Casing Integrity in Hydrate Bearing Sediments Reem Freij-Ayoub, Principal Research Engineer CESRE Wealth from Oceans.

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