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International Journal of Greenhouse Gas Control 30 (2014)
1933
Contents lists available at ScienceDirect
International Journal of Greenhouse Gas Control
j ourna l h o mepage: www.elsev ier .com/ locate / i jggc
preliminary assessment of geological CO2 storage in Cambodia
hanrithyrouth Maoa,, Yasuhiro Yamadaa,b, Toshifumi Matsuokaa
Department of Urban Management, Kyoto University, Katsura,
Nishikyo, Kyoto 615-8540, JapanJapan Agency for Marine-Earth
Science and Technology (JAMSTEC), 3173-25, Showa-machi, Kanazawa,
Yokohama 236-0001, Japan
r t i c l e i n f o
rticle history:eceived 19 December 2013eceived in revised form
15 August 2014ccepted 18 August 2014vailable online 14 September
2014
eywords:O2 storagehmer Basinaline aquiferydrodynamic trapatched
storage capacity
ambodia
a b s t r a c t
This study screens and rank Cambodian sedimentary basins in
terms of their containment, capacity, andfeasibility for the
geological storage of CO2. The results of the screening and ranking
procedure indicatethat the Khmer Basin is the most suitable basin,
followed by the Kampong Saom and Tonle Sap basins. Aquantitative
volumetric assessment-based evaluation of CO2 storage capacity is
performed on these threesuitable basins. The evaluation yields a
range in the national CO2 storage capacity of 90 Mt (in
structuraltraps) to 45 Gt (in hydrodynamic traps), representing
low- and high-case estimates, respectively. Thesaline aquifers
associated with this storage capacity should be considered
prospective storage optionsas hydrodynamic traps because of
containment and capacity issues associated with the structural
traps.Eight major point sources of CO2 are identified that have a
combined output (estimated for 20082024)of 43.1 Mt annually and 82
billion m3 in place, and the potentially prospective matched
storage capacityis assumed. Overall, a combination of the initial
suitabilities of the basins and estimates of prospectivematched
storage capacity shows that the Khmer, Kampong Saom, and Tonle Sap
basins may provide a
solution to the problem of reducing future atmospheric emissions.
The present results should assist bothexploration geologists and
experts in carbon capture and storage to gain a better
understanding of theCO2 storage resources of Cambodia. However, the
results should be regarded as preliminary because ofthe limited
available data on which the assessments were based; future
geological and geophysical datashould improve the reliability of
the estimates of carbon storage capacity reported here.
2014 Elsevier Ltd. All rights reserved.
. Introduction
Cambodia is located in the Indochina Peninsula and has a
trop-cal climate in both offshore and onshore areas. The
Cambodianational Petroleum Authority (CNPA) states that numerous
CO2mission point sources are present in both the on- and
off-shorenvironments of Cambodia, and there are significant
concerns overhe contribution of the CO2 produced by these sources
with respecto the abundance of greenhouse gases in the atmosphere
and cli-
ate change.The geological storage of CO2 is a viable method to
reduce
O2 emissions into the atmosphere (Wilson et al., 2003;
IPCC,005). The safe storage of CO2 in a sedimentary basin
requires
hat CO2 is stored in favorable geological porous media at
deptharies from 800 to 1000 m for a cold sedimentary basin
(geother-al gradient 40 C/km) (so that the stored CO2 willbe in the
dense phase); the porous media also need to be cov-ered by thick
regional cap rocks so that CO2 cannot penetratevertically upwards
through the overlying sedimentary sequence(Bachu, 2003; IPCC,
2005). The injection of CO2 at shallower depths(
-
20 C. Mao et al. / International Journal of Greenhouse Gas
Control 30 (2014) 1933
Table 1Methodology for estimating CO2 emissions from stationary
sources (US DOE-NETL, 2012).
