C of Fig. 2B; Fig. 3A is a side cross-sectional view of a top sub of the mill of Fig. IA taken on line 3A-3A of Fig. 3B; Fig. 3B is a top plan view of the top sub of Fig. 3A; Fig. 4A is a side cross-sectional view of a retain¬ ing plate of the mill of Fig. IA; Fig. 4B is a top plan view of the retaining plate of Fig. 4A; Fig. 5A is a side cross-sectional view of a shear sub of the mill of Fig. IA taken on line 5A-5A of Fig. 5B; Fig. 5B is a top view of the shear sub of Fig. 5A; Fig. 6A is a side cross-sectional view of a labyr¬ inth piston of the mill of Fig. IA taken on the line 6A- 6A of Fig. 6B; Fig. 6B is a top view of the labyrinth piston of Fig. 6A; Fig. 7A is a side cross-sectional view of a top piston rod of the mill of Fig. IA taken on line 7A-7A of Fig. 7B; Fig. 7B is a top view of the top piston rod of Fig. 7A; Fig. 8A is a side cross-sectional view taken on line 8A-8A of Fig. 8B of a lower piston of the mill of Fig. IA; Fig. 8B is a top view of the lower piston of Fig. 8A; Fig. 9A is a side cross-sectional view of shear ring of the mill of Fig. IA taken on line 9A-9A of Fig. 9B; Fig. 9B is a top view of the shear ring of Fig. 9A; Fig. 10 is a side view of a milling system; Fig. 11 is a side view of a retrieval tool system; Fig. 12 is a side view of a milling system accord- ing to the present invention; Fig. 13A is a side cross-sectional view of a whip¬ stock; Fig. 13B is a side cross-sectional view of the upper portion of the whipstock of Fig. 13B; Fig. 13C is a side cross-sectional view of a lower portion of the whipstock of Fig. 13A; Fig. 13D is a cross-sectional view taken on line 13D-13D of Fig. 13A; Fig. 14A is a perspective view of a pilot lug of a whipstock according to the present invention; Fig. 14B is a front view of the pilot lug of Fig. 14A; Fig. 15A is a side view in cross-section of a whip¬ stock system; and Fig. 15B is another side view of the whipstock system of Fig. 15A. Referring to Figs. IA - IC, a starting mill M according to the present invention has a body 10 with a central longitudinal (top-to-bottom) fluid flow bore 100 extending therethrough. Typically the bottom of the mill M is releasably secured to the top of the concave of a whipstock (see Fig. 12). A plurality of milling blades 20 are secured (e.g. by welding) to the exterior of the body 10. Such a mill is useful for milling a hole in casing in a wellbore. Fluid flow through the body 10 is selectively controlled by flow control apparatus in the body 10 that includes a lower piston 60 releasably secured in a lower part of the bore 100 and movable therein after release; and a labyrinth piston 40 (and associated apparatus) releasably secured in an upper portion of the bore 100 and movable with respect to a top piston rod 30 upon release. A retaining plate 80 stabilizes the top end 161 (see Fig. 7A) of the top piston rod 30. A top sub 90 is releasably secured to a top end 102 of the body 10. The labyrinth piston 40 is initially secured in place by shear pins 14 that extend through holes 153 in the labyrinth piston into recesses 143 in a shear sub 50 (see Figs. 5A and 6A) which is affixed about the top piston rod 30. The portion of the fluid flow bore 100 below the labyrinth piston 40 defines a chamber which is filled with clean fluid (e.g., but not limited to, water, drilling fluid, ethylene glycol solution, or a combination thereof). Shearing of the pins 14 in re¬ sponse to fluid pumped into the wellbore at a first fluid pressure releases the labyrinth piston 40 for movement in the bore 100 and the force transmitted by the clean fluid effects breaking of a plug 185 in a male connector 120 so that fluid flows through an hydraulic line (not shown) to set an anchor (not shown) below the whipstock. The lower piston 60 is initially secured in place by shear pins 16 extending from holes 193 (see Fig. 9A) in a shear ring 70 in the bore 100 into recesses 180 in a bottom end 172 of the lower piston 60 (see Fig. 8A). Shearing of the pins 16 in response to fluid at a second fluid pressure (greater than the first fluid pressure) releases the lower piston 60 for downward movement in the bore 100 so that fluid flow ports 110 adjacent the