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以二连盆地下白垩统为例,研究了小型断陷湖盆有效烃源岩分布特征与分布模式。根据烃源岩热解分析指标S1与有机碳含量的关系,建立了有效烃源岩有机质丰度的下限标准,对二连盆地有效烃源岩进行了识别,研究了有效烃源岩的分布。研究发现小型断陷湖盆有效烃源岩分布特征明显不同于大型湖盆有效烃源岩主要分布在深湖—半深湖区的特征,其有效烃源岩的分布有3种模式,即深洼型、近洼缓坡型和深洼—缓坡型。边界断层规模大、活动性强的小型断陷湖盆一般深洼带宽度与盆地宽度比值大,有效烃源岩主要分布于深洼带;边界断层规模小、活动性弱的小型断陷湖盆深洼带宽度与盆地宽度比值小,有效烃源岩主要分布于近洼缓坡带;边界断层规模中等、活动性适中的小型断陷湖盆深洼带宽度与盆地宽度比值居中,有效烃源岩在深洼带和近洼缓坡带均有分布。小型断陷湖盆凹陷结构和形成机制的差异控制了湖盆的沉积速率、古生产力和水体氧化-还原条件,决定了有效烃源岩的形成和分布。
Taking the Lower Cretaceous in Erlian Basin as an example, the distribution characteristics and distribution patterns of available source rocks in small faulted lacustrine basin were studied. According to the relationship between the index S1 of hydrocarbon source rock and the organic carbon content, the lower limit of the organic matter abundance of the effective source rock is established, and the effective source rock of Erlian basin is identified and the distribution of available source rocks is studied. It is found that the distribution of available source rocks in small fault-depressed lake basins is obviously different from that of the effective source rocks in large-scale lakes mainly distributed in the deep-lacustrine-semi-deep lake. There are three modes of effective source rock distribution, namely, deep depression Type, near depression and deep depression - gentle slope type. In the small fault basin with large boundary and active activity, the ratio of the depth of deep depression to the width of basin is large, and the effective source rocks are mainly distributed in the deep depression. The small fault basin with small boundary and weak activity The ratio of deep belt width to basin width is small, and the effective hydrocarbon source rocks are mainly distributed in the near depression depression zone. The ratio of deep depression width to basin width is medium in medium-sized and moderately active fault basins, and the effective source rocks There are distributions in both deep and near depression belts. The differences in the structure and formation mechanism of the small fault depression lake basins control the sedimentation rate, paleoproductivity and oxidation-reduction conditions of the lake, which determine the formation and distribution of effective source rocks.