柴达木盆地东部天然气地球化学特征与勘探方向

柴达木盆地东部三湖地区天然气分布广泛,除已发现5个气田和2个含气构造外,还有大量的气显示.该地区天然气地球化学特征为甲烷碳同位素组成轻、重烃气含量低,经成因判识为典型的生物气,甲烷成因主要与二氧化碳还原作用有关.部分样品中检测到一定含量的C_5-C_8烃类,个别样品乙烷和丙烷碳同位素组成偏重,揭示该地区天然气中可能混有一定量热成因气.综合分析认为,柴达木盆地东部三湖地区生物气成藏具备良好的烃源条件和较好的保存条件.建议在天然气勘探中积极扩大目标领域,适当关注浅层和极浅层生物气、深层生物气以及深部热成因油气.图12表1参20

Geochemical characteristics and play targets of gas in eastern Qaidam Basin, NW China

Natural gas exists extensively in the Sanhu region of eastern Qaidam Basin, NW China, where five gas fields and two gas-bearing structures have been discovered, and lots of gas shows have been found. The gas was identified as typical biogas with geochemical characteristics of light methane carbon isotope ratio and low content of heavy hydrocarbon gas. The generation of methane was mainly related to the CO2 reduction. The existence of C5-C8 hydrocarbons in gas samples and heavy carbon isotope values of ethane and propane in a few gas samples indicate that natural gas in this region may contain some thermal gas. It can be concluded that favorable source rock and conservation conditions exist for the formation of biogas reservoirs. Expanding exploration domain, especially paying more attention to reservoirs of shallow and ultra shallow biogas, deep biogas, and deep thermal hydrocarbon, was suggested for the future exploration activities.