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Corso di Geologia Marina 2021-22

Università di Trieste

Corso di Laurea in Geologia

Anno accademico 2021 - 2022

Geologia Marina

Parte IV Modulo 4.4/5

Identificatori di movimento di fluidi: Idrati del metano Docente

A. Camerlenghi

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B2 - Outline

Review of main mechanisms of fluid flow:

• Mud diapirs and mud volcanoes

• Gas chimneys

• Pockmarks

• Seafloor vents in general

• Polygonal fault systems

• Diagenetic fronts

Gas hydrates

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NATURAL GAS HYDRATES ARE CONSIDERED AS:

• Natural controllers of climatic change

• Geo-hazards

• Potential energy source

• Controllers of deep sea eco-systems

• Potential safe and effective way of methane transport

• Problem in pipelines

• Possible cause of ship and airplane disappearance in the

Bermuda triangle

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Corso di Geologia Marina 2021-22

METHANE

Is the simplest saturated hydrocarbon gas (alkane):

CH 4

Other common hydrocarbon gases are:

ethane (C

2

H

6

), propane (C

3

H

8

) butane (C

4

H

10

)

When the number of carbon atoms exceeds 5, the name of gases is from Greek numbers: pentane, hexane, heptane...

The general formula of hydrocarbon gases is:

C n H 2n+2

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Human-related sources

• Landfills (waste disposal)

• Natural gas and petroleum systems (natural gas production)

• Coal mining

• Livestock enteric fermentation

• Livestock manure management

• Wastewater treatment

• Rice cultivation

Natural sources

• Wetlands

• Termites

• Oceans (anaerobic digestion in marine zooplankton and fish, and also from methanogenisis in sediment )

• Hydrates

• Juvenile

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Corso di Geologia Marina 2021-22

HYDRATES OF NATURAL GAS

(discovered in 1810)

• Gas hydrates are a solid phase composed of water and low- molecular weight gases (predominantly methane)

• Water molecules form an ordered crystalline solid matrix which includes gas molecules with weak electro-static bounds

• The state of saturation of hydrates is a function of

pressure and temperature. They form under conditions of low temperature, high pressure, and adeguate gas

concentration

• The ion content of water and the type of gas (methane,

propane, pentane…) affect the phase diagram of the gas

hydrate

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Corso di Geologia Marina 2021-22

+

1 m

3

GAS HYDRATE 164 m

3

GAS

0.8 m

3

WATER

Hydrate crystal

Methane molecule Water molecule

@ standard pressure and temperature Methane molecule

Water molecule Bohrmann and Torres, 2006, in Schulz, Horst D.; Zabel,

Matthias (Eds.) Marine Geochemistry

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Corso di Geologia Marina 2021-22

Courtesy:

Carlo Giavarini, Filippo Maccioni and Maria Laura Santarelli Università di Roma "La Sapienza Dipartimento di Ingegneria Chimica.

RCOM - University of Bremen

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Corso di Geologia Marina 2021-22

TEMPERATURE ( C)

-10 0 10 20 30

1

10

100 PRESSURE

(MPa)

METHANE GAS +

WATER

METHANE GAS

ICE+

METHANE HYDRATE

WATER+

METHANE HYDRATE

ICE+

PHASE DIAGRAM OF METHANE HYDRATES

0.1

Ice Water

Meth ane Ga

s Me

than e Hyd

rate

-10 0 10 20 30

(10)

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Alaska Highway Pipeline

TransCanada

Hydrate formation in arctic gas pipelines reduces or blocks

methane flow. Chemical additives are necessary to prevent

hydrate formation.

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LIQUID NATURAL GAS TRANSPORT

IS EXPENSIVE AND DANGEROUS

Methane is condensed into a liquid at almost atmospheric pressure

(Maximum Transport Pressure set around 25 kPa) by cooling it to

approximately -163 C.

LNG is transported by specially

designed cryogenic sea vessels and cryogenic road tankers, and stored in specially designed tanks.

