MILLING TOOL, WHIPSTOCK, MILLING SYSTEM AND METHOD OF FORMING A WINDOW IN THE WALL OF A TUBULAR

Abstract: A milling tool (110) is provided with a valve member (122) which can be displaced to inhibit the flow of drilling fluid through the milling tool (110). A whipstock (150) is provided with a stop (155) which the valve member (122) engages as the milling tool (110) moves down the whipstock (150). Further downward movement of the milling tool (110) relative to the whipstock (150) displacing the valve member (122) relative to the milling tool (110) and inhibits the flow of drilling fluid therethrough. This results in a decrease in flow and increase in pressure at the mud pumps signifying that milling should cease. If the milling tool (110) is being driven by a mud motor (156) which exhausts through the milling tool (110) the mud motor (156) will stop when the flow through the milling tool is inhibited.

Description: Milling Tool, Whipstock, Milling System and Method of forming a window in the wall of a Tubular This invention relates to a milling tool, a whip¬ stock for use with said milling tool, a milling system including said milling tool and said whipstock, a method of forming a window in the wall of a tubular using said milling tool and said whipstock, and a method of forming a window in the wall of a tubular using said milling system. Typically, when it is desired to cut a window in the wall of a tubular a whipstock is lowered down the tubular and set in the desired position with its concave appropriately orientated. A starting mill is then low¬ ered onto the concave and rotated. The concave is ta- pered so that as the starting mill is lowered it is deflected laterally towards the wall in which it cuts an elongate window. Drilling mud is pumped down the well through the starting mill and, on its return to the surface, en- trains swarf and debris from the milling operation. The initial window is subsequently elongated and the sides of the window are made smoother by treating the initial window with one or more special purpose mills as required. Once the window has been completed a new wellbore is drilled through the window and completed as required. The whipstock is then recovered for future use. Typically, the concave comprises a tapered support portion made from stainless steel and provided with a layer of sacrificial bearing material, such as brass, which is worn away by the mill. The tapered support portion of the concave is extremely expensive to manufacture. However, if the whipstock is correctly used it can be refurbished by simply replacing the sacrificial bearing material. One of the difficulties which arises in current practice is that unless the starting mill is stopped at the appropriate time, not only will the mill remove part of the sacrificial bearing material but it will also cut away part of the tapered support portion and, in a serious case, could prevent the concave being refur¬ bished or even being removed from the well. This problem rarely arises when the whipstock and the starting mill are lowered on a workstring of tubulars since the relative depths of the whipstock and the starting mill are well known from the number of tubulars. However, the problem is quite common where one or both the whipstock and the starting mill are lowered on coil tubing and the exact location of the parts is less well defined. Coil tubing will generally be used if the starting mill is to be driven by a mud motor. According to one aspect of the present invention there is provide a milling tool having a passageway for the flow of drilling fluid therethrough, characterised in that said milling tool further comprises means for inhibiting the flow of drilling fluid through said passageway. Preferably, said milling tool further comprises a mill and said means comprises a housing which projects beyond said mill. Advantageously, said milling tool further comprises a valve member at least a part of which can enter said housing. In one embodiment, said valve member is captive in said housing. Advantageously, said valve member is provided with a tip which project beyond said housing when said valve member is in at least one position relative to its housing. Advantageously, said valve member has a portion which, in use, when said valve member is displaced in one sense relative to said housing moves to a closed position to inhibit the flow of drilling fluid through said passageway, and which is further provided with a plurality of flow ports which, in use, when said valve member is in an open position permit the flow of dril¬ ling fluid through said passageway. Preferably, said housing is provided with a bushing which has a passageway to slidably