四川盆地乐山—龙女寺古隆起地区震旦系储层沥青地球化学特征及意义

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。

Geochemical Characteristics and Significance of Sinian Reservoir bitumen in Leshan-Longnvsi Paleo-uplift Area,Sichuan Basin

Through whole rock microscopic determination of reservoir bitumen samples from new drilling data of Leshan-Longnvsi Paleo-uplift area,a large number of reservoir bitumens are found in the Sinian Dengying Formation in the Leshan-Longnvsi paleo-uplift area of Sichuan Basin.Combined with determination of bitumen reflectance,organic elemental analysis and carbon isotope analysis of these samples,the results show that: the equivalent vitrinite reflectance (R_O′) of Dengying reservoir bitumen ranges from 2.06% to 3.0%,with an average of 2.62%,H/C and O/C atomic ratios are only 0.30-0.43 and 0.01-0.03,respectively,which reflect that the bitumen maturity is high,basically in the mature-overmature stage;S/C atomic ratio is only 0.03-0.06,and is somewhat low in comparison to reservoir bitumen from Changxing(P₂ch) and Feixianguan(T₁f) Formations,which indicate that Dengying Formation reservoir bitumens in ancient uplift area were slightly affected by thermochemical sulfate reduction (TSR);the value of stable carbon isotope is from -36.8‰ to -34.5‰,with an average of -35.7‰,which is the lowest compared with carbon isotope of kerogen and bitumen in each layer of Sichuan Basin,even lower than the carbon isotope of marine oil in Tarim Basin.Combined with the geological and tectonic background and carbon isotope of source rock kerogen in Sichuan Basin,the reservoir bitumen in this area is epigenetic - reservoir bitumen,sourced from Lower Cambrian Qiongzhusi Formation,which belongs to thermal evolution bitumen-pyrobitumen of the ancient reservoir when it cracked into gas during deep burial under high temperature and pressure. 