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1. Study the terms:

Oil extraction, n – getting oil from the ground (syn. recovery)

Reservoir drive, n – natural forces that push oil to the surface

Displace, v – to take the place of something by pushing it out

Expansion, n – the result of becoming wider or larger

Gravity drainage, n – a gravitational reservoir drive, free flow of oil inside the reservoir

Force, v – to make something happen using power or strength

Diminish, v – to decrease, slow down

Inject, v – to pump down

Artificial, adj – man-made, not natural

Wellbore, n – the borehole of the well

Enhanced, adj – increased, improved

Surfactants, n – reagents which are active on the surface

Detergents, n – cleaning reagents

Residual oil, n – oil which is left in the reservoir after the recovery

Permeability, n – the ability to let liquids flow through

Lease pumper, n – an oil production operator at the site

2. Match the words 1-14 to their translations a-n:

1) external

2) submersible

3) bottom

4) density

5) viscosity

6) water flooding

7) surface tension

8) waste heat

9) recovery rate

10) shale

11) sandstone

12) rocks

13) tar

a) дно

b) внешний

c) заводнение

d) плотность

e) погружной

f) вязкость

g) порода

h) дебит нефти

i) остаточное тепло

j) поверхностное натяжение

k) сланцевая глина

l) гудрон (вязкий остаточный нефтепродукт)

m) песчаник

3. Choose the odd one out in each line and explain your choice:

1) permeability, density, viscosity, recovery

2) external, bottom, arificial, residual

3) steam, shale, sandstone, tar

4) inject, tension, displace, diminish

5) expansion, tension, gravity, surfactant

4. Match the two parts of the sentences:

1) In most cases it is vital to apply enhanced

2) Gas cap drive is a natural

3) Steam is injected into the reservoir to force

4) After the pressure in the reservoir

5) Secondary and tertiary recovery methods are applied in order to increase

6) One of the most common secondary recovery method is

a) reservoir drive which includes the expansion of the natural gas at the top of the reservoir

b) diminishes, secondary recovery methods are applied.

c) oil recovery techniques to increase extraction.

d) water flooding.

e) the oil to the surface.

f) the recovery rate.

5. Read the text and say if the statements are true or false:

1) There is only one natural drive that pushes oil to the surface.

2) Primary recovery gives the least recovery rate.

3) During secondary recovery external energy comes from injections of fluids into the reservoior.

4) In some tertiary recovery techniques, oil is heated in order to increase its viscosity.

5) Tertiary recovery is used only when it is economically profitable.

6) The lighter the oil, the easier it is to recover.

Primary recovery

D uring the primary recovery stage, reservoir drive comes from a number of natural mechanisms. These include: natural water displacing oil downward into the well, expansion of the natural gas at the top of the reservoir (gas cap drive), expansion of gas 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.

Fig. 1 А gas-cap-drive reservoir

While the underground pressure in the oil reservoir is sufficient to force the oil to the surface, all that is necessary is to place an arrangement of valves (the Christmas tree) on the well head to connect the well to a pipeline network for storage and processing. Recovery factor during the primary recovery stage is usually 5-15%.

Sufficient, adj – достаточный

Storage, n – хранение (v – store)

Process, v – перерабатывать (syn. refine)

Beam pump, n – балансировочный насос

Properties, n – свойства

Secondary recovery

O ver the lifetime of the well the pressure will fall, and at some point there will be insufficient underground pressure to force the oil to the surface. After natural reservoir drive diminishes, secondary recovery methods are applied. They rely on the supply of external energy into the reservoir in the form of injecting fluids to increase reservoir pressure, as a result replacing or increasing the natural reservoir drive with an artificial drive. Sometimes pumps, such as beam pumps and electrical submersible pumps (ESPs), are used to bring the oil to the surface. Other secondary recovery techniques increase the reservoir's pressure by water injection, natural gas reinjection and gas lift, which injects air, carbon dioxide or some other gas into the bottom of an active well, reducing the overall density of fluid in the wellbore. Typical recovery factor from water-flood operations is about 30%, depending on the properties of oil and the characteristics of the reservoir rock. On average, the recovery factor after primary and secondary oil recovery operations is between 30 and 50%.

Tertiary recovery

Tertiary, or enhanced oil recovery (EOR) methods increase the mobility of the oil in order to increase extraction.

Thermally enhanced oil recovery methods (TEOR) are tertiary recovery techniques that heat the oil, thus reducing its viscosity and making it easier to extract. Steam injection is the most common form of TEOR, and is often done with a cogeneration plant. In this type of cogeneration plant, a gas turbine is used to generate electricity and the waste heat is used to produce steam, which is then injected into the reservoir. In-situ burning is another form of TEOR, but instead of steam, some of the oil is burned to heat the surrounding oil.

Occasionally, surfactants (detergents) are injected to change the surface tension between the water and oil in the reservoir, mobilizing oil which would otherwise remain in the reservoir as residual oil.

Tertiary recovery begins when secondary oil recovery isn't enough to continue adequate extraction, but only when the oil can still be extracted profitably. This depends on the cost of the extraction method and the current price of crude oil. When prices are high, previously unprofitable wells are brought back into use and when they are low, extraction is curtailed. Tertiary recovery allows another 5% to 15% of the reservoir's oil to be recovered.

Cogeneration plant, n –

когенерационная тепловая установка

In-situ, wc – на месте проведения работ

Curtail, v – сокращать

Adjacent water, n – прилегающие воды

Evaluate, v – оценивать (syn. estimate)

Appropriate, adj – подходящий

Recovery rates

The amount of oil that is recoverable is determined by a number of factors including the permeability of the rocks, the strength of natural drives (the gas present, pressure from adjacent water or gravity), and the viscosity of the oil. When the reservoir rocks are "tight" such as shale, oil generally cannot flow through but when they are permeable such as in sandstone, oil flows freely. The flow of oil is often helped by natural pressures surrounding the reservoir rocks including natural gas that may be dissolved in the oil (gas oil ratio), natural gas present above the oil, water below the oil and the strength of gravity. Oils can be of a large range of viscosity from liquids as light as gasoline to heavy as tar. The lightest forms result in higher extraction rates.

Petroleum engineering is the discipline responsible for evaluating which well locations and recovery mechanisms are appropriate for a reservoir and for estimating recovery rates and oil reserves before actual extraction.

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