Mechanics Of Foam Flow In Porous Media And Applications

Abstract

Abstract Foams are receiving increasing attention in the petroleum industry in a number of roles, notably as mobility control agents and blocking materials in enhanced recovery operations. This paper discusses the rheology of foams in general, and then examines the mechanics of foam flow through porous media. It is shown that appropriate foams can indeed improve the recovery efficiency of a given process, and foams can serve as temporary blocking agents. The paper discusses the mechanics of foam generation, and the effects of the nature of surfactant, concentration, shear rate-related to pore velocity, pressure and temperature on foam quality and stability, both in a porous medium and in capillaries. These two characteristics are intimately related. The apparent viscosity and mobility of a foam in a porous medium is of direct concern in any process where foam is used as a mobility control agent. It is seen that the apparent viscosity decreased with increased shear rate and decreasing quality. The flow mechanics of foam are still open to question. This paper examines both views, viz. foam flowing as an integral material. and gas flowing separately. The importance of the type of porous medium in foam viscosity is pointed out. The blocking action in a porous medium is also discussed. Experimental evidence suggests that foam tends to flow in the larger pores, while temporary blockage seems to occur in the smaller pores. Capillary forces have considerable influence in this regard. Twenty one experimental runs have been conducted in the presence of oil and water in this run. A few other runs were conducted to investigate the foam flow mechanism in the presence of water alone. In the presence of oil, the flow of foam has been experimentally investigated both in homogeneous and in heterogeneous (in the presence of a bottom-water zone) porous media. Surfactant concentration, injection pressure, oil-to- water viscosity ratio, and oil-to-water zone thickness and permeability ratios appear to have a prominent role in oil recovery with foam. In the presence of bottom water, foam is very effective in blocking the bottom-water zone for subsequent nitrogen injection. Consequently, the oil recovery with foam is improved manifold over conventional waterflooding. Introduction Fried(1) was the earliest researcher who studied the usefulness of foam in enhancing the displacement efficiency in oil recovery. He reported that foam causes a rapid reduction in gas phase relative permeability, leading to delayed gas breakthrough. Hecontended that the presence of surfactant alone did not improve the oil recovery and that the improvement with foam was mainly due to reduction in gas permeability. He observed that the presence of surfactant increased the residual gas saturation. His observation would suggest that the relative permeability to gas is not a single-valued function of saturation and the curve shifts to the left as the interfacial forces resisting flow increase. He showed that the flow resistance of the foam increases with increasing surfactant concentration. Therefore, the effective permeability to gas is also a multivalued function of surfactant concentration.