川东飞仙关组烷烃气碳同位素特征与成因分析

飞仙关组作为川东主力气层,陆续已经发现了普光、毛坝、东岳寨、渡口河等一系列大中型气藏,展示了极其重要的战略地位。目前常规的组成分析方法已经不能满足该层天然气类型及成因的判别要求。通过分析烷烃气碳同位素特征,判识天然气类型、分析其成因机制。实验分析显示部分样品C_1~C_3烷烃气的碳同位素比值呈δ~(13)C_1δ~(13)C_2δ~(13)C_3分布(倒转),显示为多源、多期天然气混入。同时根据C_1/C_2+C_3与δ~(13)C_1及ln(C_1/C_2)与In(C_2/C_3)的值域变化特征,最终判断川东大多气藏以原油裂解气为主,混入一定的煤型气。川东飞仙关组古油藏于晚侏罗世沉积期,其埋藏深度介于5 300~8 200 m之间,油藏温度普遍超过150℃,油发生热裂解,生成烷烃气及沥青,持续时间大于30 Ma。

Sichuan Feixianguan group analysis of alkane carbon isotopic characteristics and Genesis

Feixianguan shut as the East Sichuan gas reservoir in the main, gradually has discovered Puguang, Maoba, Dongyue leggings, Dukouhe, a series of large and medium gas reservoir, showing the extremely important strategic position. At present, the conventional analysis method can not meet the requirements of the natural gas type and cause of formation. Through the analysis of alkane carbon isotope, identifying the type of natural gas, analysis of its formation mechanism. The experiment and analysis show some samples of C1-C3 alkane carbon isotope ratios was Delta 13C1 < Delta 13C2 < Delta 13C3 distribution (reverse), showing for the multi-source, multi period of natural gas mixed with. Also according to the range of variation of C1/C2+C3 and delta 13C1 and ln (C1 / C2) and ln (C2 / C3), final judgment in eastern Sichuan, most of the gas reservoir in crude oil cracked gas mainly, mixed with a certain coal type gas. In eastern Sichuan, Feixianguan Formation of paleo oil reservoir in the late Jurassic period, between the buried depth ranged from 53 to 8200m, reservoir temperature, generally more than 150 DEG C, oil thermal cracking, generating alkane hydrocarbon and asphalt lasting more than 30mA.