中国煤层气井产出水地球化学研究进展

Research progress on produced water geochemical from CBM wells in China

针对煤层气井产出水地球化学研究对判识排采水来源、揭示其地质意义的重要作用,系统总结了煤层气产出水在常规离子、微量元素和氢氧同位素方面的化学特征及其地球化学响应作用,并探讨了现今产出水研究中存在的问题和未来发展趋势。研究表明:世界各地煤层气产出水具有相似的离子特征,不同排采阶段特征不同。随排采进行,特征微量元素含量呈先上升后下降的趋势。产出水氢、氧同位素组成多分布在区域大气降水线附近,属大气降水来源,具有明显的D漂移特征。Na+、K+、HCO-3、CO2-3、Cl-、微量元素浓度较高和氢氧同位素偏重暗示封闭型水文环境,有利于煤层气富集保存。建立了多种反映煤层气富集高产的综合地化指标和产出水来源判识模板。最后指出,煤层气井产出水来源准确判识、煤层气高产的地球化学预测模型建立、排采过程中气水联动关系深入探讨和压裂液影响的定量表述和消除等方面值得更多关注。

According to the important role that geochemical study of produced water from coalbed methane( CBM) wells to the identification of the sources of drainage water and its geological significance,this paper systematically summarizes the geochemical characteristics of conventional ion,trace elements and hydrogen and oxygen isotopes and its geochemical response in CBM wells produced water,and discusses the existing problems and future development trends in the currentstudy of produced water.The research shows that worldwide CBM wells produced water has similar ionic characteristics,but with different ion features in diverse drainage phases.With the drainage development,the contents of characteristic trace elements increased first and then decreased. The hydrogen and oxygen isotopic compositions in CBM wells produced water are mostly distributed near the regional atmospheric precipitation line and have obvious D drift characteristics,which explaines a source of atmospheric precipitation.When the contents of Na+,K+,HCO-3,CO2-3,Cl-and trace elements,are relatively high,and hydrogen and oxygen isotopes are relatively heavy,it will imply a closed hydrological environment,conducive to the CBM enrichment and preservation.And a variety of geochemical comprehensive indexes,reflecting CBM enrichment and high production,and identification templates of produced water source,have been established.Finally,it is pointed out that more attentions should be paid to the accurate identification of CBM wells produced water source,the establishment of geochemical prediction model for CBM high production,the further discussion of gas and water linkage interaction during drainage process,and the quantitative description and elimination of fracturing fluid effects.