Abstract: Based on the theory of flow in porous media, the analysis shows that the current flow of underground water cannot become the real cause of water-oil contact (WOC) dipping in most cases. According to the theory of petrophysics, the reasons of dipping of WOC could be related to the difference of petrophysical properties resulted from ancient flow direction, and the difference results in the different capillary pressure curves of rocks. Finally, these differences cause the dipping of WOC upward along the ancient flow direction.

Key words: formation, water-oil contact, WOC, capillary pressure, outcrop