Method and apparatus for top to bottom expansion of tubulars

Abstract

An apparatus and method are disclosed that allow for downhole expansion of long strings of rounded tubulars, using a technique that expands the tubular from the top to the bottom. The apparatus supports the tubular to be expanded by a set of protruding dogs which can be retracted if an emergency release is required. A conically shaped wedge is driven into the top of the tubing to be expanded. After some initial expansion, a seal behind the wedge contacts the expanded portion of the tube. Further driving of the wedge into the tube ultimately brings in a series of back-up seals which enter the expanded tube and are disengaged from the driving mandrel at that point. Further applied pressure now makes use of a piston of enlarged cross-sectional area to continue the further expansion of the tubular. When the wedge has fully stroked through the tubular, it has by then expanded the tubular to an inside diameter larger than the protruding dogs which formerly supported it. At that point, the assembly can be removed from the wellbore. An emergency release, involving dropping a ball and shifting a sleeve, allows, through the use of applied pressure, the shifting of a sleeve which supports the dog which in turn supports the tubing to be expanded. Once the support sleeve for the dog has shifted, the dog can retract to allow removal of the tool, even if the tube to be expanded has not been fully expanded.