Abstract: The measurement of the cap rock sealing capability to the nonwetting fluids is one of the key tasks in the quantitative assessment of the cap rock. The existing measures cannot represent the sealing mechanism of cap rock thickness. A new method in terms of the Front Displacement Work (FDW) is developed to overcome this disadvantage. This measurement is the work that the fluid front pressure performs at the front displacement during the quasistatic displacement process, and therefore has a clear physical meaning. This measurement covers the two primary sealing mechanisms, i.e. the capillary sealing mechanism and the overpressure sealing mechanism. More importantly, it can reflect the sealing role of the cap rock thickness. Then, this measurement is compared with a newly presented methodology in the literature and applied to evaluate the cap rock sealing capability of Shasan segment of Dongying Depression. The results show that the Lijin depressing has the highest sealing capability and Niuzhuang depression has a lower sealing capability. The sealing capability is relatively low in the south slope area. The new measurement predicts the similar trend of sealing capability. This new measurement is very simple and it can simultaneously reflect the primary sealing mechanism.

Key words: Cap Rock, Sealing, Sealing Capability, Front Displacement Work, Dongying Depression