Transportation of waxy crudes in multiphase pipelines
Hans Petter Rønningsen Statoil NTNU, 27.03.2006
Outlin inee of presentati tio on
Flow assurance
Phase behaviour
Solids precipitation
Wax deposition
Preve revent ntio ion n and and miti itigati gation on sol soluti utions ons
Rheology and gelling of waxy crudes
Outlin inee of presentati tio on
Flow assurance
Phase behaviour
Solids precipitation
Wax deposition
Preve revent ntio ion n and and miti itigati gation on sol soluti utions ons
Rheology and gelling of waxy crudes
Flui Fl uid d an and d fl flow ow as assu sura ranc ncee 400
Phase Pha se behaviour behaviou r 300 r a b , e r u 200 s s e r P
Bubble point Production pathway Hydrates (H) Wax (W) Asph altenes (A)
Scale
100
As ph phalt alt enes
0 0
100
200
300
400
500
600
Temperature, °C
Wax
Corrosion
Fluid behaviour behaviour and control Emulsions
Hydrates
Fluid flow
Concept choice : Field development solutions
Multiphase flow assurance " The ability to produce and transport multiphase fluids fro m reservoirs to processing plants in economically and technically feasible way"
Production Tasks Phenomena
Field installations
Conceptual design
Reservoir and wells
Fluid and flow pr ediction
PVT/fluid pro pereties Prevention methods
Asphaltenes Scale
Mitigation methods
Sands/solids Multiph ase flow Slugging
Remediation methods Operational guidelines
Hydrates Waxes Emulsions Foam Flowlines and facilities
Operations support
Multiphase flow engineering Fluid mechanics: Governed by Newton
Fluid r heology: Governed by the fluid
Pipeline dimension (sizing)
Pipeline pressure drop (capacity)
Undesirable phenomena – Slugging – Flow restrictions etc.
Flow assurance: Governed by us!
Flow assurance = Minimization of undesirable phenomena
Composition of petroleum fluids
Flu id behavi ou r and control
Enormous range and variety of components with regard to boiling point, molecular weight, polarity and carbon number
Thousands of components from methane to large polycyclic compounds with atmospheric equivalent boiling points higher than 800°C
Molecular weights range from 16 g/mole upto several thousand g/mole
Carbon numbers from 1 to at least 100 (for heavy oils probably about 200)
Heavy and waxy crudes
Typical phase envelope of a reservoir oil 400
Tres; Pres
Liquid 300
Cricondenbar
) r a b ( e r 200 u s s e r P
Bubble point line
Tc; Pc Cricondenterm
Gas
100
Dew point line
0 -100
0
100
200
300
400
Temperature (deg C)
500
600
700
Phase envelopes of complex mixtures 500 98% C1 95% C1 93% C1
400
Texas gas cond . N. Sea gas cond. Near-crit. gas cond.
) r 300 a b ( e r u s s 200 e r P
N. Sea volatil e oil N. Sea black oil N. Sea asphaltic oi l N. Sea heavy oi l Critical points
100
0 -200
-100
0
100
200
300
400
Temperature (deg C)
500
600
700
800
Hydrate and wax phase boundaries
350 Saturation curve
300
Wax Hydrate Critical point
250
Res. conditions
) r a 200 b ( e r u s 150 s e r P
100
50
0 -100
0
100
200
300
Temperature (°C)
400
500
600
Complex phase behaviour Secondary solid and liquid phases 400
Single-phase liqu id
t es
Bubble point Hydrates (H) Wax (W) As ph alt enes (A)
r a
d
300
y H
Asphaltenes + liquid
r a b , e r 200 u s s e r P
Gas
100
Wax
0 0
100
200
300
Temperature, °C
400
500
600
Compact hydrate plug Ref. Kværner report on cold spots in Kristin X-mas tree and choke module
Wax ’slug’ in pig trap at Statfjord B
Wax ’porosity’ Composition of wax deposit from Snorre-Statfjord pipeline
Water content (wt%) Wax content Not purified (wt%) Purified Dry solid content (wt%) Ignition residue /dry (wt%) “Organic” content /dry (wt%) Ignition residue 950 °C /dry (wt%)
Sample no. 1 8,88 45,3 26,8 80,7 0,1 99,9 0,1
Sample no. 2 0,03 47,3 32,8 82,0 <0,02 100 <0,02
Ca. 45% wax Ca. 55% non-wax
Wax precipitation curve Waxy crude oil Norne crud e at 1 bar 8 7
x 6 a w 5 d i l o 4 s % t 3 W 2 1 0 -20
-10
0
10
20
Temperature (°C)
30
40
50
Wax deposition test with Snøhvit oil-condensate mixture: Effect of dT/dr ( T)
Some wax
Oil 10oC Wall 4oC
Less wax
Very little wax Oil 8oC Wall 4oC
Oil 6oC Wall 4oC
No wax Oil 4oC Wall 4oC
Conclusion: Wax deposition vanishes when there is no temperature difference between the oil and the wall (even if the oil temperature is far below WAT.
