casing integrity in hydrate bearing sediments reem freij-ayoub, principal research engineer cesre...
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Casing Integrity in Hydrate Bearing Sediments
Reem Freij-Ayoub, Principal Research EngineerCESRE
Wealth from Oceans
Well integrity in hydrate bearing sediments (HBS) JIP sponsors
ShellGlobal Solutions
Heriot Watt UniversityInstitute of
Petroleum Engineering
Outline
• What are gas hydrates• Possible drilling and well completion problems• The model• The dissociation algorithm• Cases studied • Results• Conclusions/Future work
• Ice-like structures composed of water and natural gas molecules
• Under conditions of high pressure and low temperature, water molecules form cages which encapsulate gas molecules inside a hydrogen-bonded solid lattice
• Large gas storage capacity:1 volume of gas hydrate contains up to 180 volumes of gas at stp
Gas hydrates
Drilling and well completion problems
Gas hydrate-related drilling problems (Adapted from
Maurer Engineering, Inc.)Gas hydrate-related casing problems (Adapted from
Maurer Engineering, Inc.)
Productionfacilities
Free-gas
HydrateCollapsedcasing
Casedborehole
Production of hot hydrocarbons
Hole enlargement Casing collapse
Hydrate dissociation Gas release (gasified mud) Loss of cohesion
Model
Casing heating • During drilling of lower
sections of the wellbore or• During production
Temperature Evolution
286
288
290
292
294
296
298
300
1 2 3 4 5 6
Normalized distance inside the formationTem
pera
ture
(K
) .
.
Dissociation algorithm
Φ: current porosityΦ: current porosityΦΦoo: initial porosity: initial porosity
VVcc:: volume of the Structure I crystal volume of the Structure I crystal
RTPn /
8/nNh
vchtt AVNV 1
Hydrates Phase Boundary
0
10
20
30
40
50
60
70
80
90
100
270 275 280 285 290 295 300 305 310
Temperature (K)
Po
re P
ress
ure
(M
Pa)
Porosity EvolutionStrong Cement & Hydrates
0.2
0.25
0.3
0.35
0.4
0.45
0.5
0.55
1 2 3 4 5 6
Normalized distance inside the formation
Po
rosi
ty
0.01 day
0.5 day
1 day
2 days
4 days
6.5 days
Porosity
Pore Pressure Profiles
16
17
18
19
20
21
22
23
1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 3
Normalised Distance Inside Formation
Po
re P
res
su
re (
MP
a)
P at 0.14 hrs
P at 2.78 hrs
P at 5.56 hrs
P at 8.33 hrs
Phase boundary at 0.14 hrs
Phase boundary at 2.78 hrs
Phase boundary at 5.56 hrs
Phase boundary at 8.33 hrs
Pore Pressure
Friction Angle Porosity Dependence
15
20
25
30
35
0.2 0.3 0.4 0.5 0.6
Porosity
Fri
ctio
n a
ng
le (d
eg
)
0
1
2
3
4
5
6
7
0.2 0.3 0.4 0.5 0.6
Porosity
MP
a UCS
cohesion
tensile strength
Strength degradation with hydrate dissociation
Friction angle
UCS, cohesion, tensile strength
)/cossin- (10.5 tttt UCSc
8287.0)5766.203631.0(log8036.0106194.0 txUCSt
t0.5225 -46.23 t
/12 tt UCST
C is cohesion in MPaUCS is unconfined compressive strength in MPaΦ is angle of internal friction in degrees (o) is tensile strength in MPa
porosity in percent (%).
