Determination method and its application of effective period for transporting oil and gas by the oil source fault of reservoir separated by caprock

In the combination of source rock and reservoir separated by the caprock of a petroliferous basin, the scale of oil and gas accumulation is controlled by the relative length of the effective period of oil and gas transported by the oil source fault. The accurate determination of the effective period of oil and gas transported by the oil source fault in the combination of source rock and reservoir separated by caprock plays an essential role in identifying the oil and gas distributions and guiding oil and gas exploration. Based on a study of the oil–gas transport mechanism and the effective period by the oil source fault of reservoir separated by caprock, a set of determination methods of the effective period for transporting oil and gas by the oil source fault of the reservoir separated by caprock was established herein by coupling the period for transporting oil and gas by the oil source fault and that when the source rocks expelled hydrocarbon. The period for transporting oil and gas by the oil source fault was determined by determining the period when the faults started to destroy the sealing capacity of the mudstone caprock, the period when the faults stopped their activity, and the period when the fault fillers began sealing. The geochemical characteristics of the source rock were used to determine the period when the source rocks expelled hydrocarbon. The application results show that at line L2, the effective period for transporting oil and gas from the F1 oil source fault to the reservoir of the 1^st member of Dongying Formation (E₃d₁) is relatively long (i.e., time: 5.3 Ma). This is conducive to transporting the oil and gas generated by the source rocks of the 1^st member of Shahejie Formation (E₃s₁) to the 3^rd member of Dongying Formation (E₃d₃) through the mudstone caprock of the 2^nd member of Dongying Formation (E₃d₂) to accumulate in the reservoir of E₃d₁ (the upper part of the structure has not been drilled yet). At line L8, the effective period for transporting oil and gas from the F1 oil source fault to the reservoir of E₃d₁ is relatively short (i.e., time: 2.4 Ma). Oil and gas are mainly transported by fault fillers, which is not conducive to transporting the oil and gas generated by the source rocks of E₃s₁ to the E₃d₁ through the mudstone caprock of E₃d₂ to accumulate in the reservoir of E₃d₁. The results are coincident with the fact that small-scale oil and gas have been found near line L8 of the F1 oil source fault in E₃d₁ of the Nanpu 5^th structure, suggesting that the method is feasible for application in the determination of the effective period for transporting oil and gas by the oil source fault of a reservoir separated by caprock.