Abstract: The surface of weighting agent in oil base drilling fluid is often hydrophilic. It disperse in a water-in-oil emulsion，
will directly influence the drilling fluid static density. At the same time，the hydrophilic clay particles in the formation tend to
combine with water particles aggregation when penetrating the oil base drilling fluid will. Thereby it will have an effect on the
rheological properties of drilling fluids. To solve the above problem，we also study the evaluation method of selecting wetting
agents that prevent the aggregation. It can be known by analysis that the barite’s sagging volumes are different in several oil
phases with different wetting agents. The wettability of large numbers of narrow passages forming inside of barite powder
during sagging will affect the barite’s sagging volumes. If the wetting agents wettability is stronger，the barites sagging volume
will be less because less oil phase is bounded inside barite powder. On the contrary，the barite’s sagging volume will be more.
So the barites sagging can evaluate the wetting agent’s wettability，which is handy and convenient for appraising the wetting
agent.

Key words: wettability, barite, sagging, contact angle, evaluating