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通过对四川盆地海相层系天然气组分和碳同位素以及储层固体沥青元素分析,四川盆地海相层系天然气地球化学特征不同于我国典型煤成气,而与油型气相似,热演化程度普遍很高,已处于油气裂解阶段。烷烃气碳同位素组成普遍存在局部倒转现象,即δ13C1>δ13C2<δ13C3。造成烷烃气碳同位素倒转的原因可能是后期热化学硫酸盐还原反应(TSR)改造;四川盆地海相层系储层沥青元素与陆相碎屑岩明显不同;在川东北地区非海相砂岩中储层固体沥青贫S并具有较低反射率;而海相层系固体沥青中富S。海相层系固体沥青主要为原油热裂解和TSR共同作用产生的,而陆相则仅为原油裂解产生。
Based on the analyzes of natural gas composition, carbon isotopes and solid bitumen in marine strata in the Sichuan Basin, the geochemical characteristics of natural gas in the marine strata of the Sichuan Basin are different from those of typical coal-formed gas in China and similar to the oil-type gas. The degree of thermal evolution Generally high, has been in the oil and gas cracking stage. Alkane carbon isotope composition prevails in the phenomenon of local reversal, that δ13C1> δ13C2 <δ13C3. The carbon isotope inversion of alkane gas may be due to the late thermochemical sulfate reduction (TSR) modification. The bitumen elements in the marine strata of the Sichuan Basin are obviously different from the continental clastic rocks. In the non-marine sandstone in the northeastern Sichuan Basin, Reservoir solid bitumen is depleted in S and has a lower reflectivity; whereas in marine bitumen solid bitumen is S rich. The marine bitumen solid bitumen is mainly produced by pyrolysis of crude oil and TSR, while the continental facies is only produced by the cracking of crude oil.