大兴矿煤层气井排采水化学成分形成机理分析

Analysis of Formation Mechanism of Chemical Composition of Drainage Water in Coalbed Methane Wells from Daxing Well Field

基于大兴矿煤层气井排采水的化学离子测试数据,应用数理统计方法和Aquachem、PHREEQC、SPSS等软件,总结了排采水化学成分化特征,分析了其形成机理,结果表明:排采水中阴、阳离子浓度表现为HCO_3^->CO_3^(2-)>Cl^->SO_4^(2-)、Na^+>K^+>Ca^(2+)>Mg^(2+),为弱碱性、碱性咸水; SO_4^(2-)、K^+、Na^+、pH、Cl^-、HCO_3^-、Mg^(2+)、TDS主要为弱变异,Ca^(2+)为弱至中度变异,CO32-主要为中度变异;排采水主要为HCO3-Na型,苏打化严重,碱化特征显著;水中离子浓度主要受溶滤、阳离子交替吸附、脱硫酸、溶解/沉淀、煤层气生产等作用影响;水中各种离子最初来源于溶滤作用,后来受脱硫酸作用与阳离子交替吸附作用影响,SO42-、Ca^(2+)、Mg^(2+)减少,HCO3-、Na^+、K^+增多,煤层气生产过程中Ca^(2+)、Mg^(2+)浓度进一步降低,溶解/沉淀作用也在一定程度上影响水中CO32-、Ca^(2+)、Mg^(2+)的浓度。

Based on the test data of chemical ions in drainage water of coalbed methane(CBM)wells from Daxing Well Field,through the application of mathematical statistics,Aquachem,PHREEQC and SPSS,the characteristics and formation mechanism of chemical composition of the drainage water were studied.The results showed that the concentration of anions and cations in the drainage water was HCO3->CO32->Cl->SO42-,Na+>K+>Ca2+>Mg2+,and the drainage water was weak-alkaline,alkaline salt water;SO42-,K+,Na+,pH,Cl-,HCO3-,Mg2+,TDS were mainly weak variation,Ca2+was weak tomoderate variation,CO32-was mainly moderate variation;the hydrochemical type of drainage water was mainly HCO3-Na,the characteristics of sodium carbonate decahydrate and alkalization were obvious;the concentration of ions was affected by the effect of lixiviation,cationic adsorption,removal of sulfuric acid,dissolution/precipitation and production of CBM wells;a variety of ions in the water originally derived from the lixiviation of groundwater,then by the impact of removal of sulfuric acid and cationic adsorption,SO42-,Ca2+,Mg2+decreased and HCO3-,Na+,K+increased,and the concentration of Ca2+and Mg2+in the process of production was further reduced,dissolution/precipitation also affected the concentration of CO32-,Ca2+,Mg2+in the drainage water to a certain extent.