Application of Pyrolysis and Gas Chromatography to Geochemical Characterization of Kerogen in Sedimentary Rock

Abstract

Pyrolysis and gas chromatography are combined in a new technique which characterizes the kerogen in a sedimentary rock. This technique makes it possible to determine with very small quantities (50-100 mg) of rock material, such as drill cuttings, the origin of the matter and its degree of evolution. The technique was tested on a clay-bearing formation from North Africa which was very well defined both geologically and palynologically. The tests gave the following results: (1) low-temperature pyrolysis (250°C) of continental deposits yields degradation products which are rich in aromatics (benzene, toluene, xylene, cumene, etc.), whereas products rich in paraffinic hydrocarbons are derived from marine deposits; (2) the relative concentrations of light hydrocar ons in some samples indicate whether gas or oil has originated from a particular source rock; and (3) the evolution of the kerogen (which results in an increase in the C/H ratio) can be estimated from the nature of the degradation products and more especially from the degree of degradation of the kerogen at high temperatures. The results seem to be consistent with those obtained from parallel studies of the carbonization of spores and organic microfossils and the crystallization of clays.