Gas Hydrates in Low Water Content Gases: Experimental Measurements and Modelling Using the CPA EoS Antonin Chapoy, Hooman Haghighi, Rod Burgass and Bahman Tohidi Hydrafact Ltd. & Centre for Gas Hydrate Research Institute of Petroleum Engineering Heriot-Watt University Edinburgh EH14 4AS, UK Ecole des Mines de Paris - Paris, France, Thursday, September 3th, 2009
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Gas Hydrates in Low Water Content Gases: Experimental Measurements and ModellingUsing the CPA EoS
Antonin Chapoy, Hooman Haghighi, Rod Burgass and Bahman TohidiHydrafact Ltd. & Centre for Gas Hydrate ResearchInstitute of Petroleum Engineering
Heriot-Watt University Edinburgh EH14 4AS, UK
Ecole des Mines de Paris - Paris, France, Thursday, September 3th, 2009
Outline
• Introduction / Scope of work
• Experimental
– Materials
– Experimental setup
– Procedures
– Validation
• Thermodynamic Modelling
• Results - Discussions
• Remarks and Conclusions
Background• Natural gases are normally saturated
with water at reservoir conditions
• Reducing the water content of gas streams is commonly used as a means of preventing gas hydrate (gas lift..)
• However, severe hydrate blockages have occurred in pipelines transporting so-called dry gas
• Capability to accurately predict the water content is therefore essential to plan potential flow assurance issues associated with condensed water
• Lack of experimental data, especially for gas mixtures
What are gas hydrates ?What are gas hydrates ?
• Gas hydrates or clathrate
hydrates are:
– Ice-like crystalline
compounds
– Composed of water + gas
(e.g. methane, CO2)
– Formed under low
temperatures and elevated
pressures
– Stable well above the ice-
point of water Methane hydrate: the
burning snowball
Hydrate StructuresHydrate Structures
3
16
2
2 Methane, ethane, carbon dioxide….
Propane, iso-butane, natural gas….
Methane + neohexane, methane + mch….
6
8
1 Structure H
Structure 2
Structure 1
51268
51264
51262
512
435663
+
P T and
suitable guests
Flow Assurance- Hydrates: The problems
• Hydrate blockages are major
flow assurance problems in
offshore and deep water
operations
• Economic and safety hazard
• Challenges
– Long tiebacks
– High pipeline residence times
– Low T / high fluid P Gas hydrates removed from
a subsea transfer line
(Courtesy of Petrobras)
Avoiding Hydrate Problems - Current practice
• Increasing the system temperature- Insulation- Heating
• Reducing the system pressure
• Injection of thermodynamic inhibitors- Methanol, ethylene glycol, ethanol