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Introduction
Welcome to the Introduction to Production and Gas Processing Facilities core module
In this module, we are going to do a high-level review of production facilities and gasprocessing facilities
Introduction
SectionOne
State typical crude oil and produced water specifications Describe process flows for each stream in production facilities List problems associated with and strategies to deal with solids production,
e.g. sand, wax, asphaltenes
SectionTwo
List the components, including contaminants, found in produced gas streams State typical natural gas sales or transportation specifications Calculate higher heating value and Wobbe number List the products of a typical natural gas processing plant, their associated
markets, and describe common terminology
SectionThree
Describe typical process flows for each stream in gas processing facilities Explain the difference between gas conditioning to meet a HCDP
specification and gas processing to recover NGLs Describe shrinkage and how it is calculated
SectionOne
State typical crude oil and produced water specifications Describe process flows for each stream in production facilities List problems associated with and strategies to deal with solids production,
e.g. sand, wax, asphaltenes
SectionTwo
List the components, including contaminants, found in produced gas streams State typical natural gas sales or transportation specifications Calculate higher heating value and Wobbe number List the products of a typical natural gas processing plant, their associated
markets, and describe common terminology
SectionThree
Describe typical process flows for each stream in gas processing facilities Explain the difference between gas conditioning to meet a HCDP
specification and gas processing to recover NGLs Describe shrinkage and how it is calculated
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Production Facilities
Introduction to Production and Gas Processing Facilities Core
This section will cover the following learning objectives:
Learning Objectives
State typical crude oil and produced water specifications
Describe process flows for each stream in production facilities
List problems associated with and strategies to deal with solids production(e.g., sand, wax, asphaltenes)COPYRIG
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Crude Oil Value Chain
Why Is Processing Necessary?
To meet sales/disposal specifications• Crude oil / natural gas / NGLs
– Specifications are set contractually by:
1) The buyer
2) The transporter, or
3) By subsequent processing requirements
• Water– Disposal specifications are set externally by regulatory bodies or internally by reservoir/production
requirements
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Crude Oil Specifications
Water content (BS&W)• Typically varies from 0.3 to 3.0 vol%
• May be set by salt specification
Crude Oil Dehydration or TreatingWash Tanks/Settling Tanks/GunbarrelsHeater TreatersElectrostatic Treaters
Heater Treaters:
Used to heat the oil to lower its viscosity,
which makes it easier for water droplets to settle out of the oil.
Crude Oil Specifications
Water content (BS&W)• Typically varies from 0.3 to 3.0 vol%
• May be set by salt specification
Crude Oil Dehydration or TreatingWash Tanks/Settling Tanks/GunbarrelsHeater TreatersElectrostatic Treaters
Electrostatic Treaters:
A high voltage electric field that causes water droplets to vibrate and collide and form larger droplets that can more
easily settle out by gravity.
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Crude Oil Specifications
Vapor pressure• Typically near 1 atm, e.g., 10 psia [69 kPa],
12 psia [83 kPa], etc.
• Can be specified as a True Vapor Pressure(TVP) or Reid Vapor Pressure (RVP)
Crude Oil StabilizationStage SeparationCrude Oil Stabilizers
Stage Separation:
The most common way to meet a vapor pressure specification is to simply flash the oil from higher
pressures to lower pressures using a series of separators. The volatile components vaporize in
each separator and are removed from the oil.
Crude Oil Specifications
Vapor pressure• Typically near 1 atm, e.g., 10 psia [69 kPa],
12 psia [83 kPa], etc.
• Can be specified as a True Vapor Pressure(TVP) or Reid Vapor Pressure (RVP)
Crude Oil StabilizationStage SeparationCrude Oil Stabilizers
Crude OilStabilizers:
A distillation process that flashes out the volatile components
by the addition of heat.
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Crude Oil Specifications
Salt• Typical specification is 10 lb/1000 Bbl [30
g/m3]
• When the salt content > 200,000 to 300,000ppm, the BS&W of the oil leaving the lastdesalter stage should be 0.1% or lower
DesaltingDesalters (basically crude oil dehydration but salt content of water is diluted by injecting fresh water into the oil)
Desalting crude oilrequires two steps:
1) Dilute the salt content of theproduced water by mixing fresh
water into the oil stream.
2) Dehydrate the oil to a verylow BS&W specification to
minimize the amount of water in the oil.
Crude Oil Specifications
H2S• Typical specification is 50 ppmw
• Don’t confuse with organic sulfur
H2S StrippingHeat and stripping gas
Heat and Stripping Gas:
When we talk about an H2S specification, we're not talking
about organic sulfur, we're talking about soluble H2S in the crude oil. The most common way to meet
the H2S specification is to heat the oil and inject sweet natural gas to
strip the H2S out of the oil.
