火山碎屑岩的储层物性——以松辽盆地营城组为例

Porosity and Permeability of Pyroclastic Rocks of the Yingcheng Formation in Songliao Basin

对松辽盆地营城组35口盆内深层钻井和2口剖面浅钻全取心井的对比研究揭示：在浅层（埋深〈500 m）,火山碎屑岩储层物性（平均孔隙度18.7%、渗透率0.32×10^-3μm^2）好于熔岩（14.0%,0.18×10^-3μm^2）;在深层（埋深〉2 800 m）,火山碎屑岩物性（2.6%,0.05×10^-3μm^2）明显差于熔岩（7.3%,0.07×10^-3μm^2）。熔岩和火山碎屑岩的储层物性总体上都随埋深增加而变差,但火山碎屑岩的变化率显著大于熔岩;所以当大于一定埋深（2 500～3 000 m）时,熔岩的物性优于火山碎屑岩而成为主力储层。熔岩与火山碎屑岩物性随埋深变化的差异主要源于它们成岩方式的不同：前者冷凝固结,骨架体积受压实影响很小;后者压实固结成岩,其特点同沉积岩。在中浅层勘探中（埋深小于2 500 m）火山碎屑岩可作为重点目标。

Correlation among 35 in-basin boreholes and 2 continuous field coring sections resulted that porosity and permeability of pyroclastic rocks（mean 18.7%,0.32×10-3μm2） are higher than that of volcanic lava rocks（mean 14.0%,0.18×10-3μm2） in the shallow part of basin with burial depth less than 500 meters,while contrarily in the deep part of basin with burial depth more than 2 800 meters,porosity and permeability of pyroclastic rocks（mean 2.6%,0.05×10-3μm2） are rather poor than volcanic lava rocks（mean7.3%,0.07×10-3μm2）.Generally,porosity and permeability of both two types of rocks decrease with increasing burial depth,however,the changing rate of pyroclastic rocks is remarkably larger than that of volcanic lava rocks.Therefore,volcanic lava rocks become primary reservoir due to higher porosity and permeability than pyroclastic rocks when burial depth range is below 2 500 to 3 000 meters.This is mainly contributed by their differences in diagenesis as volcanic lavas are concreted by cooling so that their framework volume is hardly affected by compaction,while pyroclastic rocks are consolidated by compaction,similarly to sedimentary rocks.Therefore,petroleum exploration in the middle and shallow part of basin（burial depth less than 2 500 meters） could attentively aim at pyroclastic rocks.