Introduction to Multiphase & Wet Gas Flows - NEL to Muph and wet gas.pdf · Introduction to...
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Introduction to Multiphase & Wet Gas Flows Emmelyn Graham Flow Measurement Engineer
Transcript of Introduction to Multiphase & Wet Gas Flows - NEL to Muph and wet gas.pdf · Introduction to...
Introduction to Multiphase
& Wet Gas Flows
Emmelyn Graham
Flow Measurement Engineer
• Introduction to Multiphase & Wet Gas Flows
• Flow Patterns
• Characterisation & Terminology
• Traditional Measurement Methods
• Wet-Gas Flow Measurement
• Multiphase Flow Measurement Technologies
• Flow Meter Selection & Verification
Contents
Oil / Gas not produced as a single phase fluid • Water and gas present
Technically speaking it’s actually multi-component flow
OIL
GAS
WATER
Multiphase Flow Measurement
CHARACTERISED BY : Volumetric Flowrate Ratios
GAS
OIL
WATER
ALSO CHARACTERISED BY : Flow Regime / Pattern
GASQ
OILQ
WATERQ
Gas
OIL
WATER
• Simultaneous flow of oil, water and gas
• Gas Volume Fraction, GVF : 0 -100%
• Water Cut, WC (or Water liquid ratio, WLR) : 0 – 100%
• Variety of flow patterns
• May contain sand, wax, etc
Description of Multiphase Flow
gas
water
oil
Description of Wet-Gas Flow
Wet gas is a mixture consisting mostly of gas with a small amount of liquid.
• Liquid can be water and /or hydrocarbon • Water cut - 0% to 100%
How is wet gas defined?
• Gas volume fraction > 90%
• Lockhart-Martinelli parameter < 0.3
These terms will be
covered shortly
gas
liquid
Flow Regimes
• The phases can be distributed over a pipe cross
section in many different ways
• Flow pattern depends on the amount of each
phase, liquid and vapour properties, pressure
and velocities
• Different for horizontal and vertical flows
Flow Patterns / Regimes
Horizontal Flow Patterns
Stratified flow regimes
STRATIFIED
STRATIFIED WAVY
Occur at relatively low velocities for both phases
Surface becomes wavy as gas velocity increases or pipe inclines
Horizontal Flow Patterns
Intermittent flow regimes
PLUG
Alternating regions of high and low liquid hold-up
As liquid flowrate increases liquid phase dominates flow
SLUG
Horizontal Flow Patterns
Occurs at high liquid velocities
Gas bubbles are suspended in continuous liquid phase
BUBBLE
ANNULAR
Occurs at high gas velocities
Gas flows in central core / liquid as film on pipe walls
Horizontal Flow Patterns
Increasing gas velocity and / or gas density
The liquid becomes completely entrained as droplets in the gas flow
MIST
As gas velocity and / or gas density increases the liquid starts to
becomes entrained as droplets in the gas flow
ANNULAR MIST
Horizontal Flow Patterns
TYPICAL HORIZONTAL FLOW PATTERN MAP (2 phases)
Not general!
Applies only to a
specific fluid and
pressure
Horizontal Three-Phase
Flow Patterns Separation of oil and water • Occurs in stratified and slug flow • Possibility of oil and water travelling at different velocities
Mixing of oil and water • Emulsions • Increased liquid viscosity • Slower film drainage
GAS
OIL
WATER
GASQ
OILQ
WATERQ
Vertical Flow Patterns
Bubble Flow Liquid phase continuous
Dispersed gas bubbles
Slug Flow Small bubbles coalesce
Taylor bubbles (slugs)
Churn Flow Irregular gas slugs
Liquid rises and falls
Annular Flow Gas flows in core
Liquid flows in annulus
Mist Flow Liquid entrained as droplets
INCREASING GAS VELOCITY
Bubble Slug Churn Annular Annular
Mist
Mist
Vertical Flow Patterns
TYPICAL VERTICAL FLOW PATTERN MAP (2 phases)
Not general!
Applies only to a
specific fluid and
pressure
Vertical Flow Patterns
• No major effects
–Oil and water are usually well mixed
–No separation due to gravity
• Transitions are not affected by water cut
–Effects due to liquid density changes eliminated
• Flow pattern maps are based on test sections in
well developed flow
• Long, straight pipe lengths
• Upstream conditions (bends, valve, etc.) affect
flow pattern
• Can use this to advantage by conditioning flow
• For example, use mixer to get closer to homogeneous
flow
• Blind tee used in multiphase flow measurement
Effect of Upstream Conditions
Characterisation & Terminology
Void Fraction and
Liquid Hold-Up
GAS
OIL
WATER
GASQ
OILQ
WATERQ
Gas
OIL
WATERGas “Void Fraction” = GAS
Liquid “Hold-up” = OILWATER
Carry-over and Carry-under
GAS
WATER OIL
Volume flowrate of one phase relative to total
volume flowrate
e.g. GVF = Gas volume flowrate / Total volume
flowrate
GVF = Gas Volume Fraction
Phase Volume Fraction
21 llg
g
QQQ
QGVF
Cross sectional area locally occupied by one
phase relative to the total cross sectional area of
the pipe at that point.
