Gas Hydrates as Potential Energy Resource and Trigger of … · Methane Hydrate (CH 4 nH 2 O) Carbon Dioxide Hydrate (CO 2 nH 2 O): Recognized as a potential future energy resource

Gas Hydrates as Potential Energy Resource

and Trigger of Submarine Slope Failure

Nagoya Institute of Technology

Prof. (Assistant)

Hiromasa Iwai

The First JSCE-CICHE Joint Workshop

~Sustainability and Disaster Reduction~

May 22-23, 2016

@Garden Villa Hotel, Kaohsiung, Taiwan

1/24

What is Gas Hydrate ?

Gas Hydrate consists of guest gas trapped

inside cage-like structures of water molecules.

: H

: C

: O

n=5.75 for structure I hydrate

4 2 ( )CH nH O hydrate

2 4( ) ( )nH O water CH gas

Burning MH

The gas interacts with the water under the

conditions of low temperature and high

pressure to form ice-like structure.2/24

Gas Hydrate dissociation process

4 2 4 2( ) ( ) ( )CH nH O hydrate CH gas nH O liquid

1m3 165m3 0.8m3

A unit volume of gas hydrate dissociates into approximately 165 times the

volume of guest gas and 0.8 times of water (at 0C and atmospheric

pressure).

Solid Gas Water(Liquid)

Methane Hydrate (CH4nH2O)

Carbon Dioxide Hydrate (CO2nH2O)

: Recognized as a potential future energy resource

: Recognized as a new material for CCS

Gas hydrate can exist only in a low temperature and high pressure

conditions. The gas hydrate will dissociate by heating and depressurizing

3/24

MH production test in Japan

The first offshore production test site.

North latitude: 3356

East latitude: 13719

Japan Oil Gas, and Metals National Corporation (JOGMEC) conducted the

first offshore methane hydrate production trial in March 2013 in the eastern

Nankai-Trough, Japan.

In the test, depressurization method was

adopted for methane gas production.

MH in sand layer

4/24

MH-bearing layer

Water flow

Gas flow

Dissociation frontMH-bearing layer

Water flow

Gas flow

Settlement

Dissociation frontMH-bearing layer

Water flow

Gas flow

Dissociation front

Settlement

Excess pore pressure

Sand

Cracks

Depressurization method

1,000m

300m

50~60m

The seabed ground surface is at a

water depth of about 1,000m in

eastern Nankai-Trough.

MH-bearing layer lies at a depth of

300m from the top of the ground

surface with a thickness of 50 or 60m.

270 275 280 285 290 295 300 305 310 3150

5

10

15

20

25

30

gas water

hydrate

Po

re p

ress

ure

(M

Pa)

Temperature (K)

Equilibrium curve of

Methane Hydrate

Pump up the sea-water inside the

production well, and the pore

pressure in the MH-layer will decrease.

5/24

Gas hydrates-bearing layer

Slope failureBubbles

Turbidity current

Tsunami

Production well

Settlement

×Cut submarine cables

and pipelines

Geological and Geotechnical problemsIn contrast to the aspects of the expected energy source, gas hydrates have

been believed to play a important role in the failure of submarine sediments.

The slides can cause tsunami…

“In 1979 a 0.15-km3 slide off Nice airport caused a tsunami that killed 11people.”

Nisbet, E.G. and Piper, D.J.W. 1998, Nature, 392(6674), pp.329-330.

Gas hydrates break down was involved in the creation of the megaturbidite.

6/24

Before dissociation

Soil particlesPore water

Gas hydrate

After dissociation

Gas hydrate morphology in sediments

Gas hydrate in the pores works as

additional soil particles.

Bond between soil particles.

Hydrate morphology affects the stiffness,

strength, and dilation.

Dissipation of the hydrate particles will

cause decrease of the material density.

Lost of bonding effects or load bearing

effects will reduce the stiffness and

strength.7/24

We have developed a temperature pressure controlled triaxial apparatus,

which can recreate low-temperature and high-pressure environment like

deep seabed-ground.

We have conducted a series of undrained triaxial compression tests and

dissociation tests on gas hydrate-containing sand specimens.

CO2-hydrate is used instead of methane hydrate considering safety of the

experiment, because it is non-flammable gas.

