DETAILED DESCRIPTION OF THE DRAWINGS
FIG. 1 is a section view of a set down weight version of the mill of the present invention shown in the run in position;
FIG. 2 is a pressure actuated embodiment of the design of FIG. 1.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 shows a top sub 10 that has a string connected at thread 12 that is not shown. A bottom sub 14 supports at thread 16 a window mill that is not shown. For the purposes of focus on the invention the surrounding casing and the whipstock and its anchor are all not shown as these are items well known in the art. While a single watermelon mill 18 of the present invention is shown, those skilled in the art will appreciate that, if desired, more than one such mill can be mounted in series for sequential widening of a window made by a window mill. In the preferred embodiment, the variability of the watermelon mill 18 allows for sufficient widening of a window so as to shorten the bottom hole assembly by just using one watermelon mill 18. For example, mill 18 has a run in hole drift of 4.125 inches and get enlarge to about 5.00 inches when enlarging a window.
The way it changes dimensions in the FIG. 1 embodiment is by setting down weight on top sub 10. Top sub 10 is connected to bottom sub 14 by splines 20 that prevent relative rotation so that applied torque on top sub 10 is transferred to bottom sub 16 and to the window mill (not shown). When weight is set down on top sub 10 a shear pin 22 breaks and top sub 10 moves down with respect to bottom sub 14. Ramp surface 24 is connected to the stationary bottom sub 14 while blades 26 with lower ramp surface 28 ride up ramp surface 24 and wind up on support surface 30. Top 32 and bottom 34 of each blade is retained by the top sub 10 against relative rotation so that turning of the top sub 10 with blades 26 extended results in inserts 36 which are preferably tungsten carbide or polycrystalline diamond or a combination of both attacks the window to ream it out to the larger dimension of the mill 18 as the assembly advances downhole.
As an alternative, shown in FIG. 2, to using set down weight, the same result can be obtained using pressure supplied to a piston through passage 38 by simply increasing flow rate to build back pressure through port 39 to the piston 41 to drive the subs 10 and 14 together to force the blades 26 onto surface 30 against the force of a return spring 43 such that releasing the pressure will allow the return spring 43 to extend the tool and retract the blades 26. Simply pulling up without applied pressure in passage 38 will also extend the tool and get the same result so that the assembly can be pulled from the well as the mill 18 goes to its small dimension.
Optionally, the initial or window mill can be configured in this manner to vary the milling diameter as the window is initially formed by employing the structure described above for the subsequent or watermelon mill. Those skilled in the art will appreciate that mills of various external shapes can be used for the initial window and for subsequently widening it and that reference to a window mill is but one style of mill that can be made variable in dimension for window initial milling or widening. A watermelon mill just happens to be a shape of a mill frequently used for the purpose of widening a window but other mill types are within the scope of the invention. Using more that one mill with capabilities to change dimension including the initial window mill is also within the scope of the invention. The window need not be started by a mill. It can be created explosively or with chemicals or by other techniques.
The above description is illustrative of the preferred embodiment and many modifications may be made by those skilled in the art without departing from the invention whose scope is to be determined from the literal and equivalent scope of the claims below.
Patent Application
20080093075
