沁水盆地南部煤层气田产出水地球化学特征及其来源

Chemical characteristics and origin of produced waters from coalbed gas field in the southern of Qinshui Basin

分析煤层气田产出水的组成和变化,研究煤层气田产出水的水文地球化学特征及其来源,对于认识煤储层中水的解吸与渗流过程以及煤层气的富集机理具有重要意义。通过沁水盆地南部煤储层水化学特征、氢氧同位素和碘同位素特征分析,探讨了煤层气田产出水的来源,研究结果表明:根据采样点数据,沁水盆地南部煤层气田产出水的水质类型多以Na-HCO3型为主,有少量Na-Cl型和Na-SO4-Cl型,煤层气产出水的矿化度大多中等,介于690~2 150 mg/L;沁水盆地南部煤层气田产出水的δD值介于-82‰^-68‰,δ18O值介于-11.5‰^-10.1‰,并且均落在当地大气降水线附近,说明研究区煤层气田产出水主要来源于当地大气降水,并且部分区块煤层气田产出水还与CO2及周围煤岩发生了氢氧同位素的交换反应;ρ(129I)/ρ(127I)校正值介于10.21×10-12~40.59×10-12,通过129I衰变规律计算沁水盆地南部富集区煤层气田产出水年龄为3.3 Ma至今,揭示了沁水盆地南部煤层气田产出水主要来源于古大气降水(上新世和早更新世大气降水)和现代大气降水,并且大气降水对沁水盆地南部煤层气赋存起到保压富集的控制作用。

It is of significance to investigate the water types,the characteristics of hydro-geochemistry and the origin of produced waters from coalbed gas field,which are beneficial to study the desorption and seepage of water in coal seams,and the coalbed methane enrichment mechanism.In this paper,the characteristics of hydro-geochemistry and origin of produced waters from coalbed gas well were studied on the basis of water chemistry and isotopes including the characteristics of water chemistry,oxygen and hydrogen stable isotopes,and radioactive isotope ratio of129 I /127 I in the southern of Qinshui Basin.The results show that the water types are mainly Na-HCO3,while Na-Cl and Na-SO4-Cl types are in a minority in the study area with total dissolved solids(TDS) varying from 690-2 150 mg / L,which are conducive to accumulating gas.The value of δD varies from-82‰ to-68‰,and the value of δ18O is between-11.5‰ and-10.1‰.Hydrogen and oxygen isotope data line is in the vicinity of the Meteoric water line,indicating meteoric water's play an important role in the southern of Qinshui Basin.The corrected129 I /127 I ratios range is from10.21 × 10-12 to 40.59 × 10-12.The age of the produced waters from coalbed gas field samples,obtained through the129 I decay curve method,ranges from 0.8 Ma to 3.3 Ma,suggesting that the ancient atmospheric precipitation were mainly the Pliocene epoch and early Pleistocene atmospheric precipitation.Furthermore,the produced waters from coalbed gas field can keep the pressure of gas reservoir and make gas accumulate.