Low-Temperature-Oxidation Reaction Kinetics and Effects on the In-Situ Combustion Process

Abstract

The kinetics of low-temperature oxidation (LTO) of crude oils in porous media was studied. Isothermal integral reactor data were analyzed to obtain rate equations for the over-all rate of the partial oxidation reactions at temperatures below partial oxidation reactions at temperatures below 500 deg. F. The reaction order with respect to oxygen was found to be between 0.5 and 1.0. The order of the reaction was dependent upon the crude but independent of the properties of the porous medium. The activation energy of the reaction was insensitive to the type of crude or porous medium and is in the neighborhood of 31,000 Btu/lb mol. LTO reactions were found to be in the kinitics-influenced region. The measured reaction rates for a 19.9 deg. API and a 27.1 deg. API crude indicated higher oxidation rates under similar reaction conditions for the higher API gravity crude. Light crudes appear to be m ore susceptible to partial oxidation at low temperatures because of the react ed oxidation reactions rather than by carbon oxidation. Other information includes the fraction of reacted oxygen utilized in carbon atom oxidation by the LTO reaction and the molar ratio of CO2 and CO produced in the low-temperature region. Effect of partial oxidation of the crude on the in-situ combustion process was studied by experimentally simulating the zones preceding the combustion front where temperatures and injection rates of linear reservoir model were programmed with time according to a predesigned schedule. Oxidation of the crude at temperatures below 400 deg.F had significant effects on the behavior of the crude-oil/water system in the porous medium at elevated temperatures and on the fuel available for combustion. A substantial decline in the recoverable oil from the evaporation and cracking zones, an increase in fuel deposition, and drastic changes in fuel characteristics and coked sand properties were obtained when the crude was subjected to LTO during the simulation process. Introduction The application of thermal energy to petroleum reservoirs as a means of increasing crude oil recovery has been given a great deal of attention. In underground combustion, thermal energy is induced by the partial burning of the crude oil in situ. The production of heat by the exothermic oxidation reactions of the hydrocarbons constitutes a unique feature of the in-situ combustion process. The chemical reactions and the accompanying heat released create a new temperature profile and cause drastic redistribution in the reservoir fluid saturations. With oxygen available in the transient zones of variable temperature and hydrocarbon saturations, several oxidation reactions of differing nature can take place during an underground combustion process. Because of the complex composition of process. Because of the complex composition of crudes and the great number of reaction products that can be produced, it is convenient to classify the hydrocarbon oxidation reactions ascombustion reactions that take place in the high-temperature combustion zone (above 600 deg. F) with CO2, CO, and H2O as the principal reaction products andpartial oxidation or low-temperature products andpartial oxidation or low-temperature (LTO) reactions that occur in zones where the temperature is lower than 600 deg. F. Several partial oxidation reactions are known to take place, producing primarily water and oxygenated producing primarily water and oxygenated hydrocarbons such as carboxylic acid aldehydes, ketones, alcohols, and hydroperoxides. High-temperature combustion reactions are desirable because they generate most of the heat required for the in-situ combustion process. Partial oxidation reactions, on the other hand, are in most cases undesirable because of their adverse effect on the viscosity and distillation characteristics of the crude. SPEJ P. 253

Supporting Technology for Enhanced Oil Recovery-EOR Thermal Processes Report IV-12

“…Alexander et d( 1962) and Al-Saadon (1970) showed that fuel availability was increased when LTO of crude oil took place. Dabbous and Fulton (1974) corroborated this and also found that LTO causes a substantial decline in recoverable oil from the distillation and cracking zones, an increase in the fuel deposition and marked changes in the fuel characteristics and coked sand properties. Weijdema (1968) and Fassihi (198 1) found that the order for the LTO reaction, in terms of the partial pressure of oxygen, was close to unity.…”

In-Situ Combustion Handbook -- Principles and Practices

“…It has been shown that LTO reaction increases the amount of fuel available for combustion (Alexender et al, 196;A1-Saadon, 1970) and causes a substantial decline in recoverable oil from the distillation and cracking zones (Dabbous and Fulton, 1974), Low air fluxes in the oxidation zone resulting from reservoir heterogeneities and oxygen channeling promote LTO reactions. Poor combustion characteristics of the crude also tend to promote LTO due to low oxygen consumption.…”

“…Some investigators (Dabbous et al, 1974;Lin et al, 1984) found that the combustion reaction was diffusion controlled, while others found it to be chemical reaction controlled (Hughes et al, 1987;Fassihi and Brigham, 1982;. Islam et al, 1989, contend that the laboratory experiments are almost always conducted under rather ideal conditions, and the experiments conducted under such ideal situations permit oxygen interracial mass transfer rate to be quite high and thus likely to mask the influence of diffusion on the combustion reactions in the reservoir.…”

“…This widely accepted model is given by: High temperature carbon and crude oil oxidation studies by Bousaid (Bousaid and Ramey, 1968) and others (Dabbous and Fulton, 1974) indicates first order reaction dependency on fuel concentration and 0.5-1.0 order dependency with respect to oxygen partial pressure; i.e., 'a' = 1.0 and 'b' = 0.5 to 1.0.…”

Liquid phase oxidation kinetics of oil sands bitumen: Models for in situ combustion numerical simulators

“…Cram and Redford (1977), Dietz (1 970), Dietz and Weidjema (1 968), Morse (1 976), Nelson and McNiels (1956), Showalter (1963), Smith and Perkins (1973), Reed et al (1960), andWalter (1977). The performance of in situ combustion processes depends on the accompanying low-temperature oxidation (LTO) reactions (Alexander et al, 1962;Dabbous and Fulton, 1974;Burger and Sahuquet, 1973). Furthermore, results of published laboratory and field studies indicate that more meaningful analysis of combustion data cannot be made until the LTO reaction kinetics are studied and the reaction mechanisms elucidated.…”