Detailed investigation on the oxidation behavior and kinetic triplet of tight oil via TG-DSC-PDSC analyses

Abstract

It remains some barriers for continental tight oils to enhance oil recovery owing to low or ultra-low permeability in China. Whether low temperature combustion mode (or deflagration fracturing) could be employed to expand the fracture, is an interesting but debatable topic in consideration of the not well-understood oxidation behavior and kinetic mechanism for the tight oil. This study initiated a comprehensive characterization on the oxidation behavior and kinetic triplet for the Mahu tight oil via the combination of atmospheric and pressurized thermal analyses (TG/DTG, DSC/DDSC, PDSC) and unconventional Popescu method. Threshold, peak, and end temperatures were shifted to higher temperature ranges following lower cumulative heat emission (from 13.21 to 9.15 kJ·g−1) with the heating rate increment from 5 to 15 K·min−1. Inversely, a more thorough oxidation process with higher cumulative heat releases (8.69 kJ·g−1 for LTO, 4.48 kJ·g−1 for HTO) was presented under elevated pressure condition. In order to elucidate the latent reaction mechanism, seven sequential temperature subzones were divided to acquire the most probable mechanism function G(α) and corresponding kinetic parameters. The results indicated that, owing to the high reservoir pressure, generated enormous heat in LTO stage had a significant acceleration to initiate and sustain the low temperature combustion process, which in some degree was conducive to update and expand the understanding of the low temperature in-situ combustion mode of air injection in low permeability and tight oil reservoirs via fracturing reservoir matrix.