Abstract: A whole set of log explanaticrs for old sells in Sichuan where the data are not enough is presented in this paper.On the basis of dividing permeable formations qualitatively and judging oil-gas formations quantitatively, the concept of elcctrcde relative value of limestone is presented here for the first time, which is used to divide gas or water formations semiquantitatively,calculate pcrosity, permeability and oil saturation of reservoirs, divide gas-water formations quantitatively，and determine classification evaluation criterions of gas formations .The set of log explanations is believable and feasible for the purpose of reservoir evaluation, and the choice and reproduction of
formations in old wells of carbonate rocks in Sichuan.

Key words: Log explanation, Explanation model, Relative permeability curve, Reservoir of carbonate rocks