Low-temperature gas from marine shales: wet gas to dry gas over experimental time

We recognize the similarities between low-temperature gas generation reported here and the natural progression of wet gas to dry gas over geologic time. There is now substantial evidence for natural catalytic activity in source rocks. Natural gas at thermodynamic equilibrium and the results reported here add to that evidence. Natural catalysis provides a plausible and unique explanation for the origin and evolution of gas in sedimentary basins.Marine shales release gas under isotherm gas flow at low-temperatures [1]. Gas is released discontinuously, in distinct aperiodic episodes that continue over time. It is nonlinear kinetic behavior resembling chaotic catalysis by transition metals [2]. Trace levels of oxygen suppress gas emission, and gas compositions reflect equilibrium control. The recent disclosure of natural gas at thermodynamic equilibrium and catalytic gas from marine shales similarly constrained, strongly suggests natural catalysis as the source of natural gas [3].The origin of natural gas remains controversial, however. Many believe that thermal cracking is the source and cite various pyrolysis simulation experiments to support this view [4-14]. Recent hydrous pyrolysis experiments would seem to rule out natural catalytic activity in general [15], and activity by transition metals [16] in particular. This conclusion was based on the premise that any natural catalytic activity that might exist would express itself under hydrous pyrolysis conditions. However, natural activity is a low-temperature phenomenon that is not observed at pyrolysis temperatures (> 300°C) [1].Here we address catalytic gas generation under open and closed conditions to distinguish it from alternative explanations, desorption and thermal degradation in particular. Gas compositions change very little over time in thermal degradation experiments under open and closed conditions. Methane concentrations remain within a narrow range between 20 and 60% vol (C1-C5) irrespective of kerogen