blades 20 are exposed to fluid flow. Fluid under pressure to facilitate evacuation of debris and cuttings away from the blades 20 flows out from the bore 100 through fluid flow ports 110 which exit the body 10 near the lower parts 196 of the blades 20. Figs. 2A - 2C illustrate the body 10 and its bore 100. The body 10 has a top shoulder 105; an upper shoulder 104; a top cavity 106; an enlarged cavity 107; a plate shoulder 108; a mid-cavity 109; fluid flow ports 110; a lower piston shoulder 111; a lower shoulder 112; and a bottom shoulder 113. Ratchet teeth 116 are provided on a side of the lower end 103 of the body 10. The teeth 116 are pro- filed so that upon pushing down on the body 10 the teeth contact and engage teeth on a whipstock and downward force is transmitted to the whipstock via the teeth while the downward force is isolated from a shear stud (not shown) extending through a hole 101 in the body 10 into a pilot lug of the whipstock (not shown). The teeth 116 are also profiled so that in response to an upward pull on the body 10 there is no isolating engage¬ ment with the corresponding teeth on the pilot lug, the shear stud is not isolated from the force of such upward pulling, and the shear stud is shearable when enough upward force is applied, e.g. 9100 to 13600kg (twenty thousand to thirty thousand pounds) . Figs. 3A and 3B show the top sub 90 which has a top end 122, a lower shoulder 123, and upper shoulder 125, and a mid-portion 120. A lower shoulder 126 abuts the top end 102 of the body 10 of the mill M. A portion of the top piston rod 30 extends into a fluid flow bore 125 of the top sub 90. Figs. 4A and 4B show the retaining plate 80 with a body 130 and a lower shoulder 132 (which rests against the upper shoulder 104 of the body 10, Fig. IB) which has a hole 131 through which extends the top piston rod 30. Fluid flows through flow areas defined by arced portions 133 of the plate 80. Figs. 5A and 5B illustrate the shear sub 50 which has a body 140 with a top end 141, bottom end 142 and shear pin recesses 143. A fluid flow bore 145 extends through the body 140. A top shoulder 144 rests on a shoulder 164 of the top piston rod 30 (see Fig. IB) to hold the shear sub 50 in place about the top piston rod 30. Figs. 6A and 6B show the labyrinth piston 40 which has a body 150, a top end 151, a bottom end 152, an inner shoulder 154, and a fluid flow bore 155 through the body 150. Controlled leakage around the labyrinth piston 40 is provided by one or more exterior labyrinth grooves 156 and interior labyrinth grooves 157. Shear pins 14 (Fig. IB) extend into shear pin recesses 143 (Fig. 5A). An exterior surface 158 of the labyrinth piston 40 contacts an interior surface of the body 10 (see Fig. IB) to confine clean fluid in the top cavity 106 of the body 10. Figs. 7A and 7B show the top piston rod 30 which has a body 160 with a top end 161, a shoulder 164, a bottom end 162 and a piston rod plate 163. The piston rod plate 163 rests against the plate shoulder 108 (see Fig. IB) of the bore 100 of the body 10. Fluid flows past the piston rod plate 163 through flow areas defined by arced portions 165 of the plate 163. Figs. 8A and 8B show the lower piston 60 which has a body 170 with a top end 171, a bottom end 172 and a fluid flow bore 175 through the body 170. An O-ring 182 (Fig. IB) is positioned in a groove 173 and an O-ring 181 (Fig. IB) is positioned in a groove 174 (see Fig. IB). Shear pins 16 (Fig. IB) extend into shear pin recesses 180. A shoulder 176 moves to abut the lower piston shoulder 111 of the bore 100 of the body 10 and a shoulder 179 moves so that the ring 70 abuts the lower shoulder 112 of the bore 100 of the body 10 (Fig. 2B) to prevent further downward movement of the lower piston 60 as the bottom end 172 is received in a bottom portion 129 (see Fig. IB) of the bore 100. Figs. 9A and 9B show the ring 70 which has a body 190 with a top end 191, a bottom end 192 and a fluid flow bore 195 through the body 190. Holes 193 receive the shear pins 16 (Fig. IB) to initially prevent move¬ ment of the lower piston 60. The body 10 is provided with eight blades 20, but any desired number (one, two, three, four, etc. ) may be used. Each blade 20 has three primary milling surfaces: a lower part 196; a mid-portion 197; and a top part 198. It is within the scope of this invention for any or all of these parts to be dressed with any known milling inserts, matrix material, or combination thereof in any known disposition, configuration, array, or pattern. During assembly a ring 70 is secured with shear pins 16 to the lower piston 60, the number of shear pins being well above the pressure at which the anchor is to be set. Such shear pins are made from, e.g., low carbon steel or brass; and the major parts of the mill are made from steel or alloy steel, e.g. 4140 steel. A male connector 120 is connected to a bottom of the mill body 10 and the mill body 10 is filled with clean fluid. The shear sub 50 is installed in and pinned to the labyrinth piston 40 and then the shear-sub-labyrinth-piston combi- nation is slid onto the top piston rod 30. The weight of this combination may result in the displacement of fluid from within the body 10 across and out from above the labyrinth piston. By way of example, where an anchor packer is to be set at 2000 p.s.i., four shear pins are used which each shear at 875 p.s.i. and fluid at 3500 p.s.i. is circulated to shear the pins and insure setting of the packer. The retaining plate 80 is then installed on the top piston rod 30. A releasable retaining cap (made from e.g. plastic or aluminum) is placed over the mill body 10 for shipment and movement. The retaining cap is removed at a rig site. The mill M is then secured to a whipstock with a shear stud passing through the hole 101 and into a pilot lug of the whip- stock. The bottom of the whipstock is connected to an anchor. The whole assembly is then introduced on a drill string into a cased wellbore filled with drilling fluid. If increased temperature is encountered as the assembly moves down in the drilling fluid, clean fluid leakage past the labyrinth piston increases to accommo¬ date expanding clean fluid so that the anchor is not prematurely set. The labyrinth piston 40 also acts as a debris barrier to inhibit the hydraulic line from being clogged during anchor setting. Air anywhere in the system beneath the labyrinth piston 40 can escape up past the labyrinth so that the hydraulic line and other devices are filled with fluid. For a chamber of a volume of about forty cubic inches, about three cubic inches may leak out; and for a chamber with a volume of about one hundred cubic inches about nine cubic inches of fluid may leak out. When the whipstock reaches the desired position fluid is pumped by surface pumps down into the mill M, until the leakage past the labyrinth piston is overcome and the pressure is sufficient to shear the shear pins 14, freeing the labyrinth piston 40 to move and displa¬ cing fluid so that it flows out from the mill M to set the anchor. Packer setting is verified by lowering the travelling block and noting the reduction in load. Sufficient downward force is then applied to effect pivoting of the concave of the whipstock against the casing wall. Then the drill string is pulled upwardly to shear the shear stud and break the hydraulic line from the mill M to free the mill M from the whipstock. The hydraulic line connects the mill M to the anchor or to a line or bore through the whipstock to the anchor. Pumps on the surface then pump fluid down through the mill M at a pressure sufficiently high to overcome flow out through the lower exit port 185 and to shear the shear pins 16 freeing the lower piston 60 for downward movement to expose the blade flow ports 110 to fluid. -Fluid is then pumped out past and upwardly away from the blades 20 as the string is rotated to mill the casing. Once the casing has been initially milled, an additional milling system (e.g. with a watermelon mill and a window mill) may be inserted in another trip into the wellbore to accomplish additional milling. Alternatively, the window mill may be mounted above the starting mill. Upon removal of the additional system from the wellbore a drilling system is introduced into the wellbore to commence drilling a new borehole through the window that has