Also referred to as:
• Void fraction (gas)
• Hold up (liquid)
Phase Area Fraction
gas
liquid
• Important to distinguish between gas volume fraction and gas void fraction
• Gas Volume Fraction based on flowrates (GVF)
• Gas Void Fraction based on local areas
• They are usually unequal
• For example:
• 70% gas void fraction could
be 95% gas volume fraction
as the gas is travelling at
higher velocity.
GVF
Phase Slip
• Gas and liquid travel at different velocities
• Mean gas velocity is greater than mean liquid velocity
• Difference known as “slip”: vR = vg – vl
or “slip ratio”: K = vg /vl
• Note: GVF is related to void fraction eg and slip ratio K through
K
KGVF
gg
g
ee
e
1
Example: If εg = 70% and K = 8.1, then GVF = 95%
• If a multiphase flow meter measures local mean density
given by
• Use phase densities to obtain the void fraction εg
• Use K to obtain GVF from εg
• How to determine K (Slip Model)?
• Apply semi-empirical model for flow pattern, OR
• Perform laboratory or test facility experiments with known GVF, and develop correlation for K using appropriate physical variables
• Strictly only applies to range of conditions of experiments and ideally should not be extrapolated
Phase Slip (contd)
lggg ee 1
εg
1-εg
Areas
Homogeneous Flow
• Liquid and gas travel at same mean velocity (v)
gl vv
• For homogeneous flow, K = 1, so equation from previous slide gives
GVFg e
• A homogeneous flow can be assigned a single value of properties like density, viscosity, etc based on weighted average of phase mass fractions
oil - continuous
water - continuous
inversion region
45% < water cut < 75%
THE INVERSION POINT MOVES
Inversion Region
The velocity a particular phase would have if the
same volume flowrate flowed alone in the pipe
e.g. Pipe diameter = 6 inch
Gas flowrate = 950 m3/hr
Liquid flowrate = 50 m3/hr
Superficial Gas Velocity (SGV) = 14.9 m/s
Superficial Liquid Velocity (SLV) = 0.8 m/s
Superficial Phase Velocity
Froude number, Fr, of each phase
• High Fr: Kinetic energy dominates
• Low Fr: Gravity forces dominate
Froude Number
gl
ggs
ggD
v
,Fr
gl
lls
lgD
vFr
,
Liquid Gas
• Lockhart-Martinelli parameter, X
• General definition
(subscripts G, L refer to gas or liquid phase)
• Used to describe wet-gas flows where X < 0.3
• Wet-gas flow are normally with GVF > 90%
Key Definitions
g
l
g
l
l
g
g
l
G
L
Q
Q
m
m
Fr
FrX
CFD Modelling of
Multiphase Flows
Traditional Measurement Methods
Traditional Measurement
MULTIPHASE FLOW
GAS
WATER OIL
Measure separated phases – using traditional meters: – GAS: Orifice, Vortex … – LIQUID: Turbine, PD, Coriolis … – WLR: Coriolis, grab samples … (2-phase separators)
Traditional Measurement
MULTIPHASE FLOW
GAS
WATER OIL
– Poor level control, foaming, emulsions etc. phase contamination
– Liquid carry-over, gas carry-under, water-in-oil may be unmonitored
– Capital, operating and infrastructure costs can be high
– Only periodic testing may be possible (oilfield “well test”)
Wet-Gas Flow Measurement
- High GVF Multiphase Flows
Differential Pressure Meters
• Must correct for presence
of liquid as causes meter
to over-read
• Need info on wetness to
correct the gas flowrate
• Cheapest option
• New ISO Technical Report
Wet-Gas Flow Measurement
Commercial Wet-gas
Meters
• Provides water, oil and
gas flowrates
• Can use multiphase
metering technology
Wet-Gas Metering
Multiphase Flow Measurement
Technology
Multiphase Metering
Technologies
• MULTIPHASE METERS – GENERAL METHODOLOGY
– Measure BULK flowrate of MIXTURE : QMIX Differential Pressure device
Positive Displacement meter
Cross Correlation technique etc.
– Measure PHASE FRACTIONS : O , W , G Gamma-Ray Absorption
Electrical Properties
Microwave etc.
