幔源CO对渤海海域秦皇岛29构造带油气成藏的影响

Influence of mantle-derived CO on hydrocarbon accumulation in Qinhuangdao 29 tectonic zone， Bohai Sea

李威 徐建永 刘志峰 李友川 朱文奇

Wei LI Jianyong XU Zhifeng LIU Youchuan LI Wenqi ZHU

秦皇岛29构造带是渤海海域为数不多的典型高含CO气体的油气带，研究油气充注与高丰度CO气体运移、聚集之间的相互关系，对于油气勘探和CO气藏的发现都具有重要意义。基于原油饱和烃和芳烃等地球化学实验分析结果以及流体包裹体岩石学特征等，系统开展了CO气体充注与秦皇岛29构造带油气成藏的相互关系及影响，研究并深入探讨了秦皇岛29构造带高含CO气体的油气藏形成机理。研究认为：①构造带油气主要赋存于沙河街组一段（沙一段）和东营组，油气来源于秦南凹陷沙一段和沙三段烃源岩，以沙一段为主；②构造带油气藏经历了两期油气充注事件，早期以原油充注为主，运移方向以横向为主，石油自北向南沿着砂体运移，由秦南凹陷运移至凸起带，晚期发生了岩浆热流体引起的气体瞬时充注事件，以垂向运移为主，富含烃类的超临界CO流体先沿着深大断裂向上运移，进入主力油层后，自南向北横向运移；③构造带油气藏气洗作用比较明显，形成了主力油气藏底部富集稠油和沥青、中部为轻质油、上部为凝析油，以及顶部以CO气体为主要气层的油气分布格局。

Reservoirs of high CO content are rarely found in Bohai Sea， offshore of the Bohai Bay Basin， and Qinhuangdao 29 tectonic zone （QHD29） is one of the few typical reservoirs of the type. To study the correlation of hydrocarbon accumulation with the migration and accumulation of high-CO-content gas is of great significance to oil and gas exploration and the discovery of CO gas reservoirs. Based on geochemical analysis of saturated and aromatic hydrocarbons， petrologic characteristics of fluid inclusions， we systematically discuss the interrelationship between CO charging and hydrocarbon accumulation in QHD29 tectonic zone and the genetic mechanism of hig-CO-content reservoirs in the tectonic zone. The results are shown as follows. First， the hydrocarbons sourced from the source rocks of the first and third members of Shahejie Formation （E and E） mainly accumulate in the E， followed by Dongying Formation （E）. Second， QHD29 reservoirs underwent two stages of hydrocarbon charging. The early stage features crude oil charging dominated by north-south lateral migration from the Qinnan Sag to the uplift along the sand bodies； and the late stage features instantaneous gas accumulation caused by magmatic-hydrothermal fluid as dominated by vertical migration. The supercritical CO， fluid rich in hydrocarbons， moved upward along the deep-rooted faults， entered the major oil reservoirs， and then moved laterally from south to north. Third， QHD29 reservoirs obviously experienced gas washing under both early oil and late gas accumulation events， forming a hydrocarbon distribution pattern with heavy oil and bitumen enriched at the bottom， light oil and gas condensate in the middle， and CO gas dominating on top of the major reservoirs.

10.11743/ogg20230213