Pore-Scale Study on Shale Oil-CO2-Water Miscibility, Competitive Adsorption, and Multiphase Flow Behaviors

Due to the fracturing fluid imbibition and primary water,oil-watertwo-phase fluids generally exist in shale nanoporous media. The effectsof water phase on shale oil recovery and geological carbon sequestrationvia CO2 huff-n-puff is non-negligible. Meanwhile, oil-CO2 miscibility after CO2 huff-n-puff also has animportant effect on oil-water two-phase flow behaviors. Inthis work, by considering the oil-CO2 competitiveadsorption behaviors and the effects of oil-CO2 miscibilityon water wettability, an improved multicomponent and multiphase latticeBoltzmann method is proposed to study the effects of water phase onCO(2) huff-n-puff. Additionally, the effects of oil-CO2 miscibility on oil-water flow behaviors and relativepermeability are also discussed. The results show that due to Jamin'seffect of water droplets in oil-wetting pores and the capillary resistanceof bridge-like water phase in water-wetting pores, CO2 canhardly diffuse into the oil phase, causing a large amount of remainingoil. As water saturation increases, Jamin's effect and thecapillary resistance become more pronounced, and the CO2 storage mass gradually decreases. Then, based on the results frommolecular dynamics simulations, the influences of oil-CO2 miscibility on oil-water relative permeability incalcite nanoporous media are studied, and as the oil mass percentagein the oil-CO2 miscible system decreases, the oil/waterrelative permeability decreases/increases. The improved lattice Boltzmannmodel can be readily extended to quantitatively calculate geologicalCO(2) storage mass considering water saturation and calculatethe accurate oil-water relative permeability based on the real3D digital core.

Automated summary

In this study, an improved multicomponent and multiphase lattice Boltzmann method is proposed to investigate the effects of water phase on CO2 huff-n-puff in shale nanoporous media. The competitive adsorption behaviors between oil and CO2 and the miscibility of oil-CO2 are considered. Additionally, the effects of oil-CO2 miscibility on oil-water flow behaviors and relative permeability are discussed. The results show that water phase has a significant impact on oil recovery and CO2 storage, and the oil-CO2 miscibility affects the oil-water relative permeability in calcite nanoporous media.