Bulgaria has had or has oil and gas finds in several places, including Chiren, Boutan, Burdarski Geran, Dolni Loukovit and Uglen, to name just some. Hydraulic fracturing, or hydro-fracking, has been used before in the country to prospect and extract oil and gas. It is difficult to give an exact number of how many times, but the latest, according to well engineer Assen Georgiev, was at Buzovets in 1993, using pressure of 500 atmospheres. It was done by the Bulgarian state-owned oil and gas exploration company.

To stimulate extraction rates, the productive rock layer containing oil or gas is fractured by injecting water and sand under pressure. Sometimes, the mix included ceramic grains and, depending on the characteristics of the rock layer, minimal quantities of hydrochloric or sulphuric acid (for carbonate and clay collector layers, respectively). This is done to artificially create new channels in the rock for the gas to flow, raising the effective permeability of the rock layer and opening pathways for the extraction of gas.

Before fracturing, however, the geologic conditions of each location are explored in depth to ascertain whether there are existing underground fractures that would allow the fracking fluid to migrate and contaminate the surrounding geologic area, mainly underground aquifers. A number of criteria need to be satisfied before hydro-fracturing is employed.

The method has been used dozens of times (although it is doubtful anyone has kept any record of the exact number) and there have been no accidents in Bulgaria. I know that from my colleagues who have extensive geological experience in oil extraction.

After fracturing, the wellbore is covered with surfactants – organic compounds, based on hydrocarbons, that increase extraction rates.

There is no fixed range of atmospheric pressure applied in fracking; it all depends on the depth and the exact contents of the rock layer being fractured. As a rule, it has to exceed the geostatic pressure of the rock layer itself, but these are determined in each individual case using lab stress tests and math calculations. According to data from engineer Hristo Kazandjiev, hydro-fracturing in Bulgaria has been carried out with under pressure ranging between 500 and 700 atmospheres.

Parliament's moratorium, which bans any geologic work exceeding pressure of 20 atmospheres, prevents any drilling activity, which is absurd, an opinion shared by the Bulgarian Chamber of Mining and Geology. For example, under this stipulation, should an existing well experience a sudden inflow of hydrocarbons, the engineers would not be allowed to exercise pressure from the top, which would allow the gas to fountain and self-combust, leading to possible injury to the people working on the well.

Hydro-fracking is used in a number of engineering activities; the practice demonised by protesters is not a horrifying prospect, rather a method that has been employed for more than 40 years to serve the energy needs of the Bulgarian society. Hydro-fracking for shale gas extractions is just the next stage in the development of this classic technology.

If fracking is used to prospect for shale gas in Bulgaria, then the horizontal wellbores and the fractures would be between two and three kilometres below the aquifer. Black shale has been discovered in Dobroudja by wellbores at depth between 2.5km and 3.5km as far back as the 1950s. It is known that black shale dates back to the same geologic period as the existing finds of shale gas in the world. The probability that this geologic barrier, thick between three and four kilometres, is fractured in such a way as to allow communication with the aquifer layer is minimal.

The risk lies elsewhere – aquifers always get contaminated in the same way, and that is where the wellbore passes through the aquifer and if is not well isolated. This is why these stretches are made water-tight and cemented additionally, with the quality of the insulation tested before drilling goes any deeper.

There are already more than 200 wellbores in Dobroudja. On each one, the depth of the aquifer is well-known in advance and for that stretch, the well bore is surrounded by several metal pipes, each larger than the other, with the cavity between the pipes filled with cement. This insulation is tested at high pressure to ensure that it is hard enough to resist under strain.

Several finds in Dobroudja – at Tyulenovo, Kamen Bryag and Shabla – are at the same depth with the aquifer; there we have water, oil and a gas cap co-existing in the same porous rocks of the Valanginian aquifer. Oil is being extracted there, but that does not mean that the drinking water in Dobroudja or the seaside resorts, which is extracted from the same rocks, is polluted. If you see it on the spot, you will understand how overblown the fears are.

The two largest accidents ever to happen in Bulgaria – at Chiren and Boutan – are the result of not observing technological procedures and careless actions by the workers on the wellbores. As a result, one person died in the accident at Chiren, while the Boutan wellbore overflowed and caught fire. Both of these were the result of human errors, but had no negative impact on the environment.

Concerning the chemicals used in hydro-fracking, there has been a lot of speculation. I have mentioned earlier what has been used in Bulgaria, but in the world, there are ongoing experiments using fully recyclable gels that can be reused without leaving any traces in the rocks. This solves the issue of the large quantities of water needed for hydro-fracking, but they remain expensive; with the amount of investment in the sector, the prices are expected to go down within several years.

Insofar as prospecting is concerned, prior to the actual drilling, this is 100 per cent safe. Before drilling, a prospective area has to be studied, and that includes geological maps, seismic profiles, geochemical studies of the organic substance that may yield hydrocarbons and physical-mechanical properties of rocks – all of it done in labs. Only four to five years after the start of that process will a first wellbore be drilled to ascertain whether the right kind of rocks is present. If so, a small horizontal wellbore of less than 100m will be drilled to test the possibility of hydro-fracturing and whether it is commercially viable to extract gas.

No reputable expert will claim that this is a 100 per cent safe technology because there are no safe technologies. But Bulgaria's natural environment is damaged much worse by the coal-burning power plants – the most polluted fields in Europe are those covered with ash from the power plants and that can be seen on satellite photographs. We now use that energy because we do not have an alternative. But if we do have an alternative and can reduce the risk to a minimum, as the developed economies of Canada and US are doing, it could be more kind on our nature. This is why the world looks at shale gas as a new green energy source that can ensure humanity's transition from fossil fuels to renewable energy sources.

Kristalina Stoikova holds a Ph.D in geology and is the scientific secretary of the Geological Institute of the Bulgarian Academy of Sciences. She has worked as a scientific consultant for several oil and gas exploration companies, including Texaco, acquired by Chevron in 2001. This first appeared in Capital weekly on January 26.