Evaluation On Vertical Sealing Ability Of Fault In Ed₂ Mudstone Caprock Of Main Oil-gas Structures Of Nanpu Sag

Through the internal structure of fault zone and its sealing mechanism, it can be found that fault rock constitutes an important part of fault and its distribution in fault is universal, the vertical sealing ability of fault is mainly determined by the displacement pressure difference of fault rock in caprock and the underlying reservoir rock, fault sealed when the displacement pressure in the direction of oil-gas migration of fault rock greater than that of reservoir rock. The sealing ability determined by the degree of displacement pressure difference, the greater the difference, the stronger the sealing ability of fault, and vice versa. The displacement pressure of fault rock mainly depends on the clay content and diagenetic degree of fault rock, while diagenetic degree of fault rock has relation with the diagenetic pressure and diagenetic time of fault rock. In previous research on vertical sealing ability of fault, the considering factors are not comprehensive and the application of technical means are not so perfect, do not recognized the impact of internal structure of fault rock on evaluation results. Therefore, this article based on the influential factors and proposed a new method of fault vertical sealing.To evaluated the vertical sealing ability of fault more accurately, based on the vertical sealing mechanism of fault, measured results of displacement pressure in mudstone samples of different angles under laboratory conditions, decomposition relation between fault rock and reservoir rock, multiple geological factors which affect the vertical sealing ability of fault are taken into consideration,and then established a set of method which considering the direction of displacement pressure of fault rock to evaluated the vertical sealing ability of fault.Taking the main oil-gas structure of Nanpu Sag in Bohai Bay Basin as an example, fully analyzed of the development of fault in Ed2 mudstone caprock and the distribution of oil-gas, and then evaluated the vertical sealing ability of typical faults in Ed2 mudstone caprock of Nanpu Sag quantitatively. The results indicated that, the proposed method could evaluate the vertical sealing ability of fault perfectly, and considerations are more comprehensive, technical means are more scientific and reasonable. The evaluation results accord better with the actual distribution of underground oil-gas and water. It can greatly reduce the risk of drilling in fault traps and avoid unnecessary drilling investment.Althrough the proposed method of fault vertical sealing ability in this paper would reflect the distribution of oil-gas in a certain view, the strong vertical sealing ability areas are not necessary for oil-gas distribution. The development charactristics of faults, strata and source-reservoir-caprock combinations should be consided either. There are only when the vertical sealing ability of fault is strong, and other accumulation factors are preferably, then the target faults are favorable for oil-gas accumulation.