Chapter 8

Chapter 8
Separating and Treating Well Fluids
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Chapter 8 Separating and Treating Well Fluids
- - Well fluids produced - - Mixture of oil, gas and water
 the force of gravity
Separation of oil, gas and water
Principles and Operation of Production Separators
─ Gas, oil and water separation was achieved by
the difference in gravity, or weight, of each fluid.
─ Production separator do the same job, except they
are built to handle a continuous-flow stream and
have features to improve separation efficiency
under flow conditions.
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Three general types of separators
─ Horizontal separator
─ for high-pressure and medium-pressure service
─ Vertical separator
─ for low-pressure service (generally)
─ Spherical separator
─ more compact and cheaper
─ limited separation space and liquid surge capacity
─ for low-volume remote platforms
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Internal Structure of Separators
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Separation methods
─
Stage separation method
─
Low-temperature separation method
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Stage separation method (two stage separation)
Any number of separators may be used in stage separation as
long as stage operates at successively lower pressures.
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Low-temperatures separation method

It is used to handle the production from high-pressure gas
wells

Well fluids – a mixture of gas & some light liquids

Dehydration – the removal of water vapor from gas
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Low-temperature separation method
For high-pressure gas wells (well fluids: mixture of gas and
some light liquids)
─ Dehydration to remove water vapor from gas
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Emulsion

Water and oil are immiscible.
 These two liquids will form an emulsion only
(1) if there is sufficient agitation to disperse one liquid as
droplets in the other , and
(2) if there is an emulsifying agent , or emulsifier , present.

Emulsifying agents – asphalt 瀝青 柏油
resinous substances
oil-soluble organic acids.
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
Stable emulsion – will not break down into its components
without some form of treating.

Emulsion – tight (difficult to break) or loose (easy to break)
Depending on –
(1) the properties of the oil & water
(2) the percentage of each found in the emulsion
(3) type and amount of emulsifier present .
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Treating oil-field emulsions
Emulsion 之定義
dispersion

water
phase


continuous
Oil - Water Emulsion (oil in water) 


 oil - dispersed phase
Water - oil Emulsion (water in oil)
Oil and water to form an emulsion only
(1) sufficient agitation
asphalt 瀝青


(2) emulsifying agent or emulsifier exist  resinous substances
 oil - soluble organic acid

Tight 
 difficult to break
Emulsion
Loose
 easy to break





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Water removal
─Treatment of free-water
using
Free water knock out (FWKO)
─Treatment of oil-water or water-oil emulsion
（1）Heat
（2）Chemicals
（3）Electricity
（4）Combination of these (heater- treater)
flow treater or emulsion treated
（5）Gun barrel or wash tank if emulsion is not stable
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Application of heat

One theory assumes that very small droplets, like those found
in emulsions, are in constant motion even when the emulsion
itself is not rest .
Application of heat
(1) Heat increases the movement are makes the droplets strike
each other with greater force and frequency.
(2) Heat also reduces the viscosity – the resistance to flow – of
the oil.
Heater (加熱器)
(1) direct heater
(2) Indirect heater—water bath (fig5.22 P.161)
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Application of chemicals

One theory suggests that chemical should be used strictly to
neutralize the emulsifying agent.
Thus, to break a water-in-oil emulsion,
another emulsifying agent to produce oil-in-water emulsion
should be added.

Another theory suggests the chemicals should make the film of
emulsifying agent around the water droplet in a water-in-oil
emulsion very rigid.
Thus, to break rigid film
apply heat or
add chemical.
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Heater-treater

also called a flow treater or an emulsion treater.

Heater-treater (or call flow treater, or emulsion treater)


apply the effects of
Chemicals, heat , settling, and often electricity
Any or all of the following elements may be included in a treater:
•
•
•
•
•
•
•
oil-gas separator,
free-water knockout,
heater,
water, wash, filter section,
stabilizing section,
heat exchanger, and
electrostatic field.
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Treater

Treater can be operator at atmospheric pressure,
often be operated under low working pressure.
 A low-pressure, second-stage separator as well as
treating unit.
When flow-line pressure are low, it can be used as a
primary separator thus eliminating the need for a regular
separator. (fig 5.25, P.164)
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Treating natural gas

Field processing of natural gas consist of four basic processes:
(1)
the gas must be separated from free liquids such as crude oil,
hydrocarbon condensate, water , and entrained solids,
(2) the gas must be processed to remove condensable and
recoverable H.C. vapors
(3) the gas must be treated to remove condensable water vapor,
which might cause hydrate formation
(4) the gas must be treated to remove other undesirable components,
such as hydrogen sulfide or carbon dioxide.
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Treating Natural Gas
The primary treatments for natural gas involve
（1）prevention of hydrate formation
Heat
Hydrate inhibitor: ammonia
brine
glycol (乙二醇)
methanol (甲醇)
（2）dehydration,
absorption (吸收) – Liquid 乾燥劑
adsorption (吸附) – Solid 乾燥劑
（3）The removal of undesirable components (H2O、CO)
Alkanolamine process
Iron-sponge process
Glycol/amine process
Sulfinol process
Molecular-sieve removal
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Removal of undesirable components
Hydrogen sulfide (H 2S) 

  acid gases
 Carbon dioxide (CO 2 ) 

Alkanolamine process
-- It is a continuous-operation liquid process that uses absorption
for the acid-gas removal, with subsequent heat addition to string
the acid-gas component from absorbent solution.

Other processes that are used to removal H2S & CO2 are
The Iron-sponge process,
The glycol/amine process,
The sulfinol process, and
The molecular-sieve removal.
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Typical Natural Gas Components
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
Casinghead gas
-- gas produced with oil from an oil well.

Residue gas
-- any gas suitable for as commercial natural gas that comes
from a processing plant.

Sweet gas
--the content of hydrogen sulfide, other sulfur compounds,
and carbon dioxide is low enough that gas may be sold
commercially without further effort to remove these
compounds.

Sour gas
--the opposite of sweet gas.
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Types of Natural Gas Liquids

Commercial propane (丙烷)
-- propane and/or propylene (at least 95%)
-- vapor pressure < 215 psig at 100 0F

Commercial Butane (丁烷)
-- butanes and/or Butane (at least 95%)
-- vapor pressure < 70 psig at 100 0F
-- At least 95% must evaporate at 34 0F or lower in a
standard test.

Liquefied Petroleum Gas (LPG)
-- A mixture of commercial propane and commercial butane.
-- maximum vapor pressure < 215 psig at 100 0F
At least 95% must evaporate at 34 0F or lower in a
standard test.
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Types of Natural Gas Liquids

Natural Gasoline
--This petroleum product is extracted from natural gas
--specifications:
• Vapor pressure:10-34psi
• Percentage evaporated at 140 F: 24-85%
• Percentage evaporated at 275 F: not less the 90%
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The Storage System
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The Storage System
Stock tanks (or storage tanks)
─Tank battery
─separation equipment
treating equipment
storage facilities
tank battery
─stock tanks
Bolted steel tank – 500 bbls or larger; assembled on location
Welded steel tank – 90 bbl to several thousand bbls;
welded in a shop and then transported
as a complete unit to the site
─Vapor Recovery System
─LACT (Lease automatic custody transfer) unit
Oil sampling
thief – sampling method
Botlle – sampling method
Gas sampling
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
Low – temperature separation method

uses the cooling effect of expanding high – pressure gas
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