One of the 2 basic technologies for shale gas production is hydraulic fracturing. Hydraulic fracturing is a process that involves injecting a mixture of water, sand and chemicals into gas-bearing rocks under extremely high pressure (500-1500 atm).
The pressure causes tiny cracks to form that allow the gas to escape. This entire fracture system connects the well to the productive parts of the reservoir away from the bottomhole. To prevent the fractures from clamping together after the pressure is reduced, coarse sand is added to the fluid injected into the well. The radius of fractures can reach several tens of meters.
The fracture process is highly dependent on the physical properties of the fluid and, in particular, its viscosity. In order for the fracture pressure to be lowest, it is necessary for it to be filterable. Increasing the viscosity as well as reducing the filterability of fluids used in fracturing is accomplished by introducing appropriate additives. Such thickeners for hydrocarbon fluids used in fracturing are salts of organic acids, wax molecular and colloidal compounds of oil (e.g., oil tar and other oil refining wastes).
Some oils, kerosene-acid and oil-acid emulsions used in fracturing carbonate reservoirs, and water-oil emulsions have significant viscosity and high sand-bearing capacity. These fluids are used as fracturing fluids and sand-bearing fluids when fracturing oil wells.
The use of hydrocarbon-based fracturing fluids and sanding fluids to fracture formations in water-injection wells can lead to deterioration of water permeability due to the formation of water-hydrocarbon mixtures. To avoid this phenomenon, formations in water injection wells are fractured with thickened water. Sulfide-alcoholic bordeaux (SAB) and other cellulose derivatives that are well soluble in water are used for thickening. As a rule, fluids used in hydraulic fracturing are carcinogenic. A special danger is the possibility of chemical reagents used in hydraulic fracturing getting into formations containing artesian water used for drinking.
The main environmental hazard in shale gas extraction is the use of large quantities of chemicals that are mixed with water and sand. Hydraulic fracturing (fracking) has to be repeated up to 10 times a year in one area. During fracking, the chemical mixture soaks into the rock, contaminating large areas as well as groundwater.
This is why shale gas extraction has been banned in New York State in the USA. In Europe, where environmental legislation is stricter than in the USA, this may be the main reason why shale gas extraction will not become more widespread.
