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Equations of State for Gas Condensates
Curtis H. Whitson NTNU & PERA SPE ATW Gas Condensate, Nov , 2002 London
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Key PVT Data EOS Modeling
Gas Z-factor C1 volume shift Gas Z-factor is the only PVT property which always needs accurate determination in a gas condensate reservoir. Initial gas and condensate in place. Gas and condensate recovery as a function of pressure during depletion drive. Don’t change without checking against measured Z-factor data. … for any pure component.
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Key PVT Data EOS Modeling
Gas Z-factor Condensate Gravity C1 volume shift Cn+ volume shifts
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Key PVT Data EOS Modeling
Gas Z-factor Condensate Gravity Dewpoint C1 volume shift Cn+ volume shifts Cn+ & C1 K-values Pressure where wellstream starts becoming significantly leaner. Pressure where incipient oil first appears.
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Key PVT Data EOS Modeling
Gas Z-factor Condensate Gravity Dewpoint Cn+ in Equilibrium Gas C1 volume shift Cn+ volume shifts Cn+ & C1 K-values Cn+ K-values Condensate rate profile. Condensate recovery. Define Gas Cycling Potential.
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Key PVT Data EOS Modeling
Gas Z-factor Condensate Gravity Dewpoint Cn+ in Equilibrium Gas Equilibrium Liquids “Oil” Composition Condensate Vro & o C1 volume shift Cn+ volume shifts Cn+ & C1 K-values Cn+ K-values
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Key PVT Data EOS Modeling
Gas Z-factor Condensate Gravity Dewpoint Cn+ in Equilibrium Gas Equilibrium Liquids “Oil” Composition Condensate Vro & o Condensate Vaporization Moles Equilibrium Oil C1 volume shift Cn+ volume shifts Cn+ & C1 K-values Cn+ K-values
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Key PVT Data EOS Modeling
Dewpoint Cn+ in Equilibrium Gas Equilibrium Liquids “Oil” Composition Condensate Vro & o Condensate Vaporization Moles Equilibrium Oil Cn+ & C1 K-values Phase Equilibria
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K-value Control Cn+ Component Properties EOS Constants A & B
Critical Pressure Critical Temperature Acentric Factor EOS Constants A & B
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K-value Control Cn+ Component Properties
Critical Pressure Critical Temperature Acentric Factor EOS Constants A & B Binary Interaction Parameters (BIPs) C1 – Cn+ Cn+ – Cn+ Intermediates C1 – CI & CI – Cn+ Non-hydrocarbons CnHC – CHC
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K-value Control Understanding Cause-and-Effect
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K-value Control Understanding Cause-and-Effect
Low-p K-values to pv(T) to acentric factor () to Tb.
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K-value Control Understand Cause-and-Effect
Low-p K-values to pv(T) to acentric factor () to Tb. Effect of on vapor pressure curve at relevant T. Effect of (Tc,pc) on vapor pressure curve at relevant T.
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K-value Control Understand Cause-and-Effect
Low-p K-values to pv(T) to acentric factor () to Tb. Effect of on vapor pressure curve at relevant T. Effect of (Tc,pc) on vapor pressure curve at relevant T. Relation of low-p K-values to high-p K-values.
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K-value Control Understand Cause-and-Effect
Low-p K-values to pv(T) to acentric factor () to Tb. Effect of on vapor pressure curve at relevant T. Effect of (Tc,pc) on vapor pressure curve at relevant T. Relation of low-p K-values to high-p K-values. K-value behavior towards the convergence pressure.
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K-value Control Understand Cause-and-Effect
Low-p K-values to pv(T) to acentric factor () to Tb. Effect of on vapor pressure curve at relevant T. Effect of (Tc,pc) on vapor pressure curve at relevant T. Relation of low-p K-values to high-p K-values. K-value behavior towards the convergence pressure. Effect of BIP kij on K-values Ki & Kj.
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K-value Control Understand Cause-and-Effect
Low-p K-values to pv(T) to acentric factor () to Tb. Effect of on vapor pressure curve at relevant T. Effect of (Tc,pc) on vapor pressure curve at relevant T. Relation of low-p K-values to high-p K-values. K-value behavior towards the convergence pressure. Effect of BIP kij on K-values Ki & Kj. Rank component’s K-value impact on phase equilibria.
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K-value Control Understand Cause-and-Effect
Low-p K-values to pv(T) to acentric factor () to Tb. Effect of on vapor pressure curve at relevant T. Effect of (Tc,pc) on vapor pressure curve at relevant T. Relation of low-p K-values to high-p K-values. K-value behavior towards the convergence pressure. Effect of BIP kij on K-values Ki & Kj. Rank component’s K-value impact on phase equilibria. What causes three-phase behavior.
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K-value Control Constraints
Monotonic volatility according to boiling point. Avoid crossing K-values as function of (p,T,x).
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K-value Control Constraints
Monotonic volatility according to boiling point. Avoid crossing K-values as function of (p,T,z). Avoid three-phase behavior.
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K-value Control Constraints
Monotonic volatility according to boiling point. Avoid crossing K-values as function of (p,T,z). Avoid three-phase behavior. Honor measured K-value data.
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K-value Control Measured Data K-values practically never available.
Maybe from material balance. Critical transition.
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K-value Control Measured Data K-values practically never available.
Often, only indirect phase behavior data available. Dewpoint Critical (bubblepoint-to-dewpoint) transition Liquid dropout
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K-value Control Measured Data K-values practically never available.
Usually indirect phase behavior data available. Reliability of & QCing measured compositions? Sampling techniques. GC methods. Material balance. Graphical consistency.
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K-value Control Measured Data K-values practically never available.
Usually indirect phase behavior data available. Reliability of & QCing measured compositions? Industry – what to do? Know what and why to measure. Demand quality.
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K-value Control Measured Data K-values practically never available.
Usually indirect phase behavior data available. Reliability of & QCing measured compositions? Industry – what to do? Labs – what to do? Measure compositions reliably. Develop better flash-GC methods. Measure flashed-liquid molecular weights.
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Conclusions Volumetric properties are almost predicted always accurately enough – if volume shift factors are determined properly. Don’t change pure-component volume shift factors… without having measured data for that component. Always determine volume shifts of Cn+ fractions to honor the individual-fraction specific gravities.
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Conclusions Phase equilibria data are often not predicted accurately.
Phase equilibria is – for gas condensates.
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Conclusions Phase equilibria data are often not predicted accurately.
Phase equilibria is – for gas condensates. K-values control phase behavior. Controlling K-values from an EOS is a non-trivial task requiring measured K-value data, compositions, indirect phase behavior data (e.g. dewpoints), and a phase behavior program that allows all such data to be matched.
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