苏北盆地溱潼凹陷北汉庄油田油气成藏地球化学特征

Geochemical Characteristics and Accumulation Process of Beihanzhuang Oilfield of Qintong Depression,Northern Jiangsu Basin

苏北盆地溱潼凹陷划分为断阶带、深凹带和斜坡带3排构造带,受溱潼凹陷构造带的控制,油田呈条形分布特征,北汉庄油田分布在外斜坡带。通过对北汉庄油田的原油和烃源岩的分子生物标志化合物相关参数与浓度的分析,结合常规的地质—地球化学的方法,系统研究了溱潼凹陷的北汉庄油田的油气成藏过程。研究结果表明,北汉庄油田的原油可以划分为2类:第一类原油分布于垛一段与阜三段,主要来源于深凹带阜二段烃源岩;第二类原油分布在阜一段,主要来源于深凹带阜一段烃源岩。含氮化合物浓度及其相关参数分析表明,油气沿砂体自深凹带向北汉庄油田运移,运移趋势明显,再根据深凹带烃源岩生排烃史、断层封闭史以及油气成藏期次分析,阜二段烃源岩在戴南组末期开始生烃,新近纪达到生烃高峰,与油气成藏期有较好的匹配关系,三垛组运动以后,断层垂向封闭性较强,阜二段烃源岩生成的油气通过阜三段的砂体自深凹带横向运移至北汉庄地区聚集成藏,形成了以岩性构造油气藏为主的圈闭。

Qintong depression are divided by three structure belts, the faulted belt, the deep sag belt and the slope belt, controlling the banded distribution of oil-fields. Beihanzhuang oil-field is in the exterior slope belt. According to the analysis of biomarker parameters and concentration in extracts of source rock and oil, combined with the routine geological and geochemical methods, the process of migration and accu- mulation of Beihanzhuang oil field is studied systematically. The results indicate that two types oil could be identified. The first type is Es1 and E f3 member oil, which is derived from E f2 member source rock of deep sag. The second type is E f1 member oil which is derived from E fl member source rock of deep sag. Integrated with the analysis of pyrrolic nitrogen compounds and its parameters, Beihanzhuang E f3, E f1 and ESl member oil migrated from deep sag to Beihanzhuang structure belt apparently. Also, in accordance with of the generation and discharging history of hydrocarbon, the faulted sealing capacity and the forma- tion stage of accumulation, E f2 member source rock generated and expulsed hydrocarbon during the Dain- an formation period and reached the generated hydrocarbon peak during the Eogene period, which is matched with the E f3 member the formation stage of accumulation. After Sanduo movement, the vertical sealing capacity of Beihanzhuang faults was competent so that the E f3, E f1 , ESl member oil was generated from El2 and E f1 source rock and migrated by El3 and E f1 member sand body from deep sag to slope belt forming the lithologic-structrual oil reservoirs dominantly.