Measured Kinetics — Are They Useful Basin Model Inputs?
Basin models are more valuable when appropriate kinetics parameters - activation energy distributions and frequency factors - are available for the proposed source unit. These parameters can be inferred based on organic facies or kerogen type(s) using published values - “standard kinetics”. Alternatively, specific source rock samples may be analyzed to derive sample-specific values - “measured kinetics”. Given natural lateral and vertical source rock variability, and analytical imprecision, it is not clear whether the use of measured kinetics provides more useful values than standard kinetics for basin model input. A suite of Type II and Type IIS source rock samples was analyzed via Rock-Eval at five heating rates, and results were reduced to a frequency factor (A) and an activation energy (E) distribution. In addition, kinetics values obtained by this approach were tested in various basin modeling scenarios. The sample suite included “natural precision” and analytical precision checks. TOC contents ranged up to 12%; most samples were thermally immature (< 0.5% Ro). Results indicate that analytical and natural imprecision is significant. We observe temperature variations greater than 20°C at 50% transformation ratio (TR) for multiply run samples and for multiple samples of the same source unit at the same location; calculated VR values vary accordingly. Our findings are consistent with previously published work showing similarly large temperature variations in sample suites of a single kerogen type and even those from a single source rock unit. More importantly, the mid-point of the observed temperature variation at 50% TR commonly occurs at or near the temperature derived from standard kinetics. In other words, the use of standard kinetics based on kerogen type (e.g., LLNL) or organofacies type (e.g., Pepper/Corvi) accurately takes into consideration natural and analytical imprecisions inherent in measurements of a small source rock sample set. Our results indicate that (a) measured Rock-Eval kinetics values on a small sample set provide no additional utility over standard kinetics when used as basin model input, and may instill misplaced confidence in the results, and (b) single heating rate Rock-Eval kinetics experiments are useful in place of multiple heating rate experiments if a common A is agreed upon, supporting previous published results.
AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California