The characteristics and dynamic changes of produced water from coalbed methane wells in Zaoyuan block

The produced water from CBM well in Zaoyuan block of Qinshui CBM field is characteriaed by high salinity and high mineralization. direct discharge may damage the ecologic environments. Based on the continuous tracking collection of the produced water samples of CBM wells and the systematically testing 25 physical and chemical parameters, the dynamic changes of the salinity and various anions and cations were analyzed. The results show that the concentration of salinity, chloride ion and sodium ion change from high to low, but the concentration of bicarbonate ion changes conversely with the trend from low to high. The water changes from Cl-Na type to Cl· HCO₃-Na type and HCO₃·Cl-Na type. The cations are mainly K⁺ and Na⁺ ions, and there is no obvious dominant anions, HCO₃^-and Cl^- values are close in the produced water. According to the changes of the ions, the model of chloride ion concentration in the water was established using nonlinear regression analysis.