ESTIMATING KINETIC-PARAMETERS FOR GENERATION OF PETROLEUM AND SINGLE COMPOUNDS FROM HYDROUS PYROLYSIS OF SOURCE ROCKS

Kinetic modelling of petroleum generation gives important information on the chemistry of the generation process and provides parameters that are used in basin modeling and petroleum exploration. However, parameter estimates and measures of their precision are not easily determined and depend both on the experimental method and the calculation procedure. In this work, results from simulated maturation of source rocks by hydrous pyrolysis are used to determine the energy parameters of petroleum generation under laboratory conditions. A two-step kinetic model of petroleum generation with normally distributed activation energies and residue generation included in the model is fitted to the generation curves. The Arrhenius activation energy and preexponential factor and their confidence limits are estimated by a least-squares inversion procedure. The limitations of the experimental system preclude the simultaneous determination of Arrhenius parameters and activation energy distributions, so fixed energy distributions are used. Energy parameters with confidence limits are calculated for five experimental series using different source rocks. Single compound yields are also modeled. Reasonable values for the Arrhenius parameters are found for bitumen and gas generation, and for methane, acetic acid, and carbon dioxide generation for some experimental series. The effects of the confidence limits of the parameters on extrapolations to geologic times scales are shown in transformation ratio plots for a typical thermal history.