Clarifying the microscale gas–water flow behaviors
in a
mixed wettability reservoir is of great importance for underground
engineering. A numerical model of mixed wettability based on circular
particles was constructed using the MATLAB stochastic distribution
program, and the gas–water flow was simulated based on the
phase-field method. The Navier–Stokes equations were solved
by the finite element method. The work analyzed the effects of the
content of heterogeneous wetting particles, wettability, and inversed
wettability of the matrix on the flow path and pressure distribution
of the mixed wettability model. Besides, the two-phase flow behaviors
were evaluated in microscale mixed-wettability porous media. The simulation
results revealed that (i) the residual saturation of the gas phase
showed a positive correlation with the hydrophobic particle content,
and closed gases only existed in isolated pore channels with small
content. Isolated closed gases gradually connected as the content
increased. (ii) The residual gas content in the corner and tail end
increased as the hydrophobicity of particles increased in hydrophilic
matrices. Hydrophobic matrices showed a negative correlation, with
the greatest pressure drop due to capillary resistance and step changes
in the neutral-hydrophobic transition zone. (iii) Water-phase breakthrough
time and gas-phase residual saturation showed a negative correlation
change. The more space occupied by the gas phase, the faster the water-phase
breakthrough. Moreover, the saturation no longer changes after the
breakthrough. The work provides a guideline for determining the dominant
flow path of phase displacements and the distribution of residual
phases.
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