Characteristics and origins of the gas hydrates in the Muli coalfield of Qinghai

Gas hydrates samples are successfully obtained by drilling in the Muli coalfield of Qinghai Province, which makes China the country which firstly discovers gas hydrate in the permafrost of the medium and low latitudes. The gas hydrates are preserved in the pores and cracks of the siltstone layers sandwiched in the oil shale member of the Middle Jurassic Jiangcang Formation. The gas in the gas hydrates is dominated by heavy hydrocarbons, with the methane accounting up to 52 %~68 %. The δ¹³C of the gas hydrates is-50.5 ‰(PDB) and demonstrates a trend of δ^l3C_l<δ¹³C₂<δ¹³C₃<δ¹³iC₄<δ^l3nC₄. The δD values range between-266 ‰ and-262 ‰(VSMOW). These facts indicate that the gas in the gas hydrates in the Muli Coalfield is from pyrolysis in the deep Earth. In consideration of coalbed methane geology of the Muli Coalfield, we proposed that the coalbed methane is the main source of the gas in the gas hydrates in the Muli Coalfield and we name the gas hydrates “coal-prone gas hydrates”