石油与天然气地质2025，Vol.46Issue(6)：1860-1873,14.DOI:10.11743/ogg20250608
四川盆地二叠系大隆组硅质页岩碳酸盐交代作用及其对页岩储层发育的影响
Carbonate metasomatism in siliceous shales of the Dalong Formation,Sichuan Basin and its impact on shale reservoir development
摘要
Abstract
By integrating multiple analytical techniques,including X-ray diffraction(XRD),scanning electron microscopy(SEM),electron probe microanalysis(EPMA),and carbon-oxygen isotope analysis,we investigate the origin of micritic calcites in the siliceous shale of the Upper Permian Dalong Formation,northeastern Sichuan Basin,along with their impacts on reservoir development.The siliceous shales generally exhibit a high quartz content,followed by carbonate minerals,with the clay mineral content proving low overall.Microscopic observations reveal that the siliceous shales contain a large quantity of radiolarian bioclasts,which are distributed in densely packed and scattered patterns within the siliceous mineral matrix.Radiolarian skeletons in the siliceous shales display iridescence unique to carbonate metasomatism under orthogonal-polarized light.Under SEM,these skeletons show representative pseudomorphic textures of partial and complete replacement.These observations,combined with the energy dispersive spectroscopy(EDS)analysis,demonstrate that the radiolarian skeletons are formed by diagenetic metasomatism.Metasomatism also occurs synchronously within the siliceous mineral matrix,which acts as the rock framework.The calcitereplacement appear in two forms:highly euhedral individual grains and poorly euhedral or even anhedral aggregates.These calcites occur within the siliceous mineral matrix in irregularly dotted or contiguous patterns,resulting in the formation of mosaic textures.The oxygen isotopic composition indicates that calcites in the siliceous shales are formed in a low-temperature environment.The EPMA results show that the calcites exhibit high silicon and anomalous strontium concentrations,which can be attributed to pore fluid-rock interactions in the early diagenetic stage.These interactions led to the infilling and destruction of numerous primary inorganic pores among quartz grains,thereby reducing the available in-situ space for the retention of liquid hydrocarbons generated in the late stage.The pore modification further affected the quantity of secondary organic pores and the total porosity in the highly-to over-mature stage.Therefore,carbonate metasomatism represents a significant mechanism governing the development of high-quality reservoirs in the siliceous shales of the Dalong Formation within the northeastern Sichuan Basin.Accordingly,its differential impact should be fully considered when selecting the optimal shale gas sweet spot intervals.关键词
方解石/放射虫/碳酸盐交代作用/硅质页岩/大隆组/四川盆地Key words
calcite/radiolarian/carbonate metasomatism/siliceous shale/Dalong Formation/Sichuan Basin分类
能源科技引用本文复制引用
卢龙飞,刘旺威,刘伟新,鲍芳,周圆圆,俞凌杰,申宝剑..四川盆地二叠系大隆组硅质页岩碳酸盐交代作用及其对页岩储层发育的影响[J].石油与天然气地质,2025,46(6):1860-1873,14.基金项目
国家油气重大专项(2025ZD1404102) （2025ZD1404102）
企业创新发展联合基金(U24B6001). （U24B6001）
