Status: Draft

Composition & PVT (Fluid properties as a function of Pressure, Volume and Temperature)

Statoil module – Field development

Magnus Nordsveen

Status: Draft

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

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

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: =

Status: Draft

Gas chromatography Fingerprint analysis

’Normal’, paraffinic oil

Status: Draft

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

Status: Draft

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

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

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

Status: Draft

Status: Draft

Content

• Compositions

• Phase transfer, phase envelops and reservoir types

• Water and Hydrates

Status: Draft

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

Phase diagram for C3 (99%) and nC5 (1%)

Status: Draft

Gas

Liquid

Gas & Liquid

Phase diagram for C3 (50%) and nC5 (50%)

Status: Draft

Liquid

Gas

Gas & Liquid

Bubble point line

Dew point line

Status: Draft

2 phase mixture

Phase envelope of an oil reservoir

Status: Draft

Phase envelope of a gas condensate reservoir

2 phase mixture

Liquid Gas

Tres, Pres

Status: Draft

Phase envelops for 3 reservoir types

C

C

C

Gas Condensate

OilHeavy oil

C = Critical point

Temperature

Pres

sure

Phase envelope and P, T conditions from reservoir to platform (oil field)

Status: Draft

2 phase mixture

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

Status: Draft

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)

Status: Draft

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 =

Status: Draft

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

Status: Draft

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.

Status: Draft

Content

• Compositions

• Phase transfer, phase envelops and reservoir types

• Water and Hydrates

Status: Draft

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

Gas hydrates (Burning “snow”)

Status: Draft

•  Ice/snow crystals of water and gas molecules

• Can cause pipeline blockage

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.

Gas hydrates

Status: Draft

Gas molecules stabilise cages made of water molecules.

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.

Status: Draft

Status: Draft

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

Status: Draft

Thank you