A Current Review of Forward Combustion

Abstract In-situ combustion methods of oil recovery generally involve heat transfer with phase change and chemical reaction coupled with the hydrodynamics of multi-phase flow through porous media. To date, a vast amount of work has been carried out in this area and a. number of successful projects have been reported. This paper examines only a portion of this field. It presents an over-all view of the forward combustion process by reviewing the results of some of the key experimental and theoretical studies and field tests. Introduction ALTHOUGH THE FORWARD COMBUSTION PROCESS may be described by means of an intricate ensemble of a number of individual physical and chemical processes, the over-all mechanism has been initially described simply as follows. The process is initiated by injecting air for a short period, so as to establish a continuous gas phase between the injecting- and producing wells. Once this is accomplished, heat is introduced into the injecting well so as to raise the temperature of the formation in the vicinity of the wellbore. When the formation temperature has been raised sufficiently, the formation oil, in vicinity of the wellbore, is ignited. As air injection continues, the burning gradually progresses from the injecting to the producing well When burning stabilizes, the process may be described by means of a series of zones, as is shown in Figure, 1. In short, this series consists of a? burned zone, a combustion front, a hot water zone, a light hydrocarbon zone, an oil bank and an original or unaltered zone. At the Fifth World Petroleum Congress, Tadema(1). using the results of recent investigations(2), (3), (4) proposed a more detailed representation of the over-all mechanism, as is shown in Figure 2. In his representation, the series of zones consists of a burned zone, a combustion zone, a multiphase zone, a three-phase zone, an oil bank zone and an original zone. These zones contain air, coke, (steam, gases, hot water and light hydrocarbons). (gases, oil and water), (oil and gas) and original oil, respectively. According to this model, the temperature distribution assume the shape of a heat wave and is characterized by a peak temperature in the combustion zone, a steep front followed by a steam plateau downstream, and a graduate decline upstream. In general, the heat-wave propagation velocity does not appear to be influenced b:v oil or rock type hut is directly related to air flux and oxygen content. That is as air flux and oxygen content are decreased the temperature profile tends to elongate. The Combustion Zone In the multiphase zone, crude oil is vaporized and cracked or carbonized to produce a residuum or coke deposit on the sand surface. This deposit serves as fuel in the combustion zone. Heat is then carried forward by convection by the water resulting from combustion, vaporized formation water hot gases and combustion products. Generally the peak temperature in the combustion zone varies between 700 and 1,000 °F. Combustion itself is believed to occur in two steps.