This is a liquid with a salt content greater than 5%. Brine on the ground surface is called surface brine or lake brine, and brine below the ground surface is called underground brine. It is called petroleum brine when it is associated with crude oil. Based on the underground enrichment conditions, brine can be classified into pore brine, intercrystal brine and fissure brine. Based on the hydraulics, brine can be divided into submerged brine and pressurised brine. Brine often contains ions of K+, Na+, Ca2+, Mg2+, Cl−, SO4−, CO3−, HCO3−, B, Li, Br, I, Sr, Rb and Cs.