by Chris Marker
Fossil fuels have long been the main source of energy for the world. With oil and coal reserves being gradually depleted, natural gas from shale is becoming a more important fossil fuel.
Shale is a fine grained sedimentary rock. It was formed millions of years ago by the accumulation of sediments typically deposited in very slow moving water such as swamps, lakes, floodplains etc. With time and pressure, organic material such as plants and animals buried within this sediment produces the gas methane. Conventional natural gas resources are created by the methane gas moving from the organic-rich source formation into a permeable reservoir rock. This reservoir rock is trapped by an overlying layer of impermeable rock. Shale gas resources form within the organic-rich shale source rock. The low permeability of the shale means most of the gas is prevented from moving into more permeable reservoir rocks.
Shale gas was first extracted in the 1800s but it is only since the 1970s that significant research in the area has been performed and commercially viable production only started in the 1980s. To extract the shale gas a process of hydraulic fracturing or “fracking” is used. In this process a hole is drilled down into the shale rock layer; often the layer will be wider than it is thick so the drill bit can be turned to face horizontally when it reaches the layer. A long channel or well bore will be then be created, down which concrete will be pumped to stop the leaking of fluids. An electric current is then used to create holes in this concrete casing and the surrounding shale. Water, sand and chemicals are injected into the well bore and the holes at high pressure where it fractures the shale causing gas in the shale to be pushed into the well bore. By inserting a temporary plug into the well bore the process of perforating and fracking can be repeated and the gas can be released to the surface by drilling out these plugs.
Shale gas and fracking has proved controversial for a number of reasons:
• The water used in fracking can contain harmful chemical substances that could be released by leaks or faulty well construction. This polluted water could contaminate drinking water sources. There have been some claims in America that shale gas production has caused tap water to ignite. There is also the question of where to get the large amounts of water needed for fracking from, the environmental impact of this and also how to deal with the large amounts of wastewater produced by the fracking process.
• There is a concern that fracking can produce small earthquakes. The wastewater produced in the process is frequently injected into deep wells in the subsurface of the earth causing small earthquakes. Two small earthquakes of 1.5 and 2.2 magnitude hit the Blackpool area in England this year after fracking operations had been performed.
• The environmental question of using fossil fuels also needs to be considered. Shale gas produces significantly lower levels of the harmful greenhouse gas carbon dioxide than oil or coal. Unlike some green energy sources, however, it still produces this gas and many advocates of green energy worry that funds for research into this may be diverted to shale gas production instead.
Despite these controversies production of shale gas is increasing. Shale gas significantly boosts the world supplies of natural gas and proponents argue that, as long as it is performed and regulated properly, fracking is safe. It is estimated that there could be as much as £70bn of reserves in rocks deep under south Wales, whilst the US and Canada could have enough reserves to provide 100 years of gas energy. The production of more shale gas offers western governments the prospect of increased energy security and could also drive gas prices down, good news for consumers at a time of increasing energy prices. Until a permanent green energy solution to our worlds energy needs is discovered, shale gas and fracking is here to stay.
Inspec covers all aspects of shale gas and fracking, control terms include:
• drilling (geotechnical)
• fossil fuels
• geophysical prospecting
• hydrocarbon reservoirs
• natural gas technology
• natural resources
• offshore installations
• shale gas
• A8605 Energy and environmental policy, economics and legislation
• A8610B Fossil fuels
• A8670 Environmental science
• A8675T Waste disposal (environmental science technology)
• A9160B Mechanical and acoustic properties of rocks, minerals and soil
• A9130B Seismic sources
• A9165 Geophysical aspects of geology and mineralogy
• B7730 Pollution detection and control
• B8210 Energy resources
• E0230 Environmental issues
• E3020 Mining, oil drilling and natural ga