Patent ID: 8256535

Claim:
A process for drilling a sidetrack wellbore into a desired formation, wherein the process comprises: a. installing a liner within the formation, wherein the liner includes an outer diameter and an inner diameter; b. installing a tubing string within the formation, wherein the tubing string includes an inner diameter and an outer diameter, wherein the tubing string is divided into a first section and a second section; c. installing a tailpipe releasably attached between the first section and the second section of the tubing string, wherein the tailpipe includes an inner diameter and an outer diameter, wherein the tailpipe is positioned within the liner with the use of millable stabilizing bands, wherein the millable stabilizing bands are connected to the outer diameter of the tailpipe, wherein the outer diameter of the tailpipe is increased until the clearance between the tailpipe and the liner is such that the tailpipe can be safely run into the formation, wherein a diametrical clearance between the tailpipe and the liner is between about ⅛ inch to about ¼ inch, wherein the inner diameter of the tailpipe is larger than the inner diameter of the tubing string, wherein the tailpipe is fabricated from a durable material capable of being milled; d. installing a packer assembly, wherein the packer assembly is located along the tubing string and above the tailpipe; e. installing a whipstock assembly, wherein the whipstock assembly includes an inclined guide surface, wherein the whipstock assembly includes a heel, wherein the tailpipe positions the whipstock assembly near a centerline within the liner, wherein the difference between the inner diameter of the liner and the maximum deviation of the whipstock from the centerline in the formation is minimized to about ½ the value of the diametrical clearance, thereby reducing the distance between the heel of the whipstock to the inner wall of the liner, wherein the whipstock assembly is guided into the formation to a desired location within the tailpipe, wherein the whipstock assembly is then set in place at the desired location within the tailpipe; f. guiding a milling assembly into the formation through the tailpipe and onto the inclined guide surface of the whipstock assembly, wherein the milling assembly is a straight motor mill; and g. milling through the tailpipe and the liner in a single milling operation.