Chapter 1: Properties of Natural Gas

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Chapter 1 Properties of Natural Gas

• Topics to be covered today
• Gas viscosity
• Water Vapor Content of Gas
• Gas Hydrates

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Chapter 1 Properties of Natural Gas

• Topics to be covered today
• Gas viscosity
• Water Vapor Content of Gas
• Gas Hydrates

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Viscosity of Gas Mixtures

• Lee- Gonzales-Eakin (LGE) method (1966)
• Where

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Viscosity of Gas Mixtures Cont.
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Viscosity of Gas Mixtures Cont.

• And
• rg Gas density at reservoir pressure and
  temperature lb/ft3
• T Reservoir Temperature in Rankin
• M Apparent molecular mass of the gas mixture

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Example on gas Viscosity Calculations

• Calculate the gas viscosity using LGE method
• Given
• Ppr 4.46
• Tpr 1.7
• Pressure 3000 psia
• Temperature 150o F
• M 17.415

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Solution

• Z factor from chart is 0.89
• Gas density is

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Solution Cont.

• Calculate K, X, and Y

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Solution Cont.

• The gas viscosity is

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Chapter 1 Properties of Natural Gas

• Topics to be covered today
• Gas viscosity
• Water Vapor Content of Gas
• Gas Hydrates

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Chapter 1 Properties of Natural Gas

• Water Vapor Content of Gas
• The amount of vapor present in the gas depend on
• Pressure
• Temperature
• Composition

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Water Vapor Content of Gas

• Bukacek Developed Empirical correlation for Water
  Vapor Content of Natural Gas
• Where
• A(T) and B(T) are functions dependant on
  temperature
• W is water vapor content in lbm/MMscf
• P is absolute pressure psia

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Water Vapor Content of Gas

• The temperature functions of Bukaceks
  correlation are
• Where
• T is temperature in oR

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Water Vapor Content of Gas (graphical technique)

• McCain graphs from Bukaceks data

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Water Vapor Content of Gas Example 1.20

• Calculate W vs. p at 300 oF
• For Pressures
• 2000
• 4000
• 6000
• 8000

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Solution Example 1.20

• Calculating the temperature functions for
  Bukaceks correlation

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Solution Example 1.20

• Calculating W using Bukaceks correlation

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Chapter 1 Properties of Natural Gas

• Topics to be covered today
• Gas viscosity
• Water Vapor Content of Gas
• Gas Hydrates

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Gas Hydrates

• Hydrates are physical formation of crystalline
  solids by combination of water vapor, gas and
  pressure and temperature conditions
• This phenomenon occurs at pressure and
  temperature considerably above the freezing point
  of water

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Primary Conditions Promoting Formation of Gas
Hydrates

• Gas at or below its water dew-point
• Low temperature
• High pressure
• High velocity
• Pressure pulsation
• Introduction of a small hydrate crystal
• Agitation
• Presence of H2S and CO2

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Operating Conditions Promoting Formation of Gas
Hydrates

• Hydrate formation at constant pressure caused by
  sudden drop of temperature
• Sudden expansion will be accompanied by a
  temperature drop resulting in hydrate formation

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Physical Sites for Gas Hydrates Formation

• Pipe elbows
• Orifice
• Choke
• Backpressure regulator

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Gas Hydrates Formation Line

• The hydrates will occur on the LHS of the line

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Gas Hydrates Formation Line

• Hydrates formation lines for methane and
  different gravity gases
• Avoid LHS