In a final attempt, the residual displaced phase saturations obtained were analyzed quantitatively. Fig. 18 illustrates the residual saturations reached at the end of the experiments for four different displacement cases. This is of critical importance in developing relative permeabilities for simulation studies in which the end points (initial wetting phase and residual non-wetting phase saturations) are typically assumed to be zero in practice.
The recovery of the displaced phase varied between 10% (fr4s) and 53% (fr3) for the gas displacing water cases (shaded bars in Fig. 18a). Note that fr4s is a different model in which no rubber material was used for the lower half of the sample. This would yield a different wettability characteristic than the other samples with the lower half of the fracture made of rubber. Interestingly, significant difference in the water recovery (25%) was observed between fr4 and fr4s (the two identical models of which the lower part was made of difference material). Hence, one may conclude that when gas displaces water (unfavourable mobility), wettability influences the displacement. Interestingly, no remarkable difference was observed when fr4 was compared to fr4s for water displacing gas; they showed 95% and 90% recoveries, respectively. This implies that when water displaces gas (very favourable mobility ratio), the wettability effect is not critical and mobility controls the process.