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Gas Hydrates Challenges in Oil and
Gas IndustryProf Bahman Tohidi
Centre for Gas Hydrate ResearchInstitute of Petroleum Engineering
Heriot-Watt University, Edinburgh, EH14 4AS, UK
Contact: Prof Bahman Tohidi, Tel: +44 (0)131 451 3672, Fax: +44 (0)131 451 3127,Email: [email protected], www.pet.hw.ac.uk/research/hydrate
What Are Gas Hydrates? Crystalline solids wherein guest
(generally gas) molecules are trapped incages orme rom y rogen on ewater molecules (host)
They are formed as a result of physicalcombination of water and gas molecules
. .,CuSO4.5H2O) the ratio between waterand gas is not constant
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Hydrogen Bonding
O
O
OO
Hydrate Structure and Thermodynamics The necessary conditions:
Presence of water orice
Suitably sized gas/liquidmolecules (such as C1,
C2, C3, C4, CO2, N2,H2S, etc.)Suitable temperature
and pressure conditions
P
Hydrates
No H drates Temperature and pressure
conditions is a function ofgas/liquid and watercompositions.
T
Hydrate phase boundary
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The Gas Hydrate Structures
Water moleculeMethane, ethane,
carbon dioxide.6
cage
Propane, iso-butane,
natural gas.
512
51262
51264
Structure I
Structure II3
16 8
2
Gas molecule(e.g. methane)
Methane +
neohexane, methane+ cycloheptane.
435663
Structure H
2 1
51268
Hydrates in Subsea/Permafrost Sediments
0
275 285 295 305 315 325 335 345 355T/K
0
275 285 295 305 315 325 335 345 355T/K
5
10
15
20P/MPa
0
5
10
15
20
25
30
35
P/MPa
Depth
5
10
15
20P/MPa
0
5
10
15
20
25
30
35
P/MPa
Depth
hydrates
nohydrates
25
30
35
275 285 295 305T/K
25
30
35
275 285 295 305T/K
y ra es
no hydrates
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Zone of Gas Hydrates in Subsea
Sediments 273 283 293Temperature / K0
Hydrothermal
Sea Floor
Depth/Metre 500
1000
Hydrate Phase
Boundary
Gradient
1500
Zone ofGas Hydrates
in Sediments
GeothermalGradient
The Sediments are saturated with water
Zone of Hydrates in Permafrost273 283 293
T / K0263
Geothermal
Depth of Permafrost
PhaseBoundary
Zone ofGas Hydrates
in PermafrostGeothermal
GradientDepth/M
etre 500
1000
Permafrost
1500
The Sediments are saturated with water
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Hydrate Formation in Porous MediaHydrates
Water
Gas Bubble
Grains
50 Microns
Gas Hydrates in Marine Sediments
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Hydrate Stability Zone in Sediments
Bottom simulating reflector at the base of hydrate stability,Blake Ridge (after Shipley et al., 1979)
Methane Hydrate Discoveries
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Methane Hydrates
Natural Gas (135) Oil (142)
Coal (498)
Gas Hydrates (2171 for 15% recovery factor)
Future Energy Sources (109 TOE)Y. Makogon SPE 77334
Carbon Balance
Hydrate Formers and StructuresAr
Kr N24
6(CH2)3O
C HsII
Hydrogen Hydrates
O2CH4
Xe; H2S
5CO
7
i-C4H10
n-C4H10
sII
sII double
C2H6
C-C3H6
enzene
Adamantane
Methyl Cyclopentane8 Cyclo octanesI
sH (double)
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History of Gas Hydrates Scientific curiosity (1810)
Potential source of energy (1960s)
Some of the current issues: Storage and transportation of natural gas and hydrogen, CO2 capture
and storage, source of energy, wellbore integrity in hydrate bearingse men s, su sea an s es, po en a azar n eepwa er r ng,
separation of oil and gas, global climate change
Potential gas production from hydrates (2016)
Important Properties
Capture large amounts of gas (up to 15 mole%)
Remove light components from oil and gas
Form at temperatures well above 0 C
Generally lighter than water Need relatively large latent heat to decompose
Exclude salts and other impurities
Result from h sical combination of water and as
Hydrate composition is different from the HC phase
Large amounts of methane hydrates exist in nature
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Friend or Foe? Foe Pipeline blockage
Subsea landslides
Deepwater drilling and production (hydrate formation, wellboreintegrity, casing collapse, etc)
Friend Source of energy
Climate change CO2 capture, transport, and storage
Phase change materials
Foe: Dangers to Deepwater Production
uncontrolled gas blowout
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Well Clean-up and Testing
Foe: Gas Hydrates and Seafloor Stability
u sea an s es
can generate tsunamis
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Foe: Gas hydrates and Seafloor StabilitySubsea Land SlidesDissociation ofmarine gas hydratesis believed to beresponsible for hugesubsea landslides.
