A DRILLING TOOL

摘要

A casing drilling shoe (1) is disclosed which is adapted for attachment to a casing string and comprises an outer drilling section (2) constructed of a relatively hard material such as steel and an inner section (4) constructed of a readily drillable material such as aluminium. The drilling shoe further includes a means (7) for controllably displacing the outer drilling section to enable the shoe to be drilled through using a standard drill bit and subsequently penetrated by a reduced diameter casing string or liner.