THE EFFECT OF ORGANIC MATTER MATURITY ON KINETICS AND PRODUCT DISTRIBUTION DURING KEROGEN THERMAL DECOMPOSITION: THE BAZHENOV FORMATION CASE STUDY

Abstract In this study, we obtained the first data on the compositional kinetics of the Bazhenov kerogen decomposition, which are essential for estimation of the amount and composition of hydrocarbon products in petroleum system modeling and for simulation of organic matter transformation in the processes of thermal enhanced oil recovery. The Bazhenov Formation is one of the priority oil shale formations in the world and is the principal source rock in the West Siberian Petroleum Basin, Russia. The kinetic study was performed on source rock samples with organic matter spanning the range of thermal maturity from immature to early and middle mature. The experiments included (1) the determination of bulk kinetic spectrum from pyrograms obtained using linear heating of rock samples, (2) a series of isothermal pyro-GС-TOFMS/FID experiments carried out at several levels of organic matter conversion, and (3) the calculation of the compositional kinetic spectrum from the experimental data. The kinetic characteristics of the samples were correlated with organic matter maturity. We have demonstrated that with an increase of organic matter maturity, the maximum of activation energy distribution shifts from 51 to 53 kcal/mol (for a fixed frequency factor A = 1×1014 s-1). The kerogen destruction products analyses reveal that for the immature sample the total gas yield is 39%, the percentage of heavy hydrocarbons С16+ is 16%, and the percentage of С7-C10 is two times higher than that of С11-C15: 30 and 15%, respectively. With the increase of organic matter maturity, the proportion of gas and heavy products decreases. Regardless of organic matter maturity nor conversion degree, the main products of the Bazhenov kerogen transformation are liquid hydrocarbons C7-C10, the percentage reaches 54% in the maximum of oil generation.