ome sc en s s
explain themysteries ofBermuda trianglewith gas hydrates.
Foe: Oil and Gas Exploitation
Drillin o eration
Gas hydrates formation could cause serious operational andsafety problems. Some of the scenarios are:
Long tie-backs and deepwaterproduction
Gas expansion and coolingeffect
Start up and shut down Well clean-u and testin Logging operation WAG (Water Alternating Gas)
Injection
Processing
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Avoiding Hydrate Problems Water removal (De-Hydration) Increasing the system temperature Hydrates
Wellhead
conditions Heating
Reducing the system pressure Injection of thermodynamic inhibitors
Methanol, ethanol, glycols
Using Low Dosage Hydrate Inhibitors
Pressure
Downstream
conditions ne c y ra e n ors
Anti-Agglomerants (AA)
Various combinations of the above Cold Flow/HYDRAFLOW
No Hydrates
Temperature
Avoiding Hydrate Problems-Dehydration
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Avoiding Hydrate Problems-Temperature
Hydrates
Wellhead
conditions
Pressure
Reducing Heat Loss, orIncreasing Temperature
Temperature
No HydratesLw-LHC-H-VDownstreamconditions
Avoiding Hydrate Problems-Pressure
No HydratesHydrates
Wellhead
conditions
Pressu
re
Reducing System PressureGenerally not used as apreventive measure
Only used in hydrate plug
Temperature
Lw-LHC-H-V Downstreamconditions
removal
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Avoiding Hydrate Problems-ThermodynamicInhibitors
No Hydrates
Hydrates
Wellhead
conditions
Pressure
Thermodynamic InhibitorInjectionLimitations:- water cut- cost (CAPEX and OPEX)- environmental impact
Temperature
Lw-LHC-H-V
Downstream
conditions- flow regime- operational difficulties- other problems
Avoiding Hydrate Problems-Kinetic HydrateInhibitors (Generally accepted view)
Hydrates Upstream
conditions1800
2000
18
20
Induction Time
Pressure
- - -
Downstream
conditions
T
0
200
400
600
800
1000
1200
1400
P/p
sia
0
2
4
6
8
10
12
14
T/o
P/psia
T/C
min max
Temperature
w HC 0 500 1000 1500 2000Time/min
Induction time should be longer than the residence time!
Test Conditions: Minimum Temperature & Maximum Pressure!!!
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Avoiding Hydrate Problems-Anti-Agglomerants
Hydrates Upstream
conditions
Pressure
Downstream
conditions
T
min max
Temperature
No HydratesLw-LHC-H-V
19 0
20 0
21 0
45
50
50
60PTtor ue
Avoiding Hydrate Problems-Anti-Agglomerants
P/ba
r
80
90
10 0
11 0
12 0
13 014 0
15 0
16 0
17 0
18 0
T/oC
5
10
15
20
25
30
35
40
Torque/
N.cm
10
20
30
40
t ime /h r .
