PRELIMINARY COMMENT ON THE VARIATION OF CARBON ISOTOPIC COMPOSITION OF METHANE IN COAL MEASURE GAS AND SEAM GAS, AND ITS CONTROLLING FACTOR

The genetic types of natural gases are discussed according to the stable carbon isotopic composition of natural gases.It is found that the coal measure gas and the seam gas with the same maturity show great differences both in chemical and carbon isotopic composition.After various cor-relative analyses were made,the author proposes that the controlling factors of the differences are mainly,(1) the influence of biogenic methane in coalbed;and (2) the exchange of carbon isotopes between CH₄ and CO₂.