# Kerogen type and hydrocarbon generation

Exploring for Oil and Gas Traps | |

Series | Treatise in Petroleum Geology |
---|---|

Part | Critical elements of the petroleum system |

Chapter | Evaluating source rocks |

Author | Carol A. Law |

Link | Web page |

Store | AAPG Store |

## Arrhenius equation

Kerogen consists of many fractions, each converting to hydrocarbons at a specified rate. This rate of conversion to hydrocarbons is defined by a first-order rate equation known as the Arrhenius equation:

where:

- A = pre-exponent factor
- E
_{a}= activation energy - T = absolute temperature (in kelvin)
- R = universal gas constant
- t = time

These are generally referred to as **kinetic parameters**. They can be measured using various pyrolysis techniques and are different for each distinct kerogen analyzed.

## Hydrocarbon generation—depth and yield

The depth of hydrocarbon generation and the yield of individual hydrocarbon phases are primarily a function of the kinetics of the kerogen-hydrocarbon conversion. Burial history and catalytic effects, due to source rock matrix chemistry, affect the rate of generation, although these effects are secondary to the kinetic effects.

Figure 1 shows hydrocarbon generation vs. depth plots for types I (left) and III (right) kerogens are based on identical burial and thermal conditions. Thus, they depict the difference in the depth of hydrocarbon generation, based on kerogen type alone. Type I kerogen generally has a shallower liquid hydrocarbon zone and generates significantly larger amounts of hydrocarbons. The onset of generation is indicated by the change in the slope of the curves.

## Timing hydrocarbon generation

Variations in the kinetic parameters affect predictions of the present-day distribution of hydrocarbon generation zones and also influence when, in geologic time, a potential source interval generated hydrocarbons. Figure 2 compares the timing of hydrocarbon generation from type I kerogen (left) to type III (right). The onset of hydrocarbon generation is indicated by the dramatic change in slope of the curves: 110-100 Ma for type I and 90-80 Ma for type III. The difference in timing shown in this example is based only on the different kinetic parameters of the kerogen types.

## Recommendations

Conduct kerogen kinetic analysis on samples from the basin being modeled. If samples are not available, standard values for types I–III are available from^{[1]}^{[2]}^{[3]}. Apply these values after carefully classifying the kerogen type in terms of the depositional environment of the individual source intervals.

## See also

- Relationships between maturity and hydrocarbon generation
- Kerogen type and maturity
- Kerogen type and transformation ratio
- Kerogen types: comparison of maturity measures
- Open- vs closed-system generation modeling

## References

- ↑ Burnham, A. K., 1989, A Simple Model of Petroleum Formation and Cracking: Lawrence Livermore Laboratory report UCID 21665, March 1989.
- ↑ Burnham, A. K., and J. J. Sweeney, 1990, Modeling Maturation and Migration of Petroleum: Lawrence Livermore Laboratory report UCRL 102602, rev. 1.
- ↑ Tissot, B. P., and J. Espitalie, 1975, L'evolution thermique de la matiere organique des sediments: aplications d'une simulation mathematique: Rev. IFP, vol. 30, p. 743–777, DOI: 10.2516/ogst:1975026