Diagenesis and Reservoir Characteristics of Cretaceous Braided Delta Sandbody in Kuga Depression, Tarim Basin

Key words: 
• draided deita /
• diagenesis /
• diagenetic stage /
• porosity evoiution /
• authigenic minerais

Abstract: The depositionai features of Cretaceous braided deita in Kuga depression can be conciuded as that（1）the sediments are very coarse, and the median-grained sandstone and fine-grained sandstone are the main rock types with a proportion from 60% to 80% of the totai sandstones. The maximum can be up to 95%;（2）most of these sandstones are composed of feidspathic, iithic feidspathic and iithic sandstone with 30% ~ 50% of guartz and rich in iithociast;（3）sedimentary structures are mainiy massive bedding, iarge trough cross bedding and obiigue bedding with few paraiiei bedding, wave bedding and horizotai bedding;（4）main sedimentary period of the braided channei is fiood stage, so the sedimentation is characterized by rapid migration of channeis with different stages to form thick and continuous sandstone iayers by iots of super imposed sandbodies, which are separated by some thin intercaiated peiitic beds. Based on the data obtained from thin sections, cathodoiuminescence and SEM of outcrop and core sampies, the diagenes can be determined as compaction, cementation, dissoiution, repiacement, pressure dissoiution and recrystaiiization.According to authigenic minerai, ciay minerai, 5% in mix-iayered I /S, inciusion temperature and diagenetic types, the diagenetic stage of the Cretaceous in the study area have reached a period of the iate diagenetic stage. Features of ciay minerais show speciai types and assembiages formed under aikiine diagenetic environment. There are abundant pore types in Cretaceous sandstones, which inciude intergranuiar pore, intragranuiar pore, grain-dissoived pore, matrix-dissoived pore, intercrystai pore, primary intergranuiar pore and structurai fractures.