0 2 4 6 8 10 1 2 1 4 1 6 1 8 2 0 2 2 2 4 2 6 2 8 3 0
P/bar
70
80
90
100
110
120
130
140
150160
170
180
190
200
210
T/oC
0
5
10
15
20
25
30
35
40
45
50
Torque/N.cm
0
10
20
30
40
50
60
PTtorque
Water/condensate/gas system (30% water) with 1% AA.Hydrate formation, but very little increase in torque.
t i me /h r .0 2 4 6 8 10 12 14 16 18 20
70 00
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New Approaches in Preventing Gas
Hydrate Problems: Cold Flow No heating No insulation ow ng promo ng y ra e orma on, u preven ng
their agglomeration Providing seeds Using Anti-Agglomerants Natural inhibitors Mechanical meansA combination of the above
Several Institutions are working on Cold Flow SINTEF-BP CSIRO/IFP ExxonMobil Heriot-Watt (HydraFlow)
Heriot-Watt HYDRAFLOW: Concept Convert all or most of the vapour phase into hydrates
(add water if necessary)
inhibitors and/or mechanism of hydrate formation
Transport hydrates as slurry Separate some of the free liquid phase (and chemicals)
and recycle (Loop Concept)
(or transport the gas in the form of hydrates, e.g., dry,hydrates in water or hydrates in oil slurries)
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HYDRAFLOW: Loop Concept Circulating liquid phase plays the role ofcarrier fluid
Gas from Well-1 is converted intohydrates
The same process will continue for otherwells
Hydrate slurry is transported to the hostfacilities
Hydrates, oil and some water are
A suitable fluid mixture is re-circulatedusing a single phase pump on the hostfacilities
HYDRAFLOW: Potential Benefits Reducing/eliminating
Gas hydrate risks
Slugging
Wax
Pipeline pigging requirement
Reducing pipeline costsBare pipes, no heating
No need for subsea and/or multi-phase pumps
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New Approaches: Hydrate Safety Margin
Monitoring and Early Detection Systems Hydrate Safety MarginMonitoring Determinin the actual amount of salt and
Wellhead
conditions
Over
inhibited
Underinhibited
inhibitor (Methanol, Glycol, Ethanol, KHI,and AA) from downstream measurement
Eliminating/reducing risk of human error orequipment malfunction
Automation, adjusting the inhibitorinjection rates
Detecting Early Signs of Hydrate
Pressur
No Hydrates
Temperature
Downstream
conditions
For most systems the initial hydrateformation may not result in pipelineblockage
Detecting the early signs of hydrateformation could result in reducing gashydrate blockage risks
Hydrate risk
Low safety margin
Safe/optimised
Over inhibited
Blockage RemovalIt is not possible to prescribe a general procedure for hydrateblockage removal, as each case needs to be investigated
-
Gas hydrate blockage in the pipeline has some differences within-situ hydrates.
They are initially porous and permeable unlike in-situ hydrates
They may transfer pressure but limited in the transfer of flow
During their formation some free water have been trappedbetween hydrate crystals
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Natural Gas-Water
t = 31 hrs , P=54.9 bar, T=3.4 C t = 94 hrs , P=53.0 bar, T=3.2 C
t = 142 hr s, P=52.1 bar, T=3.2 C t=142 hrs , P=52.1 bar, T=3.2 C
Blockage Removal Through Heating
The objective isto move the Hydratessystem outsidehydrate stability
zone.
The system could Pressu
re Initial
conditions
Final
conditions w- - -V equilibria.
Temperature
No Hydrates
Lw-H-V
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Blockage Removal Through HeatingIt is often difficult to locate apipeline hydrate plug to begin Hydrates
.
Heat must be supplied with caution,beginning from the end andprogressing toward the middle ofthe plug.
If a h drate lu is dissociated in
Pressure
Lw-H-V
Initial
conditions
Final
conditions
the middle, the pressure mightincrease suddenly, resulting inequipment failure, blowouts, orhydrate projectiles in pipelines.
Temperature
Blockage Removal Through Depressurisation The objective is to move thesystem outside the hydrate stability Hydrates
Lw-H-V
. A common misconception is thatdepressurisation alone can causehydrate dissociation, forgettingabout the role of latent heat ofdissociation. When the s stem is
Pres
sure
No Hydrates
Initial
conditions
Final
depressurised, some hydratesremove heat from surrounding anddissociate, resulting in a reductionin the system temperature.
