青海木里煤田天然气水合物特征与成因

青海木里煤田成功钻获天然气水合物实物样品,使我国成为世界上首次在中低纬度冻土区发现天然气水合物的国家。通过对钻获天然气水合物样品的分析,以及对以往异常可燃气体涌出钻孔的测井曲线的重新解释和对比分析,初步确定天然气水合物赋存于中侏罗统江仓组油页岩段的细粉砂岩夹层内的孔隙和裂隙中。研究结果显示,天然气水合物中的气体以重烃类为主,甲烷达52%~68%;其δ¹³C值为-50.5‰(PDB标准),并具有δ^l3C_l<δ¹³C₂<δ¹³C₃<δ¹³iC₄<δ^l3nC₄的特征,其δD值分别为-266‰和-262‰(VSMOW标准),显示出明显的深部热解气特征。结合木里煤田煤层气地质特征,认为煤层气是木里煤田天然气水合物的主要来源,并将其命名为“煤型气源”天然气水合物。

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 δl3C_l<δ13C₂<δ13C₃<δ13iC₄<δl3nC₄. 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”