A sidetrack mill is provided for drilling through acased borehole to provide a sidetracked wellbore having a finaldiameter, the mill comprising: a pilot mill having a taperedcutting surface being, at its largest diameter, between about 50%and about 75% of the final diameter; a second stage cuttingsurface being, at its smallest diameter about the diameter of themaximum diameter of the pilot mill, and being at its largestdiameter, at least five percent greater in diameter than thelargest diameter of the pilot mill; and a final stage cuttingsurface being, at its largest diameter, about the final diameter,and at the smallest cutting surface diameter, being a diameterof at least about 5% smaller than the final diameter. This millis can rapidly penetrated casings without requiring excessivetorque. The milling can be accomplished with a single trip.In another aspect of the present invention, a method is providedto provide a sidetrack wellbore through a cased borehole thesidetracked wellbore having a final diameter, the methodcomprising: providing a whipstock, the whipstock comprising anelongated wedge shaped body having a wedge surface of a hardnessgreater than the casing, and less than tungsten carbide; securingthe whipstock in the borehole with wellbore cement; and millinga window in the casing by rotating a mill having tungsten carbidecutting elements in the wellbore along the wedge surface of thewhipstock. The staged mill described above is preferablyutilized in this method.
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