A new experimental and theoretical approach for predicting secondary oil to gas cracking kinetics in petroleum system modelling

Petroleum System Modelling often neglect secondary cracking processes. They are modelled by first order kinetic law, using simple discrete reaction scheme, excluding non-hydrocarbon components, important to explain reactivity and presence of H₂S/CO₂ into the reservoir. To improve this framework the paper shows decomposition experiments of a heavy oil analogue (phenyldodecane, PDD) in presence/absence of water and/or diethyldisulfide, using a combination of confined pyrolysis experimentation and automated reaction network modelling. PDD and mixtures of PDD with diethyldisulfide (DEDS, ∼8.5 mol.%) were reacted at constant temperature in the range 253-353°C and controlled pressure (35 MPa) in gold capsules, both in the presence and absence of subcritical water or D₂O. Remnant PDD and products were been identified by multiple techniques, including gas chromatography mass spectrometry (GC/MS), comprehensive two-dimensional GC/MS, as well as stable carbon and hydrogen isotope analyses. In general, observations support the hypothesis that organ-sulfur radicals promote hydrocarbon degradation under geologic conditions, with implications for immature petroleum decomposition and Type II-S kerogen maturation. Organ-sulfur compounds may be more reactive than previously assumed, especially in presence of water. Even though the preliminary experimental conditions adopted for this trial cannot reproduce geological settings, tests further clarify the role of water, and highlight the importance of H₂S in mediating mass transfer of H between organic liquids and water. Results demonstrate how oil to gas cracking mechanisms are better described by modern reaction network kinetic model in experimental investigations of complex petroleum system processes. The chance of including the role of non-hydrocarbon components presence in terms of changes of organic matter reactivity could explain different behavior to thermal stress leading a more reliable prediction of timing generation, quality and quantity of hydrocarbons produced and accumulated into the petroleum systems.