METHODS AND APPARATUS FOR OPEN HOLE DRILLING

摘要

A drilling assembly for open hole drilling from an offshore platform through a cased borehole at the seafloor includes a guide assembly extending from the platform to the seafloor and having a lower end extending into the cased borehole; and a bottomhole assembly disposed on a lightweight drill string extending through the guide assembly for drilling the borehole. The guide assembly is a pipe string that may include a casing and a riser attached to the casing. The bottomhole assembly includes a formation displacement member adapted to drill a borehole having a diameter greater than the diameter of the guide assembly. The drilling assembly uses a drilling fluid that flows through the lightweight drill string and the bottomhole assembly, through a fluid passageway around the bottomhole assembly, and out of the cased borehole into the sea.