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Produced Water Specifications
Typical disposal options• Onshore
– Reinject into reservoir or waste water aquifer
– Surface disposal
– Evaporation ponds
• Offshore
– Reinjection
– Disposal to sea
Produced Water Specifications
Hydrocarbon content• Dispersed/dissolved
• Offshore specifications vary from 15-50 mg/l
• Lower in inland and coastal waters
• No fixed specification for reinjection—set byreservoir characteristics
DeoilingSkim TanksCorrugated Plate and Parallel Plate Interceptors (CPI and PPI)HydrocyclonesGas Flotation Units
Deoiling:
The process of removing
hydrocarbons from the water.
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Produced Water Specifications
Solids• Sand, corrosion products, scales
• Control of solids is very important inreinjection systems
FiltrationSettling tanksSeveral different types of flow-through filters
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Production Facility Block Diagram
Production Facility Block Diagram
Crude Oil / Condensate
Storage
Compression (optional)
Compression
Gas Processing
Crude Oil / Condensate
Stabilization & Dehydration
Produced Water Treating
Gas
Oil
Oil
Water
Water OilWater to Disposal
(Reinjection or Sea)
Crude Oil / Condensate Sales
NGL Sales
Gas Sales or Reinjection
CO2 and / or Sulfur Sales
Untreated Gas To Reinjection (optional)
Reservoir
Compression (optional)
Gas / Oil Water Separation
Oil Storage Oil StorageWater
Storage
Treater
VaporRecovery Unit
Circ. Pump
Pump
Oil
Vent
To Pit
Test Separator
GAS
GAS
Water
Production Separator
Inlet Production Manifold
Field Flow Lines
Heated FWKO
Example Onshore Oil Production Facility
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Oil export1850 psig [128 barg]
Gas export1850 psig [128 barg]
To FuelGas System
110°F [43°C]1200 psig [83 barg]
120°F [49°C]1200 psig [83 barg] 120°F
[49°C]500 psig[34 barg] 130°F
[54°C]180 psig
[12.4 barg] 150°F[66°C]
50 psig[3.5 barg]
150°F[66°C]4 psig
[0.3 barg]
Example Deepwater GoM Platform
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Paraffin (Wax) Deposition
1Rafael Mendes, “Rheological behavior and modeling of waxy crude oils in transient flows”, University of Paris-Est, 2015.
• You will remember that one of the topics we mentioned inthe crude oil value chain discussion was the presence ofsolids in the production stream.
• The first solid we will discuss is wax or paraffin.
• Waxy crude oils will have a significant quantity of long,usually straight-chain alkane type molecules, that at roomtemperature, exist as a solid.
• As an example, n-C20, also referred to as isocane, has amelting point of 27°C [80°F].
• A crude oil containing significant amounts of alkane (orparaffin) hydrocarbon molecules heavier than about C18 willoften exhibit wax deposition in production and pipelinesystems.
Paraffin Deposits in Piping
Waxy Crude Oil Sample1
Paraffin (Wax) Deposition
1Rafael Mendes, “Rheological behavior and modeling of waxy crude oils in transient flows”, University of Paris-Est, 2015.
2. Pour pointThe temperature at which a fluid ceases to flow. Highpour points usually occur in crude oils that havesignificant paraffin content. This phenomenon can occurwith light oils as well as heavy oils
1. Cloud pointThe temperature at which wax crystals first start to formin a crude oil. Also referred to as the Wax AppearanceTemperature (WAT).
Paraffin Deposits in Piping
Waxy Crude Oil Sample1
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Paraffin (Wax) Deposition
1Rafael Mendes, “Rheological behavior and modeling of waxy crude oils in transient flows”, University of Paris-Est, 2015.
• Wax can precipitate in production tubing, flowlines, surfaceproduction facilities and crude oil or condensate pipelines.
• Wax precipitation increases with decreasing temperatureresulting in a rapid increase in viscosity.
• Waxy crudes are non-Newtonian fluids which means theviscosity of the crude changes with the shear rate.
• The fluid’s resistance to flow depends on the amount ofenergy imparted to the fluid to make it flow.
• Crude will exhibit residual shear stress at zero shear rate.Meaning that once flow stops, it may not be possible to restartthe flow with the available pumping power.
