松辽盆地白垩系营城组火山岩脱玻化作用及其储层意义——以盆缘剖面为例

Devitrification of the Volcanic Rocks of the Cretaceous Yingcheng Formation in the Songliao Basin and Its Reservoir Significance:An Example from a Basin Boundary Section

松辽盆地东南隆起区三台营城组火山岩岩石类型主要为：珍珠岩、流纹岩、隐爆角砾岩、角砾熔岩和凝灰岩等,其脱玻化的岩石类型主要为珍珠岩和流纹岩。在偏光显微镜下,珍珠岩的玻璃质基质的脱玻化现象表现为雏晶、骸晶（微晶）和球粒3种;而流纹岩基质的脱玻化现象则主要表现为球粒。它们发育过程由雏晶—骸晶（微晶）—球粒逐渐增强。脱玻化的发生及其强弱与岩石成分、层位和裂隙发育程度有密切联系。通过实验室测试,珍珠岩经过的脱玻化作用越强,岩石密度越小,反之,越大。岩石密度变化范围为3.13%-8.65%。假设其为封闭体系,密度的减小对应孔隙的增加,说明脱玻化作用能明显改善玻璃质火山岩这一类特殊储层的物性。

The main types of volcanic rocks of the Yingcheng Formation in Santai area, southeastern uplift of the Songliao Basin are perlite, rhyolite, hydrothermal breccia, breccia conglomerate, tuff and so on. The devitrification of perlite and rhylolite is obvious. It can be found under microscope that the devitrification of perlite is of three phenomena： crystallite, skeletal crystal （microlite） and spherulitic while the devitrification of rhyolite is mainly of spherulitic. The development process of the devitrification is featured by a gradual increasing trend from crystallite to skeletal crystal （microlite） and finally to spherulitic. The formation and intensity of devitrification are related not only to the rock composition, but also to the formation and development of cracks. Laboratory tests indicate that the density of perlite, in the range of 3.13%-8.65%, is lighter after intense devitrification and is heavier with slight devitrification. Assuming a closed system, the decreasing density of rocks is corresponding to an increase in porosity of the rocks. Devitrification processes in the area can improve the reservoir properties of the glassy volcanic rocks.