TTan et al. (2005)
0
1
2
3
4
5
6
7
0.2 0.3 0.4 0.5 0.6
Porosity
MP
a UCS
cohesion
tensile strength
Well integrity in HBS
Geomechanical strength-
petrophysical correlations
Heat transfer into the formation
Hydrate dissociation & strength degradation
algorithm
In situ stress & PP formation, cement & casing strength
Model and cases studied
Cases studied-Symbol Cement Strength
Hydrates
Case 1: strong cement and no hydrates in sediments (S-NH).
strong no
Case 2: weak cement and no hydrates in sediments (W-NH).
weak no
Case 3: strong cement with hydrate bearing sediments (S-H).
strong yes
Case 4: weak cement with hydrate bearing sediments (W-H).
weak yes
Formation properties
Parameter Value
Biot’s coefficient 1.0
Sediment porosity 0.25
Sediment porosity of the middle layer after hydrate
dissociation
0.4
Thermal conductivity 1.4 Wm-1K-1
Specific heat capacity 1.9 x103 JK-1kg-1
Linear thermal expansion coefficient of hydrates
7.7x10-5 K-1
Linear thermal expansion coefficient of pore fluid
30x10-5◦K-1
sediment solid dry density 2.800 kgm-3
Water density 1030 kgm-3
Modulus of Elasticity of sediments
807.6 MPa
Poisson’s ratio 0.35
Cohesion 1.7 MPA
Angle of internal friction
33.17º
Tensile strength 0.53 MPa
Water depth 800 m
Top level of hydrate layer below seabed
20 m
Bottom level of hydrate layer below
seabed
60 m
In-situ temperature 15 ºC (288 K)
Gas constant 8.31441 JK-1Mol-1
Hydrates crystal volume
1.728x10-27 m3
Avogadro number 6.02205x1023
In situ stress ratio 1
Cement and casing propertiesParameter Value
Casing properties
Linear thermal expansion coefficient of steel
37x10-7◦K-1
Thermal conductivity 1.4 Wm-1K-1
Casing thickness 0.635in
Casing Poisson’s ratio 0.3
Young’s modulus of steel 210 GPa
Casing yield stress 379 MPa
Casing external diameter 20 in
Cement-casing bond properties
Coupling spring tensile strength limit 1x1020 MPa
Coupling spring cohesion limit 1x1020 MPa
Coupling spring friction angle 0º
Initial temperature 3 ºC (288 K)
Casing raised temperature 33 ºC (298 K)
Casing density 7.85 x103 kg m-3
Casing top axial load 1.37 million Pound Force
Cement thermal properties
Thermal conductivity 0.66 Wm-1K-1
Specific heat 1.9x103 JK-1kg-1
Thermal expansion 7.7x10-5 K-1
Strong cement
Modulus of elasticity 55.16 GPa
Poisson’s ratio 0.4
cohesion 11.4 MPa
Friction angle 10º
Tensile strength 2.6 MPa
Weak cement
Modulus of elasticity 807.6 MPa
Poisson’s ratio 0.35
Cohesion 1.7 MPa.
Friction angle 10º
Tensile strength 0.53 MPa
Von Mises stress
Variation of Casing Stresses Along the Profile of a Heated Casing with Weak or Strong Cement- Von Mises
0.0E+00
2.0E+07
4.0E+07
6.0E+07
8.0E+07
1.0E+08
1.2E+08
1.4E+08
1.6E+08
1.8E+08
2.0E+08
0 20 40 60 80 100
Casing Length (m)
Cas
ing
Str
ess
(Pa)
S-H- 0 day
W-H- 0 day
S-NH- 1 day
W-NH-1 day
S-H-1 day
W-H- 1 day
223
231
2212
1 mVat t=0
Maximum von Mises stress
Casing Maximum Von Mises stress
1.40E+08
1.45E+08
1.50E+08
1.55E+08
1.60E+08
1.65E+08
1.70E+08
1.75E+08
1.80E+08
0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50 4.00
Heating Time (days)
Vo
n M
ises
Str
es
s (P
a)
NH_Strong
H_Strong
NH_Weak
H_Weak
Ellipse of plasticity
Ellipse of PlasticityCasing with Strong Cement no Hydrates
-150
-100
-50
0
50
100
150
-150 -100 -50 0 50 100 150
(z+Pi)/yield x 100%
(t+
Pi)
/yi
eld
x 1
00%
Failure envelope
Failure envelope
day 0
day 5 min
0.5 day
2 days
6.5 days
compression tension
colla
pse
burs
t
collapseburst
compression tension
yield
iz
yield
iz
yield
it PPP
2
1
4
31
2
ThrustVariation of Casing Resultant Stresses Along the Profile of a
Heated Casing with Strong Cement and Hydrates in The Formation- Thrust
-7.E+05
-6.E+05
-5.E+05
-4.E+05
-3.E+05
-2.E+05
-1.E+05
0.E+00
1.E+05
2.E+05
3.E+05
4.E+05
0 20 40 60 80 100Casing Length (m)
Ca
sin
g S
tre
ss
(N
/m)
0 min
5 min
0.5 day
1 day
2 days
6 days
The profile of the thrust (normal force per linear meter of casing length) along the casing for the case of strong cement, and hydrates in the sediments, tension positive compression
negative. The combined effect of heating the casing and the dissociation of hydrates creates
compressive normal forces in the casing at the interval where hydrates exist.
