Network modeling as a tool to predict three-phase gas injection in heterogeneous wettability porous media

The objective of the present paper is two-fold: to demonstrate the effect o f small scale wettability heterogeneities on gas injection efficiency, and to develop a tool to predict this impact for various patterns and spatial d istributions. To this end, an experimental investigation in transparent gla ss micromodels is performed and a theoretical simulator is developed. Diffe rent heterogeneity patterns are considered for the same oil-wet over water- wet surface ratio. A special technique to obtain oil-wet patches in a water -wet matrix by selective silane grafting on the glass surface is developed and described. The simulator properly incorporates imbibition-drainage even ts and flow through films as visualized in the experiments. Predictive effi ciency of the simulator is rested by comparing the numerical results to the experimentally obtained phase distributions and saturations. In water/oil displacement, drainage and imbibition mechanisms occur according to the loc al wettability. Three-phase gas injection is dominated by drainage mechanis ms. Oil flows through wetting films in the oil-wet regions and through spre ading films on water in the water-wet regions. Both experiments and simulat ions show that the size and distribution of wettability heterogeneities str ongly affect the microscopic and macroscopic behavior during gas injection processes. More specifically the effect of wettability heterogeneities on: (1) displacement mechanisms, (2) sweep efficiency, and (3) fluid distributi on in three-phase gas injection is clearly demonstrated and successfully de scribed by the network simulator. (C) 1999 Elsevier Science B.V. All rights reserved.