FLOW FL OW A SSURA SSURANC NCE E SOL SOL IDS Jón Steina Steinarr Guðm Guðmund undsso sson n TPG4140 Natural Gas October 3, 2012 – Flow assurance, students students and own R&D – Asphaltene, Paraffin wax, wax, Gas hydrate, Inorganic Inorganic solids – Temperature in pipelines (drops (drops quickly with distance) – Hydrate in pipelines (happens (happens when T < 20 20 C) – Antifreeze used to prevent prevent hydrate formation formation – Gas hydrates important important in drilling operations and and environmental considerations
Relevan vance of Natural Gas Hydr ydrate • Gas Gas kick kick in offs offsho hore re dril drilliling ng!! !!!! • Deposits in oil & gas pipelines!! • Storage and transport of gas! • Cold flow in subsea pipelines? • Gas resource (big claims)?? • Global wa warming (hyd. me melting)???
A: Drilling Unit, B: Production and Injection Wells, C: Process (Separation (Separation and Compression etc.), D: Storage, E: Off-Loading, F: Living Quarters, G: Riser Base, H: Template, Template, I: Flare, Flare, J: Flowlines Flowlines and Pipelines. Pipelines.
Flow Flowliline nes s and and Pi Pipe peliline nes s Natural Gas Production
Natural gas, Sour gases, Hydrocarbon condensate, Condensed water, Formation water, Liquid slugging
Flow Assurance Flow assurance is a concept used to describe the phenomena of precipitation and deposition of solids (and multiphase flow, flow, not not discus discussed sed here) here) in in flowli flowlines nes and pipelines. Flow assurance offers technical solutions at reasonable costs without risk to installations, operators and the environment. Precipitation is not the same as deposition…
Flow Assurance Solids • Asphaltene (pressure changes) – Heavy, polar molecules, amorphous solid
• Paraffin wax (pipeline cooling) – Normal paraffin C20 to C40
• Gas hydrate (pipeline cooling) – Methane, ethane, propane and butane
• Inorganic scale (fluid mixing…) – Carbonates and sulphates
Hydrocarbon Solids
A: Phase envelope, B: Gas hydrate, C: Paraffin wax, D: Asphaltene, E: Multiphase flow
Siljuberg 2012 (from Rønningsen 2006)
Asphaltene • Precipitates from crude oil when reservoir pressure falls during production • Crude oil density reduces when reservoir pressure falls, causing precipitation • Crude oil density increases again when light components have bubbled out (associated gas) • Precipitation envelope, light crude main problem • Deposition prevented by additives (wells and flowlines) to hinder agglomeration of particles
Asphaltene Precipitation
[MPa]
[kg/m3]
Temperature in Pipelines
Temperature in Pipelines q UATLMTD
q m C p (T1 T2 )
T LMTD
(T 1 T ) (T 2 T ) T 1 T ln T 2 T
T = Constant = Sea Temperature
A d ( L)
T LMTD
T 1 T 2 T 1 T ln T 2 T
m C p (T 1 T 2 ) U d ( L )
(T 1 T 2 ) T 1 T ln T 2 T
U d T 2 T (T 1 T ) exp L mC p
Temperature and Distance
Temperature in Pipelines
U d T 2 T (T 1 T ) exp L mC p Insulated pipeline on seafloor: 1 < U (W/m2.K) < 2 Non-insulated pipeline on seafloor: 15 < U (W/m2.K) < 25
Calculation Example What is temperature at 20 km? m=67 kg/s Cp=3500 J/kg.K U=2 W/m2.K d=0.370 m T=5 C T1=86 C
2 3.1416 0.370 20 10 3 71C T 2 5 (86 5) exp 67 3500
Temperature and Distance Åsgard Transport (69.4 vs . 76.9 MSm³/d) Pressure
Booster_press
Temperature
Booster_temp
210
50
200
45
190
40
) g 180 r a b ( 170 e 160 r u s 150 s e r P 140
35 30 25 20 15
130
10
120
5
110
0 0
200
400
600
) C ° ( e r u t a r e p m e T
800
Distance KP (km)
Booster compressor duty: 15.5 MW (most likely roughness) Aamodt (2006)
Wax Appearance Temperature
Crude oil and condensate WAT (=cloud point) typically at 30-40 [C]. Pour point typically 15 [C] below cloud point. Wax crystals in oil increase viscosity.
Botne 2012
Paraffin Wax Cloud point (WAT) and pour point
Wax Build-Up With time and distance dx dt
x
k 1 k 2
k 1 k 2 x
1 exp(k 2t )
Botne 2012
Botne 2012
Botne 2012
Siljuberg 2012
Water Vapour at 10 (Top), 20 Middle) and 30 (Bottom) MPa 20000
18000
16000
14000
12000 ] 3 m S / 10000 g m [
c
8000
6000
4000
2000
0 0
20
40
60
80
T [C]
100
120
140
Gas Hydrate •Major obstacle to production of oil and gas through subsea pipelines (due to cooling). Blocks pipelines. •Form when liquid water (condensed out from moist reservoir gas) and natural gas are present at “wrong” side of equilibrium line (typically 20 C and 100 bara). •Water molecules are stabilized by small gas molecules such that hydrates form (physical process, not chemical reaction). •Antifreeze chemical used/injected to lower the T at which hydrates form (lower “freezing” point of hydrate). •Typically, 50 % antifreeze (in liquid phase) required to prevent hydrate formation. Expensive, very expensive.
Equilibrium & Flow Assurance
Cooling w. distance U d L mC p
T2 Tu (T1 Tu ) exp
Carroll 2003
A: Gas reservoir, B: Oil reservoir, C: Aquifer, D: Cap rock, E: Sealing fault. A/B: Gas-oil-contact. B/C: Oil-water-contact. Gas in A saturated with water vapour (condenses out at surface). Oil formation B contains formation water (saline).
Gas Molecules Trapped in Cages 12-sided, 14-sided and 16-sided polyhedra
Small non-polar molecules, methane, ethane, propane and butane form gas hydrate. Carbon dioxide, hydrogen sulphide and nitrogen also form hydrate.
Gas Inside Ice Crystal Cages
Skalle 2009
Carroll 2003
Structure II Gas Hydrate
24 X 136 H 2O
Dissociation Pressure
Hydrate Equilibrium (Dissociation Pressure)
Dissociation Pressure Gas Hydrate 45000
40000
35000
30000
] 25000 a P k [ p 20000
15000
10000
5000
0 0
5
10
15
20
25
30
T [C]
Lower line natural gas mixture; upper line with CO2 and N2
35
Christiansen 2012
Hammerschmidt’s Equation
T
K x M (1 x)
Hydrate Equilibrium Midgard Field Gas
Lunde (2005): Design av flerfasesystemer for olje og gass, Tekna
Natural Gas Resource? Hydrate Zone Limited by Subsurface Temperature
Senger 2009
Subsurface Gas Hydrate
Mary Boatman, unknown reference
Krey et al. 2009
Global Warming & Gas Resource
William Dillon, USGS
Gas Kick in Drilling
Deepwater Horizon, GoM, Teknisk Ukeblad, May 6, 2010 Skalle 2009
NTNU Cold Flow
Sintef Cold Flow
Sintef Cold Flow
Sintef 2010
