摘要
鄂尔多斯盆地中南部地区发育含气的长7段页岩.为了充分认识长7段页岩气的生成过程、运移过程以及成藏演化过程,以气体化学与同位素化学相结合为手段,研究了不同气体组分及其同位素在解析过程中的含量变化,认为在页岩气的解析过程中,甲烷的含量逐渐降低,重烃气的含量逐渐升高,气体的干燥系数降低;甲烷的碳同位素逐渐增重,重烃气的碳同位素变化不明显.研究结果表明:解析过程中,二氧化碳体积分数变化范围为0.53%~5.15%,氮气体积分数变化范围为1.24%~4.64%,气体干燥系数在0.43~0.82之间,甲烷碳同位素变化范围为-51.6‰^-33.9‰.基于长7段页岩的气体解析特征,得出长7段页岩气为腐泥型母质生成的油型热解气;长7段页岩对二氧化碳的吸附能力最强,对甲烷的吸附能力次之,对氮气的吸附能力最弱;烷烃气体中,气体的分子体积越小,其在页岩内部的初次运移能力越强;页岩中,吸附态、溶解态及游离态3种赋存相态的页岩气在地质历史过程中不断转化与调整;长7段页岩的平均含气量大致为1.90m3/t.
The Chang 7member shale containing abundant gas is highly developed in the central south Ordos basin.Based on chemical and isotopic composition analyses,the content variations of gas components and their isotopic compositions during desorption were obtained to study the gas generation,migration and accumulation process.It is demonstrated that in the course of desorption,the content of methane gradually decreases while that of heavy hydrocarbon increases;the gas drying coefficient declines slowly;the methane carbon isotope has no obvious change.The results show that the carbon dioxide volume fraction,nitrogen volume fraction,gas drying coefficient and methane carbon isotope ranges from 0.53% to 5.15%,1.24% to4.64%,0.43 to 0.82,and-51.6‰to-33.9‰respectively.Based on desorption characteristics,Chang 7member shale gas is oil-prone pyrolysis gas generated from humic matter,andhas the strongest absorption for carbon dioxide,followed by methane,and then nitrogen.Gases with small molecules migrate faster and easier than those composed of larger molecules.Shale gases in three kinds of existing phase including dissolved gas,absorbed gas and free gas keeps on transforming and adjusting throughout the geological history.The average shale gas content in Chang 7member shale is 1.90m～3/t.
出处
《中国矿业大学学报》
EI
CAS
CSCD
北大核心
2017年第3期554-562,577,共10页
Journal of China University of Mining & Technology
基金
陕西省科技统筹创新工程计划项目(2012KTZB03-03-01-01)
延安大学博士科研启动项目(YDBK2016-15)
