检索条件"作者=QIN Shengfei1, TANG Xiuyi2. SONG Yan1 & WANG Hongyan3 1. research institute of Petroleum {2. and development, petrochina, Beijing 100083, china"
The stable carbon isotope values of coalbed methane range widely, and also are gener- ally lighter than that of gases in normal coal-formed gas fields with similar coal rank. There exists strong carbon isotope fractio...
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The stable carbon isotope values of coalbed methane range widely, and also are gener- ally lighter than that of gases in normal coal-formed gas fields with similar coal rank. There exists strong carbon isotope fractionation in coalbed methane and it makes the carbon isotope value lighter. The correlation between the carbon isotope value and Ro in coalbed methane is less obvious. The coaly source rock maturity cannot be judged by coalbed methane carbon isotope value. The carbon isotopes of coalbed methane become lighter in much different degree due to the hydrodynamics. The stronger the hydrodynamics is, the lighter the CBM carbon isotopic value becomes. Many previous investigations indicated that the desorption-diffusion effects make the carbon isotope value of coalbed methane lighter. However, the explanation has encountered many problems. The authors of this arti- cle suggest that the flowing groundwater dissolution to free methane in coal seams and the free methane exchange with absorbed one is the carbon isotope fractionation mechanism in coalbed methane. The flowing groundwater in coal can easily take more 1.CH4 away from free gas and com- paratively leave more 1.CH4. This will make 1.CH4 density in free gas comparatively higher than that in absorbed gas. The remaining 1.CH4 in free gas then exchanges with the adsorbed methane in coal matrix. Some absorbed 1.CH4 can be replaced and become free gas. Some free 1.CH4 can be ab- sorbed again into coal matrix and become absorbed gas. Part of the newly replaced 1.CH4 in free gas will also be taken away by water, leaving preferentially more 1.CH4. The remaining 1.CH4 in free gas will exchange again with adsorbed methane in the coal matrix. These processes occur all the time. Through accumulative effect, the 1.CH4 will be greatly concentrated in coal. Thus, the stable carbon isotope of coalbed methane becomes dramatically lighter. Through simulation experiment on wa- ter-dissolved methane, it had been proved that the f
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