Experimental study on history of methane adsorption capacity of Carboniferous-Permian coal in Ordos Basin, China

The knowledge of adsorption evolution in medium- to high-rank coal basins in China in the long history of tectonic subsidence and uplifting would be of great significance to the understanding of coalbed methane enrichment and accumulation. A model for calculating adsorption capacity history on major coal beds in Hancheng, the Ordos Basin, is established based on adsorption experiments in high-temperature high-pressure conditions with samples from medium- to high-rank coal reservoirs. Studies show that adsorption capacity on medium- to high-rank coal reservoirs is mainly dependent on several factors and is positively correlated with pressure and thermal evolution and negatively correlated with temperature, water content, ash content and volatile content. The model is an extended Langmuir equation mathematically built with temperature, pressure and thermal evolution and then used to reconstruct adsorption evolution on major coal reservoirs in Hancheng as per the burial history and thermal history. The results reveal three stages of adsorption in the geologic history, i.e. early steady stage with low adsorption, middle soaring stage, and late steady stage with high adsorption.