徐家围子断陷营城组火山岩气藏储层特征

RESERVOIR CHARACTERISTICS OF VOLCANIC ROCK GAS POOL IN YINGCHENG FORMATION IN XUJIAWEIZI FAULT DEPRESSION

徐家围子断陷位于松辽盆地北部,火石岭、沙河子、营城期发育3个火山喷发旋回。其中营城组火山活动最为广泛,具有早晚两个主要喷发期,早期主要形成中酸性岩,晚期主要为中基性岩。其中流纹岩和流纹质(熔结)凝灰岩为主力产气储层。文章综合应用岩心观察、薄片鉴定、荧光元素分析、激光共聚焦等手段,对该区营城组火山岩岩石矿物学进行了细致研究,划分了两大类七亚类二十余种火山岩类型,并发现流纹岩和流纹质(熔结)凝灰岩普遍具有碱交代作用,发育有火山灰溶蚀孔和玻璃基质脱玻化球粒内微孔等特殊孔隙类型,同时对火山岩储层物性与岩石类型的关系进行了定量化研究,并且分析了岩性作为物质基础直接控制储层物性演化的作用。

Xujiaweizi fault depression is located in the northern part of the Songliao Basin. During Early Cretaceous, three volcanic eruption cycles occurred in Huoshiling, Shahezi and Yingcheng ages respectively, in which volcanic activities in Yingcheng age were the most extensive and mainly erupted in an early and a late eruption stage. The extrusive rocks in the early stage mainly were neutral and acid rocks, while that in the late stage mainly were neutral and basic rocks. Among these extrusive rocks, rhyolite and rhyolitic tuff (igimbrite) are the main gas pay zones. In the paper, various methods, such as core observation, thin-section identification, fluorescent elemental analysis and laser common focus, are comprehensively used to intensively study the mineralogy of the volcanic rocks in Yingcheng Formation in the study area. The volcanic rocks are divided into two types, seven subtypes and over twenty kinds. Meanwhile, it is found that the rhyolite and rhyolitic tuff (igimbrite) have generally experienced alkaline metasomatism and have well-developed special pore types, such as dissolution pores of volcanic ash and micropores resulted from devitrification of glass matrix within spherical particles. The relationship between volcanic rock types and poroperm characteristics of reservoirs are quantitatively studied and the direct control of lithology on the poroperm characteristics of volcanic rock reservoir is analyzed.