Sedimentary Facies Analysis And Reservoir Evaluation Of The Upper Triassic Tumengela Formation And The Middle Jurassic Quemocuo Formation In The South Qiangtang Depression, Tibet

Three are potential clastic reservoirs in the top of the Tumengela Formation of the Upper Triassic and the Quemocuo Formation of the Middle Jurassic in the South Qiangtang depression. This paper, through a set of studies, mainly including field profile measurement, sample preparation, thin section analysis, sedimentary facies analysis, physical analysis and cathodoluminescence analysis, has evaluated the potential reservoir and dominant reservoirs of clastic rocks in the Southern Qiangtang depression.it shows that the lithology of reservoirs in study area mainly are lithic quartz sandstones, lithic sandstones, and a small amount of feldspar and lithic sandstones. Middle-fine sandstones are the main type of rocks. The separation is moderated and it is main as the shape of subsharp-subcircle. Generally, the maturity of structure and composition is lower. Compared with the sandstone of the Quemocuo Formation, the composition maturity is higher in the Tumengela Formation. Delta sedimentary environment is the dominant in the Tumengela Formation,while in the Quemocuo Formation,littoral facies and neritic facies are the main facies. Besides, the typical sand of littoral barrier deposits can be observed under the microscope. The clay matrix is main in sandstones, and the common cement is siliceous cements. There are generate secondary pores in the sandstones of the Tumengela Formation and the Quemocuo Formation. The main pore types are intergranular pores and intragranular pores. Compaction, pressure solution and cementation which belongs to destructive diagenesis, have made it difficult to preserve the primary porosity. And the secondary porosity has not developed enough. So viewed as a whole, physical properties of clastic reservoir of Tumengela Formation and Quemocuo Formation are inferior, and they are main compact to super-compact reservoir. The sandstone of the Tumengela Formation has little advantages in compaction resistance, the maturity of texture and composition. As the aspect of the lithology of sandstones, Lithic quartz sandstone reservoirs will be better. And based on facies analysis, superior reservoir may has developed in the delta front zone and shoreface sub-facies.