Comparative study on coal rank gradient under different types of metamorphism
Coal rank gradient is fundamental for predicting the degree of coalification in deep reservoirs.This study,based on the meas-ured maximum reflectance of vitrinite of 85 sets,the maximum reflectance of vitrinite/dry ash-free basis volatile yield of 2 213 sets from different coalbed methane blocks'geological exploration reports,and 242 sets of maximum reflectance of vitrinite post-magma intrusion in relation to the coal seam distance from the intrusion,analyzed the coal rank distribution and gradient characteristics under different types of metamorphism.The differences of gradients between deep metamorphism,regional magmatic thermal metamorphism,and contact metamorphism were compared.The results show that the coal rank gradient(Ro,max/100 m)under deep metamorphismin in different coal-bed methane blocks in China ranges from 0.013%to 0.068%,with an average of 0.032%,and shows a positive correlation with the aver-age maximum reflectance of vitrinite.Under regional magmatic thermal metamorphism,it ranges from 0.09%to 0.45%,with an average of 0.18%.Under contact metamorphism,it ranges from 20%to 454%,with an average of 106%.In the contact metamorphism induced by magmatic intrusions,the coal rank gradient exhibits a multi-stage variation.The closer the coal seam is to the intrusion,the greater the coal rank gradient.The differences in coal rank gradient under different types of metamorphism are significant,mainly determined by heat source characteristics,with coalification duration,thermal conductivity of rock layers,and maximum burial depth also playing crucial roles.China's coalification process is complex,making the study of coal grade gradient under different types of metamorphism and in dif-ferent coalbed methane blocks has guiding significance for predicting coal rank of deep reservoir and for the exploration and development of coal/coalbed methane resources.
万方数据
维普
