Chemical Kinetics Models of Organic Matter(Vitrinite and Bitumen)Reflectance:Retrospect and Advances
The chemical kinetics model of the reflectance of vitrinite and bitumen is the most used research method to calibrate the thermal history of basin and predict the thermal evolution of source rocks.In recent years,important research progress has been made,but it has not attracted much attention from domestic researchers.Based on reviewing the research process of the chemical kinetic model of organic matter,in this paper it reports the new progress of relevant research.The classical Vitrimat model and Easy％R.model are based on three principles:(1)the vitrinite reflectance is related to H/C and O/C.(2)The thermal degradation product of vitrinite was the sum of residual vitrinite and four kinds of products(H2O,CO2,CHn,CH4).(3)Thermal degradation reaction follows Arrhenius equation.Easy％Ro model has design defects:(1)the frequency factor(1×1013)is too low;(2)lack of high maturity(Ro＞2.0％)samples when optimizing activation energy distribution.The shortcomings in practical application include:(1)when the measured Ro＜0.9％,the calculated value of Easy％R.is too high;(2)when the measuredRo＞2.0％,the calculated value of the Easy％Ro model is too low.New models Basin％Ro,Easy％RoDL,Easy％RoV and Easy％RoB(bitumen)are designed to overcome the obvious shortcomings of the Easy％Ro kinetics model,but the data basis,calibration principles and potential applicability of each model are different.The"dog-leg"curve characteristic of BasinRo％model at medium-low maturity stage may not be applicable to vitrinite reflectance-depth profile;The Easy％RoDL model has strong applicability to geological conditions;Easy％RoV is more suitable for laboratory heating rate conditions.At the geological heating rate,the new chemical kinetics models developed for R have all improved the calculated values when Ro＞2.0％.Easy％RoB is a kinetics model designed for Bro based on the function relation of Bro-Vro(equivalent Vitinite reflectance)and Vitrimat 2018(Type-Ⅱ)model,which has high applicability to geological conditions.Calibration chemical kinetics module and Kinetics hydrocarbon generation kinetics module in PetroMod basin simulation platform were used to carry out three studies:(1)calibration and prediction of ultra-deep source rock maturity,(2)thermal history and basin dynamics derived from vitrinite reflectance of medium to low maturity source rocks,(3)establishment of hydrocarbon generation model combined with hydrocarbon generation kinetics parameters.In the future,attention should be paid to the study of the adaptability of the new chemical kinetics models under laboratory/geological conditions.Improving the accuracy of reflectance measurement,correctly identifying the degree of reflectance inhibition,and being coupled with low temperature thermochronology parameter inversion are of great significance for improving the accuracy of basin thermal history research using chemical kinetics models.
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