The main sources of CBM wastewater are:

(1) Drilling fluids: Drilling fluids are specialised slurries, usually with chemicals added to protect the well wall, and are usually formulated with water, bentonite and sodium hydroxide.

(2) Fracturing fluid: Fracturing fluid can be used to improve the yield of coalbed methane extraction, and it usually plays the roles of thickening, cross-linking and pH adjustment, etc. The main components of its formula are salts, strong alkaline substances and surfactants.

(3) Gas drainage: gas extraction usually adopts the drainage method, so the composition of wastewater discharged is similar to that of groundwater, and certain ions may exceed the standard in some areas.

(4) Domestic wastewater: wastewater discharged from the production site.

To sum up, the nature of CBM wastewater can be expressed in the following aspects:

(1) The extracted water contains a variety of inorganic ions, among which, the anions are dominated by Cl- and HCO-, and the cations are dominated by Na+ and K+.

(2) The most obvious characteristics of the extracted water are high salinity and high mineralisation.

(3) Due to the fracturing fluid, the wastewater will have excessive organic matter.

(4) There are problems of heavy metal ions exceeding the standard.