伊陕斜坡东南部延长组页岩气地球化学特征分析

陕西延长石油(集团)有限责任公司研究院,陕西 西安 710000

伊陕斜坡; 延长组; 页岩气; 原油伴生气; 地球化学特征; 碳、氢同位素

Geochemical characteristics of shale gas from Yanchang Formation in southeastern Yishan Slope
DU Yan,YU Bo,XU Min

(Research Institute of Shaanxi Yanchang Petroleum Group Co., Ltd.,Xi'an 710000,China)

Yishan slope; Yanchang formation; shale gas; oil associated gas; geochemical characteritics; carbon and hydrogen isotopes

DOI: 10.13800/j.cnki.xakjdxxb.2015.0111

备注

鄂尔多斯盆地陆相页岩气勘探潜力巨大,但对于陆相页岩气成因类型的研究相对滞后,限制了对页岩气的进一步勘探和开发。通过综合化学组分分析和碳、氢同位素分析的手段对伊陕斜坡东南部延长组页岩气和原油伴生气的地球化学特征及成因进行研究。研究结果表明延长组页岩气(生产气和真空解吸气)和原油伴生气都以烷烃类气体为主,其中甲烷含量都小于95%,非烃气体含量比较低。页岩解吸气中,非烃气体比例相对较高,且氧气含量异常高,这与解吸装置密封性不好或者装置本身残留空气清除不彻底有关。页岩气和原油伴生气的甲烷含量低、干燥系数(C1/C1~5)主要集中在0.6~0.9之间、C2/C3都小于3,δ13C1值分布于-52.0‰~-44.9‰之间、δ13C2值都小于-29‰,δ13C3值都小于-25.5‰和δD1都小于-150‰,指示研究区页岩气和原油伴生气以陆相环境热成因的热解湿气(油型气)为主。页岩气和原油伴生气样品有相对高的正庚烷含量和正构烷烃(nC5-7)含量,δ13C2值分布于-41.1‰~-31.1‰之间,说明延长组页岩气与原油伴生气都属于偏腐泥型天然气。此外,延长组页岩气和原油伴生气碳同位素系列基本都属正碳同位素系列,且δ13C1与δ13C2值,δ13C2值与δ13C3值有较好的正相关关系,这也表明页岩气和原油伴生气具有相同或相似的母质来源。

The terrestrial shale gas in Ordos Basin has huge exploration potential.However,the research on genetic type of the terrestrial shale gas is lagging behind,which restricts further exploration and development of shale gas.In this paper,comprehensive analysis of chemical composition and carbon as well as hydrogen isotope were made to study the geochemical characteristics and genesis of Yanchang formation in southeastern Yishan Slope,Ordos Basin.The results show that shale gas(production gas and vacuum desorption gas)and oil associated gas of Yanchang Formation in the study area mainly consist of hydrocarbon gases with methane content less than 95%,and non-hydrocarbon gases content are relatively lower.Desorption gas is composed of relatively high content of non-hydrocarbon gases,and oxygen content is abnormally high,which is related to bad sealing ability of desorption apparatus or residual air in the desorption apparatus.According to the geochemical characteristics of low methane content,dry coefficient in the range of 0.6~0.9,C2/C3 less than 3,δ13C1varying from -52.0‰~-44.9‰,δ13C2 less than -29‰,δ13C3less than -25.5‰ and δD1 less than-150‰ for shale gas and oil associated gas,indicate these natural gases are dominantly pyrolysis wet gas(oil-type gas)derived from continental environment.Shale gas and oil associated gas have relatively high n-Heptane and n-alkanes(nC5-7)content,with δ13C2 ranging from -41.1‰ to -31.1‰,which imply natural gases of Yanchang Formation belong to near-sapropelic pyrolysis gas.The carbon isotopic compositions series of shale gas and oil associated gas are positive,besides,δ13C1 and δ13C2,δ13C2 and δ13C3 have positive correlations,which also prove that shale gas and oil associated gas have the same or similar genetic sources.