Abstract There are significant differences in the gas content between the two sets of lower Paleozoic shale in south China. The nitrogen content of the lower Silurian shale gas that has been commercially developed is very low, whereas that of the lower Cambrian shale (LCS) is relatively high. Shale has complex gas-bearing mechanistic characteristics. The genesis of nitrogen is complex and sources are diverse. A gas containing high nitrogen and low hydrocarbons increases the risk and difficulty of developing a shale gas resource. Based on the key geological parameters of the LCS in the northern Guizhou area (NGA), this study investigates the characteristics of nitrogen in the highly mature shale and discusses the logging evaluation method for nitrogen-bearing shale gas reservoirs in this complex tectonic area. Changes in the gas-bearing characteristics of the LCS in the study area are complex. The shale gas composition was found to vary widely due to differential enrichment; the methane content was between 1.2% and 82.4%, and the nitrogen content was between 0.03% and 97.4%. The nitrogen-rich shale formations exhibited a high compensation density (2.46–2.58 g/cm3), high compensation neutron (10.2–17.9%), and low acoustic time difference (192–230 μs/m). There were two different types of resistivity responses in nitrogen-bearing shale gas reservoirs, which had distribution characteristics of 21–56 Ω m and 100–1000 Ω m. With these response characteristics, the logging evaluation of nitrogen-bearing shale gas reservoirs was interpreted by selecting differential gas-sensitive parameters, and different gas-bearing types were divided into dry, nitrogen, mixed, and methane gas layers. Furthermore, the identification and computational evaluation of the gas composition (methane/nitrogen) and content were carried out quantitatively. Differential gas-bearing property was characterized and that is beneficial to the exploration practice in the study area.

中文翻译：

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黔北下寒武统富氮页岩测井评价及含气差异表征

摘要 华南下古生界两组页岩含气量存在显着差异。已商业开发的下志留统页岩气含氮量很低，而下寒武统页岩（LCS）含氮量较高。页岩具有复杂的含气机理特征。氮的成因复杂，来源多样。含高氮低烃的天然气增加了页岩气资源开发的风险和难度。以黔北地区LCS关键地质参数为基础，研究高成熟页岩中氮的特征，探讨该复杂构造区含氮页岩气储层测井评价方法。研究区濒海战斗舰含气特征变化复杂。由于富集程度不同，页岩气的成分差异很大；甲烷含量在1.2%至82.4%之间，氮含量在0.03%至97.4%之间。富氮页岩地层表现出高补偿密度（2.46-2.58 g/cm3）、高补偿中子（10.2-17.9%）和低声时差（192-230 μs/m）。含氮页岩气藏存在两种不同类型的电阻率响应，其分布特征为21～56Ω·m和100～1000Ω·m。利用这些响应特征，通过选择差异气敏参数来解释含氮页岩气藏测井评价，将不同含气类型分为干、含氮、混合、和甲烷气体层。此外，还对气体成分（甲烷/氮气）和含量进行了识别和计算评估。表征了差异含气性，有利于研究区的勘探实践。