Methodology Description
1. CO2 emissions from cement plant:CCO2 = 0.9 Ecp
CO2 emissions estimate based on cement production and
combustion.Where: CCO2 = tons per yearEcp = Cement production rate
(tons per year)
2. CO2 emissions from coal fired power plant:CFCO2 = 3.664 C%
Ft
CO2 emissions estimate via combustion.Where CFCO2 = tons per
yearC% = carbon in the coal (weigh fraction; %)Ft = coal usage rate
(tons per year)
3. CO2 emissions from natural gas power plant:NGCO2 = (1100
P)/(2000)
CO2 emissions estimate calculated using a value of 1100 lb of
CO2 per MWh.Where: NGCO2 = tons per yearP = annual plant generation
(MWh)
4. CO2 emissions from oil power plant:HCO2 = (3.664 Ft C% DF
)/(2000)
CO2 emissions estimate via combustion.Where: HCO2 = tons per
yearDF = oil density (lb per gallon)C% = carbon in the oil (weight
fraction; %)Ft = oil usage rate (gallons per year)
5. CO2 emissions from refinery plant:RCO2 = 11 EP
CO2 emissions estimate based on emission factor for petroleum
refinery production(11 tons CO2 per year per barrel per day
petroleum).Where: RCO2 (tons per year)EP = petroleum plant
production rate (barrel per day)
6. CO2 emissions from fertilizer production:NH3CO2 = ENH3 (NH3 +
fuel)
Where: NH3CO2 = tons per yearNH3 + CO2 process emission factor
for NH3 production (1.2 tons CO2 per ton NH3)ENH3 = Production rate
(tons per year)fuel = CO2 combustion emission factor (0.5 tons CO2
per ton NH3)
here:= CO2
GIP = o
2do2
irbpsoCoicpoaTw(wtIhg
2
lA(u(N
7. CO2 produced from natural gas reservoir:VCO2 = Rf volume of
OGIP
WRfO
000, 2003), and Greece (Koukouzas et al., 2009), and
subsequentetailed assessment, site characterization, and economic
analysisf such basins have been undertaken in Australia (Bradshaw
et al.,004) and in the Netherlands (Ramrez et al., 2010).
The subsurface geology of mature oil-producing countriess well
known, compared with the relatively unexplored andestricted nature
of knowledge of the subsurface geology in Cam-odia. Bachu (2003)
argued that both qualitative and quantitativearameters for the
screening and ranking of basins need to beubjectively adjusted in
accordance with the economic situationf the country concerned. The
majority of sedimentary basins inambodia are still poorly explored
and are located in areas with-ut identified CO2 sources, and many
of them have no, or limitednfrastructure. Knowledge of the
subsurface geology of Cambodia isurrently restricted as a result of
oil and gas exploration policy, theresent research study aims to
provide a preliminary assessmentf the suitability of sedimentary
basins in Cambodia for CO2 stor-ge by determining which basins have
large effective pore volumes.he study examines and assesses the
structural geological frame-ork and stratigraphy of Cambodian
basins using published data
Vysotsky et al., 1994; Okui et al., 1997; Fyhn et al., 2010),
alongith information obtained via the cooperation of the CNPA (part
of
he Ministry of Mines and Energy of the Government of Cambodia).t
is the first study to focus on the existence of suitable aquifers
andydrocarbon reservoirs within the Cambodian subsurface for
theeological storage of CO2.
. CO2 emission point sources
The CO2 point sources in Cambodia are identified as twoarge
potential future natural gas plants (in Overlapping Claimsrea (OCA)
and Western Block A), four coal-fired power plants
Koh Kong, Sihanouk Ville II and III, and Kampot), one nat-ral
gas power plant (Sihanouk Ville I), one oil power plantEDC
(Electricite Du Cambodge) Phnom Penh), one refinery (Preyop), one
cement kiln (Kampot Cement), and one fertilizer
VCO2 = cubic meterrecovery factorriginal gas in place
plant (Takmau Fertilizer). Regarding the installed and
produc-tion capacity and type of industry (MME, 2009; IEEJ,
2011;2b1st-consulting, 2013; OpenDevelopmentCambodia, 2013;
CDRI,2014; Energypedia, 2014; SCG, 2014; CNPA exploration
docu-ments), total CO2 emissions were calculated using the
methodologyof US DOE-NETL (2012) (Table 1). Based on these sources,
emis-sions for 20082024 are calculated to total 48.75 million tons
(Mt)annually from industrial sources and 82 billion cubic meters
(Gm3)from natural gas in place. Fig. 1 shows the emission data,
includ-ing the locations of emission point sources, types of
stationarysource, capacities, emission rates, and sedimentary
basins. CO2gas is produced through processes involved in the
national energyproduction, and amounts to 46.1 Mt per year; the
amount poten-tially recoverable from high-CO2-content natural gas
reservoirs is82 Gm3 in total. The major stationary emissions are
concentratedin the near- and off-shore areas (Kampot, Koh Kong,
Prey Nob,Sihanouk Ville, OCA and Western Block A) of southwestern
Cam-bodia, and represent 90% of the estimated 20082024
emissions.CO2 from these major stationary point sources (about 43.1
Mt peryear and 82 Gm3 in place) has the greatest potential for
geologicalstorage.
