淮南潘集、张集煤矿次生生物气地球化学特征

GEOCHEMICAL BEHAVIORS OF SECONDARY BIOGAS IN PANJI AND ZHANGJI COAL MINES IN HUAINAN COAL FIELD

研究淮南煤田不同矿区煤层气的成因类型对于整个煤田煤层气的勘探开发意义重大。为此,利用地质和地球化学相结合的方法,对淮南煤田主要矿区——潘集煤矿和张集煤矿煤层气的成因类型进行了深入研究。结果表明:该区煤层气组分表现出了甲烷含量高、重烃和二氧化碳含量低的干燥气体的特征,与国内外含次生生物成因煤层气的组分特征一致。虽然该区煤岩的热演化程度已处于热成因气的生成阶段,但煤层气的δ13C1值的总体分布范围为-56.7‰^-67.9‰,仍属于生物成因气的分布范围。煤层气的δ13C2值主要分布在-22‰^-29‰,反映了乙烷的热成因特征,指示了该区的煤层气为热成因乙烷和微生物成因甲烷的混合。淮南煤田具有适合的煤阶、区域强烈隆升使煤层被抬升到浅部、地表水渗入煤层、生物气生成的最佳温度等次生生物成因煤层气生成的有利地质条件。因此,有利的地质条件、煤层气的组分与同位素显示的特征,相互印证了淮南煤田煤层气中有次生生物气存在的事实。

Study on genetic types of coalbed methane in different mines of the Huainan coal field is of great significance for exploration and production of coalbed methane in the whole coal field.Geological and geochemical methods are integrated to thoroughly study the genetic types of coalbed methane in the main mines of the Huainan coal field,i.e.Panji and Zhangji coal mines.It is shown that the composition of coalbed methane in the study area shows the characteristics of dry gas,i.e.high content of methane but low content of heavy hydrocarbons and carbon dioxide,similar to that of coalbed methane containing secondary biogas both at home and abroad.Although the thermal maturity of the coal rock in the study area has been at the stage of generating thermogenic gas,the overall distribution of δ13C1 values of coalbed methane ranges from-56.7‰ to-67.9‰,which is still within the range of biogenetic gas.While the δ13C2 values of the coalbed methane ranges from-22‰ to-29‰,indicating the thermogenic features of ethane.Therefore,the coalbed methane in the study area is a mixture of thermogenic ethane and biogenic methane.The Huainan coal field has favorable geologic conditions for generation of secondary biogenetic coalbed methane,such as suitable coal rank,coal beds getting shallower due to intensive regional uplifting,infiltration of surface water into coal beds,and optimal temperature for generation of biogas.Both the favorable geologic conditions and the composition and isotope features of coalbed methane verify the existence of secondary biogas.