What chemicals are used in fraccing and why?
Fraccing fluid is generally 90% water, 9.5% sand and about 0.5% chemical additives.
Most of the chemicals used in fraccing are found in familiar household products and food additives. Commonly used substances include guar gum (a thickener found in food products), acetic acid (in vinegar), sodium chloride (salt), ethanol, sodium bicarbonate (baking soda) and sodium hypochlorite and hydrochloric acid (both used in swimming pools), cellulose (used to make paper), acetic acid (the active part of vinegar) and small amounts of disinfectants.
These chemicals are all used in very low concentrations and in almost all cases they are biodegradable, meaning they break down.
Chemicals are used because the tiny cracks in the rock created by fraccing will quickly close unless they are held open in some way. This is done by injecting a proppant made from sand into the cracks. But sand does not dissolve in water so a thickener (guar gum) is needed to carry the sand. Other chemicals help reduce friction, remove bacteria and prevent scale from building up in the well.
For a list of chemicals used in Australian coal seam gas operations, see this link.