塔里木盆地碳酸盐岩层系烃源岩生烃底限探讨

Discussion on the Bottom Line of Hydrocarbon Generation of Carbonate Source Rocks in Tarim Basin

中国碳酸盐岩热演化程度较高,是否达到生烃底限或生烃死亡线,值得深入研究,这对评价中国碳酸盐岩油气潜力和勘探前景具有重要意义。根据烃源岩生烃、残留烃和排烃机理,利用有机元素变化法、生烃潜力法、生烃物质平衡优化模拟法、生烃热模拟实验法、残留烃量法和排烃量法等6类8种方法对塔里木盆地台盆区碳酸盐岩层系烃源岩生烃底限进行了研究。结果表明：不同方法确定的碳酸盐岩烃源岩生烃底限RO值介于4.2%～4.9%之间,平均为4.52%;对应的深度底限在塔中地区最大,约为9 200m;塔北和巴楚地区次之;塔东地区最小,约为5 850～6 850m。研究结果与其他学者研究结论较为相近或偏大,更符合实际地质条件下的生油气特征。除了满加尔凹陷和古城地区,塔里木盆地台盆区其他地区的寒武系—奥陶系碳酸盐岩层系烃源岩均没达到生烃底限,还具有较大的生烃潜力,深部碳酸盐岩油气藏具有广阔的勘探前景。

The carbonate rocks in China have high thermal evolution.Whether they come to the bottom line of hydrocarbon generation or the dead line of hydrocarbon generation is worth studying,which has important significance to the evaluation of the oil-gas potential and exploration value for carbonate rocks in China.According to the mechanism of hydrocarbon generation,retention and expulsion,it was thoroughly investigated through six categories of methods in carbonate source rocks of Tarim Craton basin,which included the methods of variation of organic elements,hydrocarbon generation potential,optimum modeling of organic materials based on material balance principle,thermal simulation experiment,residual amount of hydrocarbons,and expulsed amount of hydrocarbons.The ROcorresponding to the bottom line of hydrocarbon generation which is determined by different methods ranges from 4.2%to 4.9%,with an average value of 4.52%.The depth for the bottom line of hydrocarbon generation in Tazhong area is the biggest,with a depth of 9 200 m,a less depth in Tabei and Bachu areas,and the smallest in Tadong area,of 5 850-6 850 m.The bottom lines of hydrocarbon generation proposed in this study is similar and bigger than that of some other researchers and accords with the actual geological conditions of hydrocarbon generation.Apart from the Mandong Depression and Gucheng area,all the Cambrian-Ordovician carbonate source rocks in other areas in Tarim Basin Platform had not reached the bottom line of hydrocarbon generation and were still generating agreat amount of hydrocarbon.