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

Abstract

Abstract Foam has been successfully used in many areas of the petroleum industry. Since the application of foam was first proposed for the process of gas phase injection, most studies were made with respect to the properties of bulk foam. Although it seems to be unreasonable to expect flow of bulk foam through porous medium, very few papers have reported on the relative permeabilities or fluid distributions in the presence of foaming agent, especially in consolidated sand. Relative permeabilities of foaming agent solution-nitrogen gas were measured by both steady and unsteady state methods using fired Berea sandstones. These were compared with the reference relative permeability of brine-nitrogen gas. The permeability reduction factor was calculated from the ratio of the gas permeability in the presence of foaming agent to that in the absence of foaming agent. The effects of surfactant concentration and pressure gradient were investigated. This permeability reduction factor is mainly a function of lamellae stability. Although these permeabilities might more appropriately be called pseudo relative permeabilities, particularly in the case of gas phase, they do give some ideas about flow mechanism. The results show a significant difference between steady and unsteady state flows. 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 35–40% probably due to the formation of a large number of foam lamellae by the continuous supply of foaming solution. Pressures as a function of distance were measured at three pressure taps spaced at equal distances along the core. The pressure profile shows abrupt jumps in the pressure with advancement of the gas phase due to the capillary pressure. After gas breakthrough, the pressures at each tap were stabilized. The results during the steady state flow showed that the pressure drop between taps increases with the increasing distance from the inlet end of the core sample, which indicates that the higher gas fraction results in a greater blocking effect. The effluent concentrations of surfactant 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 less than 2 moles/gm of sand up to 1.0% of concentration. Introduction In any type of gas phase injection for enhanced oil recovery such as immiscible or miscible gas injection, CO2 flooding and steam drive, it is inevitable to encounter gravity override due to the density difference, gas fingering caused by an unfavorable mobility ratio, and high gas flow through thief zones. In 1958, Bond and Holbrook patented a gas drive process in the presence of surfactant having foam-producing characteristics to improve the sweep efficiency. Since then, the mechanism of foam flow through porous media in gas flooding has been studied extensively. Recently, application of foam was extended to steam drive and CO2 flooding. P. 351^