Based on the analysis of light hydrocarbon compositions of natural gas and regional comparison in combination with the chemical components and carbon isotopic compositions of methane,the indication of geochemical characteristics of light hydrocarbon on the migration features,dissolution and escape of natural gas from the Dongsheng gas field in the Ordos Basin is revealed,and the effect of migration on specific light hydrocarbon indexes is further discussed.The study indicates that,natural gas from the Lower Shihezi Formation(P1 x)in the Dongsheng gas field displays higher iso-C5-7 contents than n-C5-7 contents,and the C6-7 light hydrocarbons are composed of paraffins with extremely low aromatic contents(＜0.4％),whereas the C7 light hydrocarbons are dominated by methylcyclohexane,suggesting the characteristics of coal-derived gas with the influence by secondary alterations such as dissolution.The natural gas from the Dongsheng gas field has experienced free-phase migration from south to north and different degrees of dissolution after charging,and the gas in the Shiguhao area to the north of the Boijianghaizi fault has experienced apparent diffusion loss after accumulation.Long-distance migration in free phase results in the decrease of the relative contents of the methylcyclohexane in C7 light hydrocarbons and the toluene/n-heptane ratio,as well as the increase of the n-heptane/methylcyclohexane ratio and heptane values.The dissolution causes the increase of isoheptane values of the light hydrocarbons,whereas the diffusion loss of natural gas in the Shiguhao area results in the increase of n-C5-7 contents compared to the iso-C5-7 contents.
关键词
鄂尔多斯盆地/东胜气田/二叠系下石盒子组/轻烃化合物/成熟度/天然气成因/运移相态/散失作用
Key words
Ordos Basin/Dongsheng gas field/Permian Lower Shihezi Formation/light hydrocarbon compounds/maturity/natural gas origin/migration phase state/diffusion loss
万方数据