Analyzing geochemical characteristics and hydrocarbon generation history of the Middle and Upper Jurassic source rocks in the North Yellow Sea Basin

The North Yellow Sea Basin is still in the early stages of exploration. Oil has been recovered from Mesozoic sandstone intervals, but the characteristics of source rocks are not fully understood in this. basin. In this study, the geochemical characteristics and the hydrocarbon generation history of the Jurassic source rocks in the North Yellow Sea Basin have been evaluated. The major findings of the study are as follows: (1) The Middle and Upper Jurassic dark gray and gray black mudstones are the main source rocks in the North Yellow Sea Basin. (2) The organic matter of the Middle Jurassic source rocks is derived from terrigenous higher plants and the type of organic matter is predominantly Type III kerogen. The content of organic carbon is moderate for this type of kerogen, and the hydrogen index (HI) is below 100 mg HC/g TOC mostly; therefore, the Middle Jurassic source rocks will produce gas mainly. The organic matter in the Upper Jurassic source rocks was derived from a mixture of terrigenous higher plants and aquatic lower organisms, and is characterized by the coexistence of Types I, II and III kerogen, there are some excellent local source rock intervals with high organic carbon and higher HI values, which constitute the main oil source rocks. (3) The Middle Jurassic source rocks have fair-poor hydrocarbon-generative potential and the Upper Jurassic source rocks have fair-good hydrocarbon-generative potential. (4) Hydrocarbon generation history models indicate that the Middle Jurassic source rocks reached late mature stages and the Upper Jurassic source rocks reached the oil window at the present-day. These two sets of source rocks all didn't reach the peak of oil and gas generation in NYS2 well. (C) 2014 Published by Elsevier B.V.