川东北地区侏罗系凉高山组页岩储集空间特征及页岩油可动性探索

Reservoir space characteristics and exploration of shale oil mobility of the Jurassic Lianggaoshan Formation shale in the northeastern Sichuan Basin

侏罗系凉高山组页岩是四川盆地重点勘探层段,但其孔隙结构与页岩油可动性尚不明晰。为揭示川东北地区侏罗系凉高山组页岩储集空间特征及页岩油可动性,本文依据沉积构造和矿物组成划分岩相类型,开展总有机碳测定、岩石热解和镜质体反射率实验获取基础地化特征;利用场发射扫描电镜、核磁共振、低温氮气吸附、高压压汞手段实现孔隙度、孔隙结构的表征及评价,并对比不同岩相间储集空间特征差异;在离心时间为3 h,离心转速为11000 r/min条件下,开展核磁-离心定量评价不同岩相页岩油可动性,并明确影响因素,建立可动油量测井评价模型并选出有利岩相。结果表明:(1)川东北地区凉高山组页岩总有机碳含量主要分布在0.15%~2.95%之间,Ro值介于1.06%~1.68%之间,处于成熟-高熟阶段;轻烃恢复后,S1分布范围为0.03~3.32 mg/g;矿物类型以黏土矿物和石英为主,发育的岩相类型为纹层状黏土质页岩相、纹层状长英质页岩相、层状混合质页岩相和块状粉砂质泥岩相。(2)页岩储集空间主要发育黏土矿物晶间孔、有机孔,另外可见石英溶蚀孔、粒间孔、黄铁矿晶间孔和微裂缝;孔隙度介于1.15%~4.71%;页岩孔径分布范围较宽,孔体积主要由介孔和小于200 nm的宏孔贡献,纹层状黏土质页岩储集物性较好。(3)凉高山组页岩可动油量分布在0.25~3.26 mg/g,可动油率分布在5.13%~44.83%,纹层状黏土质页岩可动性较好,块状粉砂质泥岩可动性较差;TOC、黏土矿物含量和孔隙度是控制凉高山组页岩油可动性的主要因素,利用这3个因素建立并验证了可动油量预测模型,优选出纹层状黏土质页岩为凉高山组重点勘探对象,对四川盆地页岩油的勘探开发具有指示意义。

The Jurassic Lianggaoshan Formation shale is a key exploration interval in the Sichuan Basin,but its pore structure and shale oil mobility are still unclear.In order to reveal the reservoir space characteristics and the mobility of shale oil in the Lianggaoshan Formation,this paper divided lithofacies types according to sedimentary structure and mineral composition.Basic geochemical characteristics were obtained by total organic carbon determination,rock pyrolysis and vitrinite reflectance experiments.The porosity and pore structure were characterized and evaluated by means of field emission scanning electron microscopy,nuclear magnetic resonance,low temperature nitrogen adsorption and high pressure mercury injection.The difference in reservoir space characteristics between different rock phases was also compared.With a centrifugation time of 3 h and centrifugation speed of 11000 r/min,quantitative evaluation of the mobility of shale oil with different lithofacies was carried out by NMR centrifugation and the influential factors are clearly defined.The evaluation model of movable oil quantity logging was established and.the favorable rock facies was selected.The results show that:(1)The TOC of Lianggaoshan Formation shale is mainly between 0.15%~2.95%,the Ro is between 1.06%~1.68%,and the shale is in the mature-high mature stage.After the recovery of light hydrocarbons,the change range of S1 was 0.03 mg/g~3.32 mg/g.The mineral types are mainly clay minerals and quartz.The developed lithofacies are lamellar clay shale facies,lamellar felsic shale facies,lamellar mixed shale facies and massive silty mudstone facies.(2)Shale reservoir space types are mainly clay mineral intergranular pores,organic matter pores,in addition to quartz dissolution pores,interparticle pores,pyrite intergranular pores and microfractures.The porosity is between 1.15%and 4.71%.The shale has a wide pore size distribution.The pore volume is mainly contributed by mesopores and macropores smaller than 200 nm.Laminated clay shale has the best physical properties(3)the movable oil content of the Lianggaoshan Formation shale ranges from 0.25 mg/g to 3.26 mg/g,and the movable oil rate ranges from 5.13%to 44.8%.Lamellar clay shale has the best mobility,and massive silty mudstone has the worst mobility.TOC,clay mineral content and porosity are the key factors controlling movable oil content in the Lianggaoshan Formation.Based on these three factors,a mobile oil quantity prediction model is established and verified.Laminated clayey shale is preferred as the key exploration object of the Lianggaoshan Formation,which is indicative of the exploration and development of shale oil in the Sichuan Basin.