Paraffin Deposits in Piping
Waxy Crude Oil Sample1
Complex, polar, high MW organic moleculesconsisting of aromatic and naphthenic ringcompounds and alkane (paraffin) chains
May contain oxygen, nitrogen, and sulfuratoms as well as heavy metals such asvanadium and nickel
Are insoluble in paraffin solvents such asn-heptane but are soluble in aromatic solventssuch as toluene or xylene
Tend to precipitate as a hard crystalline solidin tubing, flowlines, surface equipment andproducing formations
Can also stabilize water-in-oil emulsionsmaking crude oil dehydration more difficult
Increasin
g A
sph
altene C
on
centratio
n in
Cru
de
Asphaltenes
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Complex, polar, high MW organic moleculesconsisting of aromatic and naphthenic ringcompounds and alkane (paraffin) chains
May contain oxygen, nitrogen, and sulfuratoms as well as heavy metals such asvanadium and nickel
Are insoluble in paraffin solvents such asn-heptane but are soluble in aromatic solventssuch as toluene or xylene
Tend to precipitate as a hard crystalline solidin tubing, flowlines, surface equipment and producing formations
Can also stabilize water-in-oil emulsionsmaking crude oil dehydration more difficult
Asphaltenes
Asphaltene Deposits in Piping
Increasin
g A
sph
altene C
on
centratio
n in
Cru
de
Asphaltenes
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Asphaltenes
Function of both temperature and pressure.
Asphaltene Precipitation Envelope1
1Numerous Authors, “Asphaltenes--Problematic but Rich in Potential”, Oilfield Review, Summer 2007
Asphaltenes
Asphaltene Precipitation Envelope1
1Numerous Authors, “Asphaltenes--Problematic but Rich in Potential”, Oilfield Review, Summer 2007
A reduction in pressure can cause asphaltenes to precipitate
Typically, this deposition occurs in the producing formation near the wellbore
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Asphaltenes
Asphaltene Precipitation Envelope1
1Numerous Authors, “Asphaltenes--Problematic but Rich in Potential”, Oilfield Review, Summer 2007
As the pressure continues to decrease, asphaltene deposition increases until we reach the bubblepoint of the crude oil
Asphaltenes
Asphaltene Precipitation Envelope1
1Numerous Authors, “Asphaltenes--Problematic but Rich in Potential”, Oilfield Review, Summer 2007
At the bubble point, gas starts to break out of the crude. Further reductions in pressure decreasedeposition
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Asphaltenes
Asphaltene Precipitation Envelope1
1Numerous Authors, “Asphaltenes--Problematic but Rich in Potential”, Oilfield Review, Summer 2007
It is important to test your crude oil in a laboratory for asphaltene precipitation before designing theproduction system
Wax and Asphaltenes: Prevention/Remediation Options
Paraffin ScraperCourtesy National Oilwell Varco
Wax Prevention• Thermal insulation and/or heat
tracing
• Dilution with a lighter substance suchas naphtha or condensate
• Paraffin inhibitors which interfere withcrystal growth
Wax Remediation• Hot oil treatments
• Paraffin scrapers
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Wax and Asphaltenes: Prevention/Remediation Options
Paraffin ScraperCourtesy National Oilwell Varco
Asphaltene Prevention
• Operate outside of the ashphalteneprecipitation envelope
• Asphaltene dispersants which keepasphaltene nanoaggreagatessuspended in the oil by preventingthem from forming clusters
Asphaltene Remediation
• Dissolve in solvent such as xylene orde-asphalted oil
• Mechanical removal such as scrapers,water blasting, steam injection
Sand
Formation Sand Production
Perforations
Sand is frequently produced with thereservoir fluids
Problems• Erosion in locations where high velocity or a
change of flow direction occurs
• Chokes, control valves, flowlines, pipingelbows, impingement plates, nozzles,pumps
• Plugging in piping and equipment where lowvelocities exist
• Lost capacity in separators due toaccumulation of sand
• Disposal: facility location or environmentalrestrictions may limit options
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Sand
Hydrocyclones
Mitigation and Remediation
Monitoring• Sand probes• Regular inspections
Equipment/Procedures• Sand traps/desanders• Jetting with HP water (often used in
separators)
Design• Proper piping layout and erosional velocity
limits• Use of erosion resistant and/or abrasion
resistant coatings• Use of gravel packs or sand screens
subsurface
Sand
Mitigation and Remediation
Monitoring• Sand probes• Regular inspections
Equipment/Procedures• Sand traps/desanders• Jetting with HP water (often used in
separators)
Design• Proper piping layout and erosional velocity
limits• Use of erosion resistant and/or abrasion
resistant coatings• Use of gravel packs or sand screens
subsurface
Centrifugal Separators
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Production Chemicals
Produced fluids often containa wide variety of chemicals.
