Geochemical Characters of Water Coproduced with Coalbed Gas and Shallow Groundwater in Liulin Coalfield of China

To reveal the geochemical characters of water coproduced with coalbed gas and shallow groundwater, water samples were collected from 12 wells of coalbed methane and 7 wells of shallow groundwater. The pH, COD_Mn? fCO₂, total dissolved solids (TDS), total hardness, and concentrations of metasilicic acid, sodium and kalium, calcium ion, magnesium ion, ammonium iron, bicarbonate ion, carbonate, chloride, sulfate ion, nitrate ion, fluoride, lithium, zinc, nickel, manganese, iron, boron, barium, etc. of the samples were measured. Research results showed the following: (1) Concentrations of TDS, chloride, fluoride, sodium and kalium, ammonium, iron, and barium in the water coproduced with coalbed gas exceeded the national standards of China; however, physical, chemical, and biological properties of shallow groundwater could meet the national standard. (2) The water produced from coalbed contained mainly Na–Cl·HCO₃, with average TDS of 4588.5 ppm, whereas shallow groundwater contained a mixture of chemicals including Na·Mg·Ca‐HCO₃·SO₄ and Na·Mg‐HCO₃·SO₄, with average TDS of 663.8 ppm. (3) In general, it was observed that bicarbonate and sodium accumulated in a reducing environment and deeper system, while depletion of hydrogen ions and dissolution of sulfate, calcium, and magnesium occurred in a redox environment and shallow system. (4) Sodium and kalium, ammonium, chloride, and bicarbonate ions were the main ions found in the study area.