2
3
D
EtFb
Maximum thrustCasing Maximum Thrust
2.50E+05
3.00E+05
3.50E+05
4.00E+05
4.50E+05
5.00E+05
5.50E+05
6.00E+05
6.50E+05
0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50 4.00
Heating Time (days)
Ca
sin
g M
ax
imu
m T
hru
st
(N/m
)
NH_Strong
H_Strong
NH_weak
H_weak
The absolute maximum thrust (hoop stress) in the casing decreases with heating. This maximum thrust occurs at the top of the casing for all the cases studied and is detected close to the base of the hydrate layer in case of its presence after 4 days of heating. No risk of hydrostatic buckling is found.
Seabed subsidence or heave
Seabed Level H-Weak Cement
-4.0
-3.0
-2.0
-1.0
0.0
1.0
2.0
3.0
4.0
5.0
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0
Distance across the model (m)
Sea
bed
Lev
el (
mm
)
t=0
t=5 min
t=12 hrs
t=1 day
t=2 days
t=6.5 days
t=8 days
Seabed Level After 8 Days of Heating
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0
Distance across the model (m)
Sea
bed
Lev
el (
mm
)H-Weak cement
NH-Strong cement
H-Strong cement
NH-Weak cement
After heatingBefore heating
Formation yield
Tensile failure
Hydrate bearing layerCasing
Formation Maximum Yield Radius
0.00
1.00
2.00
3.00
4.00
5.00
6.00
0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00
Heating Time (days)
Yie
ld R
ad
ius
No
rma
lise
d b
y W
ellb
ore
Ra
diu
s
NH_Strong
H_Strong
NH_weak
H_weak
Location Of The Maximum Yield Radius
0.00
1.00
2.00
3.00
4.00
5.00
6.00
7.00
8.00
9.00
10.00
0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00
Heating Time (days)
Lo
ca
tio
n o
f th
e N
orm
alis
ed
Ma
xim
um
Yie
ld
Ra
diu
s F
rom
Ca
sin
g U
pp
er
Tip
(m
)
NH_Strong
H_Strong
NH_weak
H_weak
After heating
Before heating Maximum yield radius
Location of maximum yield radius
Conclusion
• In the scenario considered the casing remains safe.
• The main impact of heating the casing and dissociating the hydrates was on the formation integrity.
• It is necessary to consider fluid flow (one or two phase flow) and its impact on reducing the pressure on the casing. This requires certain assumptions about the permeability of the cement and whether it will serve as a flow channel or not. Such a model should also allow for the reformation of hydrates.
• The accurate consideration of fluid flow requires modelling crack growth which can be done in a discrete modelling code.
• It is important to examine the effects of the depth-proximity to seabed- and thickness of the hydrate layer.
Model Fault reactivation and flow through faults using ABAQUS
Future work
Pore Pressure EvolutionStrong Cement & Hydrates
15
17
19
21
23
25
1 2 3 4 5 6
Normalized distance inside the formation
Po
re P
ressu
re (M
Pa)
0.01 day
0.5 day
1 day
2 days
4 days
6.5 days
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