What is shale?
Shale is a sedimentary rock characterized by schistosity and schistose structure, composed from parallel minerals oriented in one direction. Also shale is cleavage, i.e. the mineral easily decomposes into thin plates.
Unconventional hydrocarbons – oil and gas deposited in shale rocks. It is the same, as oil and natural gas produced from the other layers of the rocks, except that they are laying in tight rocks.
Shale hydrocarbons in the world
The USA and Canada are the most experienced in shale hydrocarbons exploration and production. These countries have been producing shale gas /oil for over 20 years.
According to the calculations of scientists the largest deposits of shale oil, around 2 billion barrels, lie in the underground of the USA, also approximately 50 mln barrels in Hong Kong, Italy and Brazil.
The largest hypothetic shale gas resources are expected to be in China, the USA, Argentina, South African Republic, Canada, Australia, Algeria, Brazil. Shale gas resources in France amount to around 180 trillion cubic meters, in Poland – about 187 trillion cubic meters.
More and more countries recently initiated exploration and production of these natural resources. Poland, United Kingdom, Spain are the leading countries in shale gas and oil exploration in Europe.
Shale hydrocarbons in Lithuania
Lithuanian oil producing companies are currently producing conventional oil. However, in recent years the interest arose also in unconventional hydrocarbons, i.e. shale oil and shale gas. It is believed that in Lithuania they are mostly deposited in clay. It is difficult to say how much of these natural resources are deposited in Lithuania; resources need to be prospected first.
Everything about well drilling
How is the drilling of a standard shale hydrocarbons well going on?
The first stages of the drilling of shale oil or gas well are the same as of a standard oil well. The well is being drilled vertically up to 2 km depth using water and drilling mud. This mud is used to cool a drilling bit, protect the other drilling equipment from over-heating and lift the drilling cuttings to the surface.
When the drilling string reaches the target depth, a casing made of special steel, so called “surface casing", and run into the well. The casing allows stabilizing the well. To support the wellbore even more, the casing is cemented. Afterwards, the well is cased with an intermediate casing, which is also cemented. One by one several additional steel casings are run into the wellbore.
After completion of the above initial well construction stages, it is proceeded further with the other very important stages, i.e. horizontal drilling and hydraulic fracking.
Two safe technologies tested long ago and used in the world for years are being used for the extraction of oil and gas accumulated in shale rocks, i.e. horizontal drilling and hydraulic fracking.
Horizontal drilling begins at a certain depth (it varies from well to well). At that point the trajectory of a well is directed almost horizontally to span a larger area of the underground with one wellbore.
Hydraulic fracking is a process, during which a mixture of water and sand is being pumped into a wellbore. Water and sand makes 99.5% of the mixture, while the remaining 0.5% is additives. The mixture is pumped into the rocks through the small holes of injecting unit. The mixture released with a big force creates the network of small fractures filled with sand, through which oil or gas start flowing.
Hydraulic fracking has been used all over the world for more than 60 years. This technique was and is being used in conventional oil wells in Europe as well as in Lithuania.
Hydraulic fracking method started to be applied in the wells in Lithuania almost 20 years ago.
The compounds of the mixture are the usual chemicals used in our daily life and household, i.e. soda, salt, etc.
All these materials are certified, hold safety data sheets and are permitted for the use in the entire European Union.