Abstract: Some strange phase phenomena were observed in PVT cells on the micro-scale. The degassing process of oil shows that gas gets into gas phase in bubbles other than the molecules. And the bubbles evolve at the bottom of cells. The de-oiling process of gas shows that oil gets into oil phase in dews other than the molecules. And the dews evolve at the top of cells. All the phenomena are related to solution capability of oil and gas with each other, and also to the roughness of cell surface. The micro strange phase phenomena of oil and gas due to existence of skin are called the skin effect of fluids.

Key words: crude oil, gas, phase behavior, PVT cell, reservoir, skin effect