Abstract: In view of reservoirs with different properties near and far wellbore, the mathematic model for dual porosity (inner zone)- homogeneous (outer zone) composite reservoir is presented and solved, obtaining log-log type plots of production rate, rate integration and its derivative, and making analyses of flow mechanisms and plot characteristics at each flowing stage. Study shows that when the inner zone's permeability is better, the derivative curve of rate integration at junction of inner and outer zones will bend up, otherwise, fall down. The crossflow effect and its endurance are affected by storativity ratio. When the pressure spreads to the reservoir boundary, the rate will sharply decline, and the integral and integral derivative curves assume a straight line with slope of -1, which is the indication of harmonic decline. The case study obtains the main parameters in production decline stage, which are accordant with the real situations.

Key words: composite reservoir, multi-medium, production rate, decline, model