Advanced Production Management Flare/Vent Metering If you can t t measure, you can t t manage Lex Scheers lex.scheers@shell.com Prepared for Hydrocarbon Production Accounting workshop Moscow, 16-17 Dec 2008 1
Content 2 1. Introduction 2. Flow regimes 3. Fluid properties 4. Flow measurement 5. Composition measurement 6. Design considerations 7. Operational aspects
Introduction - The product balance 3 FLARE GAS, OWN USE $ SALES GAS $ PRODUCTION FACILITY for each phase Σin = Σout $ $ $ GAS OIL WATER $ $ GAS SALES OIL $ WATER $ WATER DISPOSAL RESERVOIR
Flare en Vent yearly quantities 4 According to the Global Gas Flare Reduction (GGFR) program Estimate 150-170 * 10 9 Sm 3 /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)
World Natural Gas Consumption 2004-2030 5 (10 12 cft 33 * 10 9 m 3 ) 165 Groningen gas field (GGF) 2,850 x 10 9 Sm3 8,500 x 10 12 cft 10 14 MJ (10 17 Btu) 2,850 * 10 9 m 3 100 1 GGF 150 * 10 9 m 3
Oil Shrinkage and Gas Expansion 6 V = 10,000 Sm 3 /d ρ = 0.90 kg/m 3 M = 9,000 kg Q E=1.2094 Production Process V = 12,094 Sm 3 /d ρ = 0.85 kg/m 3 M = 10,280 kg Q Separator Q Gas to Liquid Liquid to Gas Q Stock Tank V = 100 Sm 3 /d ρ = 750 kg/m 3 M = 75,000 kg S=0.97 V = 97 Sm 3 /d ρ = 760 kg/m 3 M = 73,720 kg Total Mass M = 84,000 kg M = 84,000 kg
Conservation laws (no liquid <> gas transport) 7 Conservation of Mass (kg, tonnes) Conservation of Standard Volume (Sm 3, Scft) Conservation of Actual Volume (Am 3, cft) Conservation of Mols (kmol) Conservation of Energy (MJ, BTU, etc)?? Conservation of Misery
Continuous Flare and Vent measurement 8 Oil production facilities (associated gas) No gas infra-structure present No gas market present No economic benefit to re-inject the gas in the reservoir Often associated gas is considered as a by-product Gas production facilities Disposal of waste streams Acid gas from sweetening plant Glycol dehydration units Instrument vent gas Process flash gas In general flare and vent gas has various origins and therefore greatly varies in gas composition and quality
Intermittent Flare and Vent measurement 9 Well testing Well servicing Depressurization (manual or controlled) Compressor engine starts Process upsets Maintenance and inspection
What is the ideal Gas Flare/Vent Meter? 10 Tolerant to wet and dirty gas streams Large turndown small 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!!!
Content 11 1. Introduction 2. Flow regimes 3. Fluid properties 4. Flow measurement 5. Composition measurement 6. Design considerations 7. Operational aspects
Velocity profile and velocity integration [1] 12 Point Multi-Point Path Averaging
Velocity profile and velocity integration [2] Ref : API MPMS 14.10 [2007] 13
Content 14 1. Introduction 2. Flow regimes 3. Fluid properties 4. Flow measurement 5. Composition measurement 6. Design considerations 7. Operational aspects
Difference between Sm 3 and m 3 15 Pressure room 101.3 kpa (1.013 bar) Pressure room 405.3 kpa (4.053 bar) 1Sm 3?Sm 3 How much gas is present in the balloon?