3. Sedimentary basins of Cambodia
A number of sedimentary basins of various ages are presentin
onshore and offshore Cambodia (Fig. 1). The earliest-formedbasins
are associated with PaleozoicMesozoic regional uplifts
andPermianJurassic folding and thrusting of the Indosinian
Orogenyor Sundaland Accretion during collision between Indochina
andthe Sibumasu and South China plates; these basins are
associ-ated with Mesozoic granite magmatism (Fig. 2; Workman,
1977;Hayashi, 1988; Vysotsky et al., 1994; Lepvrier et al., 2004;
Fyhn
et al., 2010). These granites form a northsouth-trending mag-matic
arc that is thought to enter the Gulf of Thailand to the east ofthe
Kampong Saom Fold Belt and can be traced from the offshoreextent of
this fold belt across the eastern Cambodia border to south
-
C. Mao et al. / International Journal of Greenhouse Gas Control
30 (2014) 1933 21
F or geot studyt .)
CC(ctPs1dK
rsHtntPosPlel
ig. 1. Location map of Cambodia showing the major CO2 emission
point sources fhe present study (after Vysotsky et al., 1994; CNPA
internal technical report). Thiso color in this figure legend, the
reader is referred to the web version of the article
hina and farther to the northeast. This structure confines
Mesozoicambodian basin development to a once continuous, large
basinthe Cambodian Basin) that covered the entire area of the
modernountry (Fig. 2 and the index map of Indochina with selected
struc-ures of Fyhn et al., 2010). This basin is dominated by
uppermostermianTriassic syn-rift sediments and overlying post-rift
Juras-ic to Cretaceous sediments of the Bokor Formation (Vysotsky
et al.,994; Fyhn et al., 2010). The Cambodian Basin is structurally
sub-ivided into the Khorat, Tonle Sap, Preah, Chhung, Svaryrieng,
andampong Saom troughs.
After its formation, the Cambodian Basin was divided as aesult
of Paleoceneearly Eocene left-lateral transpression and ero-ion
associated with collision between India and Eurasia (i.e.,
theimalayan Orogeny), and the accretion of western Myanmar onto
he Indochina platform (Morley, 2002; Fyhn et al., 2010).
Theorthsouth-directed thrusting and uplift were concentrated
alonghe Khmer and Kampong Saom fold belts and merged with the
Maeing and Three Pagoda fault zones, which confine the onshore
andffshore basins (see Fig. 2 and the index map of Indochina
withelected structures of Fyhn et al., 2010). The activation of the
Mae
ing Fault Zone has been linked with right- and subsequent
left-ateral displacements (Morley, 2002; Lepvrier et al., 2004;
Fyhnt al., 2010). In addition, the Three Pagoda Fault Zone appears
toink up with the Khmer Fold Belt (Fyhn et al., 2010), suggesting a
logical storage (data sourced from CNPA) with the sedimentary
basins analyzed in made estimates of emissions for 20082024. (For
interpretation of the references
connection between the rifting of the western Kampong SaomTrough
and late Eocene left-lateral fault motion (Hall,
1996;Watcharanantakul and Morley, 2000). This indicates that the
Kam-pong Saom Trough in the central Gulf of Thailand underwent
bothextensional faulting and left-lateral motion along the Three
PagodaFault Zone, causing the southwestern part of the trough to
open as apull-apart basin. In turn, this led to the formation of a
new CenozoicKhmer Trough through the genesis of half-graben
complexes thataccumulated thick marine sediments during the
Cenozoic; thesesediments overlie unidentified Mesozoic units
equivalent to theKampong Saom sediments (data sourced from
CNPA).
