For more than 100 years, Australian oil and gas operators have been drilling into and through aquifers.
They are very careful to protect these aquifers and the use of any chemicals in Australian oil and gas operations is strictly regulated to minimise environmental risk, including risks to groundwater.
Regulators require monitoring and management conditions appropriate to each site during and after oil or gas production. This includes monitoring the levels and quality of local groundwater.
Australia’s oil and gas deposits are typically hundreds – or even thousands – of metres deeper that the freshwater aquifers used for domestic or agricultural purposes.
The vast majority of oil and gas deposits are separated from freshwater aquifers by thick layers of impermeable rocks. These rocks form efficient natural barriers between fresh water and gas resources.
Oil and gas wells are constructed using several layers of steel casing and cement that form a protective barrier between the well and the rock. These barriers are tested by applying pressure or by electronic sound measurements – or both.
Drilling fluids are typically water-based and contain:
- Highly absorbent clays such as bentonite (which is also commonly used to line dams to prevent leakage).
- Density control additives, such as barite, to control the weight of the drilling muds to prevent well blowouts. (Barite is also used in barium meals given to patients before CAT scans.)
- Organic-based polymer additives, such as xanthan gum or guar gum, to control viscosity. (These are common food additives.)
Fraccing fluids are about 99% water and sand. The remainder is made up of chemical additives needed to reduce friction, remove bacteria, dissolve some minerals and enhance the fluid’s ability to transport sand.
Chemicals used in Australian fraccing operations include sodium hypochlorite and hydrochloric acid (both used in swimming pools), cellulose (used to make paper), acetic acid (the active part of vinegar) and disinfectants.
For a list of chemicals used in Australian coal seam gas operations, see this link.
Low risk of soil and aquifer contamination
Typically, hundreds of metres of rock separate a fracture stimulation and any sensitive aquifers, such as those used for domestic or agricultural purposes.
The Australian Council of Learned Academics (ACOLA) has published a summary review of the risks associated with fracture stimulation and concluded that there is no evidence of hydraulic fracturing fluids moving up in the earth from a fraccing operation to a surface aquifer.
Up to 80% of the fluid used in hydraulic fracturing can be recovered. Most of this can be recycled and reused for additional hydraulic fracturing or other beneficial uses, such as irrigation of nearby crops, in the local communities.
The residue from this process is tested and, if required, removed to a licensed disposal facility.
Over the life of a well – which may be decades – the pressure gradient towards the well ensures that any chemicals that may be freed up over time are swept to the well and up to the surface for proper processing.