Composition & PVT (Fluid properties as a function of · PDF fileStatus: Draft Content •...
Transcript of Composition & PVT (Fluid properties as a function of · PDF fileStatus: Draft Content •...
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Composition & PVT (Fluid properties as a function of Pressure, Volume and Temperature)
Statoil module – Field development
Magnus Nordsveen
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Content
• Compositions
• Phase transfer, phase envelops and reservoir types
• Water and Hydrates
Comp Mole% N2 0.95
CO2 0.6 H20 0.35 C1 95 C2 2.86 C3 0.15 iC4 0.22 nC4 0.04 iC5 0.1 nC5 0.03 C6 0.07 C7 0.1 C8 0.08 C9 0.03
C10+ 0.13
Gas condensate field
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Compositions of gas and oil
Status: Draft
Comp Mole% N2 0.95
CO2 0.6 H20 0.35 C1 95 C2 2.86 C3 0.15 iC4 0.22 nC4 0.04 iC5 0.1 nC5 0.03 C6 0.07 C7 0.1 C8 0.08 C9 0.03
C10+ 0.13
C1 - methane:
C2 - ethane:
C
C
C C
nC4 – n-butane
iC4 - isobutane
Gas condensate field
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Compositions of gas and oil
• Isomers: Different structure configurations of same carbon numbers
• 75 isomers of decane C10H22 (single bounds)
• 366319 isomers of C20H42 (single bounds)
• Complexity further increased by double bounds, triple bounds, rings, other atoms
Status: Draft
C C H
H
H
H
Ethylene: =
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Gas chromatography Fingerprint analysis
’Normal’, paraffinic oil
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Characterisation of fluids based on composition
• Thousands of components from methane to large polycyclic compounds
• Carbon numbers from 1 to at least 100 (for heavy oils probably about 200)
• Molecular weights range from 16 g/mole to several thousands g/mole
Comp Mole% N2 0.95
CO2 0.6 H20 0.35 C1 95 C2 2.86 C3 0.15 iC4 0.22 nC4 0.04 iC5 0.1 nC5 0.03 C6 0.07 C7 0.1 C8 0.08 C9 0.03
C10+ 0.13
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Characterization challenge
• Low carbon number components:
– Possible to measure with reasonable accuracy
– Known properties
• Higher carbon number components:
– consists of many variations with different properties
– cannot measure individual components
• Characterization: Lump C10 and higher into C10+
Comp Mole% N2 0.95
CO2 0.6 H20 0.35 C1 95 C2 2.86 C3 0.15 iC4 0.22 nC4 0.04 iC5 0.1 nC5 0.03 C6 0.07 C7 0.1 C8 0.08 C9 0.03
C10+ 0.13
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Compositions and PVT important for:
• Value and market
• Field development solution – Reservoir (gas, oil, heavy oil)
– Wells and flowlines
– Processing (subsea, platform, onshore plant)
– Pipeline transport to shore (gas, condensate, oil)
– Offloading to ship (condensate and oil)
Status: Draft
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Compositions and PVT important for:
• Wells and flowlines
– Pressure and temperature drop • Phase transfer (gas/oil split)
• Densities
• Viscosities
• Surface tension
• Conductivities
• Heat capacity
– Wax, hydrates, Asphaltenes
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Content
• Compositions
• Phase transfer, phase envelops and reservoir types
• Water and Hydrates
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Phase diagram for a single component
Critical point
Trippel point
P
T
Solid Liquid
Gas
Dense phase
Critical point Water: Tc=374 C
Pc=218 bar
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Phase diagram for C3 (99%) and nC5 (1%)
Status: Draft
Gas
Liquid
Gas & Liquid
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Phase diagram for C3 (50%) and nC5 (50%)
Status: Draft
Liquid
Gas
Gas & Liquid
Bubble point line
Dew point line
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2 phase mixture
Phase envelope of an oil reservoir
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Phase envelope of a gas condensate reservoir
2 phase mixture
Liquid Gas
Tres, Pres
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Phase envelops for 3 reservoir types
C
C
C
Gas Condensate
OilHeavy oil
C = Critical point
Temperature
Pres
sure
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Phase envelope and P, T conditions from reservoir to platform (oil field)
Status: Draft
2 phase mixture
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Pressure drop from reservoir to platform
• Holdup: β – liquid volume fraction in the cross section
• Oil density: ρo
• Gas density: ρg
• Effective density: ρeff = βρo + (1-β) ρg
• Gravitational pressure drop: dPgrav = ρeffgH (g: gravity, H: Height)
• Total pressure drop: dP = dPgrav + dPfric
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Pressure drop from reservoir to platform
Status: Draft
Holdup Effective density [kg/m3]
Height [m]
dPgrav [bar]
dPfric* [bar]
dP* [bar]
0 80 2000 16 ? ? 0.5 440 2000 86 ? ? 1 800 2000 157 ? ?
