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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
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