摘要
This paper is the continuation of the paper published in 1985,with the emphasis on the irregular components of natural gases from the Sichuan Bsin-the isotopic compositions of C,H and S,the n-and iso-alkane predominance(C6-C13) of methane homologues,the compositional characteristics of organic sul-fur-bearing compounds including thiophen,thio-alcohol,etc.It is considered that natural gases from the Sichuan Basin have different distributional characteris-tics in different layers and locations,suggesting that they are controlled by a combination of factors such as kerogen type,maturity of organic matter and wall-rock assemblage.1.The type of source material (or precursor)is a main factor affecting the geochemical character-ictics of natural gases.T3x-h and P21 produce coal-series gases with type-Ⅲsource material dom-inant.The C and H isotopic compositions of natural gases are heavier,the contents of C6H6 and C7H8 are high,C7H8/C6H6 >1,the content of C4H4Sis low,and the predominace in isoalkane(C6-C13) is obvious.J1t,P1y,Z2b,etc.produce oil-series gases with type-I and -Ⅱ kerogens domi-nant,indicating that the geochemical characteristics of natural gases are different from those described above.2.The maturity of organic matter is an important factor affecting the composition of natural gases.With increasing maturity of organic matter,the Cand H isotopic compositions tend to become light.C1 and C2 isotopic values are nearly equal or even inverse,and C4H4S decreases in content.3.Wall-rock assemblage has apparent influence on the S isotopic composition.The Mid-dle-Lower Triassic series belongs to sulfate-carbonate formations enriched in gypsum.Therefore,the δ^34S values of natural gases are relatively high(>20‰)against the lower values for other layers due to the absence of gypsum layers.
This paper is the continuation of the paper published in 1985,with the emphasis on the irregular components of natural gases from the Sichuan Basin——the isotopic compositions of C,H and S, the n-and iso-alkane predominance (C_6-C_(13)) of methane homologues,the compositional characteristics of benzene and methylbenzene,and the distribution and geochemical characteristics of organic sul- fur-bearing compounds including thiophen,thio-alcohol,etc. It is considered that natural gases from the Sichuan Basin have different distributional characteris- tics in different layers and locations,suggesting that they are controlled by a combination of factors such as kerogen type,maturity of organic matter and wall-rock assemblage. 1.The type of source material (or precursor) is a main factor affecting the geochemical character- istics of natural gases.T_(3x-h) and P_2(?) produce coal-series gases with type-Ⅲ source material dom- inant.The C and H isotopic compositions of natural gases are heavier,the contents of C_6H_6 and C_7H_8 are high,C_7H_8/C_6H_6>1,the content of C_4H_4S is low,and the predominance in isoalkane (C_6-C_(13)) is obvious.J_1t,P_1Y,Z_2b,etc.produce oil-series gases with type-Ⅰ and-Ⅱ kerogens domi- nant,indicating that the geochemical characteristics of natural gases are different from those described above. 2.The maturity of organic matter is an important factor affecting the composition of natural gases.With increasing maturity of organic matter,the C and H isotopic compositions tend to become light.C_1 and C_2 isotopic values are nearly equal or even inverse,and C_4H_4S decreases in content. 3.Wall-rock assemblage has apparent influence on the S isotopic composition.The Mid- dle-Lower Triassic series belongs to sulfate-carbonate formations enriched in gypsum.Therefore,the δ^(34)S values of natural gases are relatively high (>20‰) against the lower values for other layers due to the absence of gypsum layers.
