Abstract
Accuracy defects exist when modeling fluid transport by the classical capillary bundle model for tight porous media. In this study, a three-dimensional simplified physical model construction method was developed for tight sandstone gas reservoirs based on the geological origin, sedimentary compaction and clay mineral-cementation. The idea was to reduce the porosity of the tangent spheres physical model considering the synergistic effect of the above two factors and achieve a simplified model with the same flow ability as the actual tight core. Regarding the wall surface of the simplified physical model as the boundary and using the Lattice Boltzmann (LB) method, the relative permeability curves of gas and water in the simplified model were fitted with experimental results and a synergistic coefficient could be obtained, which we propose for characterizing the synergistic effect of sedimentary compaction and clay mineral-cementation. The simplified physical model and the results simulated by the LB method are verified with the experimental results under indoor experimental conditions, and the two are consistent. Finally, we have carried out a simulation of gas flooding water under conditions of high temperature and high pressure which are consistent with the actual tight sandstone gas reservoir. The simulation results show that both gas and water have relatively stronger seepage ability compared with the results of laboratory experiments. Moreover, the interfacial tension between gas and water is lower, and the swept volume is larger during placement. In addition, the binding ability of the rock surface to the water film adhered to it becomes reduced. The method proposed in this study could indicate high frequency change of pores and throats and used to reflect the seepage resistance caused by frequent collisions with the wall in microscopic numerical simulations of tight sandstone gas reservoirs.
Highlights
Classical capillary bundle models rely heavily on extensions of Darcy’s law and empirical relationships that do not comprehensively capture all of the important physical phenomena at various scales [1,2,3]
Based on the geological origin of tight sandstone gas reservoirs: sedimentary compaction clay mineral-cementation, we propose two waysgas of reservoirs:the sedimentary compaction and spheres clay mineral-cementation, we propose two ways of reducing reducing porosity for the tangent physical model
12.55% higher than that of the laboratory experimental conditions when the process of gas flooding water entered into the stable state (t = 5000 s)
Summary
Classical capillary bundle models rely heavily on extensions of Darcy’s law and empirical relationships that do not comprehensively capture all of the important physical phenomena at various scales [1,2,3]. The common approach used to study two-phase of gas and water or gas alone systems in subsurface environments is to consider each phase separately using Darcy’s law and account for the characteristics of physical parameters by classical capillary bundle models [4,5,6]. This approach can’t explicitly accounted for the multidirectional transport of gas molecules and the variation of the seepage resistance caused by the higher frequency change of the flow radius on the micro-scale for tight sandstone gas reservoirs. Based on the cross-correlation-based simulation (CCSIM) combined with the three-step sample method, Ji et al [19] reconstructed stochastic
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