鄂尔多斯盆地盐池-定边地区长7烃源岩有机地球化学特征及沉积环境研究

通过对鄂尔多斯盆地盐池-定边地区长7段烃源岩的分析,研究区长7段烃源岩有机碳平均含量为3.22%,生烃潜量均值为12.8 mg/g,氯仿沥青“A”均值为0.55%,可以划分为较好-好的烃源岩,具有良好的生烃潜力。利用有机岩石学分析、热解分析,并结合饱和烃生物标志物分析,发现研究区长7段烃源岩有机质类型以Ⅱ₁型和Ⅱ₂型为主,有机质以菌藻类生源为主,并伴有部分高等植物生源。烃源岩有机质成熟度R_o值介于0.42%~0.76%之间,并且热解T_max也主要集中在440~455 ℃之间,并且正构烷烃分布特征及甾、藿烷异构化参数说明烃源岩有机质处于低熟-成熟度阶段。根据饱和烃中甾藿烷参数、三环萜烷参数、伽马蜡烷指数、β-胡萝卜烷相对含量以及姥植比参数特征,研究区长7段烃源岩沉积环境为湖相淡水弱氧化-弱还原环境。

Organic Geochemistry and Sedimentary Paleoenvironment of Chang 7 Source Rocks in Yanchi-Dingbian Area,Ordos Basin

Analysis of the Chang 7 source rocks in Yanchi-Dingbian area (Ordos Basin) indicates that the total organic carbon, hydrocarbon potential and chloroform extracted bitumen “A” are on average 3.22 %, 12.8 mg/g and 0.55 %, respectively. Based on these results, the source rocks can be classified into the fair to good categories, suggesting a high hydrocarbon potential. Organic petrology, rock-eval and biomarker evidence suggest that the main types of organic matter are Ⅱ₁ and Ⅱ₂, and that the organic matter source is dominated by algae or bacteria with minor high plant. The R_o and T_max of the source rocks are of 0.42% to 0.76% and 440 ℃ to 460 ℃, respectively. The normal distribution, steranes and hopanes isomerization parameters indicate that the organic matter varies from lowly-mature to mature. In addition, the parameters of steranes, hopanes, tricyclic terpene, gammacerane, β-carotane and Pr/Ph indicate that the sedimentary environment of Chang 7 was lacustrine-brackish, and weakly oxidized or weakly reduced.