For the purpose of safe and economical production of methane gas from

the MH reservoir, further investigations related to mechanical properties

of gas hydrate-bearing sediments are required

In addition, it is essential to understand dissociation-deformation

behavior, in order to clarify the relationship between gas hydrate

dissociation and submarine slope failure.

Main objectives for this research

8/24

Temperature and pressure controlled triaxial apparatus

Testing Apparatus

9/24

Confining fluid

thermal control tank

-35℃～ +50℃ CO

2 g

as

Confin

ing p

ressure in

tensifier

Volume change

Po

re pressu

re inten

sifier

35mm

70mm

Cell pressure

transducer

Pore pressure

transducer

Therm

oco

uple

Co

olin

g flu

id

Load cell

200kN

P

Gas flow meter

Po

re pressu

re inten

sifier

①② ③

CO

2 d

issolv

ed

water tan

k

Schematic diagram of the apparatus

10/24

• Toyoura sand for the host material.

• Initial moisture content : 11%

• Initial void ratio : 0.67

compacted in a stainless mold using the moist tamping

method with a diameter of 35mm and height of 70mm.

Material properties

Density of soil particles 2.64

D50 (mm) 0.197

Diameter (mm) 35

Height (mm) 70

Initial void ratio 0.67

Density of CO2 hydrate 1.12

Target value of initial hydrate saturation 0.55

Initial moisture content w (%) 11.0

3cms g

0e

3cmH gH

rS

*Hydrate saturation

HH

r V

VS

V

φ＝ 35mm

H = 70mm

Sample preparation

11/24

Formation process

-5 0 5 10 15 200

2

4

6

8

10

12

(1C, 10.0MPa)

(c)

CO2 gas-CO

2 liquid

water(ice)-CO2 gas-hydrate

(1C, 2.3MPa)(b)

Po

re p

ress

ure

[M

Pa]

Temperature [C]

hydrate stability region

(a)

(10C, 2.3MPa)

12/24

Case-No. Void ratio Back pressure Initial mean effective stress Temperature Hydrate saturation

Case-1 0.74 10 1.0 1.0 0.0

Case-2 0.72 10 2.0 1.0 0.0

Case-3 0.72 10 3.0 1.0 0.0

Case-1H 0.76 10 1.0 1.0 34.6

Case-2H 0.73 10 2.0 1.0 27.8

Case-3H 0.73 10 3.0 1.0 28.5

0e0 [MPa]wu 0 [MPa]p o[ C]T

H

rS

Experimental conditions

Case-1, Case-2, Case-3 : water saturated sand specimens (without hydrate)

Case-1H, Case-2H, Case-3H contain CO2-hydrate in the pores.

Initial mean effective stresses are set to be 1.0MPa, 2.0MPa, or 3.0MPa.

Strain rate is set to be 0.1%/min among all the cases.

6 cases of undrained triaxial compression tests are conducted.

13/24

0 1 2 3 4 5 60

1

2

3

4

5

6

min/%1.0a

1.20

1

Dev

iato

r st

ress

q [

MP

a]

Mean effective stress p' [MPa]

Case-1, e=0.74, SH

r=0.0 %

Case-1-H, e=0.76, SH

r=34.6 %

Case-2, e=0.72, SH

r=0.0 %


r=27.8 %

Case-3, e=0.72, SH

r=0.0 %


r=28.5 %

0 5 10 15 200

1

2

3

4

5

6

min/%1.0a

Dev

iato

r st

ress

q [

MP

a]

Axial strain a [%]

Case-1, e=0.74, SH

r=0.0 %

Case-1H, e=0.76, SH

r=34.6 %

Case-2, e=0.72, SH

r=0.0 %

Case-2H, e=0.73, SH

r=27.8 %

Case-3, e=0.72, SH

r=0.0 %

Case-3H, e=0.73, SH

r=28.5 %

Stress-strain relationship & stress path

Hydrate-bearing sand

Water-saturated sand

Both stiffness and strength in hydrate-bearing sand are greater than that of water-

saturated sand specimens.

The stress paths in hydrate-bearing specimens express larger dilation than that of

water-saturated specimens in each confining pressure.

