3. Discussion

Make a presentation on different types of oil traps. Draw a picture of principal types of oil traps and describe them.

Chapter 2.

LEARNING OBJECTIVES:

Having worked through this chapter the student will be able to:

• define the typical composition of natural gas

• describe chemical and physical properties of natural gas

• describe the discovery and early uses of natural gas

• list and describe the ways in which methane may be formed

• describe conventional gas reservoirs

• list and describe unconventional gas reservoirs

• list and describe the use and ways of measurement of natural gas

Unit 1.What is Natural Gas?

Active vocabulary

1	makeup	состав
	sulphide	сульфид
	hydrogen sulphide	сероводород
	wet gas	«жирный» газ
	He (helium)	гелий (порядковый номер в таблице Менделеева - 2)
	Ne (neon)	неон (порядковый номер в таблице Менделеева - 10)
	Xe (xenon)	ксенон (порядковый номер в таблице Менделеева - 54)
	trace	незначительное количество, остаток (чего-л.); след
	gas condensate	газоконденсат
	absorption	всасывание, впитывание; абсорбция, поглощение
	adsorption	адсорбция, поверхностное поглощение
	asphyxiant	удушающее отравляющее вещество
	blast	взрыв
	outgassing	удаление газа, дегазация
	kaolinite	каолинит, каолинитовая группа глин
	chlorite	хлорит, соль хлористой кислоты
	maturation	созревание, формирование, образование
	associated gas	попутный газ (получаемый из коллектора нефти)
	retrograde condensation	ретроградная конденсация
	flammability/ flammable	воспламеняемость, воспламенимость/ огнеопасный; легковоспламеняющийся
	formation water	пластовая вода
	carbon monoxide	окись углерода, угарный газ
	condensate accumulation/ condensate pool	газоконденсатная залежь
	clean burning	полное сгорание
	ferrous iron	двухвалентное железо
	residential use	бытовое использование
	gas utility	коммунальное газоснабжение
	natural gas liquids	газоконденсат, газовый бензин
	natural gasoline	газоконденсатный бензин; газовый бензин
	liquefied petroleum gas	сжиженный нефтяной газ (пропан-бутановые фракции)
	penetrating	проникающий
	sufficient	достаточный
	hazardous	опасный, рискованный
	odorless	без запаха, непахнущий
	pure	чистый; беспримесный
	combustible	воспламеняемый, горючий
	rare	разрежённый (о газе)
	distinct	отчётливый, определённый, явный
	confined	ограниченный в своём распространении
	to elevate	поднимать, повышать
	to refine	очищать (от примесей), рафинировать; повышать качество
	to remove	удалять; отделять
	to take up	поглощать; занимать
	to liquefy	превращаться в жидкость, таять, смягчаться
	to dull	притуплять, уменьшать
	to take up	поглощать; занимать
	to liquefy	превращаться в жидкость
	to refine	очищать (от примесей), рафинировать; повышать качество
	to remove	удалять; отделять
	to take up	поглощать; занимать
	to liquefy	превращаться в жидкость, таять, смягчаться
	to dull	притуплять, уменьшать
	to take up	поглощать; занимать
	to liquefy	превращаться в жидкость
	British thermal unit	Британская тепловая единица (БТЕ) - количество теплоты, необходимое для повышения температуры одного фунта воды на 1° F.
	ppt (parts per thousands)	частей на тысячу
	pound	фунт (мера веса=453,59 г.)
	therm	терм (единица теплосодержания газа) = 100 000 Британских тепловых единиц или 1.055 056 × 108 joules
	cubic foot	кубический фут (единица объёма = 28,317л = 28 317 см3)

Natural gas, in itself, might be considered a very uninteresting gas - it is colorless, shapeless, and odorless in its pure form. Quite uninteresting - except that natural gas is combustible, and when burned it gives off a great deal of energy. Unlike other fossil fuels, however, natural gas is clean burning and emits lower levels of potentially harmful byproducts into the air. We require energy constantly, to heat our homes, cook our food, and generate our electricity. It is this need for energy that has elevated natural gas to such a level of importance in our society, and in our lives.

