A casing is provided with a sealable shifting sleeve. A whipstock is insertable into the casing and may be supported off of the casing in a predetermined location so that it is oriented toward an open window in the casing when the shifting sleeve is selectively moved upwardly. By presenting an open window for the whipstock oriented toward the window, a drillbit may be lowered through the casing to interact with the whipstock to immediately begin the drilling of the deviated wellbore. The drillbit cuts through any cement, if present, and into the formation. A bore is presented in the whipstock to allow production from pay zones below the whipstock while it is in place. Should it become necessary, the sliding sleeve may be subsequently closed to isolate the deviated wellbore which has been drilled with the whipstock through the open window.
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