鄂尔多斯盆地延长探区延长组泥页岩有机地球化学特征及评价

鄂尔多斯盆地三叠系延长组在特殊的构造运动和沉积背景下发育了长7和长9两套暗色泥页岩层系,成为了延长组油气成藏的重要烃源岩。鉴于此,本文运用有机地球化学手段对其进行系统的特征描述并进行评价。结果表明,本区延长组泥页岩有机碳含量总体较高,质量分数为3.2%~15.2%,平均为6.8%;氯仿沥青“A”的含量为0.31%~1.15%,平均为0.71%;生烃潜量为10.20~69.93 mg/g,平均为18.28 mg/g;总体评价为好—最好烃源岩。通过热解参数和干酪根显微组分综合分析,延长组泥页岩有机质类型总体以Ⅰ型和Ⅱ1型为主,少量为Ⅱ2型。延长组泥页岩镜质体反射率R o值为0.48%~1.32%,最大热解峰温T max分布在431~474℃,平均为450.9℃,大部分进入生烃门限,主要处于低成熟—成熟阶段。该成果对中生界油气藏的勘探部署和评价有一定的借鉴意义。

Organic Geochemistry and Evaluation of the Shale of Yanchang Formation in Yanchang Exploration Area of Ordos Basin

Under the special tectonic movement and sedimentary background,the Triassic Yanchang formation in Ordos Basin developed two sets of dark shale formations—Chang-7 and Chang-9,which became an important source rock for hydrocarbon accumulation in Yanchang formation.In view of this,this paper described and evaluated systematically its characteristics by means of organic geochemistry.The results show that the organic carbon content of shale in Yanchang formation is generally high,with a mass fraction of 3.2%~15.2%,an average of 6.8%,chloroform asphalt“A”content of 0.31%~1.15%,an average of 0.71%,hydrocarbon generating potential of 10.20~69.93 mg/g,an average of 18.28 mg/g.The overall evaluation is good-best source rock.Through comprehensive analysis of pyrolysis parameters and kerogen maceral,the organic matter types of Yanchang formation shale are mainly typeⅠand typeⅡ1,and a small amount is typeⅡ2.The R o value of vitrinite reflectance of Yanchang formation shale is 0.48%~1.32%.The maximum pyrolysis peak temperature T max is 431~474℃with an average temperature of 450.9℃.Most of the shales have entered the hydrocarbon generation threshold and are mainly in the stage of low maturity-maturity.The results can be used for reference in exploration,deployment and evaluation of Mesozoic oil and gas reservoirs.