沙南凹陷西洼成藏主控因素及有利勘探区带

Main controlling factors of hydrocarbon accumulation and favorable exploration zone in West Shanan Sag

沙南凹陷西洼历经多年勘探,一直没有取得商业性突破,其勘探潜力备受质疑。文中在对该凹陷西洼整体结构及构造演化特征进行综合研究的基础上,系统分析了该区已发现油气藏的成藏类型及成藏特征。结果表明:西洼的凹陷结构类型控制了油气运移的方向,圈闭的有效性控制了油气成藏的充满度,古近系储层的发育程度控制了油气成藏的规模,断裂的活动期次控制了油气分布的层位。分析认为:勘探程度最高的沙中构造带没有处于油气运移的优势指向区,是造成西洼目前钻探成果不理想的主要原因;圈闭有效性较差及沙河街组储层不发育是油气成藏规模小的重要原因。最后指出,沙南凹陷西洼的两侧斜坡区为比较有利的勘探区带,尤其是南侧斜坡区具有较大的勘探前景。

After the exploration for many years,geologists have failed to find commercial oil and gas in West Shanan Sag,where its exploration potential has long been questioned.Based on the comprehensive study of structure and tectonic evolution characteristics of West Shanan Sag,the founded oil and gas reservoirs and hydrocarbon accumulation characteristics were analyzed systematically.The result shows that the structure style of West Shanan Sag controls the direction of oil-gas migration;the effectiveness of trap controls the fullness degree; the development of Paleogene reservoir controls the size of hydrocarbon accumulation; the movement stage of fault controls the distributed layers of oil and gas.The main reason of failure in West Shanan Sag drilling is that Shazhong structural belt,with the highest exploration degree,isn＇t located in the path of predominating migration directions; poor effectiveness of trap and poor reservoir development in Shahejie Form ation are important reasons for the small size of hydrocarbon discoveries.Finally,it is pointed out that the slope belts on both sides of West Shanan Sag are considered as relatively favorable exploration zones,in which the south slope belt has a great prospective.