Methods and apparatus for open hole drilling

Abstract

Methods and apparatus are disclosed for the open hole drilling of a borehole from an offshore platform and through a cased borehole at the seafloor. The drilling assembly 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 and preferably includes a casing and a riser attached to the casing. The lightweight drill string may be a jointed pipe, a metal coiled tubing, or preferably a composite coiled tubing. 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 drill string and the bottomhole assembly, through a fluid passageway around the bottomhole assembly, and between said lower end and the cased borehole into the sea.

Dependencies are inferred from the claim text.