Water and aromatics fraction interaction at elevated temperature and their impact on reaction kinetics of in-situ combustion
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2018 Elsevier B.V. Performance predictions of the In-Situ Combustion (ISC) process is a challenge as it involves complicated chemical reactions, fluids movement, phase changes, and heat and mass transfer. This study investigates how oil type and water presence can affect the ISC performance, based on using a combination of combustion tube and Thermogravimetric Analysis and Differential Scanning Calorimetry (TGA/DSC) experiments. Combustion tube experiments were conducted with two different crude oil without water (Swi = 0%) and with the presence of water (Swi = 34%). Experimental conditions were kept constant (3 L/min air injection rate and 100 psig pack pressure) for all four experiments conducted with two different oil samples. To determine the chemical reactions that occurred during combustion tube experiments, the initial crude oil samples and their Saturates, Aromatics, Resins, and Asphaltenes (SARA) fractions were subjected to TGA/DSC experiments under air injection at two constant heating rates with and without water addition. Because two heating rates were observed during combustion tube experiments, 5 C/min was used to represent the slow heating region (Steam Plateau, Evaporation and Visbreaking) and 20 C/min was used to mimic the rapid heating region (Cracking Region and Combustion Zone). To better understand the complicated mutual interactions of functional groups in crude oil, TGA/DSC experiments were repeated on normal-decane (an alkane), decanal (an aldehyde), decanone (a ketone), and decanol (an alcohol) which represent the low temperature oxidation (LTO) products. Note that these chemicals have a constant carbon number (C10). The combustion tube experiments showed that Oil 1 was able to burn for both conditions (with and without water), while Oil 2 could only sustain combustion with water. To determine the reason for this difference, the burning behavior of the crude oils and their individual SARA fractions with and without water additions was studied through TGA/DSC experiments. At the high heating rate (20 C/min), heat generation does not vary for both crude oil samples. However, at the low heating rate (5 C/min), Oil 1 generates a higher amount of energy at high temperature oxidation (HTO) zone. We observed similarities between the decanone (a ketone) burning behaviors with aromatics fractions for Oil 1 which indicates that the aromatics fraction may contain ketone functional groups as LTO products. Upon burning, ketones generate higher energy than any LTO products. Therefore, Oil 1 may have functional groups in its structure more like ketones which promotes its combustion more than Oil 2. While presence of water does not change the burning behavior of Oil 1, we observed that the aromatics fraction of Oil 2 in the presence of water generates components similar to decanol (an alcohol) burning behavior. Note that alcohols generate more heat than aldehydes upon burning which explains the enhancement of Oil 2 burning behavior in the presence of water. However, aldehydes produced less energy than ketones. As a result, the combustion performance of Oil 2 was poorer than Oil 1. These results suggest that the chemical structure of the aromatics fraction is critical for the success of ISC. Water and aromatics fraction interaction at elevated temperature favors ISC reactions.
