Pressure effect on the thermal cracking of the light aromatic fraction of Safaniya crude oil – Implications for deep prospects

The aim of this work is to investigate the effect of pressure on the thermal cracking of the light (C6–C14) aromatic fraction (LAF) of crude oil in order to improve simulation under geological conditions related to deep prospects. A set of closed-system pyrolysis experiments was performed at 375 °C under high pressures of 400, 800 and 1200 bars for various experiment durations. The results were compared with previous experiments classically performed under a lower pressure of 100 bars. Increased pressure decreased the cracking of the unstable molecular classes of the LAF and also secondary cracking of some newly formed heavier compounds (C15–C20 and C20+ polyaromatics). This resulted in substantial changes in the abundance of the molecular classes from the charge recovered after pyrolysis, and in reduced production of the C15–C20 and C20+ compounds while formation of insoluble polyaromatic residue was no longer observed. Differences in apparent activation energies and differences in average activation volumes due to the effect of pressure were calculated for the cracking reactions of the unstable classes, relative to pyrolyses at 100 bars. These values were used to improve the compositional kinetic model previously established from experiments at 100 bars to simulate cracking under geological conditions. Applying the simulation of the thermal cracking of light aromatics for the HP/HT reservoir of Elgin (North Sea) showed that pressure effects could shift the thermal cracking of these aromatics to higher temperatures by about 8 °C and substantially increase the amount of these compounds preserved in the reservoir.