Application of vitrinite reflectance to interpret gas content, maximum depth of burial, and paleogeothermal gradient of coal beds in Dunkard Basin.
A thorough understanding of the interrelationship of the geologic history, thermal maturation, and petrographic characteristics of a coalbed is necessary to interpret its present methane content. Coalification of organic matter occurs contemporaneously with burial through the interaction of temperature and pressure during geologic time. In initial stages of coalification, pressure is an important factor in volume, pore, and moisture reduction. In later stages of coalification, temperature and duration of heating are more significant. During this period, methane and other gases are generated as coalification by-products. The degree of coalification, referred to as rank or thermal maturity, is commonly measured by vitrinite reflectance. This value has been used by the Bureau of Mines to determine the rank of Permian and Pennsylvanian coalbeds from several boreholes in southwestern Pennsylvania. From these values, estimates of former depths of burial and coalification temperatures may be made.