页岩残留气定量方法及其地质意义

本研究设计并制造了一套可在真空条件下粉碎页岩样品并释放其中残留气的装置，该装置的粉碎系统与富集模块和气相色谱联用后，可实现残留气的有机、无机气体化学成分定量分析；同时，封存在玻璃管内的另一部分残留气可进一步开展稳定碳同位素分析，从而获得页岩残留气完整的化学成分和碳同位素组成特征。利用混合标准气体标定该装置，烃类和无机气体浓度与气相色谱响应相关系数达0.999，表明仪器状态稳定，残留气定量数据准确可信。使用不同露头页岩样品（贵州习水县下志留统龙马溪组、南京幕府山下寒武统牛蹄塘组和延安上三叠统延长组）检测该装置，页岩残留气量和碳同位素测试结果平行性良好，表明该装置系统可用于分析页岩残留气。对川南钻井龙马溪组样品残留气的测试结果表明：龙马溪组页岩残留气化学成分主要为CO₂和N₂等无机气体，烃类组分以CH₄为主，C₂H₆及更高碳数烃类含量极少；其甲烷碳同位素值为-38.1‰~-33.9‰，均值为-35.8‰，该甲烷碳同位素值与已发表的同地区页岩生产气非常接近，表明了二者的同源性，川南页岩气田中的页岩气来源于龙马溪组，符合页岩气的严格定义。此外，本研究还对宜昌地区浅钻五峰组和龙马溪组页岩开展了残留气分析，结果表明：残留烃气量与总有机碳质量分数、碳酸盐岩质量分数成呈弱正相关关系，与DFT（密度泛函理论）比表面积和BJH（Barrett-Joyner-Halenda）孔体积呈负相关关系，分析认为残留气并不是简单地以吸附或游离形式存在，而是封存于封闭孔中的极少量烃类和无机气体。

Quantitative Method of Crushed Gas in Shale and Its Geological Significance

A device was designed and manufactured to release the crushed gas in shales under vacuum. The gas from this device was geochemically and quantitatively analyzed by the device combined with the enrichment module and gas chromatography. Meanwhile, the comprehensive chemical composition and the stable carbon isotopic composition were obtained through analyzing the gas sealed in the glass tube. With the mixed standard gases calibrating, the correlation coefficient between concentrations of organic and inorganic gases and gas chromatographic response reached 0.999, which indicates that the device is stable for a quantitative analysis of the crushed gas. The result showed a good parallelism between the gas yields and stable carbon isotope values when the different outcrop shales (the Lower Silurian Longmaxi Formation in Xishui County, Guizhou, the Lower Cambrian Niutitang Formation in Mufu Mountain, Nanjing and Upper Triassic Yanchang Formation in Yan'an, Shaanxi) were analyzed, and reported the chemical and stable carbon isotopic compositions of the crushed gases of the core samples from the Lower Silurian Longmaxi Formation, southern Sichuan basin. The results revealed that the crushed gases are mainly inorganic gases (N₂ and CO₂) with a little hydrocarbon gas that are mainly composed of CH₄ and extremely low content of C₂H₆ and C₃H₈. The δ¹³C₁ values of crushed gas range from -38.1‰ to -33.9‰ with a mean value of -35.8‰, which is similar to the value of shale gas in the same area proposed by previous studies. In addition, the crushed gas of shale at low depths of (20-46) m showed a weakly positive relationship between the yield of crushed gas and w(TOC) values/carbonate content, while a negative correlation between the yields of crushed gas with DFT surface area and BJH pore volume. This suggests that the commercial shale gas is possibly originated from the Lower Silurian Longmaxi Formation, corresponding to the strict definition of shale gas. Hence, the crushed gases are neither adsorbed nor dissociated in shale gas reservoir, but sealed up in the enclosed pores in shales.