The Role Of Oil-In-Water Emulsions In Thermal Oil Recovery Processes

Abstract

Abstract It has long been known that some California oil fields produce oil, a fraction of which is in the form of an emulsion. This is particularly true of those fields producing heavy oils. This paper proposes a recovery mechanism which is thought to occur as a result of thermal operations in some California oil fields. The mechanism is the formation of oil-in-water (O/W) emulsions in the reservoir. Evidence is presented that under the right conditions such emulsions have more favorable flow characteristics than heavy oil. The mechanism is discussed in relation to cyclic steam, steamflood and in-situ combustion operations. The mechanism is thought to be more effective in the cyclic steam process than in the other two. It is also suggested process than in the other two. It is also suggested that the formation of O/W emulsions increases both the producing rate and the ultimate recovery in thermal projects. A better understanding of the mechanism should make it possible to increase its effectiveness or to induce the mechanism where the conditions we not suitable in the natural state. Introduction Since the introduction of thermal oil recovery methods, the list of recovery mechanisms thought to be effective in increasing oil recovery by these methods has grown. An early investigation by Willman et al focussed on such mechanisms as thermal expansion, viscosity reduction and steam distillation of oil. As more research followed, the complexity of the various processes became apparent. An extensive list of phenomena attributed to thermal recovery processes has recently been published by Prats. In general, the mechanisms published by Prats. In general, the mechanisms which have been postulated are the result of the elevation of reservoir temperatures, displacement of reservoir fluids by injected fluids, and chemical changes caused by the injection of foreign fluids and heat. It is the purpose of this paper to propose another mechanism which is also thought to be beneficial in increasing oil recovered by thermal methods. The proposed mechanism is thought to be the result of mechanical energy contained in or produced by fluids injected into the reservoir. produced by fluids injected into the reservoir. The mechanism is thought to be effective in certain California heavy oil reservoirs but may be effective in other oil provinces where similar conditions exist. The characteristics which make one type of crude oil more susceptible to the mechanism than another type of crude oil will be discussed. It will be shown that conditions favorable to the formation of O/W emulsions do exist and that the formation of such emulsions should be beneficial in increasing oil recovery. THEORY It is proposed that the injection of steam or air (when it supports in-situ combustion) into certain hydrocarbon reservoirs causes the formation of O/W emulsions in these reservoirs. It is suggested that such emulsions have more favorable flow characteristics, within certain temperature ranges, than the oil from which they are formed and this leads to higher oil producing rates and higher ultimate oil recovery. The mechanism will be more effective at low temperatures than at high temperatures. NATURE OF O/W EMULSIONS Becker states, "An emulsion is a heterogeneous system, consisting of at least one immiscible liquid intimately dispersed in another in the form of droplets whose diameters, in general, exceed 0.1 micron. Such systems possess a minimal stability, which may be accentuated by such additives as surface-active agents, finely-divided solids, etc." In an O/W emulsion, water is the continuous phase and oil is the dispersed phase. phase.