accommodate said valve member, and a plurality of flow ports to permit the flow of drilling fluid therethrough. In another embodiment said valve member is not secured to the remainder of said milling tool. According to another aspect, the present invention provides a whipstock for use with a milling tool in accordance with the present invention, said whipstock comprising a tapered support portion and at least one sacrificial bearing mounted thereon, characterised in that said whipstock further comprises a stop to engage said means. Preferably, said whipstock includes a plurality of sacrificial bearings spaced apart from one another on said tapered support portion. According to another aspect, the present invention provides a whipstock for use with a milling tool in accordance with the present invention, said whipstock comprising a tapered support portion and at least one sacrificial bearing mounted thereon, characterised in that said valve member is mounted on said whipstock. The present invention also provides a milling system comprising a milling tool in accordance with the present invention and a whipstock in accordance with the present invention. Preferably, said milling system includes a mud motor operatively connected to said milling tool. Advantageously, said milling system includes coil tubing attached to said mud motor. Another aspect of the present invention provides a method of forming a window in the wall of a tubular, which method comprises the steps of: a) setting a whipstock in accordance with the present invention in said tubular, and b) cutting said window with a milling tool in accor¬ dance with the invention until said means inhibits the flow of drilling fluid therethrough. A further aspect of the present invention provides a method of forming a window in the wall of a tubular, which method comprises the steps of: a) setting the whipstock of a milling system in accordance with the present invention in said tubular, and b) cutting said window with the milling tool of said milling system until the flow of drilling mud through said milling tool is inhibited by said means and thereby stops said mud motor. 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, partially in cross-section, of a first embodiment of a milling tool in accordance with the present invention with its valve in an open position; Fig. 2 is a view similar to Fig. 1 but showing the valve in its closed position; Fig. 3 is an exploded view, partially in cross- section, of the milling tool shown in Figs. 1 and 2; Fig. 4 is a view taken in the direction of arrow IV of Fig. 3; Fig. 5 is a view taken in the direction of arrow V of Fig. 3; Fig. 6 is a view, partly in section, taken on line VI-VI of Fig. 3; Fig. 7 is a view similar to Fig. 6 but showing a different mill; Fig. 8 is a side view, partly in cross-section, of a second embodiment of a milling tool in accordance with the present invention with its valve in an open posi¬ tion; Fig. 9 is a view similar to Fig. 8 but showing the valve in its closed position; Fig. 10 is an exploded view, partly in cross-sec¬ tion, of the milling tool shown in Figs. 8 and 9; Fig. 11 is a view taken in the direction of arrow XI of Fig. 10; Fig. 12 is a side view, partly in cross-section, of a third embodiment of a milling tool in accordance with the present invention with its valve in an open posi¬ t on; Fig. 13 is a section taken on line XIII-XIII of Fig. 12; Fig. 14 is a schematic representation showing the arrangement of inserts used with the mill shown in Figs. 12 and 13; Fig. 15 is a side view of part of a first embodi- ment of a whipstock in accordance with the present invention; Fig. 16 is an enlargement of part of the whipstock shown in Fig. 15; Fig. 17 is a view similar to Fig. 16 but showing the milling tool of Figs. 1 to 6 at the end of a milling operation; Fig. 18 is a front view of the whipstock and mill¬ ing tool shown in Fig. 17; Fig. 19 is a view taken on line XIX-XIX of Fig. 16; Fig. 20 is a view taken on line XX-XX of Fig. 17, but showing a different type of mill; Fig. 21 is a view on line XXI-XXI of Fig. 16; Fig. 22 is a view similar to Fig. 18 but to a re¬ duced scale and showing part of a second embodiment of a whipstock in accordance with the present invention; Fig. 23 is a schematic view of a milling system in accordance with the present invention; Fig. 24 is a schematic view of part of a fourth embodiment of a milling tool in accordance with the invention with the milling tool in use; and Fig. 25 is a view similar to Fig. 24 but showing the milling tool at the end of a milling operation. Referring now to Figs. 1 to 5, there is shown a milling tool which is generally identified by the refer- ence numeral 