– Calculate INDIVIDUAL phase flowrates from: QWAT = W . QMIX
QOIL = O . QMIX
QGAS = G . QMIX
Multiphase Metering
Technologies
• BULK FLOWRATE : P METER (e.g. VENTURI)
– Mass flow is function of DENSITY () and P
– Simple, robust design
– Need separate density measurement
– CD = f (WC, GVF, fluid properties, …) Must be characterised by testing
– Performance improved by mixing Vertical up-flow, Blinded-T on inlet
Generally still require Slip Model
– Low turndown / Finite pressure loss
ΔPρ2AεECm tD
P
• DP METER OPERATION IN VERY UNSTEADY FLOWS
• Fast sampling required to reduce “averaging errors”
1 sec
Q (l/s)
20
10
30
1 sec
P (mbar)
400
100
900
Multiphase Metering
Technologies
• BULK FLOWRATE : CROSS CORRELATION
– Compare response of 2 (+) axially displaced sensors
Capacitance probes
Densitometers
Pressure Gauges
SENSOR 2 SENSOR 1
Multiphase Metering
Technologies
• PHASE FRACTION : GAMMA RAY ABSORPTION
DE
TE
CT
OR
– Number of gamma-rays detected :
I = IO exp( - D )
– Linear Absorption Coefficient depends on fluid in pipe GAS is weak absorber ( low), WAT is strong absorber ( high)
Absorption probability also depends on gamma-ray energy (E)
Multiphase Metering
Technologies
• PHASE FRACTION : GAMMA RAY ABSORPTION − HIGH Energy Gamma: Absorption Fluid DENSITY only
GAS
OIL
WATER
Transmitted
Counts
Multiphase Metering
Technologies
• PHASE FRACTION : GAMMA RAY ABSORPTION − HIGH Energy Gamma: MIXTURE in pipeline
Interpolate between LIQ and GAS calibration rates: GVF
Observe where flow is liquid dominant Or gas dominant Transmitted
Counts
MIX
GAS
LIQ SLUG
GAS BUBBLE
Gives GAS / LIQ ratio but poor discrimination of OIL from WATER
Multiphase Metering
Technologies
• PHASE FRACTION : GAMMA RAY ABSORPTION
− For WLR include LOW E : Absorption Fluid DENSITY + TYPE
GAS
OIL
WATER
Transmitted
Counts
Multiphase Metering
Technologies
• PHASE FRACTION : GAMMA RAY ABSORPTION
− For WLR and GVF need both LOW E and HIGH E
− Plot I(EHIGH) vs I(ELOW)
− Corners = Pure Phases
− Internal points = Mixtures
− Interpolate for GVF + WC
− Salinity changes = errors
I (ELOW)
I (EHIGH)
Wat
Oil
Gas
Mix
50% WC
20% GVF
Multiphase Metering
Technologies
Flow Meter Selection and Verification
• WHAT IS THE ROLE OF THE MULTIPHASE METER ?
• Well Testing?
• Control and Monitoring?
• Production Allocation?
• WHERE WILL THE METERING BE APPLIED ?
• Onshore?
• Offshore topside (manned / unmanned)?
• Subsea?
• Mobile ?
• WHAT ARE THE CONDITIONS TO BE METERED ?
• Will the conditions change over time?
• HOW MANY METERS WILL BE APPROPRIATE ?
• Replacing test separator?
Flow Meter Selection
• Before installation
• Joint Industry Projects (JIP) to evaluate technology
• Factory Acceptance Testing (FAT)
• at independent facility like NEL
• at manufacturer’s facility
• After installation
• Against a test separator
• Other options.....
• Against another meter?
• Sampling?
• Check sensors
Validation of Flow Meters
• Flow regimes for horizontal and vertical flows
• How to describe a multiphase flow
• Challenges with measuring flow rates
• Wet-gas flow measurement
• Different multiphase metering technologies
• Considerations for selecting a meter and verifying the
performance
Multiphase flow measurement is much more
challenging than single phase metering
Summary
Any questions?
Thank you for listening
Multiphase & Wet-Gas Flow Measurement
Training Course, Aberdeen
25 February 2014
Introduction to Measurement Uncertainty
Measurement Training Course, Aberdeen
26 February 2014
Contact me at email: [email protected]
Forthcoming NEL Presentations
NEL Contacts Audit & Allocation Alick MacGillivray [email protected]
CFD Neil Bowman [email protected]
Densitometers Norman Glen [email protected]
Erosion John Peters [email protected]
Flow Consortium Phil Mark [email protected]
Heavy Oil Chris Mills [email protected]
Measurement Consultancy
Calum Hardie
Craig Marshall
Chris Mills
Measurement Uncertainty Alick MacGillivray [email protected]
Meter Diagnostics Craig Marshall [email protected]
MeterVue Phil Mark [email protected]
Multiphase Terri Leonard [email protected]
PPDS Lynn Hunter [email protected]
Single Phase Metering Bob Belshaw [email protected]
Training Helen Tulloch [email protected]
Umbilicals Janice MacLeod [email protected]
Valve Testing John Dods [email protected]
Wet Gas Emmelyn Graham [email protected]
NEL Contact Tel: + 44 (0) 1355 220222
For general queries contact the sales team on [email protected]
