Study on characterization and distribution of four regions of tight sandstone condensate gas reservoirs in the depletion development process

The traditional three-region theory cannot explain why some condensate gas reservoirs have high production in field depletion development even if the formation pressure is below the dew point. To solve this problem, the redesigned depletion development experiments are conducted under various pressure drop velocities conditions. Besides, a new quantitive method of the pressure range of different regions is established. The results show that there is a fog-state region in the porous medium, which is in the adjacent area below the dew point, and the production of the fog-state region is as high as the pure gas region. Compared with the fog-state region, the instantaneous gas and condensate production in the movable gas and immovable condensate (MIMC) region decreased by 23% and 93.8% in this work, respectively. The depressurizing velocity has a great impact on the fog-state region range, the positive coupling effect caused by a suitable depressurizing velocity can enlarge the fog-state region and compress the MIMC region, but the inertia effect caused by over-high depressurizing velocity will generate plenty of condensate bridges and reduce the recovery of gas condensate reservoirs. To our knowledge, the existence and quantitive pressure range of the fog-state region of the gas condensate reservoir in the porous medium is experimentally determined for the first time, which improves the traditional three-zone theory of the gas condensate and gives important support to reservoir-scale field application.