110. The milling tool 110 comprises a tubular body 112 having a mill 114 mounted thereon. The upper end of the tubular body 112 is provided with an upper threaded end 116 whilst the lower end of the tubular body 112 is provided with a lower threaded end 118. A central flow channel ll "7 extends the entire length of the tubular body 112. The milling tool 110 also includes a valve 120 which comprises a housing 121 which is screwed to the lower threaded end 118 of the tubular body 112, and a valve member 122 which is slidably mounted in the hous¬ ing 121. The valve member 122 is provided with a shoulder 124 which, when the valve 120 is open (Fig. 1), bears against a lip 125 which projects radially inwardly from the bottom of the valve 120. The valve member 122 comprises an upper body por¬ tion 127 and a lower body portion 129. A plurality of flow ports 126 and 128 extend through the upper body portion 127 and the lower body portion 129 respectively. As can be seen from Fig. 4, the flow ports 126 are disposed circumjacent a central portion 132 of the upper body portion 127. A portion of the valve member 122 projects down¬ wardly beyond the lip 125 of the housing 121 and termi- nates in a tip 131. When the valve member 122 is moved upwardly, as shown in Fig. 2, the central portion 132 closes off the central flow channel 117. The mill 114 shown is a typical starting mill having a plurality of tungsten carbide chips 134 mounted thereon. However, other types of mill could also be used, for example the mill 114' shown in Fig. 7 which has a plurality of slots each of which accommodates a blade 133 having tungsten carbide chips 134' mounted on the leading face thereof. Turning now to Figs. 8, 9 and 10, there is shown a second embodiment of a milling tool in accordance with the invention. The milling tool, which is generally identified by reference numeral 210, is generally simi¬ lar to the milling tool shown in Figs. 1 to 6 and parts having similar functions have been identified by the same last two reference numerals prefixed by the refer¬ ence number "2". The essential difference between the two embodi¬ ments is in the construction of the valve 220. In particular, the valve 220 comprises a housing 221 which is screwed onto the lower threaded end 218 of the tubu¬ lar body 212 of the milling tool 210, and a valve member 222 which is slidably mounted in a bushing 223 disposed in the housing 221. The bushing 223 is generally cylindrical and has a plurality of flow ports 235 extending therethrough and disposed circumjacent a central passageway 236 which accommodates the valve member 222. The valve member 222 has an upper body portion 227 and a lower body portion 229. The lower body portion 229 has a plurality of flow ports 228 therethrough whilst the upper body portion 227 has a convex central portion 232. As shown in Fig. 8, when the valve 220 is open fluid can flow freely through the milling tool 210 via the central flow channel 217, the flow ports 235 in the bushing 223 and inter alia through the flow ports 228. When the valve member 222 is displaced upwardly the central portion 232 of the upper body portion 227 ob- structs the central flow channel 217. Turning now to Figs. 12, 13 and 14 there is shown a third embodiment of a milling tool in accordance with the present invention. The milling tool, which is generally identified by the reference numeral 310 is generally similar to the milling tool shown in Figs. 1 to 6 and parts having similar functions have been iden¬ tified by the same last two reference numerals prefixed by the reference numeral "3". The essential difference between the two embodi- ments is that a stabilizer 337 is mounted on the tubular body 312 in addition to the mill 314. The mill 314 is generally similar to the mill 114' shown in Fig. 7 except that it is provided with a plur¬ ality of fluid supply ports 338 which extend from the central flow channel 317 of the tubular body 312 to outlets which are disposed to allow drilling fluid to exhaust over and across tungsten carbide inserts 334 on the blades 333 of the mill 314. As can be seen from Fig. 13 the mill 314 has eight pockets which are numbered a to h. The arrangement of inserts 334 on the blades 333 is shown in Fig. 14. Referring now to Figs. 15 and 16 there is shown part of a concave 151 of a whipstock which is generally identified by reference numeral 150. The concave 151 comprises a tapered support portion 152 which is made from stainless steel and has an arcu¬ ate surface 153 on part of which is mounted a sacrifi¬ cial bearing 154 which is made of brass and which termi¬ nates above a stop 155. In use, the whipstock 150 is made fast in the casing at the desired depth and with