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08 Solid Models in PVTsim
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Solid Models in PVTsim
Wax Definition
• Solid that precipitate when oil is cooled– typically below 80°C (176 °F)
• Paraffinic and naphtenic molecules• Wax deposition
– pipelines and process equipment– wells (rare)– not in reservoirs
Wax Modeling
Vapor
Liquid
Solid (wax)
N...,,2,1ifff Si
Li
Vi
EOS ModelVapor:
EOSfrom;Pyf Vi
Vii
Vi
EOSfrom;Pxf Li
Lii
Li
Liquid:
Wax:
1. Ideal solution (Pedersen & Rønningsen)
oSii
Si fsf
RTPPv
TT
RTHPf ref
SL
fi
fioL
ioSi
i1exp
PVTsim Model Formulation
• Ideal solid solution
• Melting enthalpy of each wax former• Melting temperature of each wax former• S-L molar volume difference • Wax forming fraction
Estimation of wax forming fraction
C
pi
pii
itoti
Wi MWBAzz
1
0
0.5
1
1.5
2
Mol
e%
C7 C8 C9 C10 C13 C16 C18 C20 C23 C27 C33 C46
Pseudo component
Live Oil
WaxNone Wax
Wax Forming Components
Pressure dependence of WAT
0
2000
4000
6000
8000
10000
12000
14000
0 50 100 150 200
T / °F
P / p
si Wax app. T
Sat P
LL+Wax
L+VapL+Vap+Wax
Asphaltene model approach PVTsim
• Theory: Asphaltene precipitation ordinary liquid-liquid split.
• Asphaltene components default C50+ aromatics.
• High Tc of asphaltenes causes precipitation.
Parameters
• Asphaltene fraction (C50+ aromatics)
• Tc of asphaltenes 1125 °C/2058 °F
• Pc of asphaltenes 15 Bar/217 psi
• kij between C1 - C9 and asphaltenes (0.017)
Gas Hydrates
• Practical problem for the petroleum industry• Potentially a huge energy resource
– Large deposits in deep waters and permafrost regions around the world
• A possible greenhouse effect accelerator
Lower T
Water Structure in Gas Hydrates
Lower T