鄂尔多斯盆地东南部宜参1井烃源岩评价及气源分析

Source rock evaluation and gas genesis of well Yican 1 in Southeastern Ordos Basin

鄂尔多斯盆地东南部宜参1井获得天然气重大突破,但对其各层系烃源岩生烃潜力并未开展研究。通过采集山西组和马家沟组烃源岩样品开展相关研究,结果表明:山西组4个泥岩样品的残余总有机碳(Total Organic Carbon,TOC)含量分布范围为0.54%~2.31%,均值为1.65%,总烃[(S 1+S 2)]含量分布范围为0.12~0.46mg/g,均值为0.34mg/g,泥岩烃源岩有机质丰度较高,生烃潜力较强;马家沟组泥岩残余TOC含量分布范围为0.09%~0.33%,均值为0.17%,(S 1+S 2)含量分布范围为0.03~0.17mg/g,均值为0.12mg/g,评价为非-差烃源岩。对比宜参1井天然气中甲烷(CH 4)和乙烷(C2H6)碳同位素含量,δ^13C 1>δ^13C2倒转的天然气主要为煤成热解气,混入了少量δ^13C2轻的油型气,其中煤成气主要来自于上古生界煤系地层,混入的少量油型气可能主要来自于上古生界太原组优质海相烃源岩。查明奥陶系马家沟组的生烃潜力及油气来源不仅可以认识奥陶系产层的油气生成和组成特征,同时对气田的形成模式、资源前景及勘探部署也具有重要意义。

A breakthrough in natural gas exploration has been made in well Yican 1 of Southeastern Ordos Basin,while the hydrocarbon potential of its source rocks hasn’t been studied.Several source rock samples collected from Shanxi and Majiagou Formation were used for relative study.The results show that the TOC content of four mudstone samples from Shanxi Formation varies from 0.54%to 2.31%,with the average content of 1.65%.(S 1+S 2)value varies from 0.12 mg/g to 0.46 mg/g,with the average value of 0.34 mg/g.Shanxi Formation mudstone source rocks have a high abundance of organic matter and strong hydrocarbon generation potential.The TOC content of dolomitic(calcareous)mudstones from Majiagou Formation varies from 0.09%to 0.33%,with the average content of 0.17%.(S 1+S 2)value varies from 0.03 mg/g to 0.17mg/g,with the average value of 0.12mg/g,which is evaluated to be poor to non-hydrocarbon source rocks.The compositions of carbon isotope in CH 4 and C 2H 6 were compared,and the results show that well Yican 1 has the characteristic of δ^13 C 1>δ^13 C 2,which indicates that the natural gas is mainly coal type gas mixed by a small amount of oil type gas.And the coal type gas is mainly from the coal layers of Upper Paleozoic,whereas the oil type gas is mainly from premium marine facies source rocks of Taiyuan Formation in Upper Paleozoic.The investigation of the hydrocarbon potential and gas genesis of Ordovician Majiagou Formation is favorable to study its gas generation and formation characteristics,and it is of great significance to the study of gas field formation model,resource prospects and exploration.