塔中隆起北斜坡志留系储层特征及控制因素

在详尽的岩石学研究基础上,阐述了塔里木盆地塔中北斜坡志留系(主要是下砂岩段)储层的特征.志留系砂岩成分成熟度总体较低(岩屑砂岩为主),但在下砂岩段下亚段常夹数层高成熟度的石英砂岩;砂岩结构成熟度较高.储层成岩压实作用较强(粒间一般以线接触为主);以碳酸盐类及硅质和高岭石为主的胶结作用总体较强;溶蚀作用一般较弱,但局部层段以碳酸盐胶结物为主的溶蚀作用强烈,对储层性质影响较大.储层孔隙类型主要有残余原生粒间孔、颗粒(长石、岩屑)溶孔、碳酸盐(主要为方解石)胶结物溶孔和微孔隙.储层孔隙类型和组合在平面和纵向上存在一定变化,多数层段以粒间孔和微孔为主,局部层段碎屑颗粒间碳酸盐溶孔占较高的比例.进而总结了影响储层性质的主要因素为压实作用、成岩胶结作用和储层岩石学特征(碎屑组分和粒级等).较为优质的储层基本为中-细粒以上石英砂岩(或成分接近石英砂岩).

Characteristics and controlling factors of Silurian reservoir in northern slope of central uplift in Tarim Basin

Tazhong northern slope is located in the central uplifting belt in Tarim Basin. Silurian is mainly tidal-flat facies sandstone and mudstone overlapped on the surface of Ordovician palaeotopography and palaeogeomorphology in the area. On the basis of detailed petrologic study, this paper expounds the (characteristics) of the Silurian (mainly lower section sandstone) reservoir. The compositional maturity of Silurian sandstone is totally lower, that is, the lithology mainly be lithic sandstone. But there exists several interlayers of higher mature quartz sandstone in the lower subsection of the lower section sandstone. Their textural maturity is higher. The compactional diagenesis of the reservoir is stronger (leading to the linear inter-granular contaction generally), so is the cementation (mainly that of carbonate, quartz and kaolinite). Dissolution in the reservoir is commonly weaker. Yet there locally exists layers in which (dissolution) (mainly that of carbonate) is stronger and they may have significant effect on the characteristics of reservoir. The main pore types in the reservoir are as follows: primary intergranular pore, innergranular (feldspar and rock debris) dissolution pore, carbonate cement dissolution pore and micropore. The pore types and combinations vary horizontall and vertically. Intergranular pore and micropore are dominant in most layers, whereas carbonate cement dissolution pore has a relatively big ratio in some layers. Further the paper sums up the dominant factors affecting the reservoir characteristics. Among them, compaction and cementation are most important. The lithologic features, such as clastic component and grain-size, are also important factors, and the relatively good quality reservoirs are basically middle-fine grained quartz sandstone or close quartz sandstone in compositionally.