Abstract: Relationship Between Vitrinite Reflectance and Generation of Methane and Molecular Hydrogen from Coals: Kinetic Modeling

Jean-Paul Boudou, Jean Espitalie

In this work, mean vitrinite reflectance is used as a maturity index for the study of the formation of methane and of molecular hydrogen from coals composed mainly of vitrinite.

Continuous detection during programmed pyrolysis of a coal series ranking from lignite until the meta-anthracite stage shows that T_max of methane and of molecular hydrogen can be correlated with mean vitrinite reflectance. Methane yield is maximum at the onset of the condensate and wet gas zone. Molecular hydrogen yield is at a minimum at the onset of the oil zone, and a maximum at the onset of the dry gas zone. During programmed pyrolysis of coal ranking from anthracite to meta-anthracite coal hydrogen is almost totally converted into molecular hydrogen.

The change of gas evolution rate with increasing pyrolysis temperature is similar to the change of gas yield as a function of mean vitrinite reflectance, indicating that open system pyrolysis can simulate the natural genesis of methane and of molecular hydrogen. Kinetic modeling of methane and molecular hydrogen formation using Optkin and Genex Software provides us with the transformation ratio of methane and molecular hydrogen as a function of mean vitrinite reflectance, of depth, and of geological age.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994