1LS, Nov 2008
Flare/Vent MeteringFlare/Vent MeteringIf you canIf you can’’t measure, you cant measure, you can’’t managet manage
Lex ScheersLex [email protected]@shell.com
Advanced Production Management
Prepared for Hydrocarbon Production Accounting workshopMoscow, 16-17 Dec 2008
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1. Introduction2. Flow regimes3. Fluid properties4. Flow measurement5. Composition measurement6. Design considerations7. Operational aspects
Content
3LS, Nov 2008
Introduction- The product balance
GAS
GAS
OIL
OIL
WATE
RW
ATE
R
RESERVOIRGA
SGA
S
WATE
RW
ATE
R
WATE
R W
ATE
R DIS
POSA
LDIS
POSA
L
SALES GASSALES GAS
SALES OILSALES OIL
FLARE GAS, FLARE GAS, OWN USEOWN USE $
$$
$$
$
$ $ $
PRODUCTION FACILITYfor each phase
Σin = Σout
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Flare en Vent yearly quantities
According to the Global Gas Flare Reduction (GGFR) programEstimate 150 - 170 * 109 Sm3/year
This equals 4 - 5% of the Global Gas Consumption
or 5 - 6% of the total “Groningen Gas Field”
Valuable energy resource wasted
Harms the environment (Green House Gasses)
5LS, Nov 2008
World Natural Gas Consumption2004 - 2030
(1012 cft ≈ 33 * 109 m3)
≈ 2,850 * 109 m3
Groningen gas field (GGF)≈ 2,850 x 109 Sm3≈ 8,500 x 1012 cft≈ 1014 MJ (1017 Btu)
100
165
1 GG
F
≈ 150 * 109 m3
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Oil Shrinkage and Gas Expansion
Separator
Q
Gas to Liquid
Liquid to Gas
ProductionProcess
Q
Q Q
V = 10,000 Sm3/dρ = 0.90 kg/m3
M = 9,000 kg
V = 12,094 Sm3/dρ = 0.85 kg/m3
M = 10,280 kg
V = 100 Sm3/dρ = 750 kg/m3
M = 75,000 kg
V = 97 Sm3/dρ = 760 kg/m3
M = 73,720 kg
Total Mass M = 84,000 kg M = 84,000 kg
S=0.97
E=1.2094
StockTank
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Conservation laws(no liquid <> gas transport)
Conservation of Mass (kg, tonnes)
Conservation of Standard Volume (Sm3, Scft)
Conservation of Actual Volume (Am3, cft)
Conservation of Energy (MJ, BTU, etc)
Conservation of Misery
Conservation of Mols (kmol)
??
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Continuous Flare and Vent measurement
Oil production facilities (associated gas)No gas infra-structure presentNo gas market presentNo economic benefit to re-inject the gas in the reservoirOften associated gas is considered as a by-product
Gas production facilitiesDisposal of waste streamsAcid gas from sweetening plantGlycol dehydration unitsInstrument vent gasProcess flash gas
In general flare and vent gas has various origins and therefore greatly varies in gas composition and quality
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Intermittent Flare and Vent measurement
Well testing
Well servicing
Depressurization (manual or controlled)
Compressor engine starts
Process upsets
Maintenance and inspection
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What is the ideal Gas Flare/Vent Meter ?
Tolerant to wet and dirty gas streams
Large turndownsmall waste streams during normal operations
large streams during blowdown and depressurization
Independent of fluid properties
Installation without a facility shut-down
Full bore measurements
Accuracy of a few percent
No upstream or downstream pipe requirements
Flow regime independent
Hence, the ideal Gas Flare/Vent meter does not exist !!!
11LS, Nov 2008
1. Introduction2. Flow regimes3. Fluid properties4. Flow measurement5. Composition measurement6. Design considerations7. Operational aspects
Content
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Velocity profile and velocity integration [1]
Path AveragingMulti-PointPoint
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Velocity profile and velocity integration [2]
Ref : API MPMS 14.10 [2007]
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1. Introduction2. Flow regimes3. Fluid properties4. Flow measurement5. Composition measurement6. Design considerations7. Operational aspects
Content
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Pressure room 405.3 kPa (4.053 bar)
1 Sm3 ? Sm3
Pressure room 101.3 kPa (1.013 bar)
How much gas is How much gas is present in the balloon ?present in the balloon ?
