Abstract: Quantitative description of reservoir characteristics and its genetic mechanism analysis are prerequisite and foundation of reservoir distribution prediction, exploitation target selection and exploitation plan design. Starting from sedimentary lithology characteristics of the reservoir, the authors quantitatively analyze its basic properties including reservoir pore space type, microcosmic pore throat structure, physical property distribution and poroperm relation by taking nonlayered carbonate oolitic limestone reservoir of Jia22 A Bed, Moxi Gas Field in Middle Sichuan as an example. The genetic mechanism of oolitic bank reservoir is also studied, and its beach body migration model is established. The study indicates that the formation and distribution of the reservoir is under the associated control of the secondary differentiation of microtopography and transgressionregression cycle in the area. On local microtopography altitude, regression lasted for a long period, sediments were completely exposed, and eluviation of atmosphere freshwater on reservoir was therefore thoroughly conducted, leading to a comparatively thicker reservoir with better quality.

Key words: oolitic limestone, reservoir characteristics, genetic mechanism, Moxi Gas Filed, Sichuan Basin