Repeatable Steady-State Foam Experimental Data and Investigations of Foam Hysteresis in a Sand Pack

Abstract

The repeatability of steady-state foam experiments in porous media had been a major concern due to either alterations in core petrophysical properties or the impact of trapped gas. Trapped gas is an important cause of history-dependent foam behavior known as foam hysteresis. The removal of trapped gas generated in a previous foam experiment can sometimes be difficult when one tries to restore the core for a subsequent experiment. This paper presents systematic studies of steady-state foam behavior without hysteresis and foam transport with hysteresis. We developed a procedure to restore a sand-pack system after a foam flood, which ensured that every foam experiment started with the same condition of the sand pack saturated with 100% surfactant solution and ruled out the impact of surfactant adsorption or gas trapping. An experimental design composed of 24 steady-state foam core floods were carried out and the local pressure drops were measured and correlated with varying phase (gas and water) velocity and foam quality. Next, two groups of foam hysteresis experiments were conducted by varying either the foam quality or the total fluid velocity. The results showed that the repeatability of the experimental data was excellent in the hysteresis-free experiments. In addition to the steady-state data obtained in traditional high- and low-quality flow regimes, we have also identified a transition to highly viscous foam where the pressure gradient increased significantly from the entrance to the exit of the sand pack at steady state. This transition has only been observed with relatively low foam qualities and high liquid velocities. Multiple pore volumes of injection before foam reached a steady state in most of the experiments were observed. Various possible reasons, such as the requirement of minimum pressure gradient and the homogeneity of the system, are discussed. In the subsequent study of foam hysteresis, the first group of experiments showed that the final steady states of foam apparent viscosity at fixed foam quality and total fluid rate were generally repeatable regardless of initial state (phase saturations) of the sand pack in the high-quality regime; however, the initial state had a significant impact on the transient process before reaching a steady state. In the second group of experiments, the results indicated that foam hysteresis had a significant influence on the final foam steady state. To our knowledge, it is the first time that such reliable and systematic data base for steady-state foam behavior in porous media without hysteresis was provided. This comprehensive data set in combination with foam-hysteresis data could therefore be used for foam-model evaluation and improvement with high confidence.

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Numerical Assessments of Key Aspects Influencing Supercritical CO2 Foam Performances when Using CO2-Soluble Surfactants

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