Heterogeneous factors that control the paleo-karstification

pressure solution and fracturing of tight Yangxin carbonate reservoirs are explored

and three grades of reservoir models are established in this paper based on geolo-gical data of south Sichuan.The distribution and origin of these special reservoirs such as paleokarst

colluvial breccia and stratiform coral reef areproposed according to Emei taphrogenesis.The main factors leading to the tightness of Yangxin carbonate rocks are pressure solution and cementation

in which the struc tures of the pressure solution can be summarised into 4types and 6 kinds.The development of the fractures in the carbonate rock sunderwent three stages

corres pondingly formed three fracturing reservoir bo-dies such as fracture swarms

dense fracture zones(potential faults)andfaulted breccia zones.In accordance with the distribution and association of the pores

vugs(or cavities)and fractures

the authors have constructed 11potential models of vadose medium reservoirs.These models are proved to beessentially effective in analysing pressure-rebuilding curves and subsurfacegeology of gas field.