木里煤田位于青藏高原东北缘,近年在木里煤田聚乎更矿区中侏罗统窑街组中发现了天然气水合物.为了对天然气水合物气源类型做出客观认识,本文对木里煤田聚乎更矿区中侏罗统窑街组烃源岩样品的有机质丰度、有机质类型、有机质热演化程度进行了详细研究,并在此基础上对比了研究区天然气水合物、煤层气中烷烃气的异同,最终确定研究区天然气水合物成因类型和气源.结果表明:①研究区中侏罗统窑街组的泥质烃源岩有机质丰度较高,属好生油岩,有机质类型属于Ⅰ型干酪根,R.值在0.65％～1.32％之间,有机质热演化程度达到了石油伴生气阶段;②天然气水合物烷烃气碳同位素特征显示大部分烷烃气呈现正碳同位素特征系列,相同碳数的天然气水合物烷烃气碳同位素较煤层气轻,天然气水合物烷烃气中甲烷含量相对煤层气较低,且天然气水合物烷烃气δ13 C2值均小于-28‰,属于油型气;③中侏罗统窑街组烃源岩碳同位素特征与天然气水合物的碳同位素具有高度一致性,表明研究区天然气水合物气源主要来自于中侏罗统窑街组的湖相泥岩和油页岩.%The Muli Coalfield,located in the northeastern part of Tibetan Plateau,was recently discovered to host gas hydrate in the Jurassic Yaojie Formation in the Juhugeng Mining area.In order to obtain understanding of gas type and sources of gas hydrate,this study carried out detailed research on organic matter abundance,organic matter type,vitrinite reflectance,alkane carbon isotopic characteristics of source rock samples from the Middle Jurassic Yaojie Formation of the Juhugeng coal mine area.On the basis of the result above,we studied the similarity and difference of alkane gas in gas hydrate and coalbed gas and finally determined the genetic type and source of gas hydrate in the study area.The results show that ① the hydrocarbon source rocks of the Jurassic are abundant in high organic matter abundance,and belong to good source rock.The organic matter type belongs to the type Ⅰ kerogen,with vitrinite reflectance of 0.65％～1.32％,and thermal evolution degree reaching the petroleum gas phase.② Carbon isotopic characteristics show that the majority of alkane belongs to positive carbon isotope series,and the values of δ13C2 are less than-28 ‰,belonging to petroliferous gases.Alkane carbon isotope series of DK-2 drilling at the depth of 141.5m is reversed,indicating the gas is a mixture of the coal gas and petroliferous gases.③ Carbon isotope characteristics of hydrocarbon from source rocks in Jurassic and gas hydrate are highly consistent,suggesting that the gas source of natural gas hydrate derived mainly from lacustrine mudstone and oil shale of the Middle Jurassic Yaojie Formation.
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