Quantitative Evaluation of Fault Vertical Sealing Ability of 1st Structure in Nanpu Sag

The study of the internal structure and its characteristics of fault zone shows that fault rock constitutes an important part of fault with universal distribution in fault, and the vertical sealing ability of fault is mainly determined by the difference of capillary entry pressure between fault rock and underlying reservoir rock. The fault is sealed when the capillary entry pressure of fault rock is not smaller than that of reservoir rock. In addition, the sealing ability is determined by the degree of capillary entry pressure difference, the greater the difference, the stronger the sealing ability of fault, and vice versa. The capillary entry pressure of fault rock depends on mud content, diagenetic degree and structure directionality of rock. The higher the mud content and the larger the degree of diagenesis, the smaller the angle between fault surface and vertical direction, which results in the greater the capillary entry pressure. Based on the fault vertical sealing mechanism and multiple geological factors, in combination with the results of capillary entry pressure of mudstone samples in different angles under laboratory conditions and the relation of rock mechanics decomposition, a set of method that could evaluate the fault vertical sealing ability is then established on the basis of determining the surrendering rock which has the same diagenetic degree with the target fault rock. Then the method was applied to evaluation of the fault sealing ability of 1^st structure of Nanpu sag. The results indicate that the differences of capillary entry pressures of fault rock and reservoir rock in different survey lines of Fault f1 are from -0.114 MPa to 1.035 MPa, the capillary entry pressures of fault rock are larger than that of reservoir rock except for the survey Lines L1 to L7, that fault is sealed invertical direction, which is consistent with oil and gas distribution law. The method is proved more feasible and credible by comparison of the results with those calculated by method which ignores the structure directionality of rock.