1. School of Petroleum Engineering, Southwest Petroleum University, Chengdu 610500, China; 2. Research Institute of Exploration and Development, Daqing Oilfield Limited Company, Daqing 163712, Heilongjiang, China

Through the testing of gas state equation ( PVT) property, saturated vapor quantity of natural gas and formation water PVT property, and the evaluation of reservoir starting pressure of full diameter core analysis, flow rate and stress sensitivity in Xushen gas field, the author have discussed the seepage mechanism of volcanic reservoir. The results show that the contents of CO₂ changes greatly in Xushen volcanic reservoir ( the highest content as 86.88 % ). Molecular weight of natural gas is positively correlated with CO₂ content. Deviation coefficient, saturated vapor quantity and natural gas content in formation water are influenced by formation temperature, pressure, gas composition and mineralization degree of formation water. The starting pressure of volcanic gas reservoir shows exponential relationship with irreducible water saturation and air permeability. Reservoir is featured by gas-liquid two-phase flow with weak speed sensitivity and strong stress sensitivity, which may bring damage to reservoir permeability and variation to pore structure.