Numerical simulation of Mesozoic hydrocarbon generation, migration and accumulation in the southern East China Sea

Comprehensive analysis and numerical simulation are conducted for hydrocarbon generation, expulsion, migration and accumulation in the southern East China Sea. Results show that the dark mudstones in the T₃-J₂ and K₁²-K₂ have similar hydrocarbon generation potential roughly in an amount of 1.2×10¹¹ t. The dark mudstone developed in J_1-2 has been proved a mature and effective source rock by oil and source rock correlation, whereas the dark mudstone deposited in the K₁²-K₂ is also a potential source rock of the study area. The hydrocarbons generated by T₃-J₂ source rocks started migration and accumulation in Early Cretaceous and peaked in Late Cretaceous, while the hydrocarbons generated by K₁²-K₂ source rocks started moving in Late Cretaceous and reached its peak in Late Paleocene. Traps formed by the Yandang movement, the Oujiang movement and the movements before them were favorable for capturing the hydrocarbons coming from the Jurassic and Cretaceous source rocks. Faults and unconformities formed by the Mesozoic-Cenozoic multi-stage tectonic movements provided prevailed paths for hydrocarbon to move and accumulate in the structural traps in the fault-zone in preferential position. The hydrocarbon accumulation in the Cretaceous is estimated three times more than that in the Jurassic. The structural type and the joint structural-unconformity type of accumulations near the unconformity surface between J₂ and K₁ is two important types of hydrocarbon accumulation in the Mesozoic. Two accumulation models i.e. the "near-source accumulation" and the "far-source accumulation", are discovered. There are three types of hydrocarbon accumulations: the accumulation synchronously generated, stored and sealed; the accumulation early generated, later stored and sealed, and the accumulations formed by later generated hydrocarbon which stored in old deposits and covered by younger sediments.