Influence of Nature and Diagenesis of Organic Matter in Formation of Petroleum

Elevation of temperature and pressure during burial of sediments results in a physiochemical transformation of the kerogen, and particularly in changes of elementary composition, infrared spectra, and thermal properties of kerogen. The combined variation of these characters defines an evolution path for each kerogen type (organic matter from similar environments of deposition group along the same evolution path). The degree of evolution of individual samples can be evaluated by using these techniques. An experimental evolution test, using thermogravimetric, infrared, and associated techniques, can reproduce the natural degradation of kerogen during its burial in a sedimentary basin. The test allows the petroleum geologist to make an evaluation of the petroleum potential of a given formation in the buried parts of a sedimentary basin, by using shallow or surface samples and simulating their degradation in the laboratory. The major products generated during the three successive steps of kerogen evolution are carbon dioxide and water; oil; gas. The relative abundance of these products depends on the composition of the original kerogen. Kerogen from a high evolution path generates abundant oil, whereas that from a low evolution path produces methane at depth, but little or no oil.