Experimental Study On The Carbon Isotope Trends During The Desorption Of Coal Seam Gas

Methane gas is the primary focus of geochemical studies regarding coal seam gas (CSG). To study the fractionation of carbon isotopes that occurs during CSG desorption from coal rocks, a wireline core sample was collected and placed inside a homemade airtight CSG/shale gas desorption cannister, where it was allowed to continue desorbing CSG. Two-hundred and fifty milliliters of CSG samples were collected for carbon isotope analysis. The experimental results indicate that delta 13C1 increases slowly during the early stages of CSG desorption. delta 13C1 increased dramatically after a certain volume of gas was de sorbed from the sample. Toward the end of the desorption process, the increase in delta 13C1 over time slowed significantly. Given a fixed desorption temperature, the delta 13C1 of the desorbed CSG can increase over time; this growth is initially slow, then becomes fast, and finally becomes slow. In most cases, CSG samples from the early stages of the desorption process will exhibit slightly lower delta 13C1 values than the CSG's actual delta 13C1 value. Therefore, sampling time is a factor that must be considered in studies about the horizontal distribution, genesis, and fractionation mechanisms of CSG methane delta 13C1 values.