Equations of state -Ideal gases 16 For ideal gases p. V = n. RT. p = absolute pressure N/m 2 V = volume at p and T m 3 n = amount of substance mol R = universal gas constant 8.314 J/(mol.K) or (kpa.m 3 )/(kmol.k) T = absolute temperature K this is 273.15 + t ( C) Note: 1 mol is the amount of substance which contains as many elementary entities (6.02 *10 23 ) as there are atoms in 12 gram of Carbon-12
Equations of state - Compressibility factor z is compressibility factor 1) z is function of p and T 2) z depends on composition p. V = z. n. RT. pv. n. RT. = z( p, T) 1.3 1.2 1.1 N 2 H 2He Ar z = 1 for 1) Ideal gases 2) Low pressure gases 1.0 0.9 0.8 0.7 Ideal gas 0 10 20 30 40 p (MPa) 17
Content 18 1. Introduction 2. Flow regimes 3. Fluid properties 4. Flow measurement 5. Composition measurement 6. Design considerations 7. Operational aspects
Terms and definitions 19 Primary devices Flow meter body Primary sensing elements Transmitters Secondary devices Other instruments measuring process conditions pressure, temperature and composition Tertiary devices Calculation devices Data loggers DCS, RTU, flow computers
Single phase flowrate measurement - Operating range 20 Operating range: Turn-down: the range of flow rates within which the specified accuracy can be obtained. the ratio of maximum to minimum flow in the operating range. Rangeability and Accuracy Max:Min 3:1 - limited range ~ 10:1 - moderate range > 20:1 - good range Accuracy (%) 40 30 20 10 0-10 Minimum at +/- 10% -20 Minimum -30 at +/- 5% -40 0 10 20 30 40 50 60 70 Flow (arbitrary units)
Bernoulli s Equation - Application to the Orifice/Venturi/Pitot devices Flow v 1, A 1, P 1 v 2, A 2, P 2 v is fluid velocity A is area P is pressure. At the same height in the flow: 1 2 1 2 P 1 + 2 ρ v1 = P2 + 2 ρv2 From continuity: Combining: v 1 = v 2 A A 2 1 = 1 2 A P 2 ρv2 1 A 2 Δ 2 2 1 Need to know the density 21
Venturi tube 22 Type of Measurement Δp (Bernoulli) Measurement point/path Cross Sectional Area Diameter 2 to 48 Rangeability 10:1 Straight pipe req ments 6-20 D upstream, 2-40 D downstream Total pressure loss 10-20% of the Δp P and T required ActVol = Yes, StdVol = Yes, Mass = Yes Uncertainty approx. 1-3% full scale Composition dependent Yes, need density Suitable in wet/dirty gas Yes, small amounts Other comments Eliminate pulsation
Orifice plate 23 Type of Measurement Δp (Bernoulli) Measurement point/path Cross Sectional Area Diameter 1 to 72 Rangeability 5:1 Straight pipe req ments 6-20 D upstream, 2-40 D downstream Total pressure loss High P and T required ActVol = Yes, StdVol = Yes, Mass = Yes Uncertainty approx. 2-4% full scale Composition dependent Yes, need density Suitable in wet/dirty gas Yes, small amounts (drainhole) Other comments Pulsation
(Averaging) Pitot tube 24 Type of Measurement Δp (Bernoulli) Measurement point/path Point or Multipoint averaging Diameter 1 to 72 (insertion) Rangeability 3:1 Straight pipe req ments 8-10 D upstream, 3 D downstream Total pressure loss Low, Nil P and T required ActVol = Yes, StdVol = Yes, Mass = Yes Uncertainty approx. 1-5% full scale Composition dependent Yes, need density Suitable in wet/dirty gas Limited Other comments Positioning critical, fouling, pulsation
(Averaging) Pitot tube 25 Endress & Hauser DP61D Endress & Hauser DP62D
(Insertion) Turbine meter 26 Type of Measurement Velocity/Volumetric Measurement point/path Point or Cross Sectional Area Diameter 1 to 24 (insertion) Rangeability 20:1 to 100:1 Straight pipe req ments 10 D upstream, 5 D downstream Total pressure loss Design dependent (insertion low) P and T required ActVol = No, StdVol = Yes, Mass = Yes Uncertainty approx. 0.5% (insertion much higher) Composition dependent No Suitable in wet/dirty gas Limited Other comments Flow straightening, fouling
