海相页岩纹层特征及其对页岩储层发育的影响——以川南长宁地区龙马溪组为例

Lamina characteristics of marine shale and its influence on shale reservoir development:a case study of Longmaxi Formation,Changning area,South Sichuan Basin

纹层作为页岩最富特色的沉积构造,广泛发育于海相页岩层系中。纹层的发育直接导致页岩非均质性变化明显,进而对页岩生烃、页岩储集性以及页岩含气性等产生影响。文中以川南长宁地区X井龙马溪组的海相页岩为例,利用取心井岩心观察、薄片鉴定、电镜扫描、全岩X衍射及物性分析等资料,开展了海相页岩纹层特征及其对页岩储层发育的影响研究。结果表明:龙马溪组发育石英纹层、黏土纹层、有机质纹层、黄铁矿纹层等4种类型,以及石英纹层-黏土纹层、黏土纹层-有机质纹层和石英纹层-有机质纹层3种组合类型;纹层的分布具有明显的非均质性,由龙S_(1)l_(1)^(1)亚段至龙S_(1)l_(1)^(2)亚段,有机质纹层发育频次呈逐渐变小的趋势,石英纹层发育频次的变化趋势与之相反,黏土纹层在整个研究层段发育相对稳定;页岩储层物性与有机质纹层发育频次呈正相关性,与黏土纹层发育频次呈负相关性,与石英纹层发育频次呈复杂相关性;只有石英纹层发育适中,才对页岩储层发育有利,石英纹层发育和欠发育对页岩储层发育均有不利影响。

As the most distinctive sedimentary structure,lamina is widely developed in marine shale striations.This resulted in obvious heterogeneity and further influenced the hydrocarbon generation,shale reservoir performance and gas-bearing characteristics.In this paper,based on drilling cores,thin sections,scanning electron microscopy(SEM),X-ray diffraction(XRD),and physical test data,the lamina characteristics and its influence on shale reservoirs in the Longmaxi Formation were studied in the Changning area,South Sichuan Basin.The results show that four types of lamina(quartz lamina,clay lamina,organic lamina and pyrite lamina)were identified by composition.Three combination types of lamina(quartz lamina-clay lamina,clay lamina-organic lamina and quartz lamina-organic lamina)were also identified.In the longitudinal direction,the density and thickness of the three layers are obviously heterogeneous.The density of organic lamina gradually decreases from S_(1)l_(1)^(1) to S_(1)l_(1)^(2),while the density of quartz lamina increases.The clay lamina are relatively stable in the whole study interval.In addition,reservoir physical properties has positive correlation with the density of organic lamina,negative correlation with the density of clay lamina,and complex correlation with the density of quartz lamina.Only moderate development of quartz lamina is beneficial to reservoir development,and both development and underdevelopment of quartz lamina have adverse effects on reservoir development.