Foams as Mobility Control Agents for Oil Recovery by Gas Displacement

Abstract

Abstract Experimental studies were conducted to facilitate understanding of the behavior of foam flow and its application in gas flooding processes. This paper presents the results of studies that involved:foam flow behavior in smooth capillary tubes and packed glass tubes;effects of changes in injection rates on foam performance;effects of foams on unsteady state gas-liquid relative permeabilities; andeffects of foams on improving gas sweep efficiency. The apparent viscosities and mobilities of foams flowing through smooth capillaries and packed glass tubes were measured. The experiments were designed to observe and quantity the behavior of foam under various conditions including foam quality, shear rate, surfactant concentration, and temperature. The bubble size distribution of pregenerated foam was measured to determine the contribution of foam texture to its flow behavior. Experimental results were evaluated using available mathematical models developed for predicting apparent viscosities of foam in smooth capillary tubes and packed glass tubes. Coreflooding experiments were conducted to evaluate effects of variations in injection rates on foam performance as a mobility control agent. Results of the experiments showed that higher injection rates of nitrogen displacing a surfactant solution resulted in foam generation that contributed to a significant increase in sustained pressure gradient across the core, The unsteady state method was used to study the effects of foam injection on gas-liquid relative permeabilities and improving sweep efficiency in Berea sandstone cores. permeabilities and improving sweep efficiency in Berea sandstone cores. The presence of foam resulted in a significant reduction of the permeability of the core to gas. The ability of a foam of known texture to permeability of the core to gas. The ability of a foam of known texture to sustain differential pressures across a core in the absence of flow was also determined. Using a parallel coreflood setup, fluid flow was preferentially diverted from a high-permeability core to a low-permeability preferentially diverted from a high-permeability core to a low-permeability core. Introduction Interest in the use of foams has resulted from their potential application as mobility control agents for improving oil recovery in enhanced oil recovery (" EOR") processes. A considerable number of technical papers have been published on studies of foam behavior in porous media. However, most of the papers deal only with phenomenological descriptions of foam behavior in laboratory phenomenological descriptions of foam behavior in laboratory coreflood tests and effectiveness in gas mobility control. Several mathematical models that can predict to some degree foam generation and propagation in porous media have been developed. Although foam applications have been successfully tested in laboratory studies, the application of foam in EOR is still in its developmental stages, primarily because of the lack of adequate models or scaling rules to describe its behavior. Research is needed on the development of quantitative relationships of foam behavior, rather than qualitative descriptions. Some progress in the development of prototype models describing foam behavior progress in the development of prototype models describing foam behavior has been made. Some correlations for the apparent foam viscosity and gas relative permeability have been presented. mechanisms of foam generation and coalescence have also been 1 studied. As shown in Fig. 1, many relationships such as the dependence of foam viscosity on foam characteristics need to be developed. This present work is designed to contribute to developments of correlations for foam apparent viscosity and effective relative permeability of foam. The complexity of foam flow in porous media necessitates the study of its behavior under conditions involving simpler constraints. Flow in smooth capillary tubes without oil present provides approximate conditions that are far simpler than those in porous media where different factors such as tortuosity, multiple phase saturations, reservoir heterogeneity, and other factors must be considered. Studying the behavior of foam in smooth capillary tubes and packed glass tubes is based on the approach of approximating flow in porous media as fluid flow in a bundle of capillary tubes. P. 689