Sampling - MassPhase Wet Gas System Agents-R2 · MassPhase Wet Gas Measurement System ... •...
Transcript of Sampling - MassPhase Wet Gas System Agents-R2 · MassPhase Wet Gas Measurement System ... •...
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MassPhase applications
• Wet gas metering • Use with existing or new wet gas meter (i.e. venturi etc)
• Measurement of liquid/gas mass ratio to allow compensation of meter for over-measurement caused by liquid content
• Using Murdoch, Chisholm, de Leeuw etc. equations
• Provide liquid and gas compositional samples.
• Hydrocarbon valuation from samples
• Well testing for high GVF wells (>95% GVF) • Higher accuracy that wet gas and multiphase meters
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MassPhase commercial benefits
• Allocation measurement• Improve measurement accuracy to reduce the taxation
revenue burden
• Better partner revenue allocation on shared production facilities
• Cost effective and accurate revenue allocation for margin assets produced using shared facilities
• Well testing• High accuracy well test data for improved reservoir
management
• Increase well test frequency reducing uncertainty
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Measurements
• Highly accurate liquid/gas mass measurement • Each system is an application specific design
• Liquid mass measurement is typically better than 0.5%
• Gas mass measurement is typically better than 0.5%
• Sample of dry gas for analysis
• Sample of liquids for analysis• Allowing determination of component ratio, densities and
valuation of any hydrocarbons
• Manual or automatic system
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The alternatives
• Spot sample• Completely unrepresentative
• Dye tracer• Expensive, difficult to operate and high uncertainty
• Wet gas meter• Measures liquid fractions but not components
• (i.e. water, methanol and condensate etc)
• Lower accuracy - typically +/- 5%
• Multiphase meter• Not suitable for applications above 95% GV
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Patented design principle
• Extract a representative bypass loop from the main pipeline
• Filter the liquids into a molecular sieve of known mass – this dries the gas
• Measure the mass of dry gas
• Measure the accumulated mass of liquid in the sieve
• Use the accumulated mass of liquid in the sieve for analysis
• Extract a sample of dry gas for analysis
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Wet gas sampling system
Molecular Sieve
Mass flow meter
Gas sample receiver
Wet Gas sample loop
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Wet gas sampling – Step 1
Loop is flowed to stabilise pipe-work (P&T)
The mass of empty molecular sieve is known
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Wet gas sampling – Step 2
Flow diverted through mole sieve and mass flow meter
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Wet gas sampling – Step 3
Mass of dry gas measured and mass of liquid accumulates in molecular sieve during sampling
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Wet gas sampling
• Dry gas mass determined by flow meter
• Liquid mass determined from increase in molecular sieve mass caused by liquid retention
• Normal dry gas sample used for composition analysis
• Liquids are removed from the molecular sieve to provide a sample for composition analysis
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Maintain representivity
• The profile probe, inlet system and loop are sized to ensure representivity, the required velocity and volume throughput
• Loop is designed with no liquid traps, drop out points or constrictions where aerosol formation could occur
• System designed so that flow rate can be adjusted/changed to meet future flow conditions
• Either using multi-stage regulated let-down (to the flare stack) or returned downstream
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Liquid mass measurement
• If you take a 1 litre spot gas sample it is not possible to determine the liquid/gas ratio or the composition because the liquids would be lost in the overall measurement. • Mass or volume is too small to measure or extract from
the sample
• Vessel: 1 litre volume (15kg)
• Liquids: 2.1ml (1.7gm) (typical)
• No mass measurement system has the required accuracy AND turndown
• Volumes so small that it is likely to be entrained on receiver walls or lost in dead volumes
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Uncertainty - conclusions
• Uncertainty is mainly determined by slipstream sampling methodology
• Slipstream error is minimised by ‘belt and braces’approach of optimising dispersion and multipoint profiling.
• Mass accuracy of loop flow meter is typically 0.35%
• Extracted liquid mass accuracy is typically 0.20% - 0.33%
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Options
• Multiple systems in single cabinet
• Manual system
• Automatic system
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BP Juno project
• Sample take-off installed downstream of venturi, in well mixed flow
• Flow regime, mist flow, no slugs predicted
• Liquids contain condensate, methanol and water
• 15:1 turndown
• Now installed offshore
• UK southern gas basin
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Data set required for system design
• Gas void/mass fraction
• Water/condensate/methanol ratios
• Fluid densities
• Liquid and gas composition
• Predicted flow regimes
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Sample recovery
• Dry gas sample from discharging constant pressure receiver
• Liquid sample extracted from mole sieve using heating/cooling process