鄂尔多斯盆地延长探区上古生界烃源岩特征及其与天然气富集之间的关系

Characteristics of Upper Paleozoic Source Rocks and Its Relationship to Gas Enrichment in Yanchang Area of Ordos Basin

为搞清鄂尔多斯盆地延长探区上古生界石炭—二叠系煤层和煤系暗色泥岩的生烃潜力,并揭示其与天然气富集之间的关系,对研究区大量烃源岩样品开展了地球化学分析,并在此基础上计算煤岩和煤系暗色泥岩的生烃强度。同时结合探区内天然气探井试气成果,探讨生气强度对产气能力的影响。研究发现:①探区内大部分烃源岩样品镜质体反射率Ro>2.0%,热演化程度较高,源岩烃类损失严重;对241个煤系暗色泥岩和25个煤岩样品生烃潜力恢复后认为,煤及煤系暗色泥岩整体达到中等—好烃源岩标准,部分煤属极好烃源岩。②生烃强度计算表明煤岩生气能力为煤系暗色泥岩的1.8倍,是探区内的主力烃源岩。③高产气井通常位于生气强度大于30×108 m3/km2的地区,而生气强度小于15×108 m3/km2的地区,气井无阻流量普遍低于1×104 m3/d,说明优质烃源岩对天然气富集成藏具有明显的控制作用。最后根据上述研究结果,指明了延长探区近期的勘探方向,对天然气勘探开发部署具有重要指导意义。

Geochemical analysis was carried out on a large number of source rock samples.And on this basis,the hydrocarbon generating intensity of coal and coal series dark mudstone was calculated.The purpose was to find out the hydrocarbon generating potential of Upper Paleozoic Carboniferous-Permian coal seam and coal series dark mudstone,and to reveal its relationship to the enrichment of natural gas in Yanchang exploration area of Ordos Basin.The results show that:①The vitrinite reflectance of the most source rock samples is more than 2.0%,which means the source rocks are in the high thermal evaluation level and leads to the serious loss of hydrocarbon in the source rocks.After the recovery of hydrocarbon generation potential of 241 coal series dark mudstone and 25 coal rock samples,it is considered that the coal and mudstone as a whole meet the standard of moderate to good source rock,and some of them are rated as excellent source rocks.②Based on the calculation of hydrocarbon generation intensity,it is shown that the coal series dark mudstone is the main source rock in the exploration area,and its hydrocarbon generation capacity is 1.8 times of that of the coal series dark mudstone.③High yield gas wells are usually located in areas with gas generation intensity of more than 30×108 m 3/km 2,while lowers often located in regions with gas generation intensity of less than 15×108 m 3/km 2.This indicates that the high-quality source rock has obvious control over the gas enrichment.Finally,the direction of exploration is pointed out for the near future according to the above research results,which is of great significance to the deployment of natural gas exploration and development.