Generation of Hydrocarbon Gases in Stepwise Pyrolysis of Artificially Matured Domanik Oil Shale Kerogen

Abstract

A series of kerogen samples were isolated from Domanik oil shale before and after hydrothermal treatment in an autoclave (at 250–375°C, for 24 h). Than composition of the C₁–C₅ hydrocarbon gases generated in stepwise (300–800°C) pyrolysis of these kerogens was characterized by gas chromatography. According to the calculated EASY %Ro and Rock-Eval pyrolysis data, the highest maturity level of the organic matter reached by the hydrothermal treatment corresponded to the MC₄ stage. As the hydrothermal treatment temperature of the oil shale was elevated up to 325°C, the dry pyrolysis of residual kerogen led to the predominant generation of wet gases in which C₂₊ prevailed over methane; at temperatures above 325°C, methane was predominant. Based on the pattern of the generation curves plotted individually for C₁, C₂, C₃, C₂–C₅, and C₄–C₅ gases, methane was found to have additional sources in the kerogen structure, compared to C₂₊ gases. Ethane and ethylene are generated simultaneously via the free-radical decomposition of alkyl structures; moreover, at high pyrolysis temperatures, ethane and ethylene have some precursors other than those of C₃₊ gases.