been milled in the casing. Fig. 10 illustrates a milling system 200 with pieces of drill pipe 201 threadedly connected to drill collars 202 and heavy pipe 203. A watermelon mill 204 is threadedly connected to the heavy pipe 203 and a window mill 205 is threadedly connected to the waterme¬ lon mill 204. Fig. 11 discloses a retrieval system 220 which has drill pipes 221 threadedly connected to drill collars 222. An orientation indicating device 223 (e.g. a measuring-while-drilling (MWD) device or a gyroscopic tool ) is interconnected between the drill collars and a jarring device 224 (any conventional commercially avail- able jar). A retrieval tool 225 with a hook 226 for insertion into a corresponding hole in a whipstock is connected to the jar 224. Such a tool is shown in U. S. Patent 5,341,873. Fig. 12 shows a system 250 according to the present invention which has drill pipes 251, drill collars 252, an orientation sensor device 253, drill pipe 254, a cross-over sub 255, a starting mill 256 (like the mill M previously described), a whipstock 258 with a concave with a concave surface 257, an hydraulic fluid line 259 intercommunicating between the starting mill 256 and an hydraulically activated anchor (anchor device or anchor packer) at a pivot device 260 (pivot device as is well known in the art) . Fig. 13A - 13D shows a whipstock 270 according to the present invention which has a top solid part 271 releasably connected to a hollow lower part 276. The top solid part 271 has a pilot lug 272, a retrieval hook hole 273, a concave inclined surface 275 and a rail 279. The lower hollow part 276 has an inner bore 277 shown filled with drillable filler material or cement 278. The cement is in the tool as it is inserted into the casing. The lower hollow part 276 has a concave in¬ clined surface 280 which lines up with the concave inclined surface 275 of the top solid part 271. As shown in Fig. 13D shear screws 281 extend through holes 283 in the lower hollow part 276 and holes 282 in the top solid part 271 to releasably hold the two parts together. The rail 279 is received in a corresponding groove 274 in the lower hollow part 276 to insure cor- rect combination of the two parts. Preferably the length of the top solid part 271 is at least 50% of the length of the inclined portion of the concave. A whip¬ stock 270 maybe used in the system 250 (Fig. 12) or any other system disclosed herein. Upon completion of an operation, the top solid part is released by shearing the shear screws with an upward pull on the whipstock, making retrieval and re-use of the top solid part pos¬ sible. The bottom hollow part need never leave the wellbore and the cement 278 can easily be drilled out. Figs. 14A and 14B show a pilot lug 350 according to the present invention with a body 352 having a hole 354 therethrough through which a shear stud or bolt (not shown) extends to releasably secure another item (e.g. a mill) to the pilot lug. Ratchet teeth 356 on the pilot lug 350 co-act with corresponding teeth on another member (e.g. teeth 116, Fig. IB) and operate, as de¬ scribed above, to isolate the shear stud from a downward force applied to a member (e.g. the mill of Fig. IB) releasably secured by the shear stud to the pilot lug 350. The lug 272 (Fig. 13B) may have the teeth 356, as may any other pilot lug or member for attaching a mill to a whipstock. Figs. 15A and 15B illustrate a whipstock 300 in a casing C in a wellbore. The whipstock 300 has an outer hollow tubular member 302 having a top end 303, a bottom end 304 and a central bore 305; and an inner solid member 306 with a top end 307, a bottom end 308, a concave 309 with a concave inclined surface 310, and a retrieval hook slot 311 in the concave 309. The hollow tubular member 302 is secured to the casing and, while in use, the inner solid member 306 is releasably secured to the outer hollow tubular member 302, e.g. by shear pins 312 extending from the inner solid member 306 into the outer hollow tubular member 302. As shown in Fig. 15B, upon shearing of the pins 312 by an upward pull with a retrieval tool T, the retrieval tool T is used to remove the inner solid member 306 for re-use.

