油气储层火山物质蚀变产物及其对储集空间的影响——以准噶尔盆地克-夏地区下二叠统为例

Alteration products of volcanic materials and their influence on reservoir space in hydrocarbon reservoirs:evidence from Lower Permian strata in Ke-Xia region,Junggar Basin

通过镜下观察(岩石、铸体薄片和扫描电镜)与岩心分析,结合地层水分析结果、岩矿组成和物性数据等,以准噶尔盆地克一夏地区下二叠统为例,系统研究了含火山物质油气储层中不同自生矿物成因机理、自生矿物对油气储集空间的影响、孔隙演化及其控制因素,对储集空间具有重要影响的自生矿物主要有绿泥石、沸石(包括方沸石、片沸石和浊沸石)、方解石、钠长石和自生石英。研究表明,酸性水的加入促使早期碱性条件下析出的沸石、钠长石和方解石易于溶蚀;钾长石或斜长石溶蚀后,非等体积矿物转化析出钠长石。早期适量的绿泥石衬边和包膜对储集空间有保护意义,但成岩后期大量的绿泥石胶结破坏孔隙。与基性岩相比,中酸性熔岩和火山碎屑岩未见大规模绿泥石胶结,储层物性较好。NaHCO_3型地层水和有机酸影响下的方沸石胶结砂(砾)岩中,次生溶孔发育,为有利的碎屑岩储层。总体上,火山物质的成岩作用及蚀变演化很大程度上改善了中深层油气储层质量。

This study investigated the genesis of different authigenic minerals in hydrocarbon reservoirs associated with alteration of volcanic materials and their influences on reservoir space, as well as the pore evolution and its control factors. A case study was carried out on the Lower Permian strata in Ke-Xia region, Junggar Basin by light and scanning electron microscopic examinations of rock samples and thin-sections and core analysis, combined with the results of formation water analysis as well as rock composition and lithological data. Authigenic minerals that exerted great influences on reservoir space mainly included chlorite, zeolites （including analcime, heulandite, and laumontite）, calcite, albite, and quartz. The addition of acidic water promoted the dissolution of zeolite, albite, and calcite that were precipitated under alkaline conditions in an early stage; after the dissolution of potash feldspar or anorthose, the non-isopyknic minerals were transformed through albitization. Proper chlorite rims in pores and grain coatings preserved reservoir pore space in an early stage; however, the presence of massive chlorite cements reduced the reservoir quality in a late stage of diagenesis. Compared with basic volcanic rocks, neutral-silicic lavas and pyroclastic rocks contain less authigenic chlorite and thus may have improved reservoir property. As influenced by NaHCO3-type formation water and organic acid, coarse glutenite bearing soluble analcime cements has well-developed secondary pores and serves as the favorable clastic reservoir. Overall, the diagenesis and diagenetic evolution of volcanic materials significantly have improved the quality of hydrocarbon reservoirs at middle-to-deep depths.