Coalbed methane

Coalbed methane is a natural gas that is adsorbed into coal, commonly known as firedamp. It is generally produced from coal seams that are either too deep, or of a

quality that is too poor for them to be mined. Coalbed methane is extracted from coal beds in more than a dozen countries throughout the world, particularly in the United States, Canada and Australia. China is also going to increase its production in the not-too-far-distant future. Coalbed methane is generally produced from vertical wells when the natural fractures (known as cleats) in the coal are large enough for them to produce significant flows of methane. When the cleats are too small, hydraulic fracturing is carried out. Horizontal wells are still only relatively rarely used because the coal seams are relatively thin (no more than a few metres). One of the distinctive features of coalbed methane is the fact that most of the methane is adsorbed into the coal itself (the rest of the gas can be contained in the coal cleats). The quantity of the methane absorbed depends on the coal’s "ranking" (see the 2010 Panorama article "World coal resources"), as well as its type. To recover this methane, the pressure has to be reduced. This is done by pumping out the interstitial water contained in the coal.

Ex.10 Retell the text “Natural power resources - fuel for the future”.

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Unit 2 Techniques of extracting oil and gas

Ex.1Read and translate the international words.

Geologist, structure, reservoir, seismic, gravimeter, magnetometer, petroleum, integrity, collection, base, mechanism, expansion, drainage, pump, technique, injection, natural gas, adequate, extraction, method, mobility, turbine, microbial, economic, start, steel, regulate, control, gravity, result, fluid, special.

Ex.2 Learn the new words.

survey – разведка, наблюдение, съемка	carbon dioxide – углекислый газ
explosion – взрыв	density- плотность
wellbore – ствол скважины	in-situ – на месте, на участке
expansion - расширение	technique – метод; аппаратура
gravity drainage - гравитационный режим пласта	steam - пар
dissolve -растворять	hydrocarbon - углеводород
beam pump - станок-качалка	conventional - обычный
enhanced – улучшенный, расширенный	well - скважина
gas lift - аэростатическая подъёмная сила, газлифт	viscosity – вязкость
reservoir drive - истечение нефти из пласта

Ex.3 Read and translate the text.

Technologies of oil and gas extracting

Geologists use seismic surveys to search for geological structures that may form oil reservoirs. The "classic" method includes making an underground explosion nearby and observing the seismic response that provides information about the geological structures under the ground. Gravimeters¹ and magnetometers² are also sometimes used in the search for petroleum.

Extracting crude oil normally starts with drilling wells into the underground reservoir. The oil well is created by drilling a hole into the earth with an oil rig. A steel pipe is placed in the hole to provide structural integrity to the newly drilled wellbore. Holes are then made in the base of the well to enable oil to pass into the bore. Finally, a collection of valves called a "Christmas Tree"³ is fitted to the top, the valves regulate pressures and control flows.

Oil extraction and recovery have three stages: primary, secondary and tertiary.

During the primary stage, reservoir drive comes from natural mechanisms: natural water displacing oil downward into the well, expansion of the natural gas at the top of the reservoir, expansion of gas initially dissolved in the crude oil, and gravity drainage resulting from the movement of oil within the reservoir from the upper to the lower parts where the wells are located.

Over the lifetime of the well the pressure falls. Then secondary recovery methods are applied. They rely on the supply of external energy into the reservoir Beam pumps and electrical submersible pumps are used to bring oil to the surface. Other secondary recovery techniques increase the reservoir's pressure by water injection, natural gas reinjection and gas lift⁴, which inject air, carbon dioxide or some other gas into the bottom of an active well, reducing the overall density of fluid in the wellbore.

Tertiary recovery begins when secondary oil recovery isn't enough to continue adequate extraction, but only when the oil can still be extracted profitably. Tertiary, or enhanced oil recovery methods (TEOR) increase the mobility of the oil in order to increase extraction.

These methods heat the oil, thus reducing its viscosity and making it easier to extract. Steam injection is the most common technique. A gas turbine is used to generate electricity and the waste heat is used to produce steam, which is then injected into the reservoir. This form of recovery is used extensively to increase oil extraction in the sites with very heavy oil. In-situ burning is another technique, but instead of steam, some of the oil is burned to heat the surrounding oil.

Microbial treatment⁵ is another tertiary recovery method. Special blends of the microbes are used to treat and break down the hydrocarbon chain in oil thus making the oil easy to recover as well as being more economic compared to other conventional methods.