Delimiting the evolutionary stages of sealing properties of fault-zone fillings：Taking the F₃ fault in K₁<italic>d</italic>₁ of Beier Depression as an example

ObjectiveThe unreasonable classification of the evolutionary stages of the sealing ability of fault-zone fillings prevents a reasonable explanation of the variations in petroleum distribution in different parts of fault traps. MethodsTo address this problem, we propose a method that evaluates and tracks the closure index and cement index for both fault-zone fillings and underlying reservoir rocks, and then comprehensively delimits the evolutionary stages of fault sealing by comparing the relative values of the closure index and cement index between fault-zone fillings and underlying reservoir rocks.The method was applied to the F3 fault in K1d1 of the Huhenuoren tectonic belt, Beier Depression, Hailar Basin. ResultsThe results show that: The fault-zone fillings of the F3 fault in K1d1 are in the stage of non-closure sealing and non-cement sealing at measurement points 2, 4, 6, and 9-11, which is unfavorable for the accumulation and preservation of petroleum in K1n2, consistent with the absence of petroleum during drilling. The fault-zone fillings of the F3 fault in K1d1 at measurement points 1, 3, and 5 are currently in the closure sealing stage. However, due to their evolutionary stages being non-closure sealing and non-cement sealing during the critical period of reservoir formation, no petroleum was obtained during drilling. The fault-zone fillings of the F3 fault in K1d1 at measurement points 7, 8, and 12-15 are in the closure sealing and cement sealing stages, which favors the accumulation and preservation of petroleum in K1n2 and has bed to the acquisition of industrial oil and gas flous. ConclusionTherefore, the proposed method for delimiting the evolutionary stages of fault-zone fillings material sealing ability is feasible, providing important insights for assessing the sealing ability and formation timing of fault traps and enhancing the efficiency of oil and gas exploration.