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Corso di Geologia Marina 2021-22

Possible ship specifically designed to carry natural gas hydrate pellets

@ -20 C and atmospheric pressure

(National Maritime Research Institute, Mitsui Shipbuilding & Engineering, and Osaka

University)

Methane Hydrate Pellets

Self-preservation is thought to be caused by a layer of ice from dissociated

hydrate; this layer coats the hydrate and seals it from further dissociation.

self-preservation

At 1 Atm, CH

4

Hydrates are stable

below -20 C.

(13)

Corso di Geologia Marina 2021-22

Modifeid from:

Bohrmann and Torres, 2006, in

Schulz, Horst D.; Zabel, Matthias (Eds.) Marine Geochemistry

Methane Hydrate Pellets

PHASE DIAGRAM OF METHANE HYDRATES IN THE NATURAL ENVIRONMENT

PERMAFROST HYDRATE

OCEANIC HYDRATE

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Permafrost is defined as soil, sediment or rock whose temperature is continuosly below 0 C for at least

two years

METANE HYDRATES IN PERMAFROST

PERMAFROST

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METHANE HYDRATES IN OCEANIC SEDIMENTS

Natural gas hydrates are distributed along the ocean

margins world wide within the Gas Hydrate Stability

Zone (GHSZ), that ranges from the seafloor down to a

maximum of 700-800 m

(16)

Corso di Geologia Marina 2021-22

ACTIVE CONTINENTAL MARGINS

Modified from Ge et alii, Eos,Vol. 84, No. 16, 22 April 2003 PASSIVE CONTINENTAL MARGINS

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Corso di Geologia Marina 2021-22

Ruppel, C. D., and J. D. Kessler (2017), The interaction of climate change and methane hydrates, Rev.

Geophys., 55, 126-168, doi:10.1002/2016RG000534.

(18)

Corso di Geologia Marina 2021-22

http://www.rcom.marum.de

(19)

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http://www.rcom.marum.de

(20)

Corso di Geologia Marina 2021-22

http://www.rcom.marum.de

(21)

Corso di Geologia Marina 2021-22

http://www.rcom.marum.de

(22)

Corso di Geologia Marina 2021-22

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http://www.rcom.marum.de

(24)

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Van Dover et al. (2003). Deep Sea Research

http://www.rcom.marum.de

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Corso di Geologia Marina 2021-22

METHODS OF DETECTION OF NATURAL GAS HYDRATES

• SEISMICS

(reflection, multichannel, OBS)

• DRILLING

(essentially through scientific drilling)

• GEOCHEMICAL

(inorganic- organic geochemistry)

• MODELLING

(laboratory models - data inversion)

• BASIN-WIDE ANALYSES

(modelling + data)

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Corso di Geologia Marina 2021-22

AIR GUNS

SEISMIC STREAMER

(28)

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OCEAN BOTTOM SEISMOMETERS

(OBS)

(29)

Corso di Geologia Marina 2021-22

SEISMICS REFLECTION The concept of Bottom

Simulating Reflector (BSR)

The BSR is a seismic reflector that simulates the sea bottom

reflector. It is produced by the acoustic

impedance contrast

between sediments with

hydrates (above) and

sediments with free gas

(below).

(30)

Corso di Geologia Marina 2021-22

SEA FLOOR

FOLDED MARINE SEDIMENTS GAS

HYDRATE BEARING

LAYER

FREE GAS LAYER

SEISMC PROFILE

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Corso di Geologia Marina 2021-22

Turbidite (Gorgoglione Flysch), Miocene, South Italy

Marne a Fucoidi (Sezione del Bosso)

Cretaceous (Albian), Central Apennines, Italy FOTO MASSIMO GALLI

Stratification in Marine Sediments

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Corso di Geologia Marina 2021-22

Makassar Straits, Indonesia

Data from TGS-NOPEC Geophysical Company, published in Max et al., 2006. Economic Geology of Natural Gas Hydrates, Springer.

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Corso di Geologia Marina 2021-22

Characteristics of the BSR

• High reflection coefficient

• Reverse polarity with respect to the seafloor reflector

• Cuts through lithologic reflectors

• Its depth approximately coincides with the theoretical depth of the base of the hydrates stability zone.

