| 摘要 |
An oil based drilling mud comprises (a) a base oil, (b) about 1 to about 170 parts by weight of an aqueous phase per 100 parts by weight of the oil, (c) about 0.25-40 g/l of at least one viscosifier, and (d) a hydrophobic weighting agent in amount sufficient to achieve a required mud density. The hydrophobic weighting agent is preferably barite. The drilling muds do not contain emulsifiers or oil wetting agents and are particularly advantageous in their reduction in oil retention on cuttings and smaller reduction in permeability of oil bearing formations. <IMAGE>
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