the desired orien¬ tation. The milling tool 110 is then lowered into contact with sacrificial bearing 154 and rotated. As the milling tool 110 is further lowered the taper of the concave 151 urges the mill 114 into contact with the wall of the casing in which it cuts a small window which gradually extend into an elongate window. As the mill 114 rotates it also wears away the sacrificial bearing 154. While the mill 114 is rotating drilling fluid is pumped down the central flow channel 117. The drilling fluid leaves through the bottom of the drilling tool 110 and flows upwardly to the surface entraining swarf and other debris from the mill 114 en route. As the milling tool 110 is further lowered the tip 131 of the valve 120 engages the stop 155. Further downward movement of the milling tool 110 causes the valve member 122 to move upwardly relative to the hous¬ ing 121 to close the valve 120 as shown in Figs. 17 and 18. The closing of the valve 120 stops (or significant¬ ly restricts ) the flow of drilling fluid through the milling tool 110 and this will immediately result in a pressure increase at the mud pumps at the surface which signals that the starting mill 114 should be stopped. The milling tool 110 is then stopped and withdrawn. When the whipstock 150 is eventually withdrawn the sacrificial bearing 154 can simply be replaced and the concave 151 is ready for re-use. Fig. 19 is a section through the concave 151 show- ing the tapered support portion 152 and the sacrificial bearing 154 prior to milling. Fig. 20 shows the tapered support portion 152 and the remains of the sacrificial bearing 154 after mill¬ ing. The mill 114"' shown is another variant which can be used. Fig. 21 shows the stop 155. It will be noted that the stop 155 only obstructs a limited area. This helps reduce the possibility of a pressure rise being detected at the surface before the milling tool 110 has actually reached its final position. Fig. 22 shows a view which is similar to Fig. 18, the only material difference being that the sacrificial bearing 154 is replaced to a plurality of sacrificial bearings 154' which are spaced apart from one another as shown. The spacing of the sacrificial bearings 154' is such that the mill 114' is always supported by at least one sacrificial bearing 154'. Often, the milling tool 114 will be lowered down the casing on a workstring which is rotated from the surface. In this case the top drive or rotary table rotating the work string will have to be stopped either manually or automatically by a detector sensitive to the flow of drilling fluid through the milling tool or an increase in the pressure at the mud pumps. However, on other occasions the milling tool may be associated with a mud motor both of which are lowered into the casing via coil tubing as shown in Fig. 23. In particular, the whipstock 150 is shown fast in a casing. The whipstock is disposed with the arcuate surface 153 of its concave 151 facing upwardly. A milling system comprising a mud motor 156 and the milling tool 110 is lowered down the casing on coil tubing 157 until the milling tool 110 comes to rest on the concave 151. At this time mud is pumped down the coil tubing 157 and rotates the milling tool 110 via a hollow drive shaft 158. The drilling fluid leaving the mud motor 156 passes through the hollow drive shaft 158 and passes through the central flow channel 117 of the milling tool 110. Milling proceeds until the valve 120 of the milling tool 110 is closed after engagement of the tip 131 of the valve member 122 with the stop 155 on the concave 151. Since closure of the valve 120 prevents fluid flowing through the milling tool 110 the mud motor 156 stops automatically. Turning now to Figs. 24 and 25, there is shown another embodiment of a milling tool in accordance with the invention which is generally identified by the reference numeral 410. The milling tool 410 is generally similar to the milling tool 110 shown in Figs. 1 to 6 except that the valve comprises a housing 421 which projects downwardly from the mill 414 and a valve member 422 which is oun- ted directly on the concave 151" of the whipstock 150". As can be seen from Figs. 23 and 24, as milling progresses the mill 114 mills away the sacrificial bear¬ ing 154" on the concave 151" until the valve member enters the valve housing and inhibits or prevents the flow of drilling fluid therethrough. It will be appreciated that the housing 421 could be dispensed with if the length of the valve member 422 is increase appropriately. As used herein the term "concave" is used to refer to the tapered part of a whipstock regardless of whether the bearing surface on which the mill rotates is arcuate (as shown) or flat.

