Abstract: In response to the problem of rapid production decline and poor development effectiveness of the main gas reservoirs in Shan2 Member, Shan1 Member and He8 Member, Well Blocks Yan145-Yan128, Ordos Basin, a comprehensive reservoir evaluation was performed on the geological characteristics of the main gas reservoirs and the sand body contact relationship by means of refined geologic studies to further definite the distribution characteristics of sedimentary microfacies in reservoirs, characterize the distribution range of high-quality single sand body reservoirs, and identify the potential area of well deployment. The study results showed that the reservoirs in Well Blocks Yan 145-Yan 128 were delta front subfacies deposits, and the sand bodies basically were continuously developed, with a general thickness of 4 to 6 m; the vertical thickness and horizontal size of multi-layer superimposed sand bodies were large, and the connectivity of sand bodies was preferable; the vertical thickness and horizontal size of the isolated sand bodies were limited, and the connectivity of sand bodies was average; single sand bodies were isolated and superimposed in the horizontal direction; for isolated sand bodies, the unperforated production was basically at the original gas reservoirs, with abundant remaining gas, so isolated sand bodies might be the key target for further tapping the potential; according to the characteristics of residual gas distribution, measures such as infilling, re-perforating and set-out, could be taken to increase the production of reserves; it was planned to add 12 infilling wells, 15 set-out wells and 36 re-perforating wells, and it was expected to increase the recoverable reserves by 83×10⁸ m³. The study provides an important reference for the development and adjustment of similar gas reservoirs.

Key words: Well Blocks Yan 145-Yan 128, main gas reservoir, single sand body, contact relationship, potential tapping analysis