Source-Rock Kinetics

We work directly with our partners at StratoChem Services to measure kinetics on source-rock samples at all levels of maturity. Pyrolysis is carried out using our Source Rock Analyzer (SRA) instrument, and the kinetic parameters are then derived by Sirius Exploration Geochemistry using the new ORFA software, which we developed jointly with StratoChem. Kinetic parameters measured on immature samples serve both as input data for computer modeling of hydrocarbon generation, and as the foundation for using Mean Activation Energy (Mean Ea) as a thermal indicator.

Left: Pyrolysis data from laboratory analysis (yellow), showing excellent quality of fit by cyan values predicted by the activation-energy distribution (right) selected by StratoChem’s ORFA software. Not shown here is the A factor, which was specified as 2*1014 s-1.

Left: Plot showing excellent fit between measured laboratory pyrolysis curve (yellow) and pyrolysis yield predicted from using the kinetic parameters derived by our ORFA software (cyan). Right: Activation-energy distribution derived by ORFA that was used in calculating the cyan pyrolysis curve. Not shown here is the A factor, specified as 2*1014s-1.

Moreover, because different types of kerogens have different activation-energy distributions, kinetics can be used to detect lateral or vertical changes in organofacies. This information can then be used to find the organofacies-related sweet spots in an unconventional play, and thus can directly affect drilling and acquisition/relinquishment programs.

Image 4

Ea distributions for four samples from a single formation in a single well. The samples contain varying proportions of the organism G. prisca. Sample on the right contains nearly 100% G. prisca, which has a very narrow Ea distribution with a maximum at 54 kcal. Sample on the left contains very little G. prisca (low amount of material at 54 kcal), and is instead dominated by other types of kerogen. Other samples show intermediate G. prisca contributions (blue arrows point to 54 kcal contribution). G. prisca is most dominant in the richest samples with the highest TOC values. These differences are not visible in the pyrograms.

Finally, source-rock kinetics can be used to evaluate both the level of hydrocarbon generation from a source rock (Transformation Ratio), and the vitrinite reflectance (Ro) value of each sample. The Ro value in turn can be used to calibrate the proposed thermal history of the sample, and thus can improve our understanding of the geological history of the study area. As Waples and Marzi (1998) showed in the figure below, there is no universal correlation between Ro and Transformation Ratio. Thus Ro can be used as a proxy for hydrocarbon generation only if the empirical relationship between Ro and TR has been established using kinetics technology.

Relationship between Ro and Transformation Ratio using published and unpublished kinetic parameters for a wide range of kerogens. Adapted from Waples and Marzi (1998) by Mark Tobey and used with his permission.

Relationship between Ro and Transformation Ratio using published and unpublished kinetic parameters for a wide range of kerogens. Adapted from Waples and Marzi (1998) by Mark Tobey and used with his permission.

The example below shows precisely how the Mean Ea-TR-Ro relationships can differ strongly from one kerogen to another.

Top: Transformation Ratio (TR) calculated as a function of Mean Ea for two different kerogens. Middle: Vitrinite reflectance (Ro) calculated as a function of Mean Ea for those kerogens. Bottom: Ro calculated as a function of TR for those kerogens.

Top: Transformation Ratio (TR) calculated as a function of Mean Ea for two different kerogens. Middle: Vitrinite reflectance (Ro) calculated as a function of Mean Ea for those kerogens. Bottom: Ro calculated as a function of TR for those kerogens.
GRS = Green River Shale