Thermal effect caused by low temperature oxidation of heavy crude oil and its in-situ combustion behavior

To investigate the thermal effect caused by low temperature oxidation (LTO) of one heavy crude oil in porous media, a combustion tube (CT) system coupled with a self-designed experimental scheme was adopted. Also, the in-situ combustion (ISC) performance of this heavy oil as well as alterations in oil properties before and after ISC was comprehensively evaluated. The results showed that there existed the apparent thermal effect induced by LTO within the researched ignition temperature (180-320 degrees C), and heat release became greater with the ignition temperature. It should be noted that the oxidation reaction rate of the heavy oil was rose remarkably releasing substantial heat when the ignition temperature was increased to 240 from 180 degrees C. The heavy oil was combusted under the ignition temperature of 350 degrees C, and the combustion front advanced sustainably. Some basic parameters during ISC, including apparent atomic H/C ratio, oxygen utilization, fuel consumption, etc., were determined, which made it accessible to predict field test performances. And the values of these parameters and post-mortem images of the CT test reflected the superior ISC performance of the heavy oil. The alterations in oil properties pre-ISC and post-ISC indicated that the produced oil encountered strong LTO reactions and thermal cracking reactions forming a considerable number of lighter oxygen-containing compounds. Comparison of differential scanning calorimetry (DSC) profiles of the crude oil and produced oil revealed that the ISC process made the heavy oil greatly upgrade.