Prediction method of vertical sealing evolution form and distribution position of oil source faults

This paper aims to study the distribution pattern of oil and gas beneath the regional mudstone caprock at oil source faults in petroliferous basins. Based on the research of the vertical sealing evolution forms of oil source faults and their distribution locations, the study is conducted from two aspects. One is to determine the vertical sealed and unsealed positions of oil source faults during the oil and gas accumulation period according to the ancient fault juxtaposition thickness of the regional mudstone caprock and the maximum such thickness for fault connection. The other is to clarify the current vertical sealed and unsealed positions of oil source faults by analyzing the mixed displacement pressure of fault rocks and the current displacement pressure of underlying reservoir rocks. By integrating these two aspects, a prediction method is established. Applied to the Dazhangtuo Fault in Qikou Sag of Bohai Bay Basin, it reveals 4 forms of vertical sealing evolution. The sealed-sealed form distributes in the west, center and east; the sealed-unsealed form is in one west location; the unsealed-sealed form is in two east locations; the unsealed-unsealed form is in one location. The distribution of sealed-sealed and unsealed-sealed forms is beneficial for oil and gas accumulation, proving the method's feasibility and providing a new perspective for related studies.But this method can only be used in basins or sags with a large number of measured displacement pressures of surrounding rocks.