Thermal evolution modeling of Mesoproterozoic source rocks in the Ordos Basin

The Mesoproterozoic is a potential stratum of gas accumulation and production of the Changqing oil field in the Ordos Basin. However, few recent studies have been made on the thermal evolution history of source rocks.Applying the PetroMod basin modeling software, the thermal evolution histories of the Proterozoic source rocks in each tectonic unit of the study area were simulated taking measured R_o values as calibration and based on the analyses of lithology, erosion thickness restoration and ancient heat flow. The differences of thermal evolution of source rocks in different tectonic units were discussed. Some favorable exploration areas were predicted combining with oil and gas system analyses. The results show that: (1)The hydrocarbon generation threshold of Mesoproterozoic aulacogens and peripheral source rocks is much earlier than others. The maturation stage of other aulacogens and peripheral source rocks is also earlier than others except for the mid-northern part of the western margin thrust belt, and it is in a stage of dry gas generation at present. The source rocks in the Changcheng System reached the hydrocarbon generation threshold at the end of the Late Permian and are generating dry gas now, except for those in the Yimeng uplift, which became mature late and are still generating wet gas. The source rocks in the Jixian System reached the hydrocarbon generation threshold from the end of the Late Permian to the beginning of the Middle Triassic, became mature as the basin depositional center migrated continuously to the west and influenced by intrusions in the northern Tianhuan syncline and western Weibei uplift, and finally entered the dry gas stage in the early Cretaceous. (2)The central area of the Weibei uplift, southern Tianhuan syncline, northwestern Yishan slope,and the central part of the Yimeng uplift in the Ordos Basin are favorable exploration areas.