Kinetic parameters for the thermal cracking of simple hydrocarbons: From laboratory to geological time-temperature conditions

- Apparent kinetic parameters were computed at 700 bar, 200 °C and 400 °C by simulation of detailed kinetic models.
- Several hydrocarbons were studied: alkanes, aromatics and naphthenes.
- Deviation due to the extrapolation of the Arrhenius law from 400 °C to geological temperature is important.
- Most hydrocarbons appear more stable at 200 °C than when extrapolating the Arrhenius law from 400 °C to 200 °C.

Apparent kinetic parameters (frequency factor A and activation energy Ea) were computed at 700 bar and two temperatures: 200 °C, a characteristic of deeply buried reservoirs of petroleum and 400 °C an average temperature used for laboratory pyrolysis to simulate thermal cracking of petroleum. Several hydrocarbons were studied by simulation: several linear alkanes and one branched alkane, toluene, 2-methylnaphthalene, 1-,3-,5-trimethylbenzene, methylcyclohexane, butylcyclohexane, tetralin and decylbenzene. The calculations were performed using detailed kinetic models (mostly free-radical mechanisms) previously constructed. The computation of Ea does not depend on the global rate law, but we assumed a first-order reaction law to compute A. The apparent kinetic parameters of all hydrocarbons are slightly modified by temperature and rather strongly for tetralin and decylbenzene. The deviation, due to the use of Arrhenius law with the apparent kinetic parameters computed at 400 °C for extrapolation to geological temperature, is important in most cases, even if the kinetic parameters do not strongly depend on temperature. In this study, most hydrocarbons appear more stable at 200 °C than it could be inferred by using the extrapolation of the Arrhenius law from 400 °C to 200 °C, except for tetralin and decylbenzene which appear more reactive. The apparent kinetic parameters that were computed at 200 °C could be implemented in global kinetic models used for the assessment of reservoirs.

Half-lives of some hydrocarbons at 200 °C, calculated with the apparent kinetic parameters computed either at 400 °C or 200 °C.58