Claims: CLAIMS : 1. A mill for wellbore milling operations, said mill comprising a body (10) with a bore (100) therethrough for fluid flow through said mill, at least one milling surface on the body, and flow control apparatus within the body for selectively controlling fluid flow through the mill. 2. A mill as claimed in Claim 1, further comprising an amount of clean fluid within the bore. 3. A mill as claimed in Claim 2, further comprising leakage apparatus for controlled leakage of part of the amount of clean fluid from the mill. 4. A mill as claimed in Claim 3, wherein the leakage apparatus comprises a labyrinth piston movably disposed in said mill body. 5. A mill as claimed in any preceding claim, wherein -said flow control apparatus includes a first flow con¬ trol device activatable by fluid at a first fluid pres¬ sure for permitting, in use, fluid at the first pressure to actuate an item below the mill. 6. A mill as claimed in Claim 5, wherein the mill is a starting mill and the item below the mill is an anchor. 7. A mill as claimed in Claim 6, wherein the starting mill is releasably connected to a whipstock and the anchor is secured to a lower part of the whipstock. 8. A mill as claimed in Claims 5, 6 or 7, wherein said flow control apparatus includes a second flow control device activatable at a second fluid pressure and mov¬ able in response thereto to permit fluid flow out through at least one port adjacent a milling portion of the mill, the second fluid pressure greater than the first fluid pressure. 9. A mill as claimed in any preceding claim, further comprising a shearable member releasably connecting the mill to another member, and isolation apparatus on the mill for isolating the shearable member from a downward force on the mill. 10. A mill as claimed in Claim 9, wherein the isolation apparatus comprises profiled teeth on the mill body for contacting and engaging corresponding teeth on another member, the profiled teeth disposed and configured so that a downward force on the mill is transferred to the another member through the profiled teeth to the corre¬ sponding teeth and an upward force on the mill is trans- ferred to the shearable member releasably connecting the mill to the another member. 11. A mill as claimed in Claim 9 or 10, wherein said another member is a whipstock with an upper concave portion and the shearable member is a shear stud con- necting the mill to the concave portion of the whip¬ stock. 12. A mill as claimed in any preceding claim, wherein the at least one milling surface comprising a plurality of milling blades on the mill body. 13. A mill for wellbore milling operations, the mill comprising a body with at least one milling surface thereon, and force isolation apparatus on the body for isolating a shearable member releasably connecting the mill to another member from a downward force on the mill. 14. A mill as claimed in Claim 13, wherein the body is provided with a bore therethrough for fluid flow through the mill. 15. A mill as claimed in Claim 13 or 14, further com- prising flow control apparatus within the body for selectively controlling fluid flow through the mill. 16. A mill as claimed in Claim 15, wherein the flow control apparatus includes a first flow control device in the bore activatable by fluid at a first fluid pres- sure for permitting fluid at the first pressure to flow from the mill for actuating an item below the mill, and a second flow control device in the bore activatable at a second fluid pressure and movable in response thereto to permit fluid flow out through at least one port adjacent a milling portion of the mill, the second fluid pressure greater than the first fluid pressure. 17. A mill as claimed in Claim 13, 14, 15 or 16, fur¬ ther comprising an amount of fluid confined within the bore prior to insertion of the mill into the wellbore, and leakage apparatus for controlled leakage of part of the amount of fluid from the mill. 18. A mill as claimed in any of Claims 13 to 17, fur¬ ther comprising a whipstock, wherein the mill is a starting mill, and the shearable member releasably connects the mill to the whipstock. 19. A method for installing a milling system in a well- -bore lined with casing, the milling system having a mill releasably connected to a whipstock and an anchor con¬ nected to the whipstock, the mill comprising a body with a bore therethrough for fluid flow through the mill, at least one milling surface on the body, and flow control apparatus within the body for selectively controlling fluid flow through the mill, the flow control apparatus including a first flow control device activatable by fluid at a first fluid pressure for permitting fluid at the first pressure to flow from the mill for actuating the anchor, the method comprising inserting the milling system into the casing, and flowing fluid at the first fluid pressure through the mill and through the first flow control device to the anchor to set the anchor in the casing. 20. A method according to Claim 19, wherein the mill further comprises an amount of fluid confined within the bore prior to insertion of the mill into the wellbore, and leakage apparatus for controlled leakage of part of the amount of fluid from the mill.

Inventors: PLEASANTS CHARLES W, PLEASANTS, CHARLES, W.
Applicants: LUCAS BRIAN RONALD, WEATHERFORD LAMB, LUCAS, BRIAN, RONALD, WEATHERFORD/LAMB, INC.
Application year: 1996
Main classification: E21B29
IPC codes: E21B7, E21B10, E21B23, E21B29, E21B34