| Abstract: | The Donghe sandstone in Bachu formation of lower Carboniferous in the central Tarim basin consists of quartzose sandstone, deposited in a shore environment, its statistical composition being quartz of 83%, feldspar of 8 %, and elastic rock 9%. This paper discusses its diagenesis by using the conventional thin section, injecting thin section and SEM observations and X-ray analysis of the clay minerals as well as pattern analysis of pore structure within two wells. Three main degenetic events, which significantly influenced the reservoir quality of the Donghe sandstone within the area are compaction, cementation, and dissolution. The calcite cementation and dissolution have the greatest effects on reservoir porosity, and the secondary porosity owing to its dissolution provided the main reservoir porosity. Assuming an initial porosity of 38M, after the porosity eviution during three stages, the Donghe sandstone will have the mean porosity of 14% based on point counting, mean porosity by core analysis may be 17% |
