Experimental Study of Foamy Oil Stability

Abstract

Abstract This paper presents the results of an experimental study of the stability of foamy oil created by liberation of dissolved gas. I Experiments were conducted in a high pressure cell. The volume of foamy oil produced, either by a step reduction in pressure or by a gradual (linear) reduction in pressure, and its subsequent decay were observed, visually. The effects of oil viscosity, asphaltene content, height of the oil, column, dissolved gas content and pressure decline rate were investigated. The experimental results show that foamy oil stability increases with higher oil viscosity, higher oil column, higher dissolved gas content and igher pressure decline rate. Asphaltene content was not observed to increase the foamy oil stability significantly. The results also show that the foam quality of foamy oils is much lower than aqueous foams. Introduction A number of heavy oil reservoirs under solution gas drive show anomalously good primary performance: high oil production rates, low produced GOR and high recovery(1, 2). These reservoirs show foamy-oil behaviour in wellhead samples. The oil is produced in the form of an oil-continuous foam which has the appearance of chocolate mousse and contains a high volume fraction of gas(3). Foamy oil may be defined as a heavy oil containing dispersed gas bubbles(4). In the context of solution gas drive its physical form could be a dispersion of gas bubbles flowing with the oil; a foam in which the continuous phase is oil; or any other form which causes trapping of a large volume of gas within the porous media. Foamy oil flow may be defined as an unusual form of two-phaseoil/gas) flow in porous media which can be invoked to explain the high solution-gas-drive recovery In some heavy oil reservoirs. Foamy oil flow behaviour is affected by the interfacial properties of the oil-gas system. It is believed that naturally occurring urface active chemicals play an important role in foamy oil flow, however, due to the extremely complex chemistry and the number of components in the system, it is impractical to determine the effect of each component. Therefore it is desirable to have an indirect method of characterizing the surface chemistry of the system. One easily measurable parameter is the stability of foam in a bulk vessel. It has been suggested that the flow behaviour of foams in porous media can be correlated with foam stability in just such a bulk vessel(5). This paper presents the results of an experimental study of foamy oil stability. The effects of oil viscosity, asphaltene content, decline rate were investigated. Literature Review The gas bubbles released from oil due to a pressure decline tend to remain dispersed in the oil to form an oil-continuous foam or foamy oil(3). Such a foam composed of a multitude of gas/liquid interfaces forms a thermodynamically unstable system whose surface energy naturally tends to decrease. In practice this results in progressive destruction of the foam until the oil and gas are entirely separated(6, 7). The rate of this destruction depends on the stability of gas-oil dispersion.