Comparison of Steady- and Unsteady-State Flow of Gas and Foaming Solution in Porous Media

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Abstract
Summary: Relative permeabilities of foaming-agent solution/nitrogen gas were measured by steady- and unsteady-state methods in Berea sandstones. Results show a significant difference between steady- and unsteady-state flow. Unsteady-state experiments show a small change of relative permeability to gas over a wide range of saturations and exhibit no complete blocking effect. In steady state, however, the simultaneous flow of liquid and gas could be stabilized only above a minimum gas saturation of about 35 to 40%, probably because of the formation of a large number of foam lamellae by the continuous supply of foaming solution. The permeability reduction factor calculated from the ratio of the gas permeability in the presence of foaming agent to that in the absence of foaming agent is mainly a function of lamellae stability. Pressures as a function of distance were measured at three pressure taps spaced at equal distances along the core. The pressure history shows abrupt jumps in pressure with advancement of the gas phase owing to capillary pressure. After gas breakthrough, the pressures at each tap were stabilized. The results during steady-state flow showed that the pressure gradient increases with increasing distance from the inlet end of the core sample, indicating that the higher gas fraction results in a greater blocking effect. The surfactant effluent concentrations were measured by a UV spectrophotometer to calculate the adsorption isotherm of this foaming agent. The dynamic adsorption of Suntech IV™ showed a Langmuir-type isotherm. The adsorption was < 2 μmol/g sand for up to 1.0% concentration.

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