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??A low productivity carbon dioxide gas reservoir was found at the well depths of 2573-2594 m of Maokou Formation-Qixia Formation?? Permian?? in well Yang-1 in Yangba Seg of Nanpanjiang Basin. It is very important for natural gas exploration in the region to find out the origins of the gas reservoir?? because this well is the first regional exploration well in the basin. On the basis of analyzing the geochemical characteristics of the natural gas?? the genesis and origins of the natural gas in the reservoir were investigated by means of the organic geochemical and organic petrological analyses of the cores of well Yang-1 and the rock samples of peripheric outcrops?? and of the thermal simulation experiments of the carbon dioxide gas source rocks. The comprehensive analysis results indicated that the hydrocarbon in the natural gas in well Yang-1 was the overmature coal??type cracking gas and came from the Permian coal measure hydrocarbon source rocks?? according to the He and Ar isotopic ratios?? the natural gas was mainly the crustal source gas?? and the carbon dioxide was mainly the petrochemical genesis?? being formed by the low temperature ????300?棩 hydrolysis of the Carboniferous-Permian carbonate rocks.

GEOCHEMICAL CHARACTERISTICS OF THE NATURAL GAS IN WELL YANG-1 IN NANPANJIANG BASIN

A low productivity carbon dioxide gas reservoir was found at the well depths of 2573-2594 m of Maokou Formation-Qixia Formation， Permian， in well Yang 1 in Yangba Seg of Nanpanjiang Basin. It is very important for natural gas exploration in the region to find out the origins of the gas reservoir， because this well is the first regional exploration well in the basin. On the basis of analyzing the geochemical characteristics of the natural gas， the genesis and origins of the natural gas in the reservoir were investigated by means of the organic geochemical and organic petrological analyses of the cores of well Yang 1 and the rock samples of peripheric outcrops， and of the thermal simulation experiments of the carbon dioxide gas source rocks. The comprehensive analysis results indicated that the hydrocarbon in the natural gas in well Yang 1 was the overmature coal type cracking gas and came from the Permian coal measure hydrocarbon source rocks； according to the He and Ar isotopic ratios， the natural gas was mainly the crustal source gas； and the carbon dioxide was mainly the petrochemical genesis， being formed by the low temperature （＜300℃） hydrolysis of the Carboniferous-Permian carbonate rocks.