Chemicals often interactcreating unforeseen operatingproblems in facilities• For example, corrosion inhibitors
often contain surfactants whichcan stabilize emulsions
Can contaminate product streams• A common hydrate inhibitor
like methanol can contaminatecondensate or NGL streams
Mitigation• Test for possible interactions and
their consequences prior to designof a chemical injection program
• Be aware of chemical properties,disposal regulations and productspecifications
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This section has covered the following learning objectives:
Learning Objectives
State typical crude oil and produced water specifications
Describe process flows for each stream in production facilities
List problems associated with and strategies to deal with solids production(e.g., sand, wax, asphaltenes)
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Natural Gas Value Chain and Introduction to Gas Processing
Introduction to Production and Gas Processing Facilities Core
This section will cover the following learning objectives:
Learning Objectives
List the components, including contaminants, found in produced gas streams
State typical natural gas sales or transportation specifications
Calculate higher heating value and Wobbe number
List the products of a typical natural gas processing plant, their associated markets,and describe common terminology
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Natural Gas Value Chain
Natural Gas Value Chain
Gas processing facilityand the markets fornatural gasCOPYRIG
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Natural Gas Value Chain
Plant condensate is theliquid that condenses inthe pipeline system fromthe production facility tothe gas processing plant
As the gas cools in thepipeline, liquidhydrocarbons condense
It is similar to fieldcondensate, but is amuch lighter stream
Plant condensate has alower boiling point thanfield condensate
Natural Gas Value Chain
Sulfur recovery is oftenrequired when we havesour gas, which is gascontaining hydrogensulfide, H2S, and othersulfur components
These sulfur componentsare limited to very lowconcentration in the salesgas, so they have to beremoved in theprocessing plant
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Natural Gas Value Chain
Carbon dioxide is used ina particular type ofEnhanced Oil Recoveryproject called a miscibleflood
Carbon dioxide isreinjected back into theproducing reservoirwhere it increases oilrecovery
It is not unusual for theCO2 concentration in thesolution gas to be as highas 60-70 mol%
Natural Gas Value Chain
Gas lift is an artificial liftoption to reduce the backpressure on the reservoirso that we can maintainhigher production ratesand maximize oilrecovery
Gas lift valves on thetubing open periodicallyand allow the lift gas toenter the tubing
Lift gas is a recyclestream
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Natural Gas Value Chain
LNG is natural gas thatexists as a liquid atatmospheric pressure
Temperature is generallyabout -160° Celsius or-260° Fahrenheit
Transported in specialships (LNG tankers orLNG carriers)
About 10% of the naturalgas sold around the worldis transported as LNG
Natural Gas Value Chain
Compressed Natural Gasor CNG is compressed toapproximately 240 barg(3500 psig)
The volume reduction forCNG is around 300 to 1
Used in short haulapplications and is alsoused as a transportationfuel in vehicles such aspassenger vehicles anddelivery vans
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Natural Gas Value Chain
There are 3 primarymarkets for natural gas:
• Residential andCommercial
• Power Generation
• Industrial
Natural Gas Value Chain
The residential andcommercial market isnatural gas that is used inhomes and businessesfor space heating, waterheating, cooking, etc.
This market is highlyseasonal, with maximumdemand in the winter andminimum demand in thesummer
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Natural Gas Value Chain
The second market fornatural gas is electricpower generation
These plants havethermal efficiencies inexcess of 50%, which ismuch higher than otheroptions
This market is alsoseasonal, with highestdemand in the summerdue to air conditioning
Natural Gas Value Chain
The industrial market isdivided into two separateuses
One is as a fuel forrefineries, chemicalplants, steel mills, etc.
Natural gas is also usedas a feedstock to makechemicals
Accounts for only a smallportion of total demand
The least seasonal of thethree main natural gasmarkets
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Natural Gas Value Chain
Supply and demand arebalanced in two ways:• Adjusting production rate
• Natural gas storage
Adjusting productionrequires no addedinfrastructure
The most commonmethod of balancingsupply and demand is tostore gas in reservoirs
Aquifers, salt caverns orpeak shaving LNGfacilities are also used
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Contaminants
Natural gas is primarily methane, but alsocontains NGL components
Hydrogen Sulfide (H2S)• Extremely toxic• Flammable: combustion products are sulfur dioxide
(SO2) and water (H2O)• Corrosion in water-wet systems
– Pitting– Sulfide stress cracking
Other sulfur compounds• Mercaptans (RSH)• Example: methyl mercaptan (CH3SH)
– Strong odor
– Can cause fouling in amine solutions
– Toxic
• Carbonyl Sulfide (COS)
– Reacts to form H2S in the presence of water• Several others including elemental sulfur• All of these can cause corrosion• Contribute to total sulfur content
Nitrogen (N2)• Decreases heating value
Water (H2O)• Corrosion• Hydrates• Ice
Carbon Dioxide (CO2)• Corrosion in water-wet systems• Decreases heating value• Freezing in low temperature processes
– NGL extraction, LNG liquefaction
Mercury (Hg)• Toxic• Corrosion
– Aluminum corrosion
– Liquid metal embrittlement (brazed aluminum heat exchanges)
Oxygen• Corrosion in water-wet systems• Decreases heating value
Gas Quality Specifications
Energy Content• Heating value (Calorific value)
• Almost always refers to the higher or gross heating value, HHV or GHV
• The higher heating value is most commonly used in gas transportation and sales contracts
• The difference between the higher and lower heating value is simply the latent heat of the water that wasformed in the combustion process
• The higher heating value includes this latent heat; the lower heating value does not
𝐻𝐻𝑉 𝐻𝐻𝑉 𝑦
Heating value ofeach component
Mol fraction ofeach component
Higher heatingvalue
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Gas Quality Specifications
Wobbe Number (interchangeability)• Provides a simple, efficient and robust measure of gas interchangeability
WO
BB
E N
UM
BE
R
Upper Wobbe
Lower Wobbe
CO, NOx, Yellow Tipping
Lift Off, CO, Blow Out
OperatingRange
HEATING VALUE
Gas relative density
𝑊𝑁𝐻𝐻𝑉
𝑟𝑒𝑙. 𝜌 .
