Physical model study and parameter recognition of phase-change porous medium during the production of unconventional oil and gas

Skeleton fabric evolution associated with phase change phenomenon occurs in the process of oil and gas drilling and production in some unconventional reservoirs and the Arctic, glacial and permafrost formations. In order to study the dynamic change laws of reservoir porosity and oil saturation in the process of oil and gas phase change-skeleton evolution, this paper took an oil sand reservoir as the example to establish a physical model of phase-change porous medium for two scenarios, i.e., asphalt phase change-pore collapse and asphalt phase change-pore expansion, respectively, by means of asphalt melting coefficient, fluid drainage coefficient and water injectability coefficient. In addition, eight application charts of asphalt melting-pore collapse/expansion at different quantitative coefficients were prepared. Then, the parameters of the physical model were recognized and analyzed based on experimental and field measurement data. It is indicated that in the process of asphalt phase change-pore collapse, porosity and oil saturation decrease and effective porosity and effective oil saturation increase with the increase of asphalt melting coefficient; while porosity and effective porosity decrease, oil saturation increases and effective oil saturation is unchanged with the increase of fluid drainage coefficient. In the process of asphalt phase change-pore expansion, porosity and effective porosity increase and oil saturation and effective oil saturation decrease with the increase of water injectability coefficient. The maximum increase amplitude of effective porosity and porosity in the micro-fracturing process of oil sand reservoir are 6.18% and 1.53%, respectively, which are only about 12% of laboratory experimental results.