阿拉善地区上古生界烃源岩评价

Hydrocarbon-generated Evaluation on Upper Paleozoic Source Rocks from Alashan Area

阿拉善地区上古生界发育石炭系和二叠系2套烃源岩,通过大量的区域地质调查及有机地球化学、无机地球化学分析,阿拉善地区上古生界烃源岩主要以暗色泥岩及碳酸盐岩为主,石炭系和二叠系的V/(V+Ni)≥0.46和富集Cu、Zn等,表明烃源岩沉积环境为还原环境,且二叠系古盐度值高于石炭系,古生产力变化规律不明显。烃源岩有机质类型较差,体现了腐殖型特征;可能与有机质热演化程度已处于高—过成熟阶段,使得烃源岩类型变差有关。垂向上,石炭系烃源岩有机质丰度优于二叠系;平面上,校育川地区暗色泥岩的有机质丰度最高,而优质的碳酸盐岩烃源岩则主要分布在呼鲁斯太地区。因此,阿拉善地区上古生界具有一定勘探潜力,但主要以寻找天然气为主。

Two sets of source rocks of Carboniferous and Permian are distributed in the Alashan area.Based on observation of regional geological survey and analysis of organic and inorganic geochemistry,the possible source rocks in this area are black mudstone and grey carbonate.The high V/（V＋Ni） ratios with value more than 0.46 and abundance of Cu and Zn suggest that the source rocks in Carboniferous and Permian were formed under an anoxic sedimentary environment,with palaeo-salinity in Permian higher than that in Carboniferous and no change of palaeo-productivity.The poor type of source rocks,which is emerged in humic property,is related to high /over thermal maturity,since the high thermal stress would cause the poor type of source rock.In the vertical section,the total organic carbon（TOC） in the Carboniferous sources is higher than that in Permian.In the regional area,the maximum value of TOC in the mudstone from the Xiaoyuchuan section occurs,in contrast that the high quality of carbonate source is distributed in the Hulusitai area.Therefore,a certain potential of oil and gas prospect in upper Paleozoic measure of the Alashan area is proposed,especially for nature gas.