The hydrate may act like additional small particles in the sand structure.14/24

0 10 20 30 40 50

100

200

300

400

500

600 Case-1, p

'

0=1.0MPa Case-1H, p

'

0=1.0MPa

Case-2, p'

0=2.0MPa Case-2H, p

'

0=2.0MPa

Case-3, p'

0=3.0MPa Case-3H, p

'

0=3.0MPa

Sca

nt

modulu

s E

50 [M

Pa]

Hydrate saturation SH

r [%]

0 10 20 30 40 500.5

1.0

1.5

2.0

2.5 Case-1,Case-1H, p

'

0=1.0MPa Case-2, Case-2H, p

'

0=2.0MPa

Case-3, Case-3H, p'

0=3.0MPa

Ehyd

rate

50

/Esa

nd

50


r [%]

Scant modulus E50

0 5 10 15 200

1

2

3

4

5

6D

evia

tor

stre

ss q

[M

Pa]

Axial strain a [%]

Case-1, e=0.74, SH

r=0.0 %

Case-2, e=0.72, SH

r=0.0 %

Case-3, e=0.72, SH

r=0.0 %

0 5 10 15 200

1

2

3

4

5

6

Dev

iato

r st

ress

q [

MP

a]

Axial strain a [%]

50

sandE

50

hydrateE

15/24

0 5 10 15 20-2

-1

0

1

2

min/%1.0a

Exce

ss p

ore

wat

er p

ress

ure

uw [

MP

a]

Axial strain a [%]

Case-1, e=0.74, SH

r=0.0 %


r=34.6 %

Case-2, e=0.72, SH

r=0.0 %


r=27.8 %

Case-3, e=0.72, SH

r=0.0 %


r=28.5 %

0 5 10 15 200.0

0.5

1.0

1.5

2.0

Case-1, e=0.74, SH

r=0.0 %


r=34.6 %

Case-2, e=0.72, SH

r=0.0 %


r=27.8 %

Case-3, e=0.72, SH

r=0.0 %


r=28.5 %min/%1.0a

Str

ess

rati

o q

/p'

Axial strain a [%]

Excess P.W.P. vs strain, Stress ratio vs strain

The reduction in the pore water pressure

becomes larger in the specimen with

hydrate.

The P.W.P profile in the hydrate-bearing

specimen behaves like a dense sand

comparing the one without hydrate.

In the case of the same confining

pressure, the maximum stress ratio of

the hydrate-bearing specimen becomes

larger than that of the water-saturated

specimen.

In the critical state, the stress ratio

settled at the same value, namely, 1.2,

among all the cases.

16/24

0 5 10 15 20 25 30 35 400

5

10

15

2.0 MPa

Case-3-H

Case-2-H

Case-1-H

min/%1.0aStr

ess

rati

o i

ncr

easeR

[

%]


r [%]

Constant strain rate test (0.1 %/min)

Strain rate change test (0.1 %/min)

max

max

1 100H

R

0 5 10 15 20 25 30 35 400

5

10

15

20

25

30

Case-1-H

2.0 MPa

Case-1-H

Case-2-H

Str

ess

rati

o i

ncr

easeR

q [

%]


r [%]

Constant strain rate test (0.1 %/min)

Strain rate change test (0.1 %/min)

Case-3-Hmin/%1.0a

max

max

1 100H

q

qR

q

Strength increase ratio vs Hydrate saturation

Increase ration in the maximum deviator stress

Increase ration in the maximum stress ratio

Increase ration in the maximum deviator stress

seems to depend on both the confining

pressure and the hydrate saturation.

Not only sand particles but also gas

hydrate might have the dependency

on the confining pressure.

Increase ration in the maximum stress ration

increases with increase in the hydrate

saturation.

17/24

Summary – undrained triaxial tests –

In order to clarify the mechanical properties of gas hydrate-bearing sediments,

we conducted undrained triaxial compression tests with different confining

pressure and different hydrate saturation.

－ Conclusions －1. Both stiffness and strength of hydrate-bearing specimen becomes larger

comparing with that of the specimens without hydrate.

2. In the case of hydrate-bearing sand, the excess pore water pressure is

reduced largely. It may be because that the hydrate acts like additional

small particles, and the apparent density of the sample increases.

