川东南二叠系龙潭组海-陆过渡相页岩气甜点评价及意义

Sweet spot assessment and its significance for the marine-continental transitional shale gas of Permian Longtan Fm. in southeastern Sichuan Basin

冯动军

Dongjun FENG

川东南二叠系龙潭组海-陆过渡相沉积是一套潜在的页岩气勘探领域，但目前面临勘探方向不清等问题。综合岩石学、有机地球化学和储层地质学，基于X射线衍射、有机岩石学分析、氩离子抛光扫描电镜、氦气孔隙度测试和联测实验等，分析了川东南地区S1井等重点井龙潭组9个小层中泥页岩有机地化、储层和含气性及其纵向变化特征，优选了页岩气富集的有利层段。研究结果表明，川东南地区龙潭组海-陆过渡相泥页岩沉积厚度大（>2 %的泥页岩累计厚度50.11 m）、黏土矿物含量高（平均值42.69 %），以煤层、炭质页岩、泥页岩、粉砂质泥岩、含灰/灰质泥岩和泥质灰岩为主。泥页岩均值为4.63 %，孔隙度均值大于2.0 %，且都具有煤>炭质页岩>泥页岩>粉砂质泥岩>含灰/灰质泥岩的变化趋势。有机质类型以Ⅲ型为主，平均为2.07 %，储层以黏土矿物孔和微裂缝为主。②—④小层、⑥小层和⑧小层的煤层和泥页岩组合具有“厚度大、有机质丰度高、孔隙度高和含气性好”的特征，是海-陆过渡相页岩气勘探的有利目标层段。

The marine-continental transitional deposits of Permian Longtan Formation in southeastern Sichuan Basin have been targeted for shale gas but without any significant success. By resorting to analyses on petrology， organic geochemistry， and geology as well as the results of X-ray diffraction， organic petrology analysis， argon ion milling scanning electron microscopy observation， helium porosity testing， and joint measurement， the organic geochemical characteristics， reservoir characteristics， gas-bearing property and their vertical variations of 9 clay mineral-rich（42.69 % on average） layers in the Longtan Formation from some key wells （including Well S1） in southeastern Sichuan Basin were studied to locate potential shale gas enrichment intervals. The results show that the marine-continental transitional shale deposits in the Longtan Formation are thick （the cumulative thickness of shale with >2 % is 50.11 m） and mainly composed of coal seams， carbonaceous shale， shales， silty mudstone， calcareous mudstones and argillaceous limest one. Their average is 4.63 % and average porosity is greater than 2.0 %， both showing a decreasing trend from coal seam， shale， silty mudstone to calcareous mudstones. The organic matter is mainly of type Ⅲ， with an average of 2.07 %. Reservoirs are dominated by clay mineral pores and micro fractures. The combinations of coal with organic-rich shale within layers ② to ④， ⑥ and ⑧ characterized by large thickness， high organic matter abundance， high porosity and gas-bearing property are deemed as potential exploration targets for making shale gas discoveries.

10.11743/ogg20230319