• It may be underlined by another reflector produced by

the base of the free gas layer (BGR)

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Corso di Geologia Marina 2021-22

http://www.jamstec.go.jp/chikyu/

How can the hydrates be identified through drilling?

• Thermal anomaly in cores

• Soupy layers

• Chlorinity anomaly

• Resistivity anomaly

• Seismic velocity anomaly

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Corso di Geologia Marina 2021-22

Thermal anomaly in cores

Gas hydrate dissociation is an endo-thermic reaction (it absorbs heat from the

surroundings >>>>> decrease in bulk sediment temperature)

G. Bohrmann, Initial results from M52/1 MARGASCH

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Corso di Geologia Marina 2021-22

Soupy layers

Gas hydrate dissociation during core recovery destroys the sediment fabric,

producing disturbed, liquified soupy sediment layers in cores

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Corso di Geologia Marina 2021-22

Chlorinity anomaly

Gas hydrate dissociation during core recovery produces residual fresh water that dilutes the

ionic concentration of the pore water

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Corso di Geologia Marina 2021-22

In situ Electrical Resistivity anomaly

The electrical resistivity of gas hydrates is higher than that of seawater.

The anomaly is identified with respect to a resistivity profile in a nearby borehole with similar sediment NOT containing hydrates

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Corso di Geologia Marina 2021-22

In situ seismic velocity anomaly

The compressional wave velocity of gas hydrates is higher than that of seawater.

The anomaly is identified with respect to a resistivity profile in a nearby borehole with similar sediment NOT containing hydrates

P waves

BSR BSR

S waves

Rossi et al., ICGH (2005)

(40)

Corso di Geologia Marina 2021-22

VELOCITY MODEL Biot-Geerstma-Smit equations

V

p

= 1

C

m

+ 4 3 µ

!

"

# #

$

%

&

& + φ

eff

k ρ

m

ρ

f

+ 1 − β − 2 ⋅ φ

eff

k

!

"

# $

% & ⋅ 1 − ( β )

1− φ

eff

− β

( ) C

b

+ φ

eff

C

f

,

- . . . . .

/

0 1 1 1 1 1

⋅ 1

ρ

m

1 − φ

eff

k

ρ

f

ρ

m

!

"

# #

$

% &

&

2 3 4 4

5 4 4

6 7 4 4

8 4 4

1/ 2

(1)

(41)

Corso di Geologia Marina 2021-22

GLOBAL ESTIMATES

Estimation as amount of Carbon atoms · 10 15 g

NATURAL GAS HYDRATES 10.000 FOSSIL FULES 5.000

SOILS 1.400

DISSOLVED IN WATER 980

TERRESTRIAL LIVING ORGANISMS 830 WETLANDS AND OTHER 500

Kvenvolden, various sources

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Corso di Geologia Marina 2021-22

HOWEVER……..

Global estimates of the volume of hydrate-bound gas in marine sediments versus the year in which the estimate

was made.

A.V. Milkov / Earth-Science Reviews 66 (2004) 183–197

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Corso di Geologia Marina 2021-22

A.V. Milkov / Earth-Science Reviews 66 (2004) 183–197

a) The distribution based on the estimate of 10000 Gt of methane carbon in gas hydrates (Kvenvolden, 1993).

b) The distribution based on the revised estimate of the global gas hydrate inventory assuming the global volume of hydrate-bound gas at upper bound.

c) The distribution based on the revised estimate of the global gas hydrate inventory assuming the global volume of hydrate-bound gas at lower bound.

Distribution of organic carbon in the Earth

(excluding dispersed organic carbon such as kerogen and bitumen)

(44)

Corso di Geologia Marina 2021-22

In spite of changing global hydrates estimates…….

• Methane is the cleanest fossil fuel:

CH

4

+ 2O

2

2H

2

O + CO

2

+ heat

• Methane is presently the preferred fossil fuel for power generation in OECD countries,

• Methane demand is increasing also in other regions such as the Middle East, China and India

• Despite current high prices, the vast majority of new power

generation on line in the review period will be gas-fired.

