| abstract |
A system is provided for drilling a borehole into an earth formation, comprising a casing arranged in the borehole, a drill string extending through the interior of the casing to a lower end portion of the borehole, and a body of drilling fluid extending into the casing, the casing having an inner surface susceptible of wear due to frictional contact with an outer surface of the drill string during drilling of the borehole with the drill string. The system further comprises means for reducing wear of said inner surface of the casing, said means including at least one of a hardened layer at the inner surface of the casing, a friction-reducing layer at the outer surface of the drill string, and a lubricating compound contained in the body of drilling fluid. |