威远地区页岩气与常规天然气地球化学特征对比  

A Comparison between Shale Gas and Conventional Gas on Geochemical Characteristics in Weiyuan Area

作　　者：吴伟[1] 黄士鹏[1] 胡国艺[1] 龚德瑜 

机构地区：[1]中国石油勘探开发研究院,北京100083

出　　处：《天然气地球科学》2014年第12期1994-2002,共9页Natural Gas Geoscience

基　　金：中国石油天然气股份有限公司"中国煤成气地球化学与成藏机制规律研究"项目(编号:2014B-0608)资助

摘　　要：威远地区不仅较早发现了大型整装常规气田,也是我国最早的页岩气先导试验区之一。根据威远地区5口井8个井次的井口气组分和碳、氢同位素分析,研究了该区龙马溪组和筇竹寺组页岩气的主要地球化学特征。威远地区页岩气烷烃气的含量高达98.47%,不含H2S,甲烷平均含量为98.01%,是典型的干气;页岩气碳、氢同位素特征与北美地区高成熟、过成熟页岩气相似,均表现为同位素倒转。通过页岩气和常规气地球化学特征的对比,认为页岩气和常规气在6个方面存在差异:1常规气含H2S;2常规气CO2、N2等非烃组分更多;3常规气CO2包含有机成因和无机成因,页岩气CO2为无机成因;4常规气组分湿度更低,甲烷碳同位素值更高;5页岩气碳、氢同位素倒转,常规气主力产层震旦系不倒转,二叠系碳同位素倒转,寒武系部分井倒转,部分井正序;6各个产层δ13C2值差异非常大,页岩气异常低。水溶脱气、TSR、N2运移能力以及早期烃类的保存条件是造成差异的主要原因,高热演化程度和较封闭体系下的混合作用是造成同位素倒转的主要原因。Being a large and old conventional gas field,Weiyuan area becomes one of the earliest shale gas exploration and development experimental areas in China.Geochemical parameters of 8gas samples from Longmaxi shale and Qiongzhusi shale in 5wells were analyzed in this study,which were also compared with the conventional gas in this area.The alkane accounts for absolute advantages in the molecular compositions of shale gas,as high as 98.47% without any H2 S.The gas is very dry and methane accounts for98.01%in an average.The carbon and hydrogen isotopes are similar to the high or over mature shale gases in North America,which is characterized by isotopic reversal.Through comparison between shale gas and conventional gas on geochemical characteristics,6kinds of differences are identified and analyzed：（1）The conventional gas has H2S;（2）Conventional gas has more non-hydrocarbon gases such as CO2 and N2;（3）The conventional CO2 is of both biogenic and abiogenic origin,but the CO2 in shale gas is derived from the carbonates;（4）The conventional gas has lower wetness and heavier carbon isotopes;（5）The carbon and hydrogen isotopes are reversed for shale gas,but the isotopic order is normal in Sinian reservoir and reversed in Permian for the conventional gases;（6）δ^13 C2 varies widely in different formations,and it is abnormally light in shale gas.Degassed water-soluble gases,TSR,the migration ability of N2 and preservation conditions for early gas are main factors to make the differences.High maturity and mixing effects in relatively closed system are the main cause for the isotope reversal.

关 键 词：页岩气 地球化学特征 碳同位素 氢同位素 同位素倒转 同位素反转 

分 类 号：TE122.113[石油与天然气工程—油气勘探]