江汉盆地南部监利地区浅层生物气的发现及成因

江汉盆地南部监利地区由于农田灌溉打水井，偶然发现井水抽出时伴有气体流出，点燃后能长时间燃烧。为此，对该地区的浅层气进行了采样分析。结果表明，浅层天然气气样CH₄含量介于44.11%~51.57%之间，均值为47.03%，不含C₂H₆及其他重烃气体，干燥系数(C₁/C_1-5)为1，属典型干气。CH₄碳同位素值介于-70.8‰ ~-71.0‰之间，均值为-70.9‰，CH₄氢同位素值介于 -223‰~-226‰之间，均值为-224‰，CO₂碳同位素值介于-12.6‰~-14.7‰之间，均值为-13.9‰，同位素特征表明研究区浅层气为氢气还原二氧化碳途径生成的生物气。通过与江浙-沿海平原、长江三角洲和洞庭盆地的第四系浅层生物气赋存特征进行对比，进一步明确了研究区内第四系生物气成藏特征，认为研究区第四系浅层生物气具有进一步勘察和研究的潜力。

Discovery of shallow biogas and cause of formation analysis in Jianli area,southern Jianghan Basin

Due to the irrigation of the farmland, shallow gas was founded and it could burn for a long time after ignition in the Jianli area in the southern part of the Jianghan Basin. Hence, we sampled and analyzed the shallow gas. The results show that these shallow gases are dominated by CH₄ (44.11%-51.57%, average 47.03%) with no C₂H₆ and other hydrocarbons, C₁/C_1-5 ratios are 1, which are typical dry gas. Their {\mathrm{\delta }}^{\mathrm{13}}{\mathrm{C}}_{\mathrm{C}{\mathrm{H}}_{\mathrm{4}}}(from -70.8‰ to -71.0‰, average -70.9‰), \mathrm{\delta }{\mathrm{D}}_{\mathrm{C}{\mathrm{H}}_{\mathrm{4}}}(from -223‰ to -226‰, average -224‰) and {\mathrm{\delta }}^{\mathrm{13}}{\mathrm{C}}_{\mathrm{C}{\mathrm{H}}_{\mathrm{2}}} (from -12.6‰ to -14.7‰, average -13.9‰) values indicate that the shallow gas samples represent biogenic gas, which is generated by CO₂ reduction. By comparing with the Quaternary shallow biogenic gas in the Jiangsu-Zhejiang coastal plain, the Yangtze river delta and the Dongting Basin, the characteristics of the Quaternary biogenic gas accumulation in the work area were further clarified. It is believed that the Quaternary shallow biogas in the study area has the potential for further exploration and research.