Abstract
The impact of rock minerals on the performance of in situ combustion (ISC) techniques for enhanced oil recovery (EOR) is very important. This work is aimed at investigating the influence of carbonate rocks (dolomite and calcite) on heavy oil oxidation by Thermogravimetry–Fourier-Transform-Infrared (TG-FT-IR) coupled analysis. Two heavy oils with 19.70° and 14.10° API were investigated. Kinetic analysis was performed using TG data by differential and integral isoconversional methods. From TG-DTG curves, three reaction stages, i.e., low-temperature oxidation (LTO), fuel deposition (FD), and high-temperature oxidation (HTO), were defined for both two heavy oil samples, and their reaction mechanism was explained combining the FT-IR data. After the addition of calcite or dolomite, three reaction stages became two with the disappearance of FD, and a significant shift of reaction stages into lower temperatures was also observed. These significant changes in oxidation behavior are because calcite and dolomite promoted the coke formation and combustion by reducing the activation energy barrier and changing reaction pathways, which results in a smooth transition from LTO to HTO. Dolomite exhibited a slightly better promotion effect on LTO-FD than calcite, while calcite exhibited a better acceleration effect on FD-HTO than dolomite in terms of shifting reaction stages. Generally, calcite exhibited a better catalytic effect than dolomite. In spite of the different catalytic performance of calcite and dolomite, they do both show positive effects on combustion process regardless of the difference in the properties and composition of heavy oils. The findings in this work indicate that calcite and dolomite rocks are favorable for the ISC process, and when it comes to the ISC kinetics, the interaction between crude oil and rock must be considered.
Highlights
The in situ combustion (ISC) technique for heavy oil recovery has several merits in comparison with other thermal enhanced oil recovery (EOR) methods, such as readily accessible injection fluid with low cost without having to consider the location of reservoirs, high oil recovery yielded by a multiple displacement mechanism, in situ upgrading of heavy oil, high thermal efficiency with less heat loss on the ground and well bore, and a wide applicability for different types of reservoir conditions [1,2,3,4,5]
This is the evaporation of water contained in the heavy oil, which can be supported by the water peak appearing in the FT-IR spectra of effluent gases (Figure 3)
The thermo-kinetic analysis was carried out to reveal the effect of carbonate rocks on the heavy oil oxidation
Summary
The in situ combustion (ISC) technique for heavy oil recovery has several merits in comparison with other thermal enhanced oil recovery (EOR) methods, such as readily accessible injection fluid (air) with low cost without having to consider the location of reservoirs, high oil recovery yielded by a multiple displacement mechanism, in situ upgrading of heavy oil, high thermal efficiency with less heat loss on the ground and well bore, and a wide applicability for different types of reservoir conditions [1,2,3,4,5]. In spite of having so many merits and a long history, ISC is still not widely applied in oil fields due to its complexity and the lack of understanding, which originally comes of the complicated chemical reactions between crude oils and air occurring in the porous media of rock in ISC processes [1,6]. These reactions strongly depend upon the composition of crude oils and rock as well as their interaction during the reactions at elevated temperatures [5,7,8,9].
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