Difference between Sm3 and m3
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Equations of state- Ideal gases
p = absolute pressure N/m2
V = volume at p and T m3
n = amount of substance molR = universal gas constant 8.314 J/(mol.K) or (kPa.m3)/(kmol.K)T = absolute temperature K this is 273.15 + t (°C)
For ideal gases
TRnVp ... =
Note: 1 mol is the amount of substance which contains as many elementary entities (6.02 *1023) as there are atoms in 12 gram of Carbon-12
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Equations of state- Compressibility factor
),(..
. TpzTRn
Vp=
1.0
0.9
0.8
0.7
1.1
1.2
1.3
p (MPa)
0 10 20 30 40
Ideal gas
H2He
N2
Ar
z = 1 for 1) Ideal gases2) Low pressure gases
z is compressibility factor1) z is function of p and T2) z depends on composition
TRnzVp .... =
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1. Introduction2. Flow regimes3. Fluid properties4. Flow measurement5. Composition measurement6. Design considerations7. Operational aspects
Content
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Terms and definitions
Primary devicesFlow meter bodyPrimary sensing elementsTransmitters
Secondary devicesOther instruments measuring process conditionspressure, temperature and composition
Tertiary devicesCalculation devicesData loggersDCS, RTU, flow computers
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Single phase flowrate measurement- Operating range
Operating range: the range of flow rates within which thespecified accuracy can be obtained.
Turn-down: the ratio of maximum to minimum flowin the operating range.
Rangeability and Accuracy
Flow (arbitrary units)
Acc
urac
y (%
)
-40-30-20-10
010203040
0 10 20 30 40 50 60 70
Minimumat +/- 5%
Minimumat +/- 10%Max:Min
3:1 - limited range~ 10:1 - moderate range> 20:1 - good range
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Bernoulli’s Equation- Application to the Orifice/Venturi/Pitot devices
vv11, A, A11, P, P11 vv22, A, A22, P, P22Flow
v is fluid velocityA is areaP is pressure.
At the same height in the flow: 222
12
212
11 vPvP ρρ +=+
From continuity:
1
2
2
1
AA
vv
=
Combining:⎥⎦
⎤⎢⎣
⎡−=Δ 2
1
222
221 1
AAvP ρ
Need to knowthe density
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Venturi tube
Type of Measurement Δp (Bernoulli)Measurement point/path Cross Sectional AreaDiameter 2 to 48”Rangeability 10:1Straight pipe req’ments 6-20 D upstream, 2-40 D downstreamTotal pressure loss 10-20% of the ΔpP and T required ActVol = Yes, StdVol = Yes, Mass = YesUncertainty approx. 1-3% full scaleComposition dependent Yes, need densitySuitable in wet/dirty gas Yes, small amountsOther comments Eliminate pulsation
23LS, Nov 2008
Orifice plate
Type of Measurement Δp (Bernoulli)Measurement point/path Cross Sectional AreaDiameter 1 to 72”Rangeability 5:1Straight pipe req’ments 6-20 D upstream, 2-40 D downstreamTotal pressure loss HighP and T required ActVol = Yes, StdVol = Yes, Mass = YesUncertainty approx. 2-4% full scaleComposition dependent Yes, need densitySuitable in wet/dirty gas Yes, small amounts (drainhole)Other comments Pulsation
24LS, Nov 2008
(Averaging) Pitot tube
Type of Measurement Δp (Bernoulli)Measurement point/path Point or Multipoint averagingDiameter 1 to 72” (insertion) Rangeability 3:1Straight pipe req’ments 8-10 D upstream, 3 D downstreamTotal pressure loss Low, NilP and T required ActVol = Yes, StdVol = Yes, Mass = YesUncertainty approx. 1-5% full scaleComposition dependent Yes, need densitySuitable in wet/dirty gas LimitedOther comments Positioning critical, fouling, pulsation
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(Averaging) Pitot tube
Endress & HauserDP61D
Endress & HauserDP62D
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(Insertion) Turbine meter
Type of Measurement Velocity/VolumetricMeasurement point/path Point or Cross Sectional AreaDiameter 1 to 24” (insertion)Rangeability 20:1 to 100:1Straight pipe req’ments 10 D upstream, 5 D downstreamTotal pressure loss Design dependent (insertion low)P and T required ActVol = No, StdVol = Yes, Mass = YesUncertainty approx. 0.5% (insertion much higher)Composition dependent NoSuitable in wet/dirty gas LimitedOther comments Flow straightening, fouling
27LS, Nov 2008
Vortex flow meter
where,f = frequency of the vortices L = characteristic length of the bluff body V = velocity of the flow over the bluff body S = Strouhal number, which is essentially a constant
for a given body shape within its operating limits
LVSf .
