Chapter 7 Separating and Treating Well Fluids

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Chapter 7 Separating and Treating Well Fluids
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Principles and Operation of Production Separators

• - Gas, oil and water separation was achieved by
• the difference in gravity, or weight, of
  each fluid.
• - Production separators 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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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
  
• uses the cooling effect of expanding high
  pressure 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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Water-removal

• Water-removal before the oil can be delivered
  to the pipeline
• Free water some of the water produced with the
  oil will not be mixed with it this is known as
  free water .

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Water removal
using

• -Treatment of free-water Free water
  knock out (FWKO)

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Treatment of oil-water or water-oil 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 ?? ??
• resinous
  substances
• 
  oil-soluble organic acids.

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Emulsions

• Emulsion a mixture in which one liquid, termed
  the
• dispersed phase, is
  uniformly distributed (usually as
• minute globules, in another
  liquid, called the
• continuous phase or the
  dispersion medium (phase))
• Oil water emulsion
• the oil is the dispersed phase, and
• the water (is ) the dispersion medium
  (or continuous phase )
• Water-oil emulsion
• the water is the dispersed phase, and
• the oil the dispersion medium

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Emulsions -- continue

• Stable emulsion will not break down into its
  components
• without some
  form of treating.
• Tight (difficult to break) or loose (easy to
  break) emulsion
• 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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Treatment of oil-water or water-oil emulsion
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 (???)
• (1) direct heater
• (2) Indirect heaterwater 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

• 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 operated 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
• 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
• by applying heat and/or
• adding hydrate inhibitor
• 
  ammonia
• 
  brine
• 
  glycol (???)
• 
  methanol (??)
• (2)dehydration,
• absorption (??) Liquid ???
• adsorption (??) Solid ???
• (3)The removal of undesirable components
  (H2S?CO2)
• Alkanolamine process
• Iron-sponge process
• Glycol/amine process
• Sulfinol process
• Molecular-sieve removal

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Prevention of hydrate formation

• Water is always necessary for hydrate formation.
• water always accelerates corrosion.

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Phase diagram for a pure single component
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Dehydration means removal of water

• Water vapors (as well as certain other vapor) are
  removes from gas by either
• (1) the absorption process, or
• (2) the adsorption process
• Absorption process --
• Water vapor may be removed from natural gas
  by bubbling the gas counter currently through
  certain liquids that have a special attraction or
  affinity for water.

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Dehydration means removal of water

• Adsorption --
• Some solids also have an affinity for water,
  and when gas flows through a bed of such granular
  solids, the water is retained on the surface of
  the particles.
• Desiccant --
• The liquid or the solids that has the
  affinity for water in either process is called a
  desiccant.
• Dehydration equipment
• -- The liquid-desiccant dehydrator
• -- The solid-desiccant dehydrator

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Removal of undesirable components

• 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 (??)
• -- propane and/or propylene (at least
  95)
• -- vapor pressure lt 215 psig at 100 0F
• Commercial Butane (??)
• -- butanes and/or Butane (at least 95)
• -- vapor pressure lt 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 lt 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 pressure10-34psi
• Percentage evaporated at 140 F 24-85
• Percentage evaporated at 275 F not less then
  90

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• Vapor pressure, usually referred to as Reid vapor
  pressure (RVP), used to designate grades.
• Motor fuels 5-8psi RVP
• Very light oils (60-70AIP) 12psi RVP
• Natural gasoline product 14-26 psi RVP

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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
  tank battery
• storage facilities
• -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
• bottle-sampling
  method
• Gas sampling

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Treatment of emulsion

• Therefore,
• To break down a petroleum emulsion
• ? the properties of emulsifying agent
  must be
• neutralized or destroyed .
• By application of
• (1) heat
• (2) chemicals
• (3) electricity, or
• (4) combination of these (heater treater )

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The well stream

• The well stream -- high-velocity, turbulent,
• constantly expanding mixture of gases and
  hydrocarbon liquids,
• intimately mixed with water vapor, free water
  solids and
• other containment.

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The bottle test

• -- It is used to help determine which chemical
  can most
• effectively break the emulsion from a
  given well, lease, or
• field.
• Result from a bottle test also indicate the
  required ratios of treating compound to emulsion.
  That is,
• the smallest around of the proper
  chemical need to
• satisfactorily break the volume of
  emulsion being
• produced.
• Application of electric current
• Usually in conjunction with heat
  chemicals.

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Gun barrel or Wash tank

• Sometimes an oil-water emulsion is not stable,
• Given enough time, the water will settle to the
  bottom of a tank and oil will rise to the top.
• The settling vessel used for this kind of
  separation method is called a gun barrel or wash
  tank.

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Stock tanks (storage tanks )

• Once the oil is clean enough to meet pipeline
  specifications, it is flowed into storage tanks,
  sometimes called stock tanks.
• Tank battery-

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Stock tanks (storage tanks )

• Two basic types of stock tanks
• bolted steel
• welded steel
• Bolted steel tanks
• - 500 bbl or larger assembled on location.
• Welded steel tanks
• - 90 bbl to several thousand bbls.
• Welded in a shop and then transported as
  a complete unit
• to the site.
• Most tanks are equipped with a bottom drain out
  let for draining off basic sediment and water
  (BSW).

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Vapor Recovery System

• when oil is treated under pressure and then goes
  to a stock tank at pear atmospheric pressure,
  some of the liquid hydrocarbons flash, or
  convent, to gas.
• -- In past years, flash gas or vapor were
  vented to the atmosphere.
• -- Governmental agencies now insist on vapor
  recovery in order to
• reduce air pollution.
• A vapor recovery unit consists of
• a control pilot mounted on a tank for
  compressor control,
• a scrubber to keep the liquid hydrocarbons
  out of the
• compressor,
• a compressor, and
• a control panel.

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Treating oil-field emulsions