四川盆地元坝地区千佛崖组页岩油气富集特征与主控因素

Accumulation conditions and controlling factors for the enrichment of shale oil and gas in the Jurassic Qianfoya Formation,Yuanba area,Sichuan Basin

以四川盆地元坝地区元页3井等重点钻井为例,通过岩心观察和实验分析,评价了该区中侏罗统千佛崖组陆相页岩油气的成藏条件。千佛崖组富有机质泥岩孔隙度高、含油气性好,是主要的储层岩相类型,而灰岩及砂岩夹层物性相对较差;孔隙类型以无机孔为主,占总孔隙的比例约为60%~80%,与海相页岩相比微孔占比降低而大孔含量更高,有利于页岩油气的采出。千佛崖组二段下部的④小层全段以富有机质泥岩为主,泥地比高,孔隙度平均达5.43%,有机碳(TOC)含量平均1.72%,冷冻碎样热解的游离烃含量S1为2.63 mg/g,测试含气量平均1.51 m^(3)/t,含油气性较好,具备陆相页岩油气形成的有利地质条件。通过与其他钻井的对比分析,认为半深湖相沉积是最为有利的沉积相带,为油气富集提供了物质基础,而较高的成熟度和裂缝的发育是油气富集高产的重要条件。

Taking key wells such as Yuanye 3 in the Yuanba area of the Sichuan Basin as examples,the accumulation conditions of continental shale oil and gas in the Middle Jurassic Qianfoya Formation in this area have been evaluated based on core observation and experimental analysis.The organic-rich mudstone of the Qianfoya Formation has high porosity and good oil and gas content.It is the main reservoir lithofacies type,while the physical properties of limestone and sandstone interlayers are relatively poorer.The pores are mainly inorganic ones,accounting for approximately 60%to 80%of the total porosity.Compared with marine shale,the proportion of micropores is lower and the content of macropores is higher,which is conducive to the production of shale oil and gas.The fourth section of the lower part of the second member of the Qianfoya Formation is dominated by organic-rich mudstone,with a high shale-to-stratum ratio,an average porosity of 5.43%,and an average total organic carbon(TOC)content of 1.72%.The free hydrocarbon content(S_(1))of frozen sample pyrolysis is 2.63 mg/g,and the average total gas content is 1.51 m^(3)/t,showing a good oil-bearing property and favorable geological conditions for the formation of continental shale oil and gas.Comparative analysis with other wells has indicated that half-deep lacustrine facies is the most favorable sedimentary facies belt,providing basic material for oil and gas enrichment,and high maturity and fracture development is the important condition for oil and gas enrichment.