08 Solid Models in PVTsim

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