SPE 131297 Effect of gas type on foam film permeability and its implications for foam flow in porous media

The ability of foam to control the gas mobility in porous media is determined in part by the trapped (stationary) fraction of foam, Xt. The common approach to determining Xt is to replace some part of the gas by a “tracer gas” during the steady-state stage of the experiments and fitting the effluent data to a capacitance mass-transfer model. Diffusion between bubbles is quantified by the film permeability coefficient, K (cm/s). We measured the film permeability coefficient of different gases for foam films made of four surfactants. The results show that the value of K is largely dependent on the dissolution of gas in the surfactant solution and increases with increasing gas solubility in the bulk liquid. The measured values of K are consistent with rapid diffusion of tracer through trapped gas adjacent to flowing gas in porous media, and difficulties in interpreting the results of tracer-foam experiments with conventional capacitance models. Effective diffusion coefficients of gases through trapped foam can be estimated from K. These diffusion coefficients differ substantially, and this implies swelling or shrinkage of trapped gas from diffusion. The implications of the results for foam flow in porous media is discussed in detail and some suggestions are given to improve the measurements and modeling of trapped fraction of foam.