Temperature
con t ons
273
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Blockage Removal Through Depressurisation The thermal gradient will result inheat flow through pipe-wall. Hydrates
Lw-H-V
The system temperature could dropto below zero and ice could form.
The second misconception is thatduring depressurisation, the hydrate
lu dissociate at its end s .
Pressure
No Hydrates
conditions
Final
conditions
In fact although the initial plugdissociation is at its ends, the hydrateplug will dissociate radially resulting inplug dislodge.
Temperature273
Blockage Removal Through DepressurisationQ
Hydrate PlugPipe-Wall
Q
Depressurisation from both endsprojectileice formation
The problem with ice formationlow heat transferprotective layerice will dissociate on temperature rise not pressurereduction
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Blockage Removal Through Inhibitor InjectionInhibitor injection will shift the hydrate phaseboundary to the left, which could result in gashydrate dissociation.
However, gas hydrate dissociation will producefresh water reducing the concentration of theinhibitor.
Also gas hydrate dissociation will result in therelease of gas (possible pressure increase) and areduction in system temperature.
Blockage Removal Through Inhibitor Injection
Initial Inhibitor
Pressu
re
Hydrates
Inhibitor
Injection
Dilution
Initial
Hydrate
Phase
Temperature
No HydratesLw-H-V
Boundary
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Case Studies Hydrates in Gas Lift
H drates in Water In ection Lines
Hydrates in Onshore Natural Gas Production
Pipeline blockage in the North Sea
Hydrate problem during logging operation
Pipeline blockage after an emergency shut-down
Hydrate problems in GOM
Summary Gas hydrates are formed as a result of physical combination
of water and suitably sized molecules
sediments and permafrost regions
They have very interesting properties, with many potentialindustrial applications They had significant impact on the past climate
industries, in particular in offshore and deepwater operation
Novel technologies/techniques are necessary for addressinggas hydrate challenges in deepwater and long tiebacks
Contact: Prof Bahman Tohidi, Tel: +44 (0)131 451 3672, Fax: +44 (0)131 451 3127,Email: [email protected], www.pet.hw.ac.uk/research/hydrate
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Gas Hydrate, Flow Assurance and PVT
Research Activities at Heriot-Watt
Contact:Professor Bahman TohidiDirector, Centre for Gas Hydrate ResearchInstitute of Petroleum EngineeringHeriot-Watt UniversityEdinburgh EH14 4AS, UKDirect Line: +44 (0)131 451 3672Fax: +44 (0)131 451 3127Mobile: +44 (0)776 116 5784Email: [email protected]://www.pet.hw.ac.uk/research/hydrate
CENTRE
FOR GAS
HYDRATE
RESEARCH
Gas hydrates in gas, water and gas water interface, as
viewed through the High Pressure Micromodel
Introduction
Heriot-Watt University is a medium size university inEdinburgh (Capital of Scotland) with some 6,000students
Institute of Petroleum Engineering (IPE) was form in1975 and has some 200 MSc, MPhil and PhD students
Some 70% of the IPE income is from research projects
There several big research groups; such as; Hydrates,Scale, Geophysics, Uncertainty, etc ----
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Background and Areas of Activities BackgroundPVT and Phase Behaviour of Petroleum Reservoir Fluids
Gas hydrate research started in 1986Centre for Gas Hydrate Research Established in Feb 2001Centre for Flow Assurance Research (C-FAR) started in 2007
Areas of Activities
Consultancy, mostly through Hydrafact (www.hydrafact.com)Training (open and in-house courses)
Research Interests PVT and Phase Behaviour of
Reservoir Fluids
Flow Assurance Gas Hydrates
Wax Salt (halite)
Asphaltene
Gas H drates ressure Hydrates
Wellhead
conditions
Hydrates could block subsea pipelines
Flow Assurance
Gas Hydrates in Sediments
Positive/other Applications of GasHydrates
No Hydrates
Temperature
Downstream
conditions
P & T profi le and hydrate phase boundary
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HYDRAFACT Ltd
HYDRAtes and Flow Assurance Consulting and Technologies Construction of equipment
Trainin /short courses
Consultancy
Software (HydraFLASH)
Commercialising novel technologies, e.g.,
(HydraCHEK)Software (HydraFLASH)
HYDRAFLOW
www.hydrafact.com
Current Joint Industry Projects Evaluation of Low Dosage Hydrate Inhibitors
Kinetic Hydrate Inhibitor and Anti-Agglomerant Evaluation
,methodology by Hydrafact (www.hydrafact.com)
One patent has already been filed
Hydrate Monitoring and Early Warning SystemA number of techniques and prototypes have been developed for
monitoring the hydrate safety margin. Two patents have been
filed. One of the devices H draCHEK is bein commercialised b.
