Carboniferous dolomite reservoirs in East Sichuan could be divided into four grade: 1.middle porsity-middle permeability(grade-I); 2. middle porosity-lower permeability (gradeⅡ); 3. lower porosity-lower permeability (grade-Ⅲ); 4. ultra low porosity-ultra low permeability (grade-Ⅳ).Reservoirs and nonreservoirs could be distinguished by 20% of porosityand 50% of water saturation. Based on the reservoir grades and their position above watergas boundary

the contrast of injected buoyance and different capillary pressures

a newmethod-bouyance-capillary pressure contrast method is proposed in this paper so as to determine a reservoir to be net pay one or not. The result suggests that the reservoirs ofgraded I above water-gas boundary 5 m

of grade-Ⅱ above the boundary 25 m

of grade-Ⅲ

A

above the boundary 60 m and of grade-Ⅲ

B

above the boundary 100 m are all net pay reservolrs.