Exothermal Property and Kinetics Analysis of Oxidized Coke and Pyrolyzed Coke from Fengcheng Extra-Heavy Oil

Abstract

The exothermic combustion characteristics of coke play a direct and essential role in artificial ignition and the stability of the combustion front during the heavy oil in situ combustion (ISC) process. However, there is little research on the exothermal properties of pure oxidized coke and pyrolyzed coke. Oxidized coke and pyrolyzed coke formed by Fengcheng (FC) extra-heavy oil in an air or nitrogen atmosphere is studied in this work to obtain the exothermal behavior of different coke utilizing TG and DSC. The kinetics of both cokes are analyzed by the Friedman and Ozawa–Flynn–Wall methods. The morphological structures and main elemental distribution of each coke are identified by SEM and EDS. Results show that oxidized coke can release more heat than pyrolyzed coke. The whole enthalpy values of oxidized coke are 25.804 kJ/g (300 °C) and 28.717 kJ/g (350 °C), which are greater than those of pyrolyzed coke (18.325 kJ/g and 25.617 kJ/g). The activation energy curves of 300 °C coke fluctuate dramatically with the conversion rates, but 350 °C coke only changes slightly. The 350 °C pyrolyzed coke has much more combustion reactivity followed by the 350 °C oxidized coke. Compared with other coke, the 350 °C pyrolyzed coke has a more obvious porous structure with a regular arrangement and has the highest relative percentage of C, which is inconsistent with its higher reactivity. Combined with the research results, we show that preheating FC heavy oil fields to 350 °C with air injection is an effective method to ensure the successful application of ISC technology and to improve oil reservoir recovery.

Oxidation Characteristics and Kinetics of Shale Oil Using High-Pressure Differential Scanning Calorimetry

“…As shown in Figure and Table , the activation energy versus conversion for shale oil and its mixtures was obtained by Friedman and OFW models. There were some minor differences in the values of activation energy determined by these two models, largely caused by their varying theoretical calculations and assumptions. − Figure presents the relation of activation energy with conversion calculated by the Friedman model for shale oil and its mixtures. Figure a shows that the activation energy of shale oil gradually ascended with conversion, different from the variation trends of the two mixtures (see panels b and c of Figure ).…”

Combustion Behavior and Kinetics Analysis of Isothermal Oxidized Oils from Fengcheng Extra-Heavy Oil

“…Researchers divided the different chemical compounds in crude oil into saturate, aromatic, resin, and asphaltene (SARA) fractions. SARA fractions were separated based on the industry standard of China Petroleum NB/SH/T 0509-2010-more experimental details for different tests have been given in our previous works [14,27,28].…”

“…In addition, our recent works explored and compared the combustion behavior of oxidized coke and pyrolyzed coke, especially their heat release and combustion reactivity during the ISC process [27]; research results verified that the combustion reactivity of coke can be improved by preheating the reservoir to a preset temperature. A large number of studies have been carried out on the LTO reaction of heavy oil so far; however, disputes remain due to the various crude oil properties, experimental methods, and laboratory apparatus, etc., involved.…”

“…; then, static isothermal oxidation experiments were carried out for 3 days in a muffle furnace at specific temperatures (50, 100, 150, 200, 250, 300, and 350 • C) and a constant pressure of 2.98 MPa (the original pressure of the FC oilfields). After isothermal oxidation reactions of FC extra-heavy oil at various experiment temperatures, oxidized oils and gaseous products were collected [25,27].…”

“…The DSC tests were kept at 30 to 600 • C at an average heating rate of 10 • C/min. The flow rates of the purge gas (high purity air) and protection gas (high purity nitrogen) were 50 mL/min and 20 mL/min, respectively, throughout all tests [27]. Each experiment was performed at least twice to guarantee reproducibility, and the error of mass loss and temperature did not exceed ±0.5 wt% and ±1 • C, respectively.…”