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利用有机质丰度、类型、成熟度及生气强度指标对鄂尔多斯盆地西南部上古生界烃源岩进行综合分析,确定主力气源岩及平面分布特征,并与苏里格地区气源条件进行对比,分析气源条件对天然气藏形成与分布的控制作用。研究表明,研究区上古生界烃源岩包括山西组、太原组的煤层和暗色泥岩,其中煤层是主力烃源岩,平均厚度为4.7m,苏里格地区煤层平均厚度为14m。烃源岩有机质丰度较高,山西组和太原组煤层残余有机碳均值分别为54.94%和66.96%,泥岩残余有机碳均值分别为2.88%和1.75%;干酪根碳同位素值介于-24.56‰~-22.05‰之间,属于Ⅲ型干酪根;镜质体反射率介于1.6%~3.2%之间,均值为2.3%,整体处于高成熟—过成熟阶段;研究区生气强度介于(8~20)×108 m3/km2之间,而苏里格地区的介于(11~29)×108 m3/km2之间。与苏里格地区相比,研究区气源条件略显较差。研究区的气源条件对气藏的形成与分布起着明显的控制作用。平面上研究区的产气井主要分布在煤层厚度大于4m,生气强度大于10×108 m3/km2的区域,且存在随着烃源岩条件的变好含气性也变好的趋势;纵向上天然气垂向运移距离与煤层厚度和生气强度存在良好的正相关关系,煤层厚度越大、生气强度越高,天然气垂向运移距离越远。
Based on the organic matter abundance, type, maturity and gas intensity index, the Upper Paleozoic source rocks in the southwestern Ordos Basin were comprehensively analyzed to determine the main source rocks and their distribution characteristics. Compared with the source conditions in the Sulige area, Analysis of gas source conditions on the formation and distribution of natural gas control role. The study shows that the Upper Paleozoic source rocks in the study area include the coal seams and dark mudstone of Shanxi Formation and Taiyuan Formation. The coal seam is the main source rock with an average thickness of 4.7m and the average coal seam thickness in Sulige area is 14m. The organic carbon abundance of source rocks is relatively high. The average residual organic carbon in coal seams of Shanxi and Taiyuan are 54.94% and 66.96% respectively, and the average residual organic carbon of mudstone is 2.88% and 1.75% respectively. The kerogen carbon isotope values are -24.56 ‰ ~ -22.05 ‰, belonging to type III kerogen. The vitrinite reflectance ranged from 1.6% to 3.2% with a mean of 2.3% ~ 20) × 108 m3 / km2, while the Sulige area is between (11-29) × 108 m3 / km2. Compared with the Sulige area, the source of air in the study area is slightly worse. The gas source conditions in the study area play a significant role in controlling the formation and distribution of gas reservoirs. The gas wells in the study area are mainly distributed in the areas where the coal seam thickness is more than 4m and the gas generation intensity is more than 10 × 108m3 / km2, and the gas content becomes better along with the change of source rock conditions. Natural gas There is a good positive correlation between the vertical migration distance and coal seam thickness and gas generation intensity. The larger the coal seam thickness, the higher the gas generation intensity, the longer the vertical migration distance of natural gas.