苏北盆地金湖凹陷三河次凹有效烃源岩评价

Evaluation on Effective Source Rocks of Sanhe Subsag in Jinhu Sag,Subei Basin

金湖凹陷是发育自晚白垩世的断陷湖盆,有效烃源岩识别对凹陷油气勘探具有重要指导作用。基于金湖凹陷三河次凹大量分析测试资料,对研究区阜二段烃源岩地球化学特征进行了系统分析。根据烃源岩演化过程中的物质平衡原理,将烃源岩现今残余总有机碳值恢复到生排烃前总有机碳值。通过烃源岩生排烃过程中饱和烃量与吸附烃量关系确定有效烃源岩下限,对研究区有效烃源岩进行综合评价。结果表明:有机质类型多为II_(1)型;总有机碳(total organic carbon,TOC)含量为0.05%~5.28%,生烃潜力(S_(1)+S_(2))为0.01~33.29 mg/g;镜质体反射率Ro为0.4%~1.2%,烃源岩主要处于低成熟-成熟阶段。研究区烃源岩总有机碳恢复系数为1.05~1.25,用恢复后的总有机碳值来确定有效烃源岩下限,避免了烃源岩生排烃作用影响及高温压物理模拟实验带来的结果偏差。确定研究区有效烃源岩下限TOC含量为1.6%,与测井TOC预测结果相结合,进一步查明了有效烃源岩分布及其厚度,深凹带是三河次凹有效烃源岩主要分布区,其厚度可达160 m以上。

Jinhu Sag is a faulted lake basin developed since the Late Cretaceous.The identification of effective source rocks plays an important role in oil and gas exploration.Based on a large number of analytical tests in Sanhe Subsag of Jinhu Sag,geochemical characteristics of source rocks in the second number of Funing Formation were systematically analyzed.According to the principle of material balance in the evolution of source rocks,the current residual total organic carbon contents were restored to the total organic carbon value before hydrocarbon generation and expulsion.The lower limit of effective source rocks was determined by the relationship between generated hydrocarbon and adsorbed hydrocarbon.According to the lower limit,effective source rocks in the study area were comprehensively evaluated.The results show that type II_(1) occupies most of the organic matter types,total organic carbon(TOC)content is 0.05%~5.28%,hydrocarbon generation potential(S_(1)+S_(2))is 0.01~33.29 mg/g,vitrinite reflectance Ro is 0.4%~1.2%.Thermal evolution of source rocks has reached a mature stage.The recovery coefficient of source rocks is 1.05~1.25.Using recovered total organic carbon value to identify effective source rocks avoid the deviation that subjective factors and physical simulation experiment conditions lead to.The lowest limit of TOC content of effective source rocks is 1.6%.Combining with log prediction,the distribution and thickness of effective source rocks were further ascertained.The deep depression zone is the main distribution area of effective source rocks in Sanhe Subsag.The thickness of effective source rocks reaches more than 160 m.