(45)

Corso di Geologia Marina 2021-22

Methane Hydrates are considered as NON CONVENTIONAL HYDROCARBONS

by most oil companies

• There is not an established extraction technology .

• The hydrates must be dissociated in situ by:

• Heat injection

• Injection of chemical inhibitors

• depressurization

• There are severe environmental implications and the methods will not be considered as economically feasible until the gas price will rise considerably.

• USA, Japan, India, Korea and other countries of the Pacific

Area have started National Plans for the gas hydrates assessment

in their Economic Exclusive Zones.

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Corso di Geologia Marina 2021-22

What Happens in Europe?

• No policy has been established so far

• Several EC projects have been dedicated to the matter from a purely scientific point of view (see next part of this talk)

• Oil companies and academia have focussed don this issue regarding the implications for submarine slope stability (see next part of this talk)

• Regional evaluations of gas hydrate potential of European Margins are in due course:

• Atlantic European Margins

• Mediterranean

• Black Sea

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Corso di Geologia Marina 2021-22

HYDRATES PROSPECTIVIY in the Mediterranean Sea

D. Praeg, V.

Unnithan, and A. Camerlenghi, American

Geohpysical Unions Fall Meeting, December 2006

Due to:

• High temperature of bottom water

• High salinity of pore water

• Presence of a salt seal (Messinian) preventing deep fluid migration

The thickness of the Gas Hydrates Stability Zone is reduced in the

Mediterranean Sea with respect to world Oceans.

EU HYDRAMED Project. Praeg et al. in progress

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METHANE HYDRATES AND

GLOBAL CLIMATE

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MILANKOVITCH ORBITAL CYCLES Frequencies of the main

Earth orbital variations

Earth axis inclination

41 kyr

Orbital Excentricity 100 - 410 kyr

Precession of the equinoxes 19 - 23 kyr

EARTH ORBIT

EARTH

ROTATION AXIS

The mean Solar radiation received by the earth changes

through time. Such changes are the primary cause of

glacial interglacial epochs and other climatic stages.

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Programma Nazionale di Ricerche in

Antartide (PNRA) European Project for Ice Coring in Antarctica (EPICA) Dome-C Station, Antarctica

(51)

Corso di Geologia Marina 2021-22

Methane and CO2 concentrations in the atmosphere since 800 ka from Environmental Protection Agency [2015]. Deep time data are from analysis of the European Project for Ice Coring in Antarctica (EPICA) Dome ice core and thus reflect Southern Hemisphere methane. Note the difference in time scales between the panels.

Ruppel, C. D., and J. D. Kessler (2017), The interaction of climate change and methane hydrates, Rev.

Geophys., 55, 126-168, doi:10.1002/2016RG000534.

(52)

Corso di Geologia Marina 2021-22

EPICA Community Members, Nature, 2006

TIME

GLACIAL PRESENT INTERGLACIAL

(HOLOCENE)

LAST GLACIAL MAXIMUM DE-

GLACIATION

PALEO-TEMPERATURE INDICATORS

(53)

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METHANE HYDRATES STORED IN

PERMAFROST AND MARINE SEDIMENTS ARE HIGHLY SENSITIVE TO AMBIENT

TEMPERATURE AD PRESSURE CHANGES

IN MARINE SEDIMENTS:

• WHEN OCEAN BOTTOM WATER TEMPERATURE RISES (DE-

GLACIACION) SOME METHANE CHANGES FROM HYDRATE FORM TO GASE FORM AND ESCAPES FROM TEH SEAFLOOR INTO THE WATER COLUMN, AND FROM THERE TO THE ATMOSPHERE.

• HOWEVER, BECAUSE SEALEVEL CHANGES ACCORDING TO

CLIMATIC CHANGES, THE INFLUENCE OF PRESSURE HAS TO BE

TEKEN INTO ACCOUNT.

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Corso di Geologia Marina 2021-22

Anaerobic oxidation of methane (AOM) via sulfate reduction.

