鄂尔多斯盆地杭锦旗地区上古生界天然气成因及来源

Origin and source of natural gas in the Upper Paleozoic in Hangjinqi area,Ordos Basin

鄂尔多斯盆地杭锦旗地区上古生界天然气化学组成、稳定碳氢同位素等综合分析结果表明,该区天然气以烃类气体为主,干燥系数介于0.80~0.94,表现为湿气特征;δ^(13)C_1和δ^(13)C_2值分别为-36.2‰^-31.7‰和-27.8‰^-23.3‰,δD_(CH_4)值为-199‰^-172‰,烷烃气碳、氢同位素总体呈现正序特征,属于有机成因气。天然气成因鉴别和气—源对比表明,该区上古生界天然气主体属于煤成气,来自太原组—山西组煤系烃源岩,但泊尔江海子断裂南北两侧天然气的来源存在差异性,南侧十里加汗区带天然气来自原地的太原组—山西组高成熟烃源岩;而北侧什股壕区带天然气则主要由断裂以南十里加汗等地区运移而来,且后期遭受一定程度的破坏而发生逸散。

The analyses of the chemical composition,stable carbon and hydrogen isotopes as well as noble gas isotopes of natural gas from the Upper Paleozoic in the Hangjinqi area of Ordos Basin showed that the natural gas was mainly composed of hydrocarbon gas,which appeared to be wet gas with a dryness coefficient from 0.80 to 0.94,lower than 0.95.Theδ13 C 1 andδ13 C 2 values range-36.2‰–-31.7‰and-27.8‰–-23.3‰,respectively,and theδD CH 4 values range-199‰–-172‰.The carbon and hydrogen isotopes of alkane gas are generally characterized by positive sequence,indicating for an organic origin.Gas origin identification and gas-source correlation indicated that the natural gas from the Upper Paleozoic is coal-derived gas with a normal to high maturity and was sourced from coa-measure source rocks in the Taiyuan-Shanxi formations.There are some obvious differences of gas-source to the south and the north of the Boerjianghaizi Fault.The natural gas in the Shilijiahan play in the south was derived from the P 1 t-P 1 s source rocks in situ with a high maturity,whereas the natural gas in the Shiguhao play in the north was mainly sourced from the Shilijiahan area,and then suffered a certain degree of damage and escaped.