=
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Vortex flow meter
Type of Measurement VelocityMeasurement point/path Cross Sectional AreaDiameter 1 to 24”Rangeability 30:1Straight pipe req’ments 10-20 D upstream, 5 D downstreamTotal pressure loss Design dependentP and T required ActVol = No, StdVol = Yes, Mass = YesUncertainty approx. 2% Composition dependent NoSuitable in wet/dirty gas LimitedOther comments Flow straightening, pulsation
29LS, Nov 2008
UltraSonic Gas Flow Measurement (transit time)
m
BAABm
mBA
mAB
vDQ
ttLv
vCLt
vCLt
.4.
11.)cos(.2
)cos(.
)cos(.
2π
ϕ
ϕ
ϕ
=
⎥⎦
⎤⎢⎣
⎡−=
−=
+=
C = Velocity of soundD = Pipe diameterL = Acoustic path length
LFlow D
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UltraSonic Gas Flow Measurement (transit time)
Type of Measurement VelocityMeasurement point/path Path or multi-pathDiameter > 3”Rangeability up to 2000:1Straight pipe req’ments 10-30 D upstream, 5-10 D downstreamTotal pressure loss NilP and T required ActVol = No, StdVol = Yes, Mass = YesUncertainty approx. 1-5% (no of paths) Composition dependent NoSuitable in wet/dirty gas Moderate (LVF < 0.5%)Other comments Elimination of swirl
31LS, Nov 2008
UltraSonic Gas Flow Measurement- Accuracy (1)
Ktt
ALQBAAB
⋅⎟⎟⎠
⎞⎜⎜⎝
⎛−⋅
⋅⋅=
11)cos(2 φ
Two uncertainty issues:
1) Travel time measurement (tAB, t BA)Instrument error
2) Installation parameters (L, A, φ)Geometry error
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GE Sensing GF 868 Flare Gas Meter
Downstream Transducers
Upstream Transducers
Pres
sure
Tra
nsm
itte
r
Temperature Transmitter
Preamplifier
Digital Analog and Alarm Output
FLOW
Spool piece• Best/Preferred solution• New build• Planned shutdownHot/ColdTap• Large Lines• Retrofit
Inside view of a bias 90 flare gas installation
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Fluenta FGM 160 Flare Gas Meter
Transducers
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Fluenta FGM 160 Flare Gas Meter
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Test facility NMI Delft
Master meter’s
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UltraSonic Gas Flow Measurement- Typical calibration curve
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Optical LaserTwoFocus
Type of Measurement VelocityMeasurement point/path PointDiameter Any (insertion)Rangeability up to 3000:1Straight pipe req’ments 10-30 D upstream, 5-10 D downstreamTotal pressure loss NilP and T required ActVol = No, StdVol = Yes, Mass = YesUncertainty approx. 3-7% Composition dependent NoSuitable in wet/dirty gas ModerateOther comments Elimination of swirl
38LS, Nov 2008
Optical Transit Time Velocimeters- LaserTwoFocus (L2F) Meters
Particle
Illuminating Optics
Detecting Optics
TSv
Δ=
Pro’s• High turn-down• High accuracy• Gas composition independent• Insertion typeCon’s• Point measurement
Photon Control L2B Optical Gas Flow Meter
39LS, Nov 2008
Thermal Mass Flow meter (Hot wire anemometer)
Type of Measurement VelocityMeasurement point/path PointDiameter Any (insertion)Rangeability 1000:1Straight pipe req’ments 8-10 D upstream, 3 D downstreamTotal pressure loss NilP and T required ActVol = Yes, StdVol = No, Mass = NoUncertainty approx. 1-3% Composition dependent Yes, need thermal conductivitySuitable in wet/dirty gas NoOther comments Positioning, fouling,
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Thermal Mass Flow meter (Anemometer)
Endress & Hausert-mass 65I
Size : 2.5-60”Turndown : 100:1Accuracy : 1%
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Technology Actual Volume Standard Volume Mass
UltraSonic (V) Output
Vortex Output
Optical Output
UltraSonic (M) Output
Thermal Output
Flowrate conversions Actual Conditions <> Standard Conditions
⎟⎟⎠
⎞⎜⎜⎝
⎛=
ffb
bbfvv ZTP
ZTPqQ
....
b
mv
qQρ
=b
vm
Qqρ
=
fvm qq ρ.=
fvm qq ρ.=
fvm qq ρ.=
⎟⎟⎠
⎞⎜⎜⎝
⎛=
ffb
bbfvv ZTP
ZTPqQ
....
