鄂尔多斯盆地东南部张家滩页岩元素地球化学、古沉积环境演化特征及油气地质意义

Characteristics of Element Geochemistry and Paleo Sedimentary Environment Evolution of Zhangjiatan Shale in the Southeast of Ordos Basin and Its Geological Significance for Oil and Gas

页岩厚度、总有机碳含量、脆性矿物含量、物性等是页岩储层评价的关键参数,明显受其沉积环境控制。因此,分析页岩形成过程中的沉积环境对页岩储层评价和甜点预测具有重要意义。系统测试了鄂尔多斯盆地中南部Y1井钻遇的张家滩页岩525组样品的40余种元素丰度,分析了其元素地球化学特征和页岩沉积环境的古气候、古水深、古盐度、古生产力、氧化还原特征。结果表明,自下而上张家滩页岩元素的丰度和比值呈周期性变化,指示其形成于温暖湿润、淡水—微咸水、缺氧等沉积环境,其中4单元发育在最潮湿的沉积环境,当时的水体最深、还原性最高,具有较高的古生产力。

Shale thickness, total organic carbon content, brittle mineral content and physical property are key parameter of shale reservoir evaluation, which are obviously controlled by the sedimentary environment. Therefore,it＇s significant to study the sedimentary environment and the evolution of the shale formation a- bout gas reservoir evaluation and desserts prediction. This paper systematically tested more than 40 ele- ment concentrations of 525 groups of samples in Zhangjiatan shale drilled by well Y1 in the South-Central Ordos Basin. Then we analyzed the evolution of the paleoclimate, the paleobathymetry, the paleosalinity, the paleoproductivity and the oxidation-reduction states of sedimentary environment. The results showed that there are significant periodical changes of the element concentrations and ratios of Zhangjiatan shale from bottom to top, indicating that Zhangjiatan shale was deposited in a warm and humid, freshwater- brackish, hypoxia sedimentary environment, between which, the @ unit was deposited in a wet sedimentary environment,when the water was deepest and highest reducing with high paleoproductivity.