Heating value of the gasWobbe number
Impact of rel. ρ (s.g.): Gas flow through burner tip slows down as the gas gets heavier
HHV & rel. ρ (s.g.)
Exercise 1: HHV and Wobbe Number Calculation
𝑟𝑒𝑙 𝜌18.6628.96
𝑊𝑁𝐻𝐻𝑉
𝑟𝑒𝑙 𝜌 .
𝑀𝑊 𝑀𝑊 𝑦 𝐻𝐻𝑉 𝐻𝐻𝑉 𝑦
𝑟𝑒𝑙 𝜌18.6628.96
𝑊𝑁𝐻𝐻𝑉
𝑟𝑒𝑙 𝜌 .
𝑀𝑊 𝑀𝑊 𝑦 𝐻𝐻𝑉 𝐻𝐻𝑉 𝑦
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Gas Quality Specifications (cont’d.)
Hydrocarbon dew point (HCDP) temperature• Temperature and pressure at which liquid
hydrocarbons condense in the system
• Must specify a pressure or pressure range
• Often a cricondentherm specification
• Sometimes specified as a liquid content, e.g., mg/Nm3
• Typically higher in warm, tropical climates
Water• Can be expressed as a water dew point temperature,
e.g., -10 C @ 70 bar(14 F at 1000 psig)
– Must specify a pressure
• Can be expressed as a water concentration,e.g., 55 mg/Nm3 (3.5 lb/MMscf)
– Does not require a pressure
• Typically higher in warm tropical climates
Pressure
Temperature
Example Natural Gas Phase Envelope
Pressure
Temperature
Example Water Dewpoint Curve
Dew Point Line
BubblePoint Line
Critical Point
Gas Quality Specifications (cont’d.)
Sulfur compounds• Hydrogen Sulfide (H2S)
• Mercaptans (RSH)
• Total Sulfur– Includes all sulfur containing components in the gas stream
• Generally expressed in ppmv, mg/Nm3 or grains/100 scf(see conversion table)– Based on elemental sulfur
Other contaminants• CO2
• N2 + inerts (He, Ar, etc.)
• O2
• Other
– Dust, gums, waxes, glycol, methanol, Hg, etc.
Unit x = Unit
ppmv 1.43 mg/Nm3
ppmv 0.059 gr/100 scf
mg/Nm3 0.70 ppmv
gr/100 scf 16.9 ppmv
Shall be commercially free from objectionable odors, dust, or
other solid or liquid matter which might interfere with its
merchantability or cause injury to or interference with proper
operation of the lines, regulators, meters or other appliances
through which it flows
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EASEE1 Recommended Gas Specifications
Specification Units Min Max Comments
Wobbe Number kWh/m3 13.6 15.8
MJ/m3 49 57
Rel. Density 0.555 0.7
HCDP oC @ 1 to 70 bar ‐ ‐2
Water Dewpoint oC @ 70 bar ‐ ‐8 approx. 68 mg/Nm3
H2S + COS mg/Nm3 ‐ 5 Expressed as S
ppmv ‐ 3.5 "
Mercaptans (RSH) mg/Nm3 ‐ 6 Expressed as S
ppmv ‐ 4.2 "
Total Sulfur mg/Nm3 ‐ 30 Expressed as S
ppmv ‐ 21 "
CO2 mol % ‐ 2.5
O2 mol % ‐ 0.01
1 European Association for the Streamlining of Energy Exchange
EASEE1 Recommended Gas Specifications
Specification Units Min Max Comments
Wobbe Number kWh/m3 13.6 15.8
MJ/m3 49 57
Rel. Density 0.555 0.7
HCDP oC @ 1 to 70 bar ‐ ‐2
Water Dewpoint oC @ 70 bar ‐ ‐8 approx. 68 mg/Nm3
H2S + COS mg/Nm3 ‐ 5 Expressed as S
ppmv ‐ 3.5 "
Mercaptans (RSH) mg/Nm3 ‐ 6 Expressed as S
ppmv ‐ 4.2 "
Total Sulfur mg/Nm3 ‐ 30 Expressed as S
ppmv ‐ 21 "
CO2 mol % ‐ 2.5
O2 mol % ‐ 0.01
1 European Association for the Streamlining of Energy Exchange
Wobbe Number from previous
slide:
49.89 MJ/m3COPYRIGHT
