Compressors

Compressors do the same for gas streams as pumps do for liquids- creating a pressure differential that moves the gas through the system.

Most oilfield compressors are large positive-displacement, reciprocating machines used to inject low-pressure associated gas into high-pressure pipelines. Large piston size is necessary because compression ratios are as high as 10: 1. That is, the gas is compressed to 1/10 of its initial volume. These machines often have multiple compression stages, and are “integrated “, with the gas-fired engine and compressor in a single package.

Centrifugal compressors are infrequently used in production operations. Pipeline boosting is the primary application for these extremely high-speed, high-volume machines.

4.7 Read and translate:

VALVES

Several types of valves are used in surface facilities. Their function is either blocking (open or closed) or control (throt -

tling). Some of the common valves are

1 Butterfly (wafer) valves are inexpensive block valves used for low-pressure, non-critical service; they consist of

a steel wafer inside the pipe that rotates 90º to either block or allow flow

2 Ball valves are used in higher-pressure, more demanding situations; a sphere with a conduit through it allows flow, or if rotated 90º, seals against flexible rings to block flow

3 Check valves have a hinged flapper that swings open to allow flow in one direction but swings shut and blocks flow in the other direction

4 Globe valves are the most commonly used control valves; they raise or lower a plug to increase or reduce flow

4.8 Speak on the types of valves

5.1 Read and translate Text 5

Text 5

LNG

(liquefied natural gas)

Liquefying methane into LNG generates a compact, higher valued form of energy that can be economically transported around the world by ship. This allows the development of gas fields that would otherwise be economic because they are too remote from potential consumers to justify construction of a pipeline.

The purpose for changing methane from a gas to a liquid is entirely to facilitate its transportation. There is no market for the liquid as such, so it is regasified at the landing port and delivered to the consumer through conventional natural gas pipeline systems. In some cases, it is blended into a gas stream to supplement local supplies of natural gas. The problem with using LNG directly is that it must be stored at cryogenic(extremely cold) temperatures to prevent vaporization. Such heavily insulated storage is too bulky and expensive for most applications, but experimentation in direct use of LNG is ongoing. For example, its use in large trucks is being examined.

5.2 Comprehension questions:

1 What allows the development of gas fields?

2 What facilitates methane transportation?

3 Does any problem with using LNG directly exist?

5.3 Make your own sentences using the following:

to deliver, gas, a pipeline, to install, gas flow, a control system, to regulate, to construct, a shore, the liquefaction plant, to transport, two-phase flow, liquid, alternating slugs.

5.4 Make all possible questions to the extract:

Although increased pressure and reduced temperature will liquefy petroleum gases, the extreme volatility of methane dictates that cryogenic cold (-260º F) be used to liquefy and transport LNG.The liquefaction plant therefore amounts to a very large refrigeration plant. The plants are built onshore and include marine loading facilities. In the future, floating plants may be used in some protected overwater situations.

5.5 Make negative sentences. Translate them.

1 Cas moving through a piping system constantly expands and contracts from the normal variations in pressure and temperature.

2 High-gravity, low-viscosity crude oil normally separates easily from water, but lower gravity, higher viscosity crudes often form emulsions that complicate separation.

3 Produced water is considered a contaminant of crude oils, so purchasers accept only traces of sediment and water.

4 Heat reduces oil viscosity and coalesces small water droplets into bigger ones; both effects help the water to settle to bottom of the treating vessel.

5 Produced fluids enter most wash tanks through flumes designed to reduce turbulence in the tank.

5.6 Retell Text 5

6.1 Read and translate Text 6

Text 6