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鄂尔多斯盆地在长81期处于浅水湖泊沉积环境,盆地东北部的陕北地区在该期湖盆底部形态相对更加平缓、水体更浅。利用测井、岩心、薄片等资料,从储层类型、时空展布、岩石学特征、物性等方面研究了长81储层特征,认为研究区长81期主要发育水下分流河道砂体和河口坝砂体,砂体单层厚度薄、泥质含量高,具有明显的多旋回性、砂体垂向和纵向上连续性差,但分布范围广;砂体为岩屑长石砂岩和长石岩屑砂岩,属于细砂岩和极细砂岩;物性整体上差,属于典型的低孔特低渗—超低渗储层。分析表明造成该类型砂体形成的主要原因是:①研究区距离物源区远,且供给量不充足;②水体浅、湖盆底部形态平缓,湖岸线波及范围广;③湖水动力和河水动力弱。因此,在上述沉积环境下,在小期次湖平面升降过程中,长81砂体形成了“拉锯”式的砂体沉积模式。
The Ordos Basin was in a shallow lacustrine sedimentary environment during the 81st period. In northern Shaanxi, the northern part of the basin was relatively flat and had a shallower water body at the bottom of the lake basin. The characteristics of Chang 81 reservoir have been studied from the aspects of reservoir type, space-time distribution, petrologic characteristics and physical properties by means of well logging, core and thin-sheet data. It is believed that the 81 reservoirs mainly developed in the study area have undergone sub-distributary channel sand bodies and estuaries The bar sand body and the sand body are thin and monolayer with high argillaceous content and obvious multi-cycle characteristics. The sand bodies are poor in vertical and vertical continuity but have a wide range of distribution. The sand bodies are lithic feldspar sandstone and feldspathite Sandstone, belonging to the fine sandstone and very fine sandstone; poor overall physical properties, belonging to the typical low porosity and permeability of ultra-low permeability reservoir. The analysis shows that the main causes for the formation of this type of sand body are: ① The research area is far away from the provenance area and the supply is not sufficient; ② The shallow water body, the gentle bottom of the lake basin and the wide range of lakeshore; ③ The hydrodynamic and hydrodynamic weak. Therefore, in the above sedimentary environment, the long 81-year sand body formed a “saw-saw ” type of sand body deposition pattern during the small-scale lake level rise and fall.