Abstract
This paper presents the results of numerical simulation of dry, forward combustion tube experiments. The kinetic aspects of in-situ combustion processes also are discussed. The goals of the study are to investigate processes also are discussed. The goals of the study are to investigate the fuel deposition mechanism and to identify the key parameters affecting the performance of in-situ combustion processes. The thermal simulator developed at Gulf R and D Co. was used in the study. It was modified to include the capillary outlet effects for a more realistic description of the oil and water productions. The following experimental data were matched: cumulative water and oil productions, position of the combustion front as a function of time, fuel consumption, position of the combustion front as a function of time, fuel consumption, temperature as a function of time and position, and the pressure drop across the tube. History matches were performed for two crude oils with distinctly different physical properties (gravities of 26.5 and 13 API [0. 896 and 0. 979 g/cm3]). The agreements between experimental data and simulation results were excellent. Results indicate that the component equilibrium K-values and the kinetics of cracking reactions are the most important parameters affecting the fuel deposition, and that the fuel deposition mechanism, the fuel composition, and the locations and sizes of the transient zones depend on the crude oil and reservoir rock properties. Simulation results are always sensitive to the K-values of the light oil component but insensitive to the K-values of the heavy oil component. Results are sensitive to the kinetics of cracking reaction only if the cracking reaction is catalytic or the peak temperature and the fuel consumption are sufficiently high. Furthermore, the fuel available may or may not be solely in the form of coke. Our study suggests that further investigations of the catalytic effect of reservoir rocks and reaction kinetics of the cracking reaction are needed. Also, more than two crude oil components may be required to simulate the evaporation effect of crude oil accurately.
Introduction
In in-situ combustion processes, many physical changes as well as chemical reactions take place simultaneously or sequentially in the vicinity of the combustion front. It is generally believed that the combustion zone is preceded by a cracking or superheated steam zone, where coke is formed and preceded by a cracking or superheated steam zone, where coke is formed and deposited on the sand grains, and some lighter crude oil components evaporate and move forward with the flowing gas phase. The kinetics of combustion and cracking reactions in the combustion zone and the cracking zone has been discussed widely in the literature. The mechanisms of the physical changes and chemical reactions occurring around the combustion zone can be studied effectively through numerical simulation by using a thermal simulator. Although a number of numerical simulations of combustion tube experiments have been performed with different thermal simulators, no conclusions regarding the mechanism of fuel deposition can be drawn from these studies. The mentioned simulations either neglect the formation of coke from cracking reaction or use a high cracking rate so that no residual oil will be present in the combustion zone. The mechanism of fuel deposition is controlled by two important processes: the evaporation of crude oil components and the kinetics of the processes: the evaporation of crude oil components and the kinetics of the cracking reaction. These two processes determine how much fuel eventually will be burned and how much fuel will be in the form of coke. It has been reported, that low-temperature oxidation can have a significant effect on the fuel deposition and fuel characteristics. However, this reaction is important only when oxygen is available downstream of the combustion front. If oxygen is used completely in a combustion tube experiment, low-temperature oxidation will not play an important role in the fuel deposition mechanism. For a system with a high cracking reaction rate, it is likely that all of the crude oil in the cracking zone will be either evaporated or coked so that coke is the sole source of fuel. However, if the cracking rate is so low that only a portion of crude oil in the cracking zone is evaporated or coked, then some residual crude oil also will be burned in the combustion zone. This is supported strongly by the experimental data of Hildebrand who conducted a number of combustion tube experiments using clean, crushed Berea sandpacks with a variety of crude oils.
SPEJ
p. 657
Aging brine-dependent deposition of crude oil components onto mica substrates, and its consequences for wettability