ABSTRACT: Determination of Kinetic Parameters for Kerogen Degradation from Rock-Eval Data

Kazuo Nakayama

As mathematical modeling for basin analysis becomes popular, the quality of input parameters, especially for hydrocarbon generation models, is important. A mathematical model usually assumes a number of parallel chemical reactions for the process. The number of reactions nowadays is set to 12 or more for smooth generation curves. For each reaction, activation energy, frequency factor, and initial concentration of kerogen convertible to hydrocarbons are the kinetic parameters to be assigned. A special pyrolysis must be undertaken for determination of these parameters; however, we try to develop here a method to estimate kinetic parameters from S₂ values provided by routinely processed Rock-Eval analysis.

S₂ value is thought to be residual potential for hydrocarbon generation of the sediment. If we assume kinetic parameters of the kerogen for a certain geologic formation, we can easily calculate the amount of hydrocarbon that had been already generated knowing the temperature history of this buried formation. Comparing the calculated amount of remaining hydrocarbon potential with the observation from pyrolysis, we are supposed to solve an inverse problem by minimizing least squares residual between the two. The kinetic parameters thus can be determined by plenty of routinely analyzed Rock-Eval data.

The method is applied to the data from the petroleum province in Japan, and the estimated values are found to differ from typical kerogens already proposed. Kinetic parameters are dependent on local geochemical environment as well as on the composition of kerogen types.

For exploration purposes there is a general absence of good depositional models for marine sandstones that formed in the North American epicontinental seas during the Paleozoic. The Misener, Spiro, and Lower Morrow sandstones represent good ancient analogs for marine sandstones deposited in local to subregional channel-like settings.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990