Thermal History of Sedimentary Basins and Kinetics of Oil and Gas Generation
B. P. Tissot, R. Pelet, Ph. Ungerer
Reconstruction of the thermal history is essential for basin modeling because temperature is the most sensitive parameter in hydrocarbon generation.
No measurable parameter can be directly converted to paleotemperature. Maturation indices, such as vitrinite reflectance, pyrolysis temperature Tmax, or concentrations of biologic markers offer an indirect approach. However, all of them are a function of the thermal history through rather complex kinetics with a frequent influence of the type of organic matter. Thus, they only provide a qualitative evaluation of the onset of the oil and gas generation zones. Another approach is to use a geodynamic model where structural and thermal histories are connected. When used alone, the precision of these models is relatively low; therefore, they must be further calibrated against the present distribution of temperatures and the present values of maturation indices, thus providing a etter evaluation of temperature history.
Hydrocarbon generation can be roughly evaluated by using an empirical index, such as the Lopatin method, or explicitly calculated by using a kinetic model. The simple Lopatin method does not allow such a quantitative evaluation. Furthermore, a calibration made in a particular basin cannot be transferred to other geologic situations. A kinetic model based on a specific calibration can simulate all types of organic matter, and burial and temperature histories, and it provides a quantitative evaluation of oil and gas generated. Further improvements may be expected to describe the composition of hydrocarbon products and simulate gas generation better.
AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.