Hydrafact
A number of techniques have been developed for hydrate earlywarning. A patent application has been filed
Organising a field trial
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Current Joint Industry Projects Gas Hydrates and Flow Assurance Thermodynamics aspects of hydrates, inhibitor distribution, water content,
salting-out, wax, etc
Solid-liquid equilibria in various glycol-water systems
The developed software (HydraFLASH) is ranked the best by Total and itis being commercialised by Hydrafact
One patent is being filed
Hydraflow: A Wet Cold Flow Solution Converting most of the gas into hydrates and transporting them as slurry
(hydrates, slugging, wax, downhill pressure recovery, reduction in
volumetric flow rate)
A high pressure flowloop has been constructed as well as a unique set oftest facilities.
A patent has been filed which will be commercialised by Hydrafact
Current Joint Industry Projects PVT and Phase Behaviour of Reservoir Flu ids
The lab has been refurbished and equipped with two major Hg-freeequipment (200 C and 15,000 psia) have been purchased
The HPHT (250 C and 30,000 psia) facilities is being equipped with asalt compatible cell (viscosity, density, three phase IFT)
Slim tube is being added to the existing capabilities Some of the topics in the current phase of the project: Viscosity (effect ofmud filtrate contamination), IFT at HPHT, Acoustic Characteristics of
Reservoir Fluids, Phase Behaviour of CO2-Oil systems, Maximum Carbon
Number in GC Analysis, etc
Impact of Aromatics on Acid Gas Injection Project sponsored by the Gas Processing Association
Joint project with Paris School of Mines
Cross-over project between hydrates and PVT project
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Current Joint Industry Projects Impact of Common Impurities on Carbon DioxideCapture, Transport and Storage
CO2 originating from capture processes is generally notpure and can contain impurities such as: H2O, CH4, N2, H2, NOx, H2S, SO2
The main aim of the proposed project is to investigate the phasebehaviour and properties of CO2-rich stream containing impurities
Phase behaviour of Saline water and CO2-rich streams
Other Projects
Towards Zero Carbon Emissions: Novel LowPressure Molecular Natural Gas/CO2/H2Stora e and Se aration usin Semi-ClathratesEPSRC One patent has been filed
Quantifying and monitoring potential ecosystemimpacts of geological carbon storage, NERC We are part of a large consortium
Hydrates in sediments
Methane hydrate formation
in high pressure glass
micromodel
2 sediments
Analysis of existing oceanographic and seismicdata Our work is on effect of hydrates on sediment
properties
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Resources Staff/Students 25 member research team with expertise in Chemical,
Mechanical, Electronic and Petroleum Engineering,Geology/Geochemistry, Physics/Geophysics,Chemistry, Radio-Physics, Polymer with more than 10nationalities.
Experimental Facilities More than 40 versatile experimental rigs, operating
from -80 oC to +350 oC and pressures up to 2,000 bar
Flow loop (1 dia, 40 m long, 200 bar, Moineau pump)in an environmental chamber (-15 to + 20 C)
Software Comprehensive phase behaviour and hydrate
programme, commercial and research versions
Database Wax predictive model
Some of the experimental facilities