Vitrinite maturation kinetics

Temperatures within the sedimentary section calculated as a fimction of time are used to estimate the maturation level of the organic matter. The kinetic model of vitrinite maturation (Sweeney and Burnham 1990) is the primary method of maturity estimation. Comparison of measured vitrinite reflectance Rg) with the calculated values and present-day temperature profile (Fig. 6.6) is used to control modeling parameters. The time-temperature index (TTI) (Lopatin 1971 Waples 1980) is also computed as a simple method to describe the paleothermal regime. 

Burnham A. K. and Sweeney J. J. (1989) A chemical kinetic model of vitrinite maturation and reflectance. Geochim. Cosmochim. Acta 53, 2649-2657. 

The experimentally determined alteration rate is defined by the expression %R = where Kq is a function of temperature, and t is in days. The overall activation energy describing the kinetics of complex devolatilization reactions responsible for increased VR measured in our laboratory experiments is 21.8 0.3 kJ mol. Combined with earlier rate studies by Dalla Torre et cd. in 1997, we conclude that the rate of vitrinite maturation apparently is imaffected by oxidation state and nature of the starting Ugnitic material (conifer or hardwood). Elevated total aqueous fluid pressure very slightly retards the rate of VR increase. Non-systematic trends are observed for the resinite exudatinite bituminite present in the run products. Our new experimental data confirm that VR is chiefly a function of temperature and time. In support of earlier field, theoretical and laboratory studies, the crucial variable that determines VR over geologic time intervals is host-rock temperature. 

Table 1. Kinetic study of vitrinite maturation, 2.0 kbar fluid pressure, 200 0...

At constant temperature, rates of vitrinite alteration under contrasting oxidation/reduction conditions (HM and FMQ oxygen buffers) are indistinguishable within the limits of error for individual experiments. Provided buffer and charge equilibrated through reaction with H2, oxidation state within this f02 range evidently does not play an important role in the kinetics of vitrinite maturation. 

Burnham AK, Sweeney JJ (1989) A chemical kinetic model of vitrinite maturation and reflectance. Geochem Cosmochim Acta 53 2649-2657 Carothers WW, Kharaka YK (1978) Aliphatic acid anions in oil-field waters - implications for the origin of natural gas. Am Assoc Pet Geol Bull 62 2441-2453 Constantinides G, Arich G (1967) Non-hydrocarbon compounds in petroleum. In Nagy B, Colombo U (eds) Fundamental aspects of petroleum geochemistry. Elsevier, New York, pp 77-108... 

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