Pyrolysis kinetics for lacustrine and marine source rocks by programmed micropyrolysis

Micropyrolysis data were obtained with a Pyromat II instrument for three synthetic polymers and 12 oil shales and petroleum source rocks. By use of an accurately calibrated thermocouple placed directly in a sample located in a relatively uniform temperature region of the furnace, data good enough for kinetic analysis were obtained. Data at multiple heating rates (normally 1, 4, 15, and 50{degree}C/min) were analyzed by several approximate and rigorous methods. The most generally reliable estimate of the mean activation energy appears to come from the simplest procedure, namely, linear regression of the shift of temperature for maximum rate of reaction (T{sub max}) with heating rate. The average E by this method for the 12 rock samples is 53 {plus minus} 2 kcal/mol. The average principal E by the discrete E-distribution analysis is 54 {plus minus} 2 kcal/mol for the rock samples. An nth-order single reaction model and a Gaussian E-distribution model give about the same primary E as the discrete distribution model, although the nth-order model does not fit most marine samples as well as an activation energy distribution model, especially when the distribution is broad. The discrete distribution model tends to work best when a significant distribution is present because the distribution can be asymmetric or bimodal. For some lacustrine samples the reaction rate profile is very narrow and the reaction mechanism is more consistent with a set of serial reactions than with the above models. Analysis of synthetic data for a sequential mechanism shows that the simple T{sub max}-shift method still gives the correct E for all multiple heating rate analyses, while the other models approach the correct E only with a very large range of heating rates.