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EASEE1 Recommended Gas Specifications
Specification Units Min Max Comments
Wobbe Number kWh/m3 13.6 15.8
MJ/m3 49 57
Rel. Density 0.555 0.7
HCDP oC @ 1 to 70 bar ‐ ‐2
Water Dewpoint oC @ 70 bar ‐ ‐8 approx. 68 mg/Nm3
H2S + COS mg/Nm3 ‐ 5 Expressed as S
ppmv ‐ 3.5 "
Mercaptans (RSH) mg/Nm3 ‐ 6 Expressed as S
ppmv ‐ 4.2 "
Total Sulfur mg/Nm3 ‐ 30 Expressed as S
ppmv ‐ 21 "
CO2 mol % ‐ 2.5
O2 mol % ‐ 0.01
1 European Association for the Streamlining of Energy Exchange
Impliedheating value specification:
36.5 – 47.7 MJ/m3
Example US Specifications - Rocky Mtn. Region
Specification Units Min Max Comments
HHV Btu/scf 950 1200
MJ/Nm3 37.4 47.3
HCDP oF @ 100 to 1000 psi ‐ 15
Water Content lb/MMscf ‐ 5 25 oF DP@ 1000 psig
H2S grains/100 scf ‐ 0.25 Expressed as S
ppmv ‐ 4.2 "
Mercaptans (RSH) grains/100 scf ‐ 0.25 to 2 Often not specified
ppmv ‐ 4.2 to 34 Expressed as S
Total Sulfur grains/100 scf ‐ 0.5 to 20 Expressed as S
ppmv ‐ 8.4 to 340 "
CO2 mol % ‐ 2 to 3
O2 ppmv ‐ 10‐10000
N2 mol % 3 Often not specified
CO2 + N2 + other inerts mol % 5
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Gas Quality Specifications (cont’d)
For gas entering a transmission system serving many customers, the specifications are typicallyset by the gas transporter and are generally non-negotiable.
For gas entering a transportation system where there is only one customer, such as a power plantor a chemical complex, the specifications are based on the buyer’s requirements and are typicallynegotiated between the buyer and the seller.
For example, a common CO2 specification for an open, multi-customer, transportation systemmight be 2.5 mol%. But for a pipeline system dedicated to one customer, the buyer might be ableto accept a gas with a much higher concentration of CO2, say 10 mol%. This could dramaticallydecrease the cost of the seller’s gas processing facility.
You will also see some flexibility in H2S specifications. As we have seen, a common specificationfor H2S in an open transmission system is about 4 ppmv. But there are some users, particularlypower plants, where an H2S concentration of 20 to 30 ppmv might not be an issue. If the buyer willagree to a higher H2S concentration, the cost of processing the gas can be reduced.
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Wobbe Number Specification Exercise
Question
Refer to the gas composition in the guided exercises
presented earlier. Assume this gas is transported in a
gas pipeline system with the EASEE specifications
discussed previously. It has been proposed to extract
the propane from this gas stream to serve a local LPG
market. If the propane is extracted, the new sales gas
composition is shown in the table on the left.
If the propane is extracted, will this gas still meet the Wobbe number
specification?
Answer: Without propane, the gas stream does not meet the minimum Wobbe
number specification, 48.87 vs. 49.