Natural gas is a hydrocarbon mixture consisting primarily of methane and ethane, both of which are gaseous under atmospheric conditions. The mixture also may contain other hydrocarbons, such as propane, butane, pentane, and hexane. In natural gas reservoirs even the heavier hydrocarbons occur for the most part in gaseous form because of the higher pressures. They liquefy at the surface (at atmospheric pressure) and are referred to as natural gas liquids, gas condensate, natural gasoline, or liquefied petroleum gas. They may separate in some reservoirs through retrograde condensation or may be separated at the surface either in field separators or in gas processing plants by means of condensation, absorption, adsorption, or other modification.

Other gases that commonly occur in association with the hydrocarbon gases are nitrogen, carbon dioxide, hydrogen, hydrogen sulfide, and such noble gases as helium and argon. Because natural gas and formation water occur together in the reservoir, gas recovered from a well contains water vapour, which is partially condensed during transmission to the processing plant.

The composition of natural gas can vary widely, but below is a chart outlining the typical makeup of natural gas before it is refined.

Typical Composition of Natural Gas
Methane	CH4	70-90%
Ethane	C2H6
Propane	C3H8	0-20%
Butane	C4H 10
Carbon Dioxide	CO2	0-8%
Oxygen	O2	0-0,2%
Nitrogen	N2	0-5%
Hydrogen sulphide	H2S	0-5%
Rare gases	A, He, Ne, Xe	trace

Natural gas is considered 'dry' when it is almost pure methane, having had most of the other commonly associated hydrocarbons removed. When other hydrocarbons are present, the natural gas is 'wet'.

The physical properties of natural gas include colour, odour, and flammability. The principal ingredient of gas is methane, which is colourless, odourless, and highly flammable. However, some of the associated gases in natural gas, especially hydrogen sulfide, have a distinct and penetrating odour, and a few parts per million is sufficient to impart a decided odour to natural gas.

Before gas is distributed to end-users, it is odorized by adding thiols, to assist in leak detection. Natural gas is in itself, harmless to the human body -- unlike carbon monoxide, for instance, it is not a poison. However, natural gas is a simple asphyxiant and can kill if it displaces air to the point where the oxygen content will not support life.

Natural gas can also be hazardous to life and property through an explosion. Natural gas is lighter than air, and so tends to dissipate into the atmosphere. But when natural gas is confined, such as within a house, gas concentrations can reach explosive mixtures and, if ignited, result in blasts that could destroy buildings. Methane has a lower explosive limit of 5% in air and an upper explosive limit of 15%.

Natural gas can be measured in a number of different ways. As a gas, it can be measured by the volume it takes up at a pressure of 750 millimetres of mercury and a temperature of 15° С, commonly expressed in cubic metres (or in cubic feet at an absolute pressure of 14.73 pounds per square inch and a temperature of 60° F). While measuring by volume is useful, natural gas can also be measured as a source of energy. Like other forms of energy, natural gas is commonly measured and expressed in British thermal units (Btu). One Btu is the amount of natural gas that will produce enough energy to heat one pound of water by one degree at normal pressure. To give an idea, one cubic foot of natural gas contains about 1,027 Btus. When natural gas is delivered to a residence, it is measured by the gas utility in 'therms' for billing purposes. A therm is equivalent to 100,000 Btu's, or just over 97 cubic feet, of natural gas.

Natural gas has many uses, residentially, commercially, and industrially. Found in reservoirs underneath the earth, natural gas is commonly associated with oil deposits. Production companies search for evidence of these reservoirs by using sophisticated technology that helps to find the location of the natural gas, and drill wells in the earth where it is likely to be found. Once brought from underground, the natural gas is refined to remove impurities like water, other gases, sand, and other compounds. Some hydrocarbons are removed and sold separately, including propane and butane. Other impurities are also removed, like hydrogen sulfide (the refining of which can produce sulfur, which is then also sold separately). After refining, the clean natural gas is transmitted through a network of pipeline. From these pipelines, natural gas is delivered to its point of use.