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通过对四川盆地乐山—龙女寺古隆起地区储层沥青样品进行全岩镜下测定,发现该区震旦系灯影组储层中存在大量储层沥青,并对样品进行沥青反射率测定、有机元素分析和碳同位素分析,结果表明:古隆起地区震旦系灯影组储层沥青等效镜质体反射率(R′O)值分布在2.06%~3.0%之间,平均值为2.62%,储层沥青H/C原子比和O/C原子比仅为0.30~0.43和0.01~0.03,表明沥青的成熟度高,基本上处于成熟—过成熟阶段,生烃潜力较低;S/C原子比为0.03~0.06,与长兴组(P2ch)和飞仙关组(T1f)储层沥青S/C原子比相比偏低,表明古隆起地区灯影组储层沥青受硫酸盐热化学还原反应(TSR)影响较小;此外,储层沥青碳同位素值分布在-36.8‰~-34.5‰之间,平均值为-35.7‰,在四川盆地各层位干酪根和沥青碳同位素值中其值最低,比塔里木盆地海相原油的碳同位素值还要低。结合四川盆地地质构造背景,对比各层位烃源岩干酪根碳同位素,认为古隆起地区震旦系灯影组储层沥青主要来源于下寒武统筇竹寺组烃源岩,属古油藏深埋时在高温、高压作用下裂解成气后的热演化沥青—焦沥青。
Through the whole rock microscopic examination of the reservoir asphalt samples in the paleo-uplift area of Leshan-Longnv Temple in the Sichuan Basin, a large amount of reservoir asphalt is found in the Dengying Formation reservoirs in the Sichuan Basin. The asphalt reflectivity of the sample is measured. Elemental analysis and carbon isotope analysis. The results show that the reflectance (R’O) value of asphalt equivalent vitrinite of Sinian Dengying formation in the paleurgeonic region ranges from 2.06% to 3.0% with an average of 2.62% The H / C atomic ratios and O / C atomic ratios of reservoir bitumen were only 0.30-0.43 and 0.01-0.03, which indicated that the bitumen was highly matured and basically in the mature-overripe stage with low potential for hydrocarbon generation. The S / C atom (0.03 ~ 0.06), which is lower than the S / C atomic ratio of P2ch and Fe (T1f) reservoirs in the paleo-uplift region, indicating that the bitumen of the Dengying Formation in the paleohigh is affected by the thermochemical reduction reaction of sulphate TSR). In addition, the δ13C values of reservoir bitumen ranged from -36.8 ‰ to -34.5 ‰, with an average value of -35.7 ‰, the lowest among the kerogen and bitumen carbon isotopic values of all layers in the Sichuan Basin , Lower than the carbon isotope value of marine crude oil in the Tarim Basin. Based on the geological tectonic setting of Sichuan Basin and comparing the kerogen carbon isotopes of source rocks in all layers, it is concluded that the reservoir bitumen of the Sinian Dengying Formation in the paleohigh is mainly derived from the Lower Cambrian Qiongzhusi source rock and belongs to the paleo-oil reservoir In the deep buried under the action of high temperature and high pressure cracked into gas after the thermal evolution of asphalt - tar pitch.