Numerical Simulation of Dry Gas Migration in Condensate Gas Reservoir

Dry gas overlies on condensate gases and flows due to the difference in density. This phenomenon affects cyclic injection exploitation and increases production costs. A mathematical model of dry gas migration was developed in this study to investigate the migration characteristics and the overlying law for dry gas in the condensate gas reservoir. On the basis of the theory of convection diffusion, the governing equations were constructed, using dry and condensate gases as two pseudo-components. The distribution and transition belt of dry gas, as well as the effects of condensate oil and the perforation method on overlying of dry gas were discussed based on the dry gas migration model. The results demonstrate that the width of the transition belt of dry and condensate gases increases gradually over time. The mole fraction of gas in the transition belt is dense in the middle, but sparse at the two ends. The overlying of dry gas is easy, taking condensate oil into consideration. The value of F increases by 0.32, but the width of the transition belt becomes narrow. The transition belt under the top perforation of the reservoir is wider than that under symmetric perforation, and the overlying degree of dry gas increases. This study provides a theoretical foundation for in situ adjustment and optimization of cyclic gas injection utilization.