江汉盆地西南缘二次生烃及其对油气成藏的影响

Researches on secondary hydrocarbon generation in Southwest of Jianghan Basin and its effects on hydrocarbon accumulations

江汉盆地西南缘地区谢凤桥、复兴场、采穴等构造带的油气富集程度差别很大,油气富集程度与早第三纪晚期构造抬升剥蚀和二次生烃潜力的大小有关。烃源岩晚期增熟、原油同源但成熟度不同以及流体包裹体等证据均证实研究区发生了二次生烃作用。研究区构造在盆地抬升前形成的油气藏在盆地抬升时部分或全部被破坏;能捕获到二次生烃的构造,油气富集程度相对较高。谢凤桥构造捕获并保存了两次生成的油气,油气富集程度最高。采穴构造和复兴场构造初次运聚的油气成藏后在盆地抬升时部分散失,但采穴构造获得二次生烃供油,油气富集程度较高,而复兴场构造未获得二次生烃供油,油气藏含油饱和度低,油气富集程度差。

Hydrocarbon enrichment varies and Caixue in the southwestern related to the uplift and erosion margin of processes dramatically in such structural belts as Xie Fengqiao, Fu Xingchang, Jianghan basin. The extent of hydrocarbon enrichment is found to be in the Late Eogene and the potentiality of secondary hydrocarbon generation. Evidences, such as the late mature of source rocks, crude with the same source but different maturities, and the fluid-inclusion anaysis, all suggest a possibility of secondary hydrocarbon generation in the study area. The oil reservoirs that were formed before the rise of basin were partly or entirely destroyed with the rise of the basin, structures that could capture the secondary hydrocarbon generation have relatively high hydrocarbon enrichment. Xie Fengqiao structure had captured and preserved the primary and secondary hydrocarbons, thus its enrichment level is the highest. Caixue and Fu Xingchang belts suffered from great loss of their primary hydrocarbons in the process of rise of the basin. However, Caixue belt has a higher enrichment of hydrocarbons for having received a supply of second hydrocarbon generation, while Fu Xingchang, without the process of secondary hydrocarbon generation, has a lower oil saturation and poor enrichment of hydrocarbons.