⎟⎟⎠
⎞⎜⎜⎝
⎛=
ffb
bbfvv ZTP
ZTPqQ
....
b
vm
Qqρ
= bvm Qq ρ.=
42LS, Nov 2008
1. Introduction2. Flow regimes3. Fluid properties4. Flow measurement5. Composition measurement6. Design considerations7. Operational aspects
Content
43LS, Nov 2008
Composition Monitoring
Some FlowMeters are composition dependente.g. Δp type of metersIs relationship composition <>correction knownIs sensitivity to composition high or low
Convert volumetric flowrate to mass or energy flowrate (or vv)Determine heating value of the gas Emission measurement, e.g. H2S, SO2 or GHG reporting
Two ways to monitor composition:
1) Sampling and analyses
2) Continuous on-line analyzers
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Composition Monitoring1) Sampling and analyses
Manual sample or auto sampler
Laboratory analyses
Low cost
Representativeness in wet gas streams Not suitable for LVF or GVF measurement
Suitable for separate liquid composition and gas composition
Flow proportionality
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Composition Monitoring2) Continuous on-line analyzers
Only applicable for clean/processed gas
Need for conditioning units (sample train)
Higher maintenance
Higher costs
Not often used
Daniel® Model 500Gas Chromatographs
46LS, Nov 2008
1. Introduction2. Flow regimes3. Fluid properties4. Flow measurement5. Composition measurement6. Design considerations7. Operational aspects
Content
47LS, Nov 2008
SafetyStaffEquipment
LocationKnock-out drums neededAccessibility Single or Multiple meters
PipingFlow profileStraight runs up- and downstreamFlow conditionersSampling arrangements
Process conditions P and T measurementComposition measurement
Requirements AccuracyAvailabilityContinuous measurement
Flare Gas Meter Min/Max flowrateMin/Max gas velocityRate of changeTypical gas composition Change of gas compositionEffect of foulingPressure rangeTemperature rangeAmbient temperatureSensitivity to liquidsGas density (z-factor)Gas flowrate calculationsMeter outputDiagnostics softwareSignal processing
CompetenceService of vendorTraining own staff
Design considerations
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Flare Meter Datasheet- Ref MPMS API 14.10
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Flare Meter Datasheet- Ref MPMS API 14.10
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Flare Meter Datasheet- Ref MPMS API 14.10
51LS, Nov 2008
1. Introduction2. Flow regimes3. Fluid properties4. Flow measurement5. Composition measurement6. Design considerations7. Operational aspects
Content
52LS, Nov 2008
Methods for spot checks
No shut down requiredPersonnel operating in flare area >>
Need for strict procedures and policies Safety
Need for sampling and injection pointsAlso for verification of primary measurements
Four ways to execute spot checks:
1) Insertion flow meters
2) End-of-pipe measurements
3) Tracer dilution technology
4) Pulse velocity technique
53LS, Nov 2008
Methods for spot checks1) Insertion flow meters
Insertion point needs 20 D upstream straight length5D downstream straight length
Thermal anemometer (thermal mass flow meter)Great sensitivityNo wet or dirty gas applicationsSubject to fouling
Pitot tubeMechanically more complexSubject to fouling
54LS, Nov 2008
Methods for spot checks2) Tracer dilution technology
Injection of tracer (with known injection rate) upstreamAfter sufficient mixing sampling of the gas Analyses for the tracer Perform mass balance to determine the total gas flowrateor in other words:the dilution of tracer is a measure for the total gas flowrateSufficient mixing of tracer is requiredSampling at least 20 D from injection tracer point Background correction
Sample without tracer injection to find out backgroundTracer requirements:
Stable or inert substanceReasonable priceEasy onside analyses Example is SF6
55LS, Nov 2008
Methods for spot checks2) Tracer dilution technology
ci = Tracer concentration in the injected solution [mol/m3]cp = Tracer concentration in the pipeline [mol/m3]Qi = Injection flow rate of tracer solution [m3/s]Qp = Liquid flow rate in pipeline [m3/s]
Provided Qp >> Qi, the concentration of tracer in the pipe is:
CiCp
x Injection flow rateGas flow rate =
Tracer mass balance:
Mixing distanceGas sample
Tracer supplybottle
Meteringpump
Ci
Wet gasflow
Cp
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Methods for spot checks3) Pulse velocity technique
Radioactive tracer injection upstream
Detection of passing the first pulse
Detection of passing of second pulse
Velocity is distance detectors (ΔS) over (ΔT) time delay
57LS, Nov 2008
Continuous flare and vent measurement- Conclusion
Ultrasonic is the preferred choiceLiquid content should be < 0.5% by volume
(if >0.5% use liquid knock out vessel)
Excellent rangeability
Good accuracy
No frequent calibration required
Independent of gas composition or density
