Heavy Oil Catalytic In Situ Upgrading in Fractured Carbonate Reservoirs. Fluid Distributions and Occurring Reactions Monitored with Marker Hydrocarbons

The effectiveness of a novel catalytic heavy oil in situ upgrading technology (ISUT) in fractured carbonate reservoirs with varying rock properties was investigated in the present study carried out with Mexican heavy crudes. The tests conducted in batch (300 degrees C under 1000 psig H-2 for 48 and 96 h) and continuous operation modes (360 degrees C, 36 h residence time, and 1450 psig pressure) were utilized to achieve up to similar to 30 wt % vacuum residue (VR) conversion and up to 65 wt % recovery. By dispersing hydroprocessing catalysts, such as Ni-Mo and/or Ni-Mo-W, in VR media and in the presence of H-2, efficient upgrading was achieved with stable produced oils. Distributions of molecular markers introduced into the matrix oil or into the injected VR (1 Me-naphthalene, phenanthrene, alpha-cholestane, fluorenone) were monitored via gas chromatography (GC)-simulated distillation and/ or GC-mass spectroscopy, indicating movement of hydrocarbons toward and out from the porous space of the carbonate matrices, suggesting successful penetration of the upgraded VR into the rock's porous space. Detection of hydrogenated compounds derived from spiked markers provided evidence of hydrotreating reactions occurring during ISUT processing. The study proposes a possible oil production mechanism that combines rock thermal expansion, solution gas drive (H-2), and solvency from generated upgraded light ends, explaining oil production within carbonate matrices when ISUT is applied to naturally fractured reservoirs. These findings highlight the immense potential of ISUT for unlocking vast oil reserves present in carbonate reservoirs worldwide.