摘要：

石炭系风化壳是准噶尔盆地火山岩油气储集层的主要类型,物性明显好于同时代原生型火山岩。通过对陆梁隆起滴西地区的铸体薄片与岩心观测,发现风化淋滤对火山岩储集性能的改造主要体现在孔隙上,对裂缝的改造作用不明显。由于火山岩形成的构造环境与古地貌存在差异,不同的海拔高度决定了其接受风化时间的长短。准噶尔盆地内石炭系不整合上覆地层时代存在明显差异,下二叠统至白垩系均有分布。最长风化时长在东部隆起约为150Ma,在陆梁隆起约为100Ma,在西部隆起约为55Ma;而3处隆起最少则仅缺失部分上石炭统—下二叠统。风化时长的长短与火山岩孔隙度的大小呈近波峰状对应关系,火山岩孔隙度初始随风化时长的增大(至约30Ma)逐渐增大,在到达峰值(对应风化时长约40Ma)后随时长的增大(55～100Ma)逐渐减小。最大的孔隙度均出现在火山角砾岩和玄武岩中,安山岩的孔隙度次之,而凝灰岩的孔隙度最小。

关键词: 准噶尔盆地, 石炭系, 火山岩风化壳, 不整合 时长

Abstract:

Carboniferous volcanic weathered crust, whose petrophysical feature is better than that of contemporary primary volcanic reservoirs, is one of the major volcanic reservoirs in Junggar Basin. The observation of casting thin sections and drill cores from Dixi area in Luliang Uplift shows that the improvement by weathering and leaching is more effective at pore space than fracture. The altitude of volcanic rocks,influenced by tectonic settings and palaeogeomorphology,determined the weathering duration. Ages of the strata overlying the Carboniferous vary from the Lower Permian to the Cretaceous,and suggest the duration of weathering changes greatly in different areas. The longest weathering duration is about 150Ma in eastern uplift,100Ma in Luliang uplift and only 55Ma in western uplift. The shortest stratigraphic break in the three uplifts,however, only lacks part of the Upper Carboniferous and Lower Permian. There is a wave corresponding relationship between the weathering duration and the volcanic reservoir porosity. The porosity increases with weathering duration changing from 0 to 30Ma,gets to the peak when weathering duration is about 40Ma,and decreases as the weathering duration gradually increases from about 55 to 100Ma. Concerning the lithological influence on porosity,volcanic lava and volcanic breccia have the largest porosity,andesite comes second and tuff has the smallest porosity.

Key words: Junggar Basin, Carboniferous, volcanic weathering crust, unconformity, time span

中图分类号: 

• TE112