The geology of these basins is described in more detail in
Sec-tion 5, including evaluation of the suitability of these basins
forgeological CO2 storage and estimates of their storage
capacity.
4. Methodology of basin assessment
4.1. Basin screening and ranking
The method of assessing the suitability of basins in Cambodia
for
their CO2 storage potential was adapted from the basin
screeningcriteria of Bachu (2003) as modified by Gibson-Poole et
al. (2008).Both Mesozoic and Cenozoic basins were evaluated using
the crite-ria in Table 2; these criteria include tectonic setting,
basin size and
-
22 C. Mao et al. / International Journal of Greenhouse Gas
Control 30 (2014) 1933
Fig. 2. Simplified geological map of Cambodia with elements of
the major geological structure (based on a CNPA internal technical
report; Workman, 1977; Vysotsky et al.,1994; Hall, 1996;
Watcharanantakul and Morley, 2000; Morley, 2002; Fyhn et al.,
2010). Prior to the development of late MesozoicTertiary
structures, the large CambodianBasin formed in association with
granite belts and regional uplifts. During basin segregation,
Paleogene fold belts outlined the boundaries of Mesozoic basins.
The ThreeP g an os etationv
drw2fCcaoi
oerwocv(
r
agoda Fault Zone was activated, possibly as a late Eocene
left-lateral fault, openinection lines shown in Figs. 3, 5 and 7
are shown as labeled red lines. (For interprersion of the
article.)
epth, faulting intensity, aquifer systems, geothermal regime,
basinesources, and industry maturity and infrastructure. The
criteriaere classified into three groups (based on Gibson-Poole et
al.,
008) that focus on CO2 containment (tectonic setting of the
basins,aulting intensity, depth of the basin, and presence of
evaporites),O2 storage capacity (basin size, hydrocarbon potential,
coal andoal bed methane (CBM), deep aquifers, and geothermal
regime),nd the technological feasibility of CO2 storage (location
onshorer offshore, basin accessibility, existing infrastructure,
CO2 sources,ndustry maturity, and the climate of the region).
Each of the criteria presented in Table 2 was given a value
basedn criterion-specific defined classes, where the lowest and
high-st values characterize the least and the most suitable
classes,espectively. An exponential parameterization of a function
(Fi)as used to define the range of numerical values for each
class
f that criterion. The numerical values of Fi were assigned to
definelasses for the criteria given in Table 2, where Fi,1 = the
minimum
alue, Fi,n = the maximum value, and n = the number of the classn =
3, 4, 5).
Each individual basin was assigned a score, Fi.c, for each
crite-ion. Individual scores (Fi.c) were normalized using the
approach of
ffshore Mesozoic trough as a pull-apart basin, forming a new
Cenozoic basin. The of the references to color in this figure
legend, the reader is referred to the web
Bachu (2003) and by considering comparative values of the
functionFi for the least suitable (Fi,1), most suitable (Fi,n), and
correspondingscores (Fi,c) for each criterion:
Pi =Fi,c Fi,1Fi,n Fi,1
(1)
where Pi is the normalized score for each criterion (i = 1, . .
., 15)ranging between Pi = 0 (least suitable in a class) to Pi = 1
(mostsuitable in a class) for a given sedimentary basin. This
normaliza-tion procedure transformed the characteristics of each
basin intoquantitative data that vary between 0 and 1. This
procedure wassubsequently incorporated into the basin-ranking
process usingweights that express the relative importance of each
criterion toproduce a general ranking score (R), which was
calculated usingthe approach of Bachu (2003) as follows:
R = sum(w P ) (2)
i iwhere wi is a weighting function that satisfies the general
conditionsum wi = 1. These weights were assigned to various
criteria relatingto the economic conditions currently prevailing in
Cambodia.
-
C. Mao et al. / International Journal of Green
Tab
le
2B
asin
crit
eria
use
d
for
scre
enin
g
for
CO
2ge
olog
ical
stor
age
(mod
ified
from
Bac
hu
, 200
3;
Gib
son
-Poo
le
et
al.,
2008
).
