Introduction To Multiphase Flow

Multiphase ?• Gas + Droplets• Liquid Hydrocarbons

– Gas bubbles– Water droplets

• Free Water– Oil droplets– Gas bubbles

• Hydrates• Wax• Sand

Multiphase flow

• Complexities– Interaction between the phases– Fluid properties– Interaction with the boundary conditions

– i.e. reservoir and process plant

– Networks• wells, flow lines, process equipment and control system

– Pipe profiles

Multiphase flow predictions

• are difficult:– Several flow regimes– Slip effects

Flow regimes in OLGA(Horizontal flow)

Stratified flow

(Annular flow)

Dispersed bubble flow

Slug flow

SEPARATED

DISTRIBUTED

Flow regimes in OLGA(Vertical flow)

Annular flow

Dispersed bubble flow

Slug flow

SEPARATED

DISTRIBUTED

Pressure and Flow

• Assume outlet pressure given and fixed

Production Rate

Inle

t P

ress

ure

Friction dominatedGravity dominated

Potential problems in multiphase flow

• HYDRODYNAMIC SLUGGING

Slug Length

Fre

qu

en

cy

b.-slug distribution

3

pipe 2 pipe 3pipe 1

1 2

a.-terrain effect and slug-slug interaction

Hydrodynamic slugging

• Two-phase flow pattern maps indicate hydrodynamic slugging, but

– slug length correlations are quite uncertain

– tracking of the development of the individual slugs along the pipeline is necessary to estimate the volume of the liquid surges out of the pipelines

Potential problems in multiphase flow

• TERRAIN SLUGGING– A: Low spots fills with liquid

and flow is blocked– B: Pressure builds up behind

the blockage– C&D: When pressure

becomes high enough, gas blows liquid out of the low spot as a slug

A. Slug formation

B.Slug production

C. Gas penetration

D. Gas blow-down

Potential problems in multiphase flow

• TERRAIN SLUGGING

– Terrain slugs can be very severe, causing large pressure variations and liquid surges out of pipeline.

– Terrain slugging is a transient situation which requires a dynamic model to predict and describe

Potential problems in multiphase flow

• PIGGING– Pigging the line will create a large liquid slug

ahead of the pig

A: Slug build-up

B. front arrival

C. slug surface

D. Pig arrival Time

Flo

wra

te

gas

liquid

A B C D

Potential problems in multiphase flow

• RATE CHANGES– Pipe line liquid inventory decreases with

increasing flow rate – Rate changes may trigger slugging

Gas Production Rate

Liq

uid

Inve

nto

ry

Initial amount

Final amount

Amount removed

Potential problems in multiphase flow

• SHUT-IN - RESTART– Liquid redistributes due to gravity during shutin– On startup, slugging can occur as flow is ramped

up

B-Gas and Liquid Outlet Flow

A-Liquid Distribution After Shutdownshutdown

Time

Flo

wra

te

gas

liquid

Other concerns with multiphase flow

– Shutdown and startup • Temperature profiles• Liquid surges during startup

– Pipeline blow down • Temperature profile, gas and liquid flow rates

– Liquid accumulation and water separation in low points

– Pigging operations– Pipeline ruptures and other accidents

The Transient Multiphase Flow Simulator

The dynamic three phase flow simulator

OLGAOLGA

8 Conserv. Equations

mass (5)momentum (2)

energy (1)

Fluid Properties

Closure Laws

mass transfermomentum transfer

energy transfer

BoundaryConditions

Initial Conditions

The OLGA three phase flow model• Mass conservation

– Gas– Hydrocarbon bulk– Hydrocarbon droplets– Water bulk– Water droplets

• Momentum conservation

– Gas + droplets– Liquid bulk

• Energy conservation

– Mixture• Constitutive equations

Variables

• Primary variables

– 5 mass fractions (specific mass)

– 2 velocities

– 1 pressure

– 1 temperature

• Secondary variables

– Volume fractions

– Velocities

– Flow rates

– Fluid properties

Modeling the pipeline profile in OLGAThe assumption

Fluid propertiesGeneral

• The fluid properties are pre-calculated tables as a function of P and T and for one fluid composition

– It follows that the total composition is constant throughout a fluid table1)

• The exact value of a property for a given P and T is found by interpolating in the relevant property table

1) Compositional tracking available with OLGA 2000 v3.00

OLGA 2000 Modules

• Slugtracking

– with pigging• Water

– three-phase flow• FEM -Therm

– conductive 2-D (“radial”) heat transfer

– finite elements– integrated with OLGA bundle– grid generator

OLGA 2000 Modules

• Comptrack

– compositional tracking• MEG-track• UBitTS

– Under Balanced interactive transient Training Simulator

• Advanced Well• Multiphase Pumps

– positive displacement– rotodynamic

• Corrosion• Wax

OLGA 2000 file structure

OLGA 2000

reflex of the Input File +results from OUTPUT

Trend Plot Fileresults from TREND

Profile Plot Fileresults from PROFILE

Restart File(binary)

Input File .inp

Fluid Properties File .tab

.out

.tpl.ppl

.rsw

ASCII file

Principles of OLGA 2000 execution

OLGA 2000 GUI

Input File .inp

OLGA 2000

PVTsim

Fluid Properties File .tab

.tpl

.ppl

.out .rsw