Abstract: The lower limit of porosity (L_φ) is one of the essential parameters determining the effective reservoir thickness and further estimating geological reserves of oil and gas reservoirs by using volumetric method. Effective reservoir refers to that has the ability to produce commercial oil and gas flows. The reservoir permeability has a better correlation with production capacity than porosity, and the lower limit of permeability (L_k) enables to more accurately classify the effective reservoir than L_φ. However, due to the technological limitations in current,L_φ is often used to classify effective reservoirs in practice instead of L_k. The carbonate reservoirs in Sichuan Basin show characteristics of high heterogeneity with diverse pore types, complex pore throat structure and uneven fracture development. In order to identify the determination method of L_φ of highly heterogeneous reservoir, the characteristics of reservoirs in the Sinian Dengying Formation in Aanyue Gasfield are analyzed by using core samples, thin sections, SEM, and mercury injection experiments, and the reservoir is divided into matrix pore type and fractured type. Furthermore, the production capacity simulation comparison experiments on these two types of reservoirs are conducted given the same conditions, which enable to determine L_k to be 0.008 mD. On the other hand, L_φ is a variable, that is, regardless of L_φ value taken in classifying effective reservoirs, a part of effective reservoir with low porosity and high permeability will be ignored, while a part of ineffective reservoir with high porosity and low permeability will be added. If an L_φ value is determined that makes these two parts of reservoir space consistent in volume, the real total volume of reservoir space can be reached by applying the current technologies. Guided by the equivalent substitution concept, and combined with production capacity simulation, as well as physical property results of 200 rock samples, L_φ of Dengying Formation reservoir in Anyue Gasfield is determined to be 1.56%.