Novel Technique for Addressing Gas Hydrate and Flow ... Heriot Watt... · 12-13 May 2009 Novel...
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DEVEX, Aberdeen, 12-13 May 2009
Novel Technique for Addressing Gas Novel Technique for Addressing Gas Hydrate and Flow Assurance: Hydrate and Flow Assurance:
Coldflow & HYDRAFLOWColdflow & HYDRAFLOW
R. Azarinezhad, A. Chapoy, and B. Tohidi
Centre for Gas Hydrate Research, Institute of Petroleum Engineering, Heriot- Watt University, Edinburgh EH14 4AS, UK
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DEVEX, Aberdeen, 12-13 May 2009
OutlinesOutlines• Background
–Gas Hydrates: What are they?–Hydrate problems, current solutions, limitations
• What is ‘Cold Flow’?
• The ‘Hydraflow’ Concept
• Laboratory results
• Future development
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DEVEX, Aberdeen, 12-13 May 2009
What are gas hydrates ?What are gas hydrates ?Gas 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
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DEVEX, Aberdeen, 12-13 May 2009
Gas Hydrates Problem• Hydrate blockages are major flow
assurance problem in offshore and Arctic operations
• Economic and safety hazard
• Hydrates can form:– In subsea long tiebacks / transfer lines– At high pipeline residence times– Across gas expansion valves (cooling)– During drilling following a gas kick Gas hydrates removed
from a subsea transfer line (Courtesy of Petrobras)
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DEVEX, Aberdeen, 12-13 May 2009
Current Approaches & Limitations:Avoiding hydrate formation:• Dehydration (Water removal)
- Requires costly/complex subsea separation units
• Active heating and/or insulation- Very high PAPEX/OPEX- Failure of insulation during shut-in- Shorter lines only
• Thermodynamic inhibition (e.g. methanol, glycols)- High dosage often required (> 50 wt% )- High water-cut = huge volumes- Can encourage salting-out- Loss to/ contamination of hydrocarbons- Need for regeneration = large/costly topside
Pres
sure
No Hydrates
Hydrates
Wellhead conditions
Temperature
Downstreamconditions
Pres
sure
No Hydrates
Hydrates
Wellhead conditions
Temperature
Downstreamconditions
Pres
sure
No Hydrates
Hydrates
Wellhead conditions
Temperature
Downstreamconditions
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DEVEX, Aberdeen, 12-13 May 2009
Current Approaches & Limitations:
• Low Dosage Hydrate Inhibitors (LDHIs):
- Kinetic Hydrate inhibitors (KHI)
- Emerging technology / not fully understood
- Limited subcooling (~ 12 !C) and pressure
- Lack of means for regeneration
- Anti-Agglomerants (AA)
- Emerging technology / lack of knowledge
- Best suited to oil/condensate system
- limited to low water-cuts (< 60%)
Prevent growth for ‘induction time’
Stop hydrate agglomeration/plugging
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DEVEX, Aberdeen, 12-13 May 2009
Cold Flow: An Alternative Approach?
What is Cold Flow?
• No active heating or insulation
• Minimal (or no) chemical additives
• Allowing / inducing hydrate formation, but preventing agglomeration / plugging
• Transporting gas/water as hydrate slurries
• Several institutes working on Cold Flow
- SINTEF/BP, NTNU, CSIRO/IFP, Shell, Petrobras…
Cold flow?
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DEVEX, Aberdeen, 12-13 May 2009
The HYDRAFLOW Concept• Convert all or most of gas to hydrates
– Add water (e.g. seawater) if necessary – Transport as hydrate/water/oil slurry to processing facilities
• Prevent hydrate blockage using AAs and/or natural crude AA properties
• At platform / processing facilities:– Dissociate hydrate to recover gas or transfer gas in the form of hydrate slurry– Separate phases for export – loop concept: Recycle some fluids / AA
• Patented concept
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DEVEX, Aberdeen, 12-13 May 2009
HYDRAFLOW ‘Loop’ Concept
• Loop connects producing wells
– Liquid (water) acts as ‘carrier’ fluid
• Gas/water from wells form hydrate slurry with oil
– Transported via loop to facilities
– AA / natural inhibitor prevent blockage
• At processing facilities
– Hydrate, oil and some water Separated
– Suitable fluid mixture +AA re-circulated
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DEVEX, Aberdeen, 12-13 May 2009
HYDRAFLOW: Potential Benefits • Reduce / eliminate
– Gas hydrate risks– slugging and wax / pigging(?)
