A model for evaluating relative gas permeability considering the dynamic occurrence of water in tight reservoirs

The evaluation of relative gas permeability in tight reservoirs has a significant challenge owing to the influence of water. In this work, the pore throat structure has been characterized through a combination of experimental methods and fractal theory. Based on the analysis of the microscopic seepage phenomena of gas and water, a pore network model has been formulated to simplify the actual pore throat. Leveraging the calculation of water film thickness via the Derjaguin-Landau-Verwey-Overbee (DLVO) theory, the traditional capillary bundle model is improved by means of probability theory and mercury injection tests. This model takes into account the twophase seepage characteristics in a more comprehensive manner, thereby quantitatively evaluating the impact of the dynamic presence of water on relative gas permeability at the core scale. The results indicate that the water film saturation in tight reservoirs is below 4%, exerting an influence on gas permeability with an impact rate below 6%. Capillary water that is distributed in the pores governed by small throats under the influence of capillary force substantially contributes to water saturation, and the ensuing crossflow and bypassing flow primarily account for the decline in relative gas permeability. The application of effective methods, including increasing the displacement pressure difference and diminishing the interfacial tension, can reduce the critical movable throat radius and enhance the spread of gas throughout the pores, which is the key to raising relative gas permeability. The constructed evaluation model has certain advantages over the traditional ones in terms of analysis for fluid occurrence states. This enables us to assess measures for enhancing gas permeability within an efficient framework.