Experimental simulation of gas generation from coals and a marine kerogen

The purpose of this work is to determine both the gas and oil potential of Type II and Type III organic matter in open and closed systems. As it is not possible to measure directly the gas generated at various depths from source rocks, due to sampling problems, we have carried out experimental simulations of coal and kerogen degradation in open and closed pyrolysis systems. In the two systems, the total effluents were quantified. For the gas mixture, non-hydrocarbon species such as CO, CO2, H2S and H2O were analyzed together with the C1–C5 hydrocarbons. In a closed system, coals generate mainly gases with a maximum yield around 70–100 mg CH4/g orgC. This methane derives mainly from dealkylation reactions of coal and is produced at high temperatures. The corresponding vitrinite reflectance ranges from 1.3 to 2.7% Ro. Marine Type II kerogen can also produce a significant amount of methane (300 mg/g orgC), which originates mainly from the secondary cracking of oil. In an open system, methane yields are much lower compared to the closed system. This means that, as far as gas generation is concerned, the cracking mechanisms are not the same for the two kinds of experiments and, consequently, estimation of gas potential strongly depends on the choice of the experimental pyrolysis system for simulating artificial maturation of organic matter.