3. Increase ratio in the maximum deviator stress may depend on both the

confining pressure and hydrate the saturation.

4. Increase ratio in the maximum stress ratio increase with increase in the

hydrate saturation.

18/24

Case-No.Initial

void ratio

Initial pore

pressure

Effective confining

pressureTemperature

Hydrate

saturation

Case-0 0.69 2.0 0.1 18.0 0.0

Case-1 0.75 4.0 3.0 18.0 39.1

Case-2 0.75 4.0 3.0 18.0 42.2

Case-3 0.79 4.0 3.0 18.0 15.4

Case-4 0.76 6.0 3.0 18.0 32.1

H

rS0e [MPa]iniP [MPa]co[ C]T

Experimental conditions

Case-0 is the one without hydrate

Case-1~Case-3: the initial pore pressure is 4.0MPa

Case-6: the initial pore pressure is 6.0MPa

Case-1~Case-4: the effective confining pressure are the same; 3.0MPa

Undrained conditions for water and gas

19/24

Experimental results -Pore pressure-

0 1 2 3 4 5

0

1

2

3

4

5

6

7 Case-0, S

H

r= 0.0%, Case-1, S

H

r=39.1%, Case-2, S

H

r=42.2%

Case-3, SH

r=15.4%, Case-4, S

H

r=31.9%

Ex

cess

po

re p

ress

ure

[M

Pa]

Time [hour]

I. In Case-0(without hydrate) , any buildup of the pore pressure was not observed.

II. The pore pressure is almost constant until one hour. After 1-hour the pore pressure

begins to increase drastically, in Case-1~Case-4.

III. In Case-2, increase rate of the pore pressure seems to be the largest. It is because

that the hydrate saturation is the largest among the cases

I

II

III

20/24

-5 0 5 10 15 200

2

4

6

8

10

12 CO

2 liquid boundary, CO

2 hdrate boundary

Case-1 (SH

r=39.1%), Case-2 (S

H

r=42.4%),

Case-3 (SH

r=15.4%), Case-4 (S

H

r=32.1%)

end

Pore

pre

ssure

[M

Pa]

Temperature [C]

Initial

The first increase in the pore pressure might be caused

by gasification of remaining liquid CO2 .

Little increase in the pore pressure can be found until the

temperature reaching the CO2-hydrate boundary.

Temperature-pore pressure path

21/24

0 1 2 3 4 5 6 7 8-4

-3

-2

-1

0

1

2

3

4

5Excess pore pressure: Case-3, Case-4

Axial strain: Case-3, Case-4

Time [hour]

Ex

cess

po

re p

ress

ure

[M

Pa]

0.8

0.6

0.4

0.2

0.0

-0.2

-0.4

-0.6

-0.8

-1.0

Ax

ial

stra

in [

%]

Compression

Expansionpeak

MAX: 2.8MPa

MAX: 0.45% in expansion

Tensile strain can be observed with increase in the excess pore pressure.

When the pore pressure reaches at the maximum, the tensile strain also reached at

the peak.

Under undrained conditions, the hydrate dissociation may lead the large build up

of the pore pressure, and decrease in the density of the sediments, simultaneously.

Excess pore pressure and axial strain

22/24

1. We have developed a temperature and pressure controlled triaxial

apparatus.

2. This new triaxial cell can make the environment where gas

hydrates can form, and we have carried out formation and

dissociation tests using carbon dioxide hydrate.

In order to investigate the fundamental behavior of the gas hydrates

containing soils associated with hydrates dissociation …

－ Conclusions －1. The hydrates dissociation will cause a significant increase in the pore

pressure, and result in a significant reduction in the effective confining

pressure under undrained conditions.

2. The reduction in the effective confining pressure is a kind of liquefaction

phenomena, which may lead to instability of the marine sediments.

3. The result indicates that both increase in the pore pressure and decrease

in the density of the sediments might be caused simultaneously.

Summary – dissociation tests –

23/24

Thank you for your kind attention.

24/24

Gas Hydrates as Potential Energy Resource and Trigger of … · Methane Hydrate (CH 4 nH 2 O) Carbon Dioxide Hydrate (CO 2 nH 2 O): Recognized as a potential future energy resource

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