东海西湖凹陷平湖组烃源岩有机地球化学非均质性评价

Evaluation of organic geochemical heterogeneity of source rocks in Pinghu formation,Xihu sag,East China Sea

西湖凹陷是东海陆架盆地最重要的含油气凹陷,烃源岩是控制油气分布的一个重要因素。西湖凹陷平湖组烃源岩非均质性强,为明确研究区不同层段和不同地区烃源岩地球化学特征,利用烃源岩的总有机碳含量、岩石热解、干酪根元素和镜质体反射率等参数,对西湖凹陷平湖组烃源岩进行综合分析研究。结果表明,平上段和平中段烃源岩属于中等—好的烃源岩,有机质都以Ⅱ_(2)型为主,平上段烃源岩处于未成熟—低成熟,平中段烃源岩处于低成熟,平下段烃源岩处于低成熟—成熟演化阶段。宝云亭和武云亭地区烃源岩属于中等烃源岩,孔雀亭地区烃源岩属于好的烃源岩,主要以Ⅱ_(1)型-Ⅱ_(2)型有机质为主,还有少量的Ⅰ型有机质。宝云亭和武云亭地区烃源岩在低成熟到成熟演化阶段,孔雀亭地区烃源岩在成熟演化阶段。生物标志化合物分析显示研究区平湖组不同层位和不同地区烃源岩沉积环境都为氧化环境,母质来源陆生植物。该研究结果对西湖凹陷平北地区的生烃潜力评价、油源对比及油气勘探开发提供地球化学依据。

Xihu depression is the most important oil-gas bearing depression in the East China Sea shelf basin,and source rock is an important factor controlling the distribution of oil and gas.Since the source rock of Pinghu formation in Xihu depression is highly heterogeneous,parameters such as total organic carbon content of the source rock,rock pyrolysis,kerogen element and vitrine reflectance of the source rock are used to define the geochemical characteristics of the source rock in different intervals and regions of the study area.The source rocks of Pinghu formation in Xihu depression are comprehensively analyzed and stud-ied.The results show that the source rocks in the upper and middle parts of Pinghe belong to the medium-good source rocks,and the organic matter is mainlyⅡ_(2) type.The source rocks in the upper part of Pinghe are in the immature and low mature stage,the source rocks in the middle part of Pinghe are in the low mature stage and the source rocks in the lower part of Pinghe are in the low mature stage.The source rocks in Baoyunting and Wuyunting areas belong to the medium source rocks,while the source rocks in Kongqueting area belong to the good source rocks.The source rocks are mainly composed ofⅡ_(1)-Ⅱ_(2) type organic matter,and there is a small amount ofⅠtype organic matter.The source rocks in Baoyunting and Wuyunting areas are in the stage of low maturity to mature evolution,and the source rocks in Kongqueting area are in the stage of mature evolution.The analysis of bi-omarkers shows that the sedimentary environment of source rocks in different layers and regions of Pinghu formation in the study area is oxidizing environment,and the parent material is from terrestrial plants.The results of this study provide geochemical basis for hydrocarbon generation potential evaluation,oil-source correlation and petroleum exploration and development in Pingbei area of Xihu depression.