摘要:
以大量烃源岩样品地球化学分析为基础,综合应用钻井以及地震等地质资料,从有机质丰度、类型、成熟度、母质来源、沉积环境以及生物标志物等方面对乌石凹陷流沙港组烃源岩地球化学特征进行了研究。研究结果表明,流三段发育于还原湖泊环境,有机质丰度较高,类型主要为Ⅱ1-Ⅱ2型;流二段沉积于弱还原至还原环境,有机质丰度最高,尤其是流二段油页岩基本为优质烃源岩,有机质类型以Ⅱ1-Ⅱ2型为主;流一段沉积于偏氧化性湖泊环境,有机质丰度最低,类型以Ⅱ2-Ⅲ型为主。依据烃源岩综合演化剖面,将其热演化过程划分为未成熟、低成熟、成熟和高成熟4个阶段,确定了烃源岩生烃门限深度为2900m,生烃高峰位于3600m。低伽马蜡烷指数显示流沙港组沉积时期水体为淡水环境,丰富的4-甲基甾烷表明水生低等植物对烃源岩母质来源有较大贡献。
Abstract:
Based on the analysis of organic geochemical data of source rocks, drilling and seismic data, the present paper focuses on the geochemical signatures of the source rocks from the Liushagang Formation in the Wushi depression, Beibuwan Basin, including organic matter abundance, type, maturity, parent rock source, sedimentary environment and biomarkers. The analytical results show that the third member of the Liushagang Formation was deposited in a reduced lake environment with higher organic matter abundances and organic matter types of II1-II2. The second member of the Liushagang Formation was deposited in a slightly reduced to reduced environment with the maximum organic matter abundances and organic matter types of II1-II2, indicating the excellent source rocks of the oil shales in this member. The first member of the Liushagang Formation was deposited in an oxidation-prone shallow lake environment with minimum organic matter abundances and organic matter types of II2-III. According to the thermal evolutionary profile of the source rocks, four stages for the thermal evolutionary processes are recognized, including immature, low mature, mature and high mature stages. The threshold depth is 2900 m for the generation of hydrocarbons, and maximum depth is 3600 m for the generation peak of hydrocarbons in the source rocks. The low gammacerane indices have reflected the freshwater environments for the deposition of the Liushagang Formation. The low aquatic plants made greater contributions to the sources of the parent rocks indicated by abundant 4-methyl steranes.
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