Simulation of geological evolution history of the Upper Permian coal seam No.8 in Shuigonghe syncline, Zhina coalfield, Guizhou

Simulation technology in burial history, thermal history and maturation of organic matter (three histories for short) has been widely applied to study petroleum geology, but its application is less in the field of coal and CBM. Based on the measured maximum vitrinite reflectance of coal, geothermal gradient and stratigraphic residual thickness, evolution process of "three histories" for coal seam No.8 in upper Permian of Shuigonghe syncline was studied using Petromod 1D simulation software. The results show that geological evolution history of Shuigonghe Syncline can be divided into three stages. At the first stage, from Late Permian to Jurassic, the burial depth of coal beds increased to the maximum of 5 925~5 959 m. Geothermal gradient is 2.91/℃ hm. Coal rank evoluted from lignite to coke due to deep burial metamorphism. At the second stage, from Late Jurassic to Late Cretaceous, the burial depth of coal bed decreased during Yanshan movement and geothermal gradient was from 3.29/℃ hm to 3.46℃/hm. Due to regional magmatic metamorphism, coal rank evoluted from coking coal to anthracite. The third stage is from the Late Cretaceous till now, coal bed firstly was deposited and then uplifted. Geothermal gradient is 2.78℃/hm. Coalification has almost stopped in the last stage. In a word, deep burial metamorphism is one of the main factors influencing CBM generation, and the time from 230 Ma to 170 Ma is the key time for CBM maturity.