Abstract: In the process of natural depletion of condensate gas reservoir, with decline of formation pressure and increase of effective stress, the pore volume of reservoir will decrease, allowing such a process to assume a declining process of the pore volume in physics rather than a process of constant volume depletion. For this reason, the mathematic model for phase equilibrium of condensate oil-gas system depletion, considering the pore volume decreasing is proposed on the basis of stress sensitivity test. The case study indicates that with respect to constant volume depletion process, the reservoir deformation will result in decrease of the pore space in it, and the lighter gas in the pore will be more discharged, forming "heavier fluid" and bigger retrograde condensed liquid saturation. So, for a reservoir with more intensive stress sensitivity, the influence of such a decline of pore volume on phase equilibrium process of condensate oil-gas depletion should be considered.

Key words: condensate gas reservoir, reservoir, deformation, low permeability reservoir, phase equilibrium