Simulating Petroleum Hydrocarbon Generation Using Hydrous Pyrolysis Experiments on Organic-Rich Samples from the Tarfaya Basin, Morocco

The generation and expulsion of petroleum from source rocks are primarily
controlled by organic-matter type, thermal maturity, and burial history. This study
investigates the thermal evolution and hydrocarbon generation potential of an
immature source rock from the Tarfaya Basin, Morocco, using hydrous pyrolysis
experiments. Experiments were conducted at 280–360°C for 72h to simulate
progressive stages of oil generation under controlled laboratory conditions. The
resulting solid residues were characterized by total organic carbon (TOC), Rock-
Eval pyrolysis, Fourier-transform infrared spectroscopy (FTIR), and organic
petrography, whereas the generated bitumen and expelled oil were analyzed by
liquid and gas chromatography. The experimental results demonstrate a
progressive transformation of the organic matter with increasing temperature,
accompanied by substantial changes in both bulk geochemical and molecular
parameters. TOC decreased from 5.86% to 2.32%, while the S2 yield declined
from 35.80 to 3.39 mg HC/g rock. In contrast, Tmax increased from 411 to 451,
vitrinite reflectance increased from 0.59% to 1.15%, and the aromaticity index
increased from 0.02 to 0.48, indicating progressive thermal maturation and
depletion of hydrocarbon-generating potential. Chromatographic profiles further
revealed an increase in n-alkanes coupled with a relative decrease in cyclic
biomarker compounds, consistent with thermally induced hydrocarbon
transformation. The expelled oil was preferentially enriched in saturated
hydrocarbons, whereas polar compounds dominated the bitumen fraction.
Overall, the hydrous pyrolysis experiments successfully reproduced key aspects
of source-rock maturation and petroleum generation, providing insights into the
progressive alteration of organic matter and the compositional evolution of
generated and expelled hydrocarbons.