Vortex flow meter f = S. V L 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 27
Vortex flow meter 28 Type of Measurement Velocity Measurement point/path Cross Sectional Area Diameter 1 to 24 Rangeability 30:1 Straight pipe req ments 10-20 D upstream, 5 D downstream Total pressure loss Design dependent P and T required ActVol = No, StdVol = Yes, Mass = Yes Uncertainty approx. 2% Composition dependent No Suitable in wet/dirty gas Limited Other comments Flow straightening, pulsation
UltraSonic Gas Flow Measurement (transit time) C = Velocity of sound D = Pipe diameter L = Acoustic path length Flow L D t t AB BA = = C + v C v m m L.cos( ϕ) L.cos( ϕ) v m = Q = L 1. 2.cos( ϕ) t π. D 4 2. v m AB 1 t BA 29
UltraSonic Gas Flow Measurement (transit time) 30 Type of Measurement Velocity Measurement point/path Path or multi-path Diameter > 3 Rangeability up to 2000:1 Straight pipe req ments 10-30 D upstream, 5-10 D downstream Total pressure loss Nil P and T required ActVol = No, StdVol = Yes, Mass = Yes Uncertainty approx. 1-5% (no of paths) Composition dependent No Suitable in wet/dirty gas Moderate (LVF < 0.5%) Other comments Elimination of swirl
UltraSonic Gas Flow Measurement - Accuracy (1) 31 Q = L A 2 cos( φ) 1 t AB 1 t BA K Two uncertainty issues: 1) Travel time measurement (t AB, t BA ) Instrument error 2) Installation parameters (L, A, φ) Geometry error
GE Sensing GF 868 Flare Gas Meter 32 Temperature Transmitter Spool piece Best/Preferred solution New build Planned shutdown Hot/ColdTap Large Lines Retrofit Digital Analog and Alarm Output Preamplifier Upstream Transducers Downstream Transducers Pressure Transmitter Inside view of a bias 90 flare gas installation FLOW
Fluenta FGM 160 Flare Gas Meter 33 Transducers
Fluenta FGM 160 Flare Gas Meter 34
Test facility NMI Delft 35 Master meter s
UltraSonic Gas Flow Measurement - Typical calibration curve 36
Optical LaserTwoFocus 37 Type of Measurement Velocity Measurement point/path Point Diameter Any (insertion) Rangeability up to 3000:1 Straight pipe req ments 10-30 D upstream, 5-10 D downstream Total pressure loss Nil P and T required ActVol = No, StdVol = Yes, Mass = Yes Uncertainty approx. 3-7% Composition dependent No Suitable in wet/dirty gas Moderate Other comments Elimination of swirl
Optical Transit Time Velocimeters - LaserTwoFocus (L2F) Meters 38 Detecting Optics Particle Pro s High turn-down High accuracy Gas composition independent Insertion type Con s Point measurement Illuminating Optics v = S ΔT Photon Control L2B Optical Gas Flow Meter
Thermal Mass Flow meter (Hot wire anemometer) 39 Type of Measurement Velocity Measurement point/path Point Diameter Any (insertion) Rangeability 1000:1 Straight pipe req ments 8-10 D upstream, 3 D downstream Total pressure loss Nil P and T required ActVol = Yes, StdVol = No, Mass = No Uncertainty approx. 1-3% Composition dependent Yes, need thermal conductivity Suitable in wet/dirty gas No Other comments Positioning, fouling,
Thermal Mass Flow meter (Anemometer) 40 Endress & Hauser t-mass 65I Size : 2.5-60 Turndown : 100:1 Accuracy : 1%
41 Technology Actual Volume Standard Volume Mass UltraSonic (V) Output Vortex Output Optical Output UltraSonic (M) Output Thermal Output Flowrate conversions Actual Conditions <> Standard Conditions = f f b b b f v v Z T P Z T P q Q.... b m v q Q ρ = b v m Q q ρ = f m q v q ρ. = f m q v q ρ. = f m q v q ρ. = = f f b b b f v v Z T P Z T P q Q.... = f f b b b f v v Z T P Z T P q Q.... b v m Q q ρ = b m Q v q ρ. =
Content 42 1. Introduction 2. Flow regimes 3. Fluid properties 4. Flow measurement 5. Composition measurement 6. Design considerations 7. Operational aspects
