溶蚀作用对火山岩有效储层形成的控制作用——以松辽盆地徐家围子断陷营城组为例

Controlling effect of dissolution on valid volcanic reservoir formation:A case study of the Yingcheng Formation in the Xujiaweizi Fault Depression,Songliao Basin

针对火山岩储层岩石类型复杂、储层非均质性较强的特点,通过大量岩心观察和铸体薄片鉴定,对松辽盆地徐家围子断陷营城组火山岩储层进行系统的成岩作用和孔隙演化研究。结果表明,研究区火山岩有效储层主要为流纹岩和晶屑凝灰岩,先后经历了6个成岩作用阶段,但是不同岩性的储层经历的成岩作用类型、阶段和演化规律有差异,从而导致孔隙演化和储层物性的差异。本区对有效储层发育贡献最大的是溶蚀作用,包括有机酸溶蚀和含CO2酸性水溶蚀两种类型,有机酸溶蚀酸性火山岩形成的次生孔隙是对形成有效储层贡献最大。控制溶蚀作用的因素包括原生孔隙体系的发育程度、后期断裂活动强度与构造裂缝的分布、火山岩顶底的不整合面等。

Volcanic reservoirs are usually characterized by complex rock types and higher heterogeneity. The paper systematically studied the diagenesis and porosity evolution of volcanic reservoirs from the Yingcheng Formation in the Xujiaweizi Fault Depression,Songliao Basin,via core observation and identification of casting thin slice. The result shows that all valid reservoir lithologies,including rhyolite and crystal tuff,underwent six diagenetic stages,while different types of diagenesis,stages,and evolution patterns occurred to different reservoir lithologies. That is why the porosity evolution and physical properties of those rocks were heterogeneous. In the study area,dissolution is the most effective diagenesis process to the formation of valid reservoir,including organic acid dissolution and CO2-bearing acidulous water dissolution.And the secondary pores mostly developed in the acid volcanic rocks after organic acid dissolution played a decisive role in forming valid reservoirs. In terms of the controlling factors for dissolution,some of the most important ones may be the extent of original primary porosity system,the intensity of fracture activity and tectonic cracking in later periods,the top/bottom unconformities of volcanic rocks,etc.