Laboratory constraints on the generation and stability of non-hydrocarbons in natural gas

Hydrous pyrolysis experiments were conducted at 125-360{degrees}C and 350 bars to examine the generation and stability of CO{sub 2}, H{sub 2}S, H{sub 2}, and light hydrocarbons during thermal maturation of Monterey, Eutaw, and Smackover Shales, and unconsolidated sediment from Middle Valley, northern Juan de Fuca Ridge. The experiments were conducted in stainless steel pipe bombs that preclude the existence of a vapor bead-space above liquid and solid reactants. Thermodynamic modelling and mass balance calculations were employed to identify sources and sinks of individual species during sediment maturation. Results of the experiments suggest that inorganic sedimentary components and liquid water participate in reactions regulating the abundance of individual organically-derived gases. Incorporation of these reactions into predictive models allows constraints to be placed on the absolute amounts and relative distribution of non-hydrocarbon and hydrocarbon gases likely to exist in sedimentary basins.