Thermal Simulation of Maturation for Coal and Peat:Evolution of Vitrinite Reflectance and Its Geological Significance

The evolution of vitrinite reflectance of coals and peat in Shanxi formation and Taiyuan formation from Qinshui basin were studied by means of thermal simulation under high temperature and pressure with two heating rates of 20 ℃/h and 2 ℃/h. The results show that 1) at the heating rates of 20 ℃/h and 2 ℃/h, the vitrinite reflectance of residues is from 1.07 % to 4.50 % and from 0.83 % to 3.97 % for Taiyuan formation coals, from 0.98 % to 4.51 % and from 0.80 % to 4.05 % for Shanxi formation coals, and from 0.96 % to 4.19 % and from 0.72 % to 3.72 % for peat at a temperature ranging from 336.8～600 ℃; 2) the cumulate vitrinite reflectance of the residues in coals and peat increases linearly with the increasing temperature and R_o values of the samples simulated at a heating rate of 2 ℃/h is higher than that simulated at a heating rate of 20 ℃/h, indicating the dependence of the evolution of organic matter maturation on heating rate;3) at two heating rates, the relative variation in R_o values of coals and peat are obvious with the increasing temperature, reflecting the stage feature of the evolutionary process of R_o values. As a whole, there are some similarities in evolutionary processes of R_o. However, the intensity of R_o variation for the coal in Taiyuan formation is higher than that in Shanxi formation; and 4) the simulation solid products in different samples are obviously different in cumulate R_o at the same temperature and the same heating rate, and the cumulate R_o is the highest for the coal in Taiyuan formation, the middle for the coal in Shanxi formation, and the lowest for peat. The significant variation of relative R_o is also observed, reflecting the influence of properties of the samples on the evolution of vitrinite reflectance R_o values. Finally, the geological significance is discussed associated with the experimental results.