• Lower pipeline– No heating/insulation– No need for subsea and/or multi-phase
• Reduce chemical costs– Only little (or no) AA required– All or part of AAs (and other chemicals) could be re-circulated
(loop concept)
• Environment– Reduce/eliminate chemical use / discharge– Green/bio-degradable AAs
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DEVEX, Aberdeen, 12-13 May 2009
Hydraflow Progress to date• Measured viscosity / transportability of:
– Water/oil emulsions – Hydrate/water/oil slurries
• For various systems…– Low to high GOR oil systems (350 to 4200 SCF/B) – Gas systems – High water cuts (e.g. mature fields…)
• Effect of:– AAs (type, concentration, partitioning, biodegradable)– Salts– Subzero conditions (cold environments, e.g. Siberia, Alaska)
• Various production scenarios (e.g. shut-in and start-up…)
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DEVEX, Aberdeen, 12-13 May 2009
Hydraflow Laboratory Proof of Concept• Materials:
– North Sea natural gas– Various real crudes – Commercial AAs
• Equipment:– 5(+) autoclave cells – Various impeller types– V = 300 to 2000 cc– Max P = 410 bar (6000 psi)– Calibrated to 4000 cp
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DEVEX, Aberdeen, 12-13 May 2009
Results: Hydrate Slurry Viscosities
10
100
1000
10000
100 200 300 400 500 600 700 800RPM
Visc
osity
/ cP
T=-14.9C & H=74.3%
T=-10.6C & H=70.7%
T=-6.9C & H=67.3%
T=-2.3C & H=64.2%
T=1.2C & H=50.2%
T=4.1C & H=50.2%
T=7.1C & H=34.2%
T=8.7C & H=28.5%
T=10.8C & H=0%
Rheological behaviour of hydrate/water/oil slurries with 1 mass% AA and 5 mass% MeOH
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DEVEX, Aberdeen, 12-13 May 2009
Results: Hydrate Slurry Viscosities
0
200
400
600
800
1000
1200
1400
-32 -27 -22 -17 -12 -7 -2 3 8 13
Temperature/ oC
Visc
osity
/ cP
W-Oil-NGW-Oil-NG-SaltW-Oil-NG-Salt-OSAA
Effect of salt and AAs on the rheological behaviour of the water-oil-natural gas system as a function of temperature.
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DEVEX, Aberdeen, 12-13 May 2009
Results: Hydrate Slurry Images
Effect of AA on the hydrate particle size in a water – oil – natural gas – salt system
No AA With AA
~ 1 cm
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DEVEX, Aberdeen, 12-13 May 2009
Results: Hydrate Formation Rate
Initial hydrate formation rate for low and high GOR oil systems at similar conditions.
0
10
20
30
40
50
60
70
80
90
Subcooling: 6 &12 C
Cooling rate: 1.7& 4.8 C/hr
Mixing rate: 350& 550 rpm
Cooling rate: 1.7& 4.6 C/hr
Mixing rate: 250& 550 rpm
Parameters effecting hydrate formation rate and their values in the first and second run respectively
Initi
al h
ydra
te fo
rmat
ion
rate
/ psi
/min
First runSecond run
Low GOR Oil
High GOR Oil
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DEVEX, Aberdeen, 12-13 May 2009
HYDRAFLOW: Future Visions• Hydraflow Cell lab studies
– Variable volume autoclave– Visual capabilities– Capability for simulating choke condition
• Upscaling: Small (autoclave) to large scale (flow loop) studies– 2.5 cm / 1“ diameter– 40 m / 130 ft length – 200 bar / 2900 psi pressure– -15 to +20 !C temperature range– Moineau pump system– Interchangeable 'test section'
• Joint Industry Funded Project (JIP)– 5 confirmed sponsors
• Design criteria and preparation for initial field trails
Upscaling
C-FAR
Hydraflow Cell
C-FAR: Centre for Flow Assurance Research at Heriot-Watt University
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DEVEX, Aberdeen, 12-13 May 2009
Thank youThank you