Wax deposition profile in Kristin-Njord Y pipeline (60% porosity, 600h simulation) Kristin-NJ/DR Wye - wax deposition and temperatur e profile after 600 h
70
0.005
60
] 0.004 m [ n o 0.003 i t i s o p 0.002 e d x a W0.001
50 40 30 20 10 0
0 0
20
40
60
Pipeline l ength [km]
80
100
] C ° [ e r u t a r e p m e T
Wax deposition Fluid temperature
Wax (or other deposits) may give severe increase of pressure drop due to increased roughness Effect of ro ugh ness on pressure drop in tu rbulent single phase flow L=10k m , Q=10 000 m ³/d, D=254 m m ,
=800 k g/m ³
40 35 r a b , 30 p o r d 25 e r u s s 20 e r P 15
Viscosity = 2 cp Viscosity = 100 cp
10 0
200
400
600
Roughness, micron
800
1000
Veslefrikk - Oseberg period 13.12.97-29.12.97 47
Veslefrikk to Oseberg 38 km pipeline
46 45 ) r 44 a b ( 43 e r u 42 s s e r 41 p . f f i 40 D 39
Effect of roughness factor
38 37
Simulation:
10
15
20
25
Date
Case B , Pressure drop and wax volume 3
3
10200 Sm /d fro m fi eld 1 and 24000 Sm /h from field 2
50
200
Pressure drop with roughness factor 0.15
180 160
45 140
) r a b ( e r u s 40 s e r P
) 120 3 m ( e 100 m u l o 80 V
Pressure drop with roughness factor 0 Pressure drop
60
Pressure drop, rough. 15% of wax layer Measured data
35
40 20
Wax volume 30
0 0
5
10
15 Time (days)
20
25
30
30
Cooldown with different overall U-values
Source: McKenchie (2001)
Methods for controlling wax deposition PP-Solid
Pipeline insulation
PP-Foam
PP-Syntactic PP-Solid PP-Adhesive FBE
Pigging Chemicals
External insulation coating on single pipes Pipe-in-pipe systems
PP-Solid
Inhibitors Dispersants Dissolvers
Hot oil flushing Heating
Bundles Electric heating (primarily hydrate control)
Wax inhibition
Wax management !
800
Waxy oils
Newtonian 30 s-1 100 s-1 300 s-1 500 s-1
700 600 ) s a 500 P m ( 400 y t i s o 300 c s i V 200
PP
WAT
100 0 0
10
20
30
40
50
60
Temperature (°C)
η =
constant
Newtonian (at T > WAT)
Shear-thinning (at T < WAT)
Time-dependent (thixotropic’)
η =
Thermal- and shear-history dependent
η =
Yield stress (at T
η = ' ∞ '
Viscoelastic (at small deformations)
η =
.
f (γ ) .
f (γ , t) .
f (γ , t, TH)
70
80
Rheology depends on composition and fluid history !
Maximum pour point condition
Minimum pour point condition
Yield stress from controlled stress flow curve Tyrihans Sør crude oil
Notice difference between thermally pretreated and non-pretreated oil!
Dynamic yield stress (fracture onset) Fracture
Static yield stress
Maximum pour point condition Mimimum pour point condition
Restart of gelled oil pipeline Single phase Gelled oil
Prestart
Q(t)
Multiphase Gelled oil
Prestart
Q(t) Void
Restart pressure vs. static yield stress Pipeline length = 8 km
Safety margin = 50%
400
) r 350 a b ( 300 e r u 250 s s 200 e r p 150 t r a 100 t s e R 50 0
5.5" 6" 9" 12"
0
20 10
40 30
60 50
80 70
Static yield stress (Pa)
100 90
Effect of ‘good’ pour point depressant on wax crystal aggregation Maximum pour point
No thermal conditioning: Chaotic soup of wax crystals
Minimum pour point
Conditioned at 80°C: Aggregates Wax-free oil
Treated with 200 ppm PPD: Ordered aggregates Wax-free oil
Backup
Integrated Production Umbilical (IPU)
Pour point
The lowest temperature at which an oil will flow under standard test conditions (ASTM D-97). Not a well-defined rheological property, but indicates gelling temperature in pipeline shut-down situations.
Follow-up with yield stress measurements if PP>0o C.
Large effect of thermal history.
Standard thermal pre-treatment (conditioning).
Typically 4-5 wt% solid wax at minimum pour point.
Large effect of dissolved gas.
Non-Newtonian viscosity model Range 0-10% wax Pedersen and Rønningsen (1999)
Non -Newton ian viscosi ty mod el 100 90
30 s-1 100 s-1
80
500 s-1
y 70 t i s o 60 c s i v 50 e v i t 40 a l e R 30
20 10 0 0
0.02
0.04
0.06
Volume fraction so lid wax
0.08
0.1