Composition Monitoring 43 Some FlowMeters are composition dependent e.g. Δp type of meters Is relationship composition <>correction known Is 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. H 2 S, SO 2 or GHG reporting Two ways to monitor composition: 1) Sampling and analyses 2) Continuous on-line analyzers
Composition Monitoring 1) Sampling and analyses 44 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
Composition Monitoring 2) Continuous on-line analyzers 45 Only applicable for clean/processed gas Need for conditioning units (sample train) Higher maintenance Higher costs Not often used Daniel Model 500 Gas Chromatographs
Content 46 1. Introduction 2. Flow regimes 3. Fluid properties 4. Flow measurement 5. Composition measurement 6. Design considerations 7. Operational aspects
Design considerations Safety Staff Equipment Location Knock-out drums needed Accessibility Single or Multiple meters Piping Flow profile Straight runs up- and downstream Flow conditioners Sampling arrangements Process conditions P and T measurement Composition measurement Requirements Accuracy Availability Continuous measurement Flare Gas Meter Min/Max flowrate Min/Max gas velocity Rate of change Typical gas composition Change of gas composition Effect of fouling Pressure range Temperature range Ambient temperature Sensitivity to liquids Gas density (z-factor) Gas flowrate calculations Meter output Diagnostics software Signal processing Competence Service of vendor Training own staff 47
Flare Meter Datasheet - Ref MPMS API 14.10 48
Flare Meter Datasheet - Ref MPMS API 14.10 49
Flare Meter Datasheet - Ref MPMS API 14.10 50
Content 51 1. Introduction 2. Flow regimes 3. Fluid properties 4. Flow measurement 5. Composition measurement 6. Design considerations 7. Operational aspects
Methods for spot checks 52 No shut down required Personnel operating in flare area >> Need for strict procedures and policies Safety Need for sampling and injection points Also 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
Methods for spot checks 1) Insertion flow meters 53 Insertion point needs 20 D upstream straight length 5D downstream straight length Thermal anemometer (thermal mass flow meter) Great sensitivity No wet or dirty gas applications Subject to fouling Pitot tube Mechanically more complex Subject to fouling
Methods for spot checks 2) Tracer dilution technology 54 Injection of tracer (with known injection rate) upstream After sufficient mixing sampling of the gas Analyses for the tracer Perform mass balance to determine the total gas flowrate or in other words: the dilution of tracer is a measure for the total gas flowrate Sufficient mixing of tracer is required Sampling at least 20 D from injection tracer point Background correction Sample without tracer injection to find out background Tracer requirements: Stable or inert substance Reasonable price Easy onside analyses Example is SF 6
Methods for spot checks 2) Tracer dilution technology 55 Provided Q p >> Q i, the concentration of tracer in the pipe is: Tracer supply bottle C i Metering pump Tracer mass balance: C i Gas flow rate = x Injection flow rate C p Wet gas flow C p Mixing distance Gas sample c i = Tracer concentration in the injected solution [mol/m 3 ] c p = Tracer concentration in the pipeline [mol/m 3 ] Q i = Injection flow rate of tracer solution [m 3 /s] Q p = Liquid flow rate in pipeline [m 3 /s]
Methods for spot checks 3) Pulse velocity technique 56 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
Continuous flare and vent measurement - Conclusion 57 Ultrasonic is the preferred choice Liquid 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