Microbial consortia of methanotrophic archaea and sulfate- reducing bacteria identified on gas hydrate-bearing samples (Boetius et al. 2000).

The archaea oxidize methane:

CH 4 + 2H 2 O >>> CO 2 + 4H 2

And sulfate reducing bacteria may act as indicated by the reaction:

SO

4

2- + CH

3

COOH + 2H + >>> 2CO

2

+ H

2

S + 4H

2

O

CH

4

+ SO

4

2- >>> HCO 3 - + HS - + H

2

O

(55)

Corso di Geologia Marina 2021-22

Authigenic carbonate precipitation Methane-derived Calcium Carbonate.

HCO 3- + OH - + Ca 2+ CaCO 3 + H 2 0 + C0 2

Bicarbonate alkaline calcium ions calcium

from bacterial action seawater present in seawater carbonate deposited

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Corso di Geologia Marina 2021-22

Bathymodiolus heckerae mussel beds. (A) Juvenile and adult mussels at Marker E . (B) Dead mussels and octopus. (C) Extensive bed of live mussels of relatively uniform size, partially covered by

bacterial mats, at Marker B . (D) Dead mussels at the eastward periphery of Marker B . (E) Mussels with a chiridotid holothurian and Alvinocaris sp. (F) Mussels with Alvinocaris sp. And ophiuroids. Scale bars: A–D : 10 cm, E; F : 5 cm.

Van Dover et al. (2003). Deep Sea Research

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Corso di Geologia Marina 2021-22

• Protists: Unicellular marine organisms

• They live in all marine environments

• They have existed since the Cambrian

• Size: from 0.01 to 5 mm (> 50 mm)

• Agglutinated

• Tectine

• Calcium Carbonate (CaCO

3

) Shell composition:

FORAMINIFERA (Marine zooplankton)

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• Foraminifera form their skeleton in isotopic equilibrium with ambient seawater

• The isotopic composition of the skeleton of benthic foraminifera reflects the micro-habitat where they live

The d 13 C of foraminifera depends on the d 13 C of the Dissolved Inorganic Carbon (DIC) of the water in which they live:

Normal marine environment: d 13 C DIC @ 0‰

(Peterson e Fry, 1987)

Methane seeps environment: d 13 C DIC @ -30/-60‰

(Aharon et al., 1992)

(59)

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Whiticar 1999_ Marine Geology

(60)

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Negative excursions of d

13

C in marine sediments during warm periods can be explained ONLY with massive

emissions of Methane from the seafloor

(61)

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Kennett et alii, Science, 2000

The Clathrate Gun Hypothesis

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Methane hydrate dissociation as source of submarine slope instability

Normark et al. Marine Geology 203 (2004) 247-259

(63)

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SEA LEVEL

PREVIOUS SEAFLOOR

SLIDE

METHANE GAS

FREE GAS LAYER

BASE OF THE THEORETICAL STABILTIY FIELS OF

GAS HYDRATES

BEFORE AFTER

GLOBAL WARMING

DEPTH (m)

(64)

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Courtesy Petter Bryn

THE STOREGGA SLIDE ON THE NORWEGIAN

CONTINENTAL MARGIN(7000 yr)

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Courtesy Petter Bryn

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Courtesy Petter Bryn

(67)

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THE STOREGGA SLIDE CAUSED A HUGE TSUNAMI

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The effect of gas hydrates

Mienert et al., 2005

Change in theoretical thickness of hydrate stability zone due to sea level change (small, negative) and bottom water temperature (locally large, positive). Biggest effect near upper headwall in

Storegga.

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THE NORTH SVALBARD SLIDE

Vanneste et al., EPSL, 2006

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BLAKE RIDGE

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AT THE EDGE OF SCIENCE

(72)

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4 scientific books

2000 2001

1998 2003

Fantascienza

Il quinto giorno (Der Schwarm)

Franz Schatzing 2006

In Italiano

Energia immensa e sfida ambientale. Gli idrati del metano

di Carlo Giavarini (Autore) Università La Sapienza, 2007

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