利用天然气地化识别技术研究了莺歌海盆地浅层天然气生物降解及混源特征。研究结果表明 ,该区天然气遭受生物降解后 ,除正构烷烃浓度降低、被降解组分碳同位素变重外 ,在降解作用微弱的天然气中还检测出生物成因的烯烃。在莺歌海盆地中央泥底辟带 ,存在母质类型相似、但处于不同演化阶段的多套气源岩 ,具有生成不同成熟度天然气的物质基础。该区普遍存在由生物气 (或低成熟气 )与热成因气 (有的已被生物降解 )混合而成的混合天然气 ,泥拱活动产生的 (微 )裂隙为天然气运移及混合提供了主要通道。随气藏埋深变浅 ,生物气 (或低成熟气 )的比例增大 ,混合天然气的δ13C1变轻。由于生物降解作用将热成因气中的CO2 转化为甲烷 ,混合作用补充了富烃的新烃气 (生物气和低成熟气 ) ,从而改善了热成因气的品质 ,有利于该区富烃天然气的形成 The natural gas biodegradation and mixed source features in the Yinggehai Basin were studied using the geochemical identification of natural gas. The results show that biodegradation of natural gas in natural gas with weak degradability is also detected after the natural gas in this area is biodegraded except for the decrease of normal paraffin concentration and the heavy carbon isotope of degraded components. In the central gneiss belt of the Yinggehai Basin, there are multiple sets of gas source rocks with similar parental types but at different evolutionary stages, which have the material basis for generating natural gas with different maturities. There is a widespread mix of biogas (or low-mature gas) with thermogenic gas (some of which have been biodegraded) and the (micro) fissures produced by mud-arch activity provide the major transport and mixing of natural gas aisle. As the burial depth becomes shallow, the proportion of biogas (or low-mature gas) increases, and the δ13C1 of the mixed natural gas becomes lighter. Due to biodegradation, the CO2 in the pyrogenic gas is converted into methane, and the mixing function complements the hydrocarbon-rich new hydrocarbon gas (biogas and low-mature gas), thereby improving the quality of the pyrogen-producing gas and contributing to the hydrocarbon-rich natural gas Formation