Oxidation kinetics of heavy oil based on stage evolution

Key words:  heavy crude oil  Coats-Redfern integral method  kinetic parameters  oil oxidation

Abstract:

Oil oxidation and relevant reactions can be divided into 4 stages during air injection process for in-situ combustion, including the initial stage of low temperature oxidation, the later stage of low temperature oxidation, fuel deposition and high temperature oxidation. To obtain the oxidation kinetics parameters of each stage, a similar oxidation mechanism function has been applied in the literature, in which the reaction characteristics of the 4 reaction stages were not fully considered. In this paper, a Coats-Redfern integral method was used to calculate the oxidation kinetic parameters. Based on a simple reaction mechanism function, the reaction order is assumed as 0,0.5 and 1, and the influence of the reaction order on the oxidation kinetics parameters was analyzed. A reaction kinetics model and its kinetic parameters were obtained via data processing using existing 30 reaction mechanism functions. It is found that the phase boundary reaction is dominant in the low temperature oxidation stage, and the three-dimensional diffusion reaction is the main stage in the high temperature oxidation stage. The Coats-Redfern integral method is suitable for the calculation of the kinetic parameters for crude oil oxidation with high accuracy.