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石炭-二叠系煤层是鄂尔多斯盆地韩城煤层气田的主力产层,煤层中水的特征对于煤层气富集的研究有着重要的意义.本文通过采集研究区煤层气井的水样,利用加速器质谱仪(AMS)测得地层水中的放射性同位素129I信息,结合卤素离子浓度和稳定氢氧同位素特征,对石炭-二叠系煤层中水的来源、年龄和演化过程进行了探讨.研究结果表明,煤层中水的矿化度为1532.29~7061.12 mg/L,属于中低矿化度水,水型以NaHCO3和NaCl水为主,129I和I/Cl值指示其经历了稀释-混合作用.地层水129I/127I的比值分布在660×10 15~145950×10 15,多数介于129I初始值和现今大气降水的129I水平之间,计算的地层水的年龄为0~18.50 Ma.研究区石炭-二叠系煤层中水有两个来源,一部分为古大气降水(中新世),特征为δD和δ18O值在全球大气降水线下方,低129I/127I值;另一部分为现代混合水,特征为较高的129I/127I值.结合地质过程,推测地层水经历了沉积水→沉积水、成岩水→古大气降水、现代混合水的演化过程.
The Permo-Carboniferous coal seam is the main pay zone of the Hancheng CBM gas field in the Ordos Basin, and the characteristics of the water in the coal seam are of great significance for the study of CBM enrichment.Based on collecting the water samples from the CBM wells in the study area and using the accelerator mass spectrometer (AMS) was used to study the source, age and evolution of water in the Carboniferous-Permian coal seam, based on the information of the radioisotope 129I in the formation water and the characteristics of stable and stable hydrogen and oxygen isotopes.The results show that in the coal seam The mineralization degree of water is 1532.29-7061.12 mg / L, belonging to low and medium salinity water, the water type is mainly NaHCO3 and NaCl, and the 129I and I / Cl values indicate that it has undergone the dilution-mixing effect. 127I are distributed in the range of 660 × 10 15 ~ 14 5950 × 10 15, mostly between the initial value of 129 I and the current 129 I level of atmospheric precipitation, and the calculated age of formation water is 0 ~ 18.50 Ma. The Carboniferous Permian There are two sources of water in the coal seam, some of which are Paleozoic Precipitation (Miocene) characterized by δD and δ18O values below the Global Atmospheric Rainfall, a low value of 129 I / 127I; the other is modern mixed water characterized by high 129I / 127I value. Combined with the geological process, It is presumed that the formation water has experienced the evolution of sedimentary water → sedimentary water, diagenetic water → paleo-atmospheric precipitation and modern mixed water.