鄂尔多斯盆地渭北隆起烃源岩成熟度分布特征与热演化史恢复

渭北隆起发育多套烃源岩，是寻找油气的重要战略区。对渭北隆起不同层位烃源岩的热演化程度变化规律及热演化历史缺乏深入研究。本文利用大量反射率测试资料及裂变径迹分析资料，确定了研究区不同层位热演化程度及变化规律，在恢复剥蚀厚度及埋藏史的基础上，恢复了渭北隆起的构造热—演化史及生烃史。研究结果表明：渭北隆起上三叠统延长组处于生油阶段、石炭—二叠系、奥陶系处于生气阶段，不同层位热演化程度总体上具有北高南低、西高东低的特点。渭北隆起不同层位镜质体反射率与深度关系为似线型，镜质体反射率随深度增加而增加。渭北隆起自早白垩世末以来经历了大规模抬升冷却，具有南早北晚的特点，40 Ma以来，研究区整体快速抬升冷却。热演化史研究表明渭北隆起不同层位最高热演化程度是在早白垩世达到的，从寒武纪到侏罗纪，地温梯度总体较低；中生代晚期早白垩世，受构造热事件影响，古地温梯度最高可达46.0 ℃/km；晚白垩世以来，由于地温梯度降低及地层大规模抬升剥蚀，地层温度明显降低。渭北隆起奥陶系、石炭—二叠系烃源岩天然气生气高峰期、上三叠统延长组烃源岩生油高峰期均在早白垩世，生油、生气高峰期受中生代晚期高地温梯度、构造热事件的控制。新生代以来渭北隆起大规模抬升剥蚀，地层快速抬升冷却，地层温度明显降低，烃源岩生烃过程停止。

Thermal maturity distribution characteristics and thermal history reconstruction of hydrocarbon source rocks in the Weibei uplift,Ordos Basin

The Weibei uplift, located in the southern Ordos Basin, is an important strategic area for oil and gas exploration with multiple sets of source rocks. However, due to the lack of effective thermal indicator data, the thermal maturity distribution and thermal history of different source rocks remains poorly constrained. In this paper, based on the large number of measured vitrinite reflectance data and fission track analysis data, we have determined thermal evolution degree of different source rocks and reconstructed tectonic-thermal history in the Weibei uplift. The results show that the thermal evolution degree of different source rocks in the Weibei uplift is generally characterized by high values in the north and west, low in the south and east. The source rocks of the Late Triassic Yanchang Formation are in the stage of maturate oil-generating, while the Carboniferous-Permian and Ordovician source rocks are in the stage of gas-generating. In addition, there is a positive correlation between the vitrinite reflectance and depth of the different layers. The apatite fission track data indicates that the Weibei uplift has undergone large-scale uplift and cooling since the end of Early Cretaceous（ca.110 Ma）, and it is also associated with characteristic of early uplift in the south and late uplift in the north. After ca.40 Ma, the whole Weibei uplift has been rapidly uplifted. The study results of thermal evolution history show that the highest thermal evolution degree in different layers was reached in the Early Cretaceous period. From the Cambrian to the Jurassic, the paleogeothermal gradient was generally lower, and the maximum paleogeothermal gradient was up to 46 ℃/km in the Early Cretaceous, which was influenced by tectonic thermal events. Since the Late Cretaceous, paleogeothermal gradient was obviously reduced. The Early Cretaceous was the main oil-gas generation period of the Ordovician, Carboniferous-Permian and Triassic source rocks, which was controlled by high geothermal gradient and tectonic-thermal events of the Early Cretaceous. Since the Cenozoic, the Weibei uplift experienced a large uplift-cooling event, as a result, the formation temperature decreased and the hydrocarbon generating process cease.