Claims: Claims 1. A milling tool (110; 210; 310; 410) having a passa¬ geway (117; 217; 317; 417) for the flow of drilling fluid therethrough, characterised in that said milling tool (110; 210; 310; 410) further comprises means (120; 220; 320; 421, 422) for inhibiting the flow of drilling fluid through said passageway. 2. A milling tool (110; 210; 310; 410) as claimed in Claim 1, further comprising a mill (114; 114' ; 114"; 214; 314; 414), and wherein said means (120; 220; 320; 421, 422) comprises a housing (121; 221; 321; 421) which projects beyond said mill. 3. A milling tool as claimed in Claim 2, further comprising a valve member (122; 222; 322; 422) at least a part of which can enter said housing. 4. A milling tool as claimed in Claim 3, wherein said valve member (122; 222; 322) is captive in said housing (121; 221; 321). 5. A milling tool as claimed in Claim 4, wherein said valve member (122; 222; 322) is provided with a tip (131; 231; 331) which project beyond said housing (121; 221; 231) when said valve member (122; 222; 322) is in at least one position relative to its housing (121; 221; 321). 6. A milling tool as claimed in Claim 4 or 5, wherein said valve member (122; 222; 322) has a portion (132; 232; 332) which, in use, when said valve member (122; 222; 322) is displaced in one sense relative to said housing (121; 221; 321) moves to a closed position to inhibit the flow of drilling fluid through said passage¬ way (117; 217; 317), and which is further provided with a plurality of flow ports (126, 128; 228; 328) which, in use, when said valve member is in an open position permit the flow of drilling fluid through said passage- way (117; 217; 317). 7. A milling tool as claimed in Claim 4, 5 or 6, wherein said housing (221) is provided with a bushing ( 223 ) , which has a passageway ( 236 ) to slidably accommo¬ date said valve member (222), and a plurality of flow ports (235) to permit the flow of drilling fluid there¬ through. 8. A milling tool as claimed in Claim 1 or 2, wherein said valve member (422) is not secured to the remainder of said milling tool. 9. A whipstock (150; 150' ) for use with a milling tool as claimed in any of Claims 1 to 7, said whipstock (150, 150' ) comprising a tapered support portion (152; 152' ) and at least one sacrificial bearing (154; 154' ) mounted thereon, characterised in that said whipstock further comprises a stop (155; 155' ) to engage said means (120; 220; 320). 10. A whipstock as claimed in Claim 9, including a plurality of sacrificial bearings (154' ) spaced apart from one another on said tapered support portion (152' ). 11. A whipstock (150" ) for use with a milling tool as claimed in Claim 8, said whipstock (150") comprising a tapered support portion (152") and at least one sacrifi¬ cial bearing (154" ) mounted thereon, characterised in that said valve member ( 422 ) is mounted on said whip- stock (150"). 12. A milling system comprising a milling tool as claimed in any of Claims 1 to 8 , and a whipstock as claimed in Claim 9, 10 or 11. 13. A milling system as claimed in Claim 12 including a mud motor (156) operatively connected to said milling tool (114). 14. A milling system as claimed in Claim 13, including coil tubing (157) attached to said mud motor (156). 15. A method of forming a window in the wall of a tubular, which method comprises the steps of: a) setting a whipstock (150; 150' ) as claimed in Claim 9, 10 or 11, in said tubular, and b) cutting said window with a milling tool as claimed in any of Claims 1 to 8 until said means (120; 220; 320) inhibits the flow of drilling fluid therethrough. 16. A method of forming a window in the wall of a tubular, which method comprises the steps of: a) setting the whipstock (150") of a milling system as claimed in Claim 14 in said tubular, and b) cutting said window with the milling tool of said milling system until the flow of drilling mud through said milling tool is inhibited by said means (120; 220; 320) and thereby stops said mud motor.

Inventors: CARTER THURMAN B, ROBERTS JOHN D, CARTER, THURMAN, B., ROBERTS, JOHN, D.
Applicants: LUCAS BRIAN RONALD, WEATHERFORD LAMB, LUCAS, BRIAN, RONALD, WEATHERFORD/LAMB, INC.
Application year: 1996
Main classification: E21B29
IPC codes: E21B7, E21B10, E21B29, E21B44, E21B47