Rock-Eval pyrolysis (by the IFP-FINA Method) provides a rapid (20 min) screening evaluation of the source potential, type, and maturity or organic matter (OM) in rocks. Whole rock samples are used, thereby eliminating time-consuming sample preparation.

The pyrolysis instrument is a dual-detector gas chromatograph to which a pyrolysis heating chamber and gas-handling circuits have been added. A small sample (0.1 g) is heated from 250 to 550°C at a uniformly increasing temperature in a furnace flushed with helium. The volatilized gases are swept either directly into the flame ionization detector or into a CO₂ trap and then into the thermal conductivity detector. The signal is fed through an integrator to a strip-chart recorder, resulting in three peaks: Peak 1, the amount of OM (mg hydrocarbons/g rock) present in the rock as oil-like components and broadly analogous to the solvent-extractable (bitumen) part of the OM; Peak 2, the amount of OM (mg hydrocarbons released/g rock) cracked from the insoluble (kerogen) part o the OM pyrolysis. The temperature of maximum evolution of Peak 2 provides an estimate of maturity; Peak 3, the amount of CO₂ (mg CO₂/g rock) derived from the oxygen in the kerogen.

Comparison of pyrolysis data with conventional geochemical data suggests the following interpretation. Peak 2--hydrocarbon potential: poor, 0 to 2.5; fair, 2.5 to 5.0; good, 5.0 to 10.0 mg hydrocarbons/g rock. Peak 2/Peak 3--expected hydrocarbon type: gas, 0 to 2.5; gas + oil, 2.5 to 5.0; oil, 5.0 to 10.0 mg hydrocarbons/g rock. Peak 1/(Peak 1 + Peak 2)--migrated hydrocarbons: present, greater than 0.2. Temperature of maximum evolution: immature, 435°C; oil-generating, 435 to 450°C; gas generating, 450 to 470°C; cooked out, 470°C or greater.

Because of problems, such as the presence of solid bitumen and mixed kerogen type, Rock-Eval does not replace conventional geochemical evaluation. Instead, pyrolysis data outline general trends facilitating the selection of samples for further analysis.

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