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漂白砂岩是证明油气是否曾经存在及其逸散规模的重要证据,对其研究具有重要的理论和实际意义.鄂尔多斯盆地东北部漂白现象主要分布在中生代地层中.通过对延安组漂白砂岩的岩石学特征、主量元素、稀土元素及微量元素分析研究以及与邻近砂岩的对比,初步确定该区漂白砂岩形成于酸性还原环境.岩石学特征主要表现为以自生高岭石胶结为主,含铁矿物边部颜色较中心浅;主量分析结果证实漂白砂岩的Al2O3含量较高,Fe3+/Fe2+比值较低,其总铁含量明显低于白色微红砂岩;稀土元素分析结果显示,漂白砂岩ΣREE较其他砂岩低,且显示Eu亏损和Ce相对富集;微量元素结果显示漂白砂岩Co含量相对较高,Sr相对亏损,Zr和Hf相对较富,与绿色蚀变砂岩值接近,略低于砂岩矿石.同时,盆地北部油砂样品地球化学特征表明,油砂是盆地中部气田石炭—二叠系的较高成熟度的煤成气逸散到地表形成的.砂岩中碳酸盐胶结物C,O同位素值较轻,分别为-11.729‰～-10.210‰和-14.104‰～-12.481‰,指示碳酸盐成因与有机质有关.综合研究表明,鄂尔多斯盆地北东部中生界砂岩漂白现象指示了天然气的逸散作用,其为上古生界天然气还原作用的结果.
Bleached sandstone is an important evidence to prove the existence of oil and gas and its evapotranspiration.The research on bleaching sandstone is of important theoretical and practical significance.The bleaching of northeastern Ordos Basin is mainly distributed in Mesozoic strata.By analyzing the lithology Characteristics, major elements, rare earth elements and trace elements and the comparison with the adjacent sandstone, the bleaching sandstone in this area was initially determined to be formed in an acidic reducing environment.The petrological characteristics mainly include the self-generated kaolinite cementation, The color of the edge of the object is shallower than that of the center. The main mass analysis results show that the content of Al2O3 in bleached sandstone is higher, the ratio of Fe3 + / Fe2 + is lower, and the total iron content of bleached sandstone is obviously lower than that of white reddish sandstone. The other sandstones are low and show the depletion of Eu and the relative enrichment of Ce. The results of trace elements show that Co content of bleached sandstone is relatively high, Sr is relatively depleted, Zr and Hf are relatively rich, close to green altered sandstone, slightly lower than sandstone ore At the same time, the geochemical characteristics of the oil sands in the northern part of the basin show that the oil sands are the higher maturity of coal-derived gas in the Permo-Carboniferous gas field in the central part of the basin To the surface. The C and O isotopic values of the carbonate cements in the sandstone are relatively light, ranging from -11.729 ‰ to -10.210 ‰ and from -14.104 ‰ to -12.481 ‰, respectively, indicating that carbonate causes are related to organic matter. The sandstone bleaching in the Mesozoic in the northeastern Ordos Basin indicates the fugacity of natural gas as a result of the reduction of natural gas in the Upper Paleozoic.