Retrievable milling guide anchor apparatus and associated methods

Abstract

In a parent wellbore casing, full bore access to the portion of the casing beneath a lateral bore liner portion therein is provided using a specially designed tubular retrievable anchor assembly hydraulically set within the casing above the liner portion and having a depending mill guide portion. A milling pipe with a first rotary mill is extended through the anchor assembly, with the mill being laterally deflected by the guide to mill a partial opening through the bottom side wall of the liner portion. The milling pipe is then withdrawn from the casing, the first mill replaced with a second rotary mill, and a specially designed tubular retrieval collet coaxially secured to the milling pipe. The milling pipe is then extended downwardly through the anchor assembly, the second mill used to enlarge the initial liner opening, and the collet snapped into the anchor assembly. The anchor assembly is then retrieved by pulling up on the milling pipe to release the anchor assembly which is removed from the casing. A full bore mill, having an elongated nose portion guidingly receivable in the partial liner hole, is then lowered into the casing and used to bore out the liner portion within the casing to provide full bore access to the parent casing portion beneath the previous location of the lateral bore liner portion therein.