Drilling through soft clay formations - by freezing the formation and using a hard-rock bit

摘要

Drilling bore holes through slate-contg. soft or plastic clay formations is carried out using a bit normally used for hard rock (esp. a diamond bit) and a drilling fluid contg sufficient coolant to freeze at least a part of the formation in the vicinity of the bit head. The drilling fluid can be a water-based, oil-based, emulsion-type or foam-type fluid contg. ice particles. The process allows soft clay formations to be penetrated at high speed without the risk of "balling up".