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ABSTRACT: In theory, from the high temperature and pressure during the coal generating gas to the present low temperature and pressure
of coalbed methane reservoir, the accumulation of coalbed methane was from oversaturated to undersaturated. The gas content
of the coalbed methane reservoir in the south Qinshui basin was 12–35.7 m3/t. According to the isotherm and measured gas content of No. 3 coal, the adsorbed gas content in some wells was highly saturated
and oversaturated, which was hard to theoretically understand. In addition, there were no thermogenic and biogenic gases at
the late stage in the south Qinshui basin. This article proposed that the overpressure was the main reason for the present
high saturation of the coalbed methane reservoir. In early Cretaceous, the coalbed methane reservoir was characterized by
overpressure and high saturation caused by gas generation from coal measure source rocks. In late Cretaceous, the coalbed
methane reservoir was rapidly uplifted, and with the temperature and pressure decreasing, the pressure condition of adsorbed
gas changed from overpressure to normal-under pressure, which resulted in the high saturation and gas content in the present
coalbed methane reservoir.
Keywordcoalbed methane-overpressure-high coal rank
Chinese Science Bulletin 05/2012; 50:124-129. · 1.32 Impact Factor
