鄂尔多斯盆地延长气田石盒子组沉积特征分析

Analysis of the sedimentary characteristics of Shihezi formation in Yanchang gasfield,Ordos Basin

鄂尔多斯盆地延长气田石盒子组储层岩性为岩屑石英砂岩,陆源碎屑占78.27%,主要为长石、石英和岩屑,长石和石英的平均含量分别为5.96%和60.14%,分别占陆源碎屑的15.6%和76.8%,阴极发光显示石英呈暗蓝紫色,为高温类石英,来源于火山岩、深成岩及接触变质岩类,石英次生加大发育。胶结物以粘土矿物、铁方解石以及石英次生加大等硅质胶结为主。石盒子组中粗砂岩分选性为较好、好-中等,次棱角,次棱角-次圆状。碎屑颗粒接触方式以点接触为主,颗粒支撑占绝对优势。石盒子组概率曲线受三角洲沉积亚相的不同沉积环境的影响,表现为两段式,多段式,一段式。砂岩的峰度值在0.87～1.22之间,为尖锐,与砂岩粒度百分含量结果一致。延长气田石盒子组发育辫状河三角洲前缘、曲流河三角洲前缘沉积亚相,三角洲前缘水下分流河道、分流间湾微相较为发育。

Lithology of Shihezi formation mainly includes lithic quartz sandstone, terrigenous clastic accounting for 78.27%, which mainly includes feldspar, quartz and cuttings. The average content of feldspar and quartz are 5.96% and 60.14% respectively ,which account for terrigenous clastic 15.6% and 76.8%. Cathodoluminescence shows that quartz is dark blue-violet, and it is a high temperature quartz mainly from volcanic, plutonic rock and contactolite. The type of cement includes clay mineral, ferrocalcite and quartz overgrowth. The sorting features of gritstone is well, good-medium and mainly is semiedge-angle and semiround. Detrital grain contact style mostly is point contact, while grain-supported accounts for absolute advantage. Probability curve is two-segment, single linear and multisection type because of the different hydrodynamic condition of delta subdivision environment. The kurtosis values of sandstone is between 0.87 - 1.22, which is consistent with sandstone grain size percentage content. Therefore, Shihezi formation develops braided delta front and braided delta front, and among them underwater distributary channel, interdistributary estuary in delta front are the main forms.