The Effect of Trace Quantities of Surfactant on Nitrogen/Water Relative Permeabilities

Abstract

ABSTRACT This paper proposes a single capillary model incorporating the mechanisms of foam generation, propagation, and rupture. It includes new features not heretofore noted and results in predictions for the influence of variables such as the gas rate, pore geometry, liquid rate, and surfactant concentration on the relative permeability to gas. Since the model is a simple one, only qualitative trends are predicted. Nevertheless apparently contradictory results can be understood in terms of the qualitative trends and new phenomena associated with the behavior of foams generated in situ are predicted. The model is a steady-state one. The generation rate of lamellae which are subsequently displaced and move along the capillary tube is a constant. To conduct experiments which are intended to confirm the model predictions one must ensure that these experiments yield truly steady-state results. This is not simple and a protocol for achieving steady state is tested. It is recommended as one approach for performing meaningful steady-state experiments. Systematic steady-state experiments are reported to demonstrate two important model predictions. The first shows the remarkable effect of even very small surfactant concentrations on the relative permeability to gas and the second set of experiments is designed to verify the model prediction that the relative permeability to gas at a fixed liquid saturation may increase or decrease with increasing liquid rates. Both trends have been reported in the literature.1,2 The correspondence between the predicted trends and those observed confirms the value of the single capillary model in understanding the complexities of mobility control using foams which are generated in situ.