Shale gas is an unconventional gas. It is extracted from dense rocks from which gas cannot easily escape (e.g., sandstones) or it is tightly absorbed into the rock (e.g., coalbed methane). Unconventional gas also occurs as pure natural gas in shale formations and as free gas in natural fractures.
How is shale gas produced?
The gas that is locked in deep shale formations can be extracted using a technology that has been in use for a decade and is called horizontal drilling or hydraulic fracturing.
Hydraulic fracturing (or “fracking” for short) involves injecting high-pressure water into the rock, which causes cracks in the rock, followed by injecting a mixture of water and a solid called proppant into the well and shale rock to help keep the cracks open. The hydraulic pressure created by injecting the fluid into the well is sufficient to create fractures (fissures) at a distance of 1000 meters in each direction from the steel pipeline. In this way, the gas is released from the rock and enters the well, which then rises to the surface.
Shale gas as a gas produced from oil shale, which is a mixture of shale and kerogen. The gas is produced from kerogen by chemical means, i.e. when kerogen is dissolved in benzene and toluene, methane, carbon dioxide and water are obtained.
An interesting fact is that most ore deposits in America are concentrated at a depth of 180-500 meters.
What are the environmental risks?
When performing hydraulic fracturing, 9,000 to 29,000 m3 of water is used for just one well. Under the terms of the draft agreement with Shell, the company has the right to use special water for free, which will not encourage it to use the extracted water rationally. Most of the water (1,300 – 23,000 m3 of water per well) is then returned to the surface. This water contains chemicals from shale rocks: heavy metals, naturally occurring radioactive materials, and various toxic substances used in injection.
Another option for storing spent drilling mud is to store it in a pit, a huge pit compacted with clay soil with minimal filtration to prevent wastewater from penetrating the groundwater table.
There is also a risk of contamination of underground drinking water sources or surface water aquifers with methane, hydrochloric acid solution, sulfates and hydrocarbons (benzene, toluene) that enter aquifers through fractures in the rock. A recent study by Duke University provides documented evidence that the aquifers above the Marcellus and Utica shale formations in northeastern Pennsylvania and upstate New York have been contaminated with methane. It was found that the concentration of methane in shallow wells near drilling sites was on average 17 times higher than in areas where no drilling was taking place.
Impact on human health
In general, chemicals can have a rapid, negative, easily diagnosed impact on human health, as well as an impact that creates a cumulative effect that cannot be diagnosed immediately but will manifest itself in months, years, and even decades. Lead is a hazardous air pollutant and has a particularly negative impact on the neurological development of children. In adults, it causes problems with the reproductive system, hypertension, and nervous disorders. A very small amount of cancer-causing benzene can contaminate millions of liters of water. Toluene, which affects the central nervous system, can cause mental disorders, including blackouts, visual and auditory hallucinations. These chemicals can cause infertility, autism, diabetes, thyroid disease, and cancer.