资源环境科技发展态势分析平台

Fluid invasion, displacement of one fluid by another in porous media, is important in a large number of industrial and natural processes. Of special interest is the trapping of gas and oil clusters. We study the impact of wettability on fluid pattern formation and capillary trapping in three‐dimensional glass beads packs (d_mean = 1 mm) during fluid invasion at capillary numbers of 10^‐7 using micro‐CT. The invading fluid was water and the defending fluid air. The contact angle of the glass beads were altered between 5° and 115° using Piranha cleaning and silanization. We analyzed the front morphology of the invading fluid, the residual gas saturation, the fluid occupation frequency of pores, and the morphology and statistics of the trapped gas clusters. We found a sharp transition (crossover) at a critical contact angle θ_c = 96°. Below θ_c the morphology of the displacement front was flat and compact caused by the strong smoothing effect of cooperative filling. Above θ_c the morphology of the displacement front was fractal and ramified caused by single bursts (Haines jumps). Across this dynamical phase transition the trapping efficiency changes from no‐trapping to maximal trapping. For θ > θ_c the experimental results show that invasion percolation governs the fluid displacement. Strong indicators are the universal scaling behavior of the size distribution of large clusters (relative data error ε_data < 1%) and their linear surface‐volume relationship (R² = 0.99).