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Wobbe Number Specification Exercise Solution
New Wobbe number calculation shown below:
Comp mol% MW (yi)(Mwi) HHV, MJ/m3 (yi)(HHVi)
N2 3.09 28.01 0.87 0 0.00
CO2 1.03 44.01 0.45 0 0.00
C1 88.66 16.04 14.22 37.707 33.43
C2 7.22 30.07 2.17 66.067 4.77
C3 0.00 44.10 0.00 93.936 0.00
MW = 17.71 HHV = 38.20
rel. ρ = 0.611 Wobbe Number = 48.87
Without propane, the gas stream does not meet the minimum Wobbe numberspecification, 48.87 vs. 49
This exercise shows how gas sales or transportation specifications may limitextraction of NGL components
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CompLean Sweet
Non-Associated GasVery Lean Sweet
Shale GasLean High CO2
Gas Condensate GasRich SweetShale Gas
He 0.060 0.000 0.000 0.000
N2 2.408 0.078 0.654 0.380
CO2 0.472 1.921 10.071 0.633
H2S 0.000 0.000 0.000 0.000
C1 91.660 97.302 86.345 79.689
C2 3.896 0.645 1.840 12.020
C3 0.956 0.038 0.487 3.803
iC4 0.166 0.004 0.111 0.553
nC4 0.214 0.004 0.106 1.117
iC5 0.077 0.000 0.044 0.336
nC5 0.062 0.000 0.025 0.409
C6 0.062 0.000 0.036 0.473
C7+ 0.027 0.008 0.279 0.587
Total 100.000 100.000 100.000 100.000
Example Separator Gas Compositions, mol%
CompHP Sweet
Solution GasLP Sweet
Solution GasRich High CO2
Gas Condensate GasRich Sour
Gas Condensate Gas
He 0.000 0.000 0.000 0.000
N2 0.956 0.883 0.866 0.302
CO2 1.291 1.649 10.696 4.127
H2S 0.000 0.000 0.006 8.958
C1 83.518 65.352 74.089 73.478
C2 6.309 10.187 7.696 7.549
C3 4.574 12.277 3.827 2.617
iC4 0.496 1.581 0.379 0.503
nC4 1.454 4.459 1.068 1.007
iC5 0.375 0.919 0.227 0.403
nC5 0.364 0.843 0.314 0.302
C6 0.234 0.596 0.403 0.503
C7+ 0.427 1.255 0.429 0.252
Total 100.000 100.000 100.000 100.000
Example Separator Gas Compositions, mol%
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NGL Products
This slide provides an overview of NGL products and their markets as well as a reminder ofcommon terminology used in the oil and gas business
NGL Products
C2Petrochemical feedstock for manufacture of ethylene
C3Petrochemical feedstock for manufacture of propylene Fuel (LPG): Commercial and residential fuel in areas not on a natural gas gridGrain dryingOutdoor grillsMotor vehicle fuel
C4Iso: Refinery feedstock to alkylation unitPetrochemical feedstock for manufacture of iso-butylene and other light olefinsGasoline (petrol) blendingComponent in LPGNormal: Petrochemical feedstock for manufacture of n-butylene and other light olefinsFeedstock to isomerization unit for conversion to iC4
Gasoline (petrol) blendingComponent in LPG
C5+In refining and petrochemical business often known as light naphthaPetrochemical feedstock for manufacture of a range of light olefinsRefinery feedstock to reformer or isomerization unit
NGL: Natural Gas Liquid
LPG: Liquefied Petroleum Gas
LNG: Liquefied Natural Gas
CNG: Compressed Natural Gas
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This section has covered the following learning objectives:
Learning Objectives
List the components, including contaminants, found in produced gas streams
State typical natural gas sales or transportation specifications
Calculate higher heating value and Wobbe number
List the products of a typical natural gas processing plant, their associated markets, anddescribe common terminology
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NGL Recovery
Introduction to Production and Gas Processing Facilities Core
This section will cover the following learning objectives:
Learning Objectives
Describe typical process flows for each stream in gas processing facilities
Explain the difference between gas conditioning to meet a HCDP specification and gasprocessing to recover NGLs
Describe shrinkage and how it is calculatedCOPYRIGHT
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Gas Processing Plant – Block Diagram
Gas Processing Objectives (Conditioning)
Meet sales gas specifications only – no further processing• Water removal
• CO2/Sulfur compound removal
• Hydrocarbon dew point (HCDP) control
Used when no profitable NGL market exists and/or NGL transportation/storage/distribution systemsare undeveloped
In addition to meeting sales gas specifications – further processing is undertaken to increase NGLrecovery
• NGLs more valuable as a saleable product than as a natural gas component– Ethane
– Propane
– Butanes
– Natural Gasoline (iC5+)
Extraction levels are limited by gas sales specifications (typically heating value) and economics
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NGL Extraction Levels
Gas conditioning to meet a hydrocarbon dew point specification which requires removalof a portion (60-70%) of the C5+ hydrocarbons in the gas stream
The heating value and Wobbe number of the sales gas are low and in some cases NGLrecovery may be limited by these gas quality specifications
NGL Extraction Economics
In general, we choose to extract NGLs from a gas stream when their value as an NGLproduct is greater than their value as a component in the sales gas stream
The reduction in the value of the sales gas stream due to the extraction of an NGLproduct is referred to as “shrinkage”