*need more detailed calculations (will be addressed later in course)
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Equations of state (EOS) & Phase envelope
• An equation correlating P (pressure), V (volume) and T (temperature) is called an equation of state
• Ideal gas law: PV = nRT <=> (good approx. for P < 4 bar)
– n: moles, R: gas constant, ν : molar volume
• Van der Waals cubic EOS:
• a: is a measure for the attraction between the particles
• b: is the volume excluded from ν by the particles
2va
bvRTP −−
=
vRTP =
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Equations of state (EOS) & Phase envelope
Family of PV isotherms for a pure component Family of PV isotherms for a cubic EOS
Measured Model prediction
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PVTSim
• In the oil industry we typically use software packages to characterize the fluid based on a measured composition
• In Statoil we use PVTSim from Calsep
• Ref: Phase Behavior of Petroleum Reservoir Fluids (Book), Karen Schou Pedersen and Peter L. Christensen, 2006.
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Content
• Compositions
• Phase transfer, phase envelops and reservoir types
• Water and Hydrates
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Water in hydrocarbon reservoirs - flowlines
In reservoir:
– Separate liquid water layer
– Water vapour in gas layer
In wells/flowlines:
– Condensed water in gas condensate flowlines
– Produced water from oil reservoirs
• Liquid water and hydrocarbons are essentially immiscible in each other
– However, liquid water and oil can form emulsions/dispersions
• With water, oil and gas present in flowlines, there are generally
– 2 liquid fields and 1 gas field
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Gas hydrates (Burning “snow”)
Status: Draft
• Ice/snow crystals of water and gas molecules
• Can cause pipeline blockage
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Gas hydrates
Status: Draft
Hydrate formation requires:
High enough pressure Hydrates can be stable at 10-15 bar
Low enough temperature But still good summer temperature
Access to small molecules C1, C2, C3, I-C4, CO2, H2S, N2
Access to free water Condensed water is good enough
Gas molecules stabilise cages made of water molecules.
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Gas hydrates
Status: Draft
Gas molecules stabilise cages made of water molecules.
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Safety Hazards of Moving Hydrate Plugs (From Chevron Canada Resources, 1992)
Status: Draft
A hydrate plug movesdown a flowline at veryhigh velocites.
Closed Valve
Closed ValveIf the velocity is high enough, themomentum of the plug can cause pressures large enough to rupture the flowline.
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End of Lecture - Composition & PVT
Content: • Compositions
• Phase transfer, phase envelops and reservoir types
• Water and Hydrates
Comp Mole% N2 0.95
CO2 0.6 H20 0.35 C1 95 C2 2.86 C3 0.15 iC4 0.22 nC4 0.04 iC5 0.1 nC5 0.03 C6 0.07 C7 0.1 C8 0.08 C9 0.03
C10+ 0.13
Gas condensate field
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Status: Draft
Thank you