松辽盆地松科1井晚白垩世沉积地层有机地球化学研究

Geochemical research on the Late Cretaceous strata of Well SK1 in Songliao Basin

松科1井是中国大陆第一口以白垩系陆相地层为主的全取心科学探井。通过取心样品的系统地球化学分析,研究了泥岩有机质丰度、类型、成熟演化及有机质沉积环境在纵向上的变化特征。结果表明:青一段泥岩有机质丰度最高,有机碳一般大于2%,平均为3.21%,发育优质烃源岩,其次在青二、三段、姚家组和嫩江组一、二段中也均发育有机质丰度相对较高的源岩层。纵向上泥岩有机质丰度显示出从高向低的9个韵律性变化,反映了湖相沉积过程中气候与水体环境、生物发育及有机质保存条件的周期性变化。青一段泥岩有机质类型主要为Ⅰ型,较高的甾烷含量反映以藻类输入为主,较高的伽马蜡烷和低的Pr/Ph及甲藻甾烷的存在反映该时期水体具有盐度分层和强还原的沉积环境,可能与海侵有关。青二、三段泥岩有机质类型主要为Ⅰ—Ⅱ型,伽马蜡烷和Pr/Ph等多项指标反映出该时期水体呈现振荡变化,有机质受陆源影响加大。姚家组有机质类型变化大,一部分为Ⅰ—Ⅱ1型,另一部分则Ⅱ2—Ⅲ型,较高丰度的泥岩通常具有较好的有机质类型,多项指标反映出该时期沉积环境波动较大。嫩江组一、二段泥岩主要以Ⅰ型和Ⅱ型为主,4-甲基甾烷的存在反映具有沟鞭藻的贡献,较高的伽马蜡烷和低的Pr/Ph反映水体有盐度分层。有机质成熟度指标反映青二、三段中部泥岩开始进入成熟,源岩开始大量生油的深度在1500m。

Well SK1 is the first whole coring hole of the Cretaceous strata in China for scientific research.Different layers of shale in the Well SK1（scientific well） in the Songliao Basin were systematically analyzed by geochemical technique to determine the profile of total organic carbon content（TOC）,maturity and depositional environment.The results show that the most organic-rich source rock is the Qingshankou 1st（K2qn1） formation with an average of TOC at 3.21% while most greater than 2%.Qingshankou 2nd-3rd（K2qn2＋3） formations,Yaojia member（K2y） and Nenjiang 1st-2nd（K2n1＋2） formations have subordinate content of organic carbon.The vertical distribution of TOC shows nine HTB（high TOC at the base,decreasing upward） units,indicating the cyclicity of climate,biomass productivity and organic preservation.The shales of Qingshankou 1st formation mainly contain lacustrine type-I kerogen and have higher content of steranes,indicating algae as the main organic input.The higher amount of gammacerane,relatively low value of Pr/Ph（pristane vs.phytane） and presence of dinosterane all suggest that the lake during the period of Qingshankou 1st formation deposition was subjected to salinity stratification,strong reducing deposition environment,and the potential marine transgression.The shales of Qingshankou 2nd-3rd formations mainly contain type-I and type-II kerogens.Multi indices such as gammacerane index and the value of Pr/Ph indicate that the fluctuating lake and the organic carbon contents must have been mixed with more terrestrial organic debris during the period of Qingshankou 2nd-3rd formations deposition.The kerogen types of Yaojia member vary widely,from type-I to type III.It is a general truth that shale with higher organic carbon content will be more oil-prone,and sections with organic-rich shale in Yaojia member are believed to have promising oil potential.Multi geochemical indices indicate that the deposition environment varied quickly during the deposition of Yaojia member.The shales of Nenjiang 1st-2nd（K2n1＋2） formations are dominated by type-I and type-II kerogens and the amount of 4-methysterane may be attributed to dinoflagellate.The relatively higher amount of gammacerane and low value of Pr/Ph indicate the salinity stratification of water column during the deposition of Nenjiang 1st-2nd formations deposition.The source rock of Qingshankou 2nd-3rd formations became mature in the mid-depth with peak oil-generation at 1500 m.