Example:• A natural gas stream contains 5 mol% propane (C3). The flowrate is
1.0 x 106 sm3/d [35.4 MMscfd]. If all of the propane is extracted from the gas in a gasprocessing plant, calculate the following:
– The reduction in the energy content of the gas stream due to propane extraction
– The value of this energy content reduction
– The amount of propane product recovered in tonnes/d [US gal/day]
– The value of the propane product if sold to an LPG buyer
– The net revenue from propane extraction
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NGL Extraction Economics
• Reduction of energy content: As a gas, propane has a heating value of 93.936 MJ/sm3 [2,516.2 Btu/scf]– (1000000 sm3/d)(0.05)(93.936 MJ/sm3) = 4,697 GJ/d
– (35,400,000 scf/d)(0.05)(2516.2 Btu/scf) = 4,454 MMBtu/d
• Value of the energy content reduction (shrinkage): The gas price is $2.84/GJ [$3.00/MMBtu]– (4697 GJ/d)($2.84/GJ) = $13,350/d– (4,454 MMBtu/d)($3.00/MMBtu) = $13,350/d
• Quantity of propane is extracted in tonnes/d [US gal/day]: The volume ratio of propane is 0.5362 sm3/kg[36.404 scf/US gal]
– (1000000 sm3/d)(0.05)/(0.5362 sm3/kg)/1000 kg/mt = 93.25 tonnes/d– (35,400,000 scf/d)(0.05)/(36.404 scf/US gal)= 48,600 US gal/d
• Value of propane extracted: The propane price is $260/tonne [$0.499/US gal]– (93.25 tonnes/d)($260/mt) = $24,250/d– (48,600 US gal/d)($0.499/USgal) = $24,250/d
• Net revenue from propane extraction:– $24,250 – $13,350 = $10,900/d
The values shown in blue were taken from Tables 3A1(a) and (b)
in Chapter 3 of Volume 1
NGL Extraction Economics
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Example
If the gas price in the previous example rose to $5.00/MMBtu [$4.74/GJ], would it still beeconomically viable to extract propane from the gas stream?
• Shrinkage:– (4697 GJ/d)($4.74/GJ) = $22,270/d
– (4,454 MMBtu/d)($5.00/MMBtu) = $22,270/d
• Net Revenue:– $24,250 – $22,270 = $1,980/d
Shrinkage Values for NGLs (US Units)
$0.455/US gal
$5.00/MMBtu
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Shrinkage Values for NGLs (SI Units)
$226/tonne
$4.74/GJ
Example
If the gas price is $5.00/MMBtu [$4.74/GJ] the net revenue from propane extraction isstill positive but not nearly as attractive as in the base case. What are some otherfactors you might consider in the decision to recover propane?
• Are the plant operating costs different if propane is not extracted from the gas?
• Will the recovery of butanes be adversely affected if propane is not extracted?
• Can we still meet the gas quality specifications if propane is not extracted?
– Heating value or Wobbe Index are the most likely gas properties that could fall outside of thespecification range.
• Are we obligated to pay “capacity reservation fees” for NGL pipeline and/or fractionationfacilities regardless of whether we extract propane or not?
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Example
NGL prices are closely related to crude oil prices because NGLs are usually sold intomarkets where they compete with crude oil products.
The shrinkage value of the NGL product is set by natural gas prices; so, when crudeoil prices are high relative to natural gas prices, NGL extraction economics aregenerally quite favorable.
On the other hand, when crude oil prices and natural gas prices are the same, theextraction of NGLs is difficult to justify.
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Gas Processing Facility Exercise
Question
A gas processing facility has the option of extracting ethane from the feed gas or
rejecting ethane to the export gas stream. The current price for ethane $0.21/US
gal [$156/tonne].
Use the following figures to answer the question.
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If the natural gas price is $4.00/MMBtu [$3.79/GJ], would they be more
likely to extract ethane or reject ethane?
Answer: The operator would be more likely to reject ethane than extract it since
ethane is worth more in the gas stream than as an NGL product.
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Gas Processing Facility Exercise Solution
$189/tonne
$0.26/US gal
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This section has covered the following learning objectives:
Learning Objectives
Describe typical process flows for each stream in gas processing facilities
Explain the difference between gas conditioning to meet a HCDP specification and gas processing to recover NGLs
Describe shrinkage and how it is calculated
Hydrocarbon Components and Physical Properties Core
Introduction to Production and Gas Processing Facilities Core
Qualitative Phase Behavior and Vapor Liquid Equilibrium Core
Water / Hydrocarbon Phase Behavior Core
Thermodynamics and Application of Energy Balances Core
Fluid Flow Core
Relief and Flare Systems Core
Separation Core
Heat Transfer Equipment Overview Core
Pumps and Compressors Overview Core
Refrigeration, NGL Extraction and Fractionation Core
Contaminant Removal – Gas Dehydration Core
Contaminant Removal – Acid Gas and Mercury Removal Core
Gas Conditioning and Processing Core
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