Abstract:

Carboniferous-Permian coal-formed gas reservoir in the northeast of Jizhong Depression is a main target exploration field.
In this work, the burial history and the thermal evolution history considering the role of magma intrusion were simulated based on a
large number of regional drilling, logging, geochemistry and paleo-temperature data. The results show that the Carboniferous-Permian strata in general experienced three stages of subsidence and two uplift stages after deposition in the northeast of Jizhong Depression. The tectonic evolution of the whole research area is similar before the Indo-Sinian orogeny, and began to show difference in the Indo-Sinian and the Yenshanian orogeny. Finally, in the Cenozoic the tectonic framework formed with uplift in the east and depression in the west. The source rocks in the region contain two styles of hydrocarbon generation: primary and secondary. The thermal evolution can be subdivided into three types, namely long-term uplift, later strong subsidence, and magmatic thermal metamorphism. The primary hydrocarbon generation occurred in the late Triassic, and the secondary hydrocarbon generation in Neogene or the magmatism period in Paleogene. Also, primary hydrocarbon generation only occurred in the shallow slope and the uplift regions and the secondary hydrocarbon generation occurred in the deep slope and sags because the later subsidence was strong. The secondary hydrocarbon also occurred in the slope and the uplift with magma intrusion caused by magmatic thermal metamorphism. The hydrocarbon was of non-accumulation potential as a result of low kerogen maturity, which was about 0.7% of Ro, in primary hydrocarbon generation period. However, the hydrocarbon was of accumulation potential because of the high maturity and over-maturity stage of the source rocks, and the good reservoir favorable conditions in the second hydrocarbon generation stage.

Key words: Jizhong Depression, Carboniferous-Permian, source rocks, thermal evolution history, secondary hydrocarbon generation