UNCERTAINTIES IN THE INVERSION OF VITRINITE REFLECTANCE PROFILE—A CASE STUDY OF WELL CHAYUAN 1, WEST HUBEI AND EAST CHONGQING

Uncertainties in the inversion of vitrinite reflectance profile are resulted from the strongly nonlinear relationship between strata temperature history and vitrinite reflectance,and as well as the parametric errors further cause the uncertainties.This uncertainties can be described and analyzed by means of Markov Chain Monte Carlo(MCMC).As for the inversion of vitrinite reflectance profile in Well Chayuan 1,the uncertainties can be summarized as:(1) Only when the strata experience the maximum paleotemperature,can vitrinite reflectance profile provide valid constraints on the geothermal gradient and corresponding denudation thickness;(2) For acceptable results,there is negative correlation between the geothermal gradient and the eroded thickness;(3) Errors in input parameters,such as thermal conductivity of rock,ancient surface temperature and relationship between porosity and depth,increase the uncertainties.The inversion results show that the heat flow of this area has decreased by about 20% since Meso-Cenozoic,from(57±4.7) mW/m² at 145 Ma to 45 mW/m² at present,and the corresponding denudation thickness is(3.4±0.4) km.