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与石炭系相比,准噶尔盆地西北缘下二叠统火山岩岩性、岩相类型丰富,研究程度低。本文利用岩心、薄片及元素地球化学资料,开展了火山岩岩石学及其与储层关系研究。佳木河组以熔岩和火山碎屑岩共同发育为特征,岩性以玄武安山岩、安山岩、英安岩为主,相对稳定;风城组火山岩在不同地区变化明显,克百地区以火山熔岩为主,属于玄武粗安岩和碱玄岩,而乌夏地区以熔结火山碎屑岩或火山碎屑熔岩发育为特征,属于流纹岩、碱玄质响岩和粗安岩。在佳木河组及克百地区风城组,(沉)火山角砾岩储层质量最好,安山岩等熔岩其次;乌夏地区风城组熔结火山角砾岩和石泡构造火山角砾熔岩储层质量最好。此外,相同岩性可能因产出环境不同而储层特征有别。尽管各地成岩作用存在差异,但火山岩优质储层仍集中于溢流(爆溢)相上部亚相、爆发相空落亚相的弹射坠落堆积和火山碎屑流亚相的水下堆积和爆发相。全区佳木河组溢流相和爆发相共同发育,而克百地区风城组以溢流相为主、乌夏地区风城组以爆发相火山碎屑流亚相为主,不同地区不同层位的有利勘探目标差异明显。除断裂带的裂缝和大型不整合面之下的风化淋滤外,岩相是控制火山岩储层质量的关键因素。
Compared with the Carboniferous, the Lower Permian volcanic rocks in the northwestern margin of the Junggar Basin have rich lithofacies types and low degree of research. In this paper, volcanic petrology and its relationship with reservoirs are studied by using core, thin slice and elemental geochemical data. The Jiamuhe Formation is characterized by the common development of lava and volcaniclastic rocks. The lithology is mainly basalt andesite, andesite and dacite, and is relatively stable. The volcanic rocks of the Fengcheng Formation vary obviously in different regions. The Kerui area is dominated by volcanic lava The main belonged to the basalt and the basalt, while the Wuxia area was characterized by the development of fused volcaniclastic rocks or volcaniclastic lava, belonging to rhyolite, basaltic rock and cambrian rock. In the Jiamuhe Formation and Kefeng area, the Fengcheng Formation and (Shen) volcanic breccia reservoirs have the best quality, followed by lava, such as andesite; and the Fengcheng Formation, the Fucheng Formation, Wuxia, has volcanic breccias and bubble volcanic breccias Lava quality is the best. In addition, the same lithology may have different reservoir characteristics due to different output environments. Despite the differences in diagenesis, the high-quality volcanic reservoirs are still concentrated in the upper subfacies of the overflow (explosive) facies, the falling and accumulation of explosive phase faulted subfacies and the underwater deposition and explosion of volcaniclastic subfacies . The overflow and facies of the Jiamuhe Formation in the whole area developed together, while the Fengcheng Formation in the Kehui area mainly dominated the overflow phase. The Fengcheng Formation in the Wuxia area mainly consisted of volcanic debris flow and subfacies in the outbreak phase, and varied in different areas Differences in favorable exploration targets are obvious. In addition to fractures in fractures and weathered leaching under large unconformities, lithofacies are the key factor controlling the volcanic reservoir quality.