Relation between the Initial and Residual Gas Saturations of Gases Trapped by Capillarity in Natural Sandstones

The saturation of gas trapped in porous rocks by capillarity depends on many factors. Herein, we focused on the effect of gas saturation at flow reversal on capillary trapping saturation. To investigate gas trapping in various sandstone cores, experiments were carried out under supercritical conditions. Residual gas saturation increased with increasing initial gas saturation. The local residual gas saturation fluctuated with heterogeneity due to the sedimentary structure. To evaluate the effect of the initial gas saturation on the residual gas saturation at the pore scale, experiments were also carried out under room temperature. For a fixed capillary injection flow rate, the initial gas saturation depended on the pore size distribution and heterogeneity due to the sedimentary layers. For vertical Berea sandstone cores, the capillary entrance pressure, associated with the layered structure, caused injected gas to enter in the porous layer of the core. However, for horizontal cores, injected gas flowed through a few layers with high permeability. On the other hand, for Kimachi sandstone cores, injected gas only entered the large pores, whereas for Tako sandstone cores, it entered both large and small pores. Therefore, high initial gas saturation can be achieved.