Sedimentary facies and hydrocarbon reservoirs from the Palaeogene Suweiyi Formation in southern Tianshan Mountains, Tarim Basin, Xinjiang

Sedimentary facies and hydrocarbon reservoirs from the Palaeogene Suweiyi Formation in southern Tianshan Mountains, Tarim Basin, Xinjiang are examined on the basis of lithologic and physical properties of the hydrocarbon reservoirs. The Suweiyi Formation is separated into two parts:sandstone intervals in the lower part and gypsum mudstone intervals in the upper part, and composed of braided delta and lake depositional systems. The hydrocarbon reservoirs mostly consist of siltstone, fine-grained sandstone, medium-grained sandstone, and gravelbearing sandstone, including feldspar quartz sandstone and lithic feldspar sandstone. The porosity types contain the primary intergranular pores and solution openings, and cracks and microcracks. On the whole, the basal sandstones especially the delta front distributary channel and sheet sandstones with excellent physical properties belong to the medium-porosity and medium-to low-permeability reservoirs with heavy heterogeneity. The main influencing factors include sedimentary facies and diagenesis in which compaction, dissolution and cementation are believed to be the main diagenetic effects.