Thes
e
crit
eria
wer
e
clas
sifi
ed
into
thre
e
grou
ps,
nam
ely
con
tain
men
t,
cap
acit
y,
and
feas
ibil
ity,
and
the
wei
ght
ofea
ch
crit
erio
n
and
the
scor
es
of
the
clas
ses
wer
e
det
erm
ined
base
d
on
thei
r
rela
tive
imp
orta
nce
wit
h
resp
ect
to
Cam
bod
ian
Bas
ins.
Cri
teri
a
and
wei
ghts
Cla
sses
and
scor
es
Cla
ss
1
Cla
ss
2
Cla
ss
3
Cla
ss
4
Cla
ss
5
Cont
ainm
ent
Tect
onic
sett
ing
0.08
Oce
anic
Bas
in1
Fore
-Arc
Bas
in
3
Intr
a-A
rc
Bas
in
7
Fore
lan
d
Bas
in
15
Cra
ton
ic
Bas
in
15Fa
ult
ing
inte
nsi
ty
0.10
Exte
nsi
vely
fau
lted
and
frac
ture
d1
Mod
erat
ely
fau
lted
and
frac
ture
d
4
Lim
ited
fau
ltin
g
and
frac
turi
ng
12
Evap
orit
es
0.02
Non
e
1
Dom
es
3
Bed
s
7D
epth
of
basi
n
0.10
Shal
low
(35
00
m)
4
Capa
city
Size
of
basi
n0.
08
Smal
l (10
005
000
km2)
1
Med
ium
(500
025
,000
km2)
3
Larg
e
(25,
000
50,0
00
km2)
7
Gia
nt
(>50
,000
km2)
15A
quif
ers
0.09
Shor
t
flow
syst
ems
1
Inte
rmed
iate
flow
syst
ems
4
Reg
ion
al
flow
syst
ems
12G
eoth
erm
al
regi
me
0.07
War
m
basi
n
(>40
C/k
m)
1
Mod
erat
e
(30
40 C
/km
)
4
Col
d
basi
n
(90
0
m)
2
Shal
low
(300
900
m)
5
Feas
ibili
tyIn
du
stry
mat
uri
ty
0.04
Un
exp
lore
d
1
Exp
lora
tion
2
Dev
elop
ing
3
Mat
ure
5
Ove
r-m
atu
re
8O
n/o
ffsh
ore
0.07
Dee
p
offs
hor
e
1
Shal
low
offs
hor
e
or
nea
rsh
ore
4
On
shor
e
12C
lim
ate
0.04
Arc
tic
1
Sub-
arct
ic
2
Des
ert
4 Tr
opic
al
7
Tem
per
ate
10A
cces
sibi
lity
0.03
Inac
cess
ible
1
Dif
ficu
lt
2
Acc
epta
ble
5
Easy
10In
fras
tru
ctu
re
0.04
Non
e
1
Min
or
3
Mod
erat
e
7
Exte
nsi
ve
15C
O2
sou
rces
0.08
Non
e
1
Few
3
Mod
erat
e
7
Maj
or
15
house Gas Control 30 (2014) 1933 23
The parameterization of the various classes and weights of
eachcriterion used in the present study were adapted from Bachu
(2003)by adjusting them to the specific circumstances for in
Cambodia.The weightings of criteria including tectonic setting
(from 0.07to 0.08), size of basin (from 0.06 to 0.08), depth of
basin (from0.07 to 0.10), faulting intensity (from 0.07 to 0.10),
aquifers (from0.08 to 0.09), hydrocarbon potential (from 0.06 to
0.10), coals andCBM (from 0.04 to 0.06), and evaporites (from 0.01
to 0.02) wereincreased. This in turn meant that to satisfy the wi =
1 relationship(Eq. (2)), weightings expressing the relative
importance of othercriteria were lowered.
4.2. Estimation of basin-wide storage capacity
This paper focuses on the identification of basins suitablefor
geological CO2 storage. However, regional extrapolations
andcalculations of basin-wide CO2 storage capacities were also
under-taken. This approach follows those outlined in previous
research(Koide et al., 1992; Bachu et al., 1994, 2007; Hendriks et
al., 2004;CSLF, 2008; US DOE-NETL, 2012), although some assumptions
weremade to simplify the estimates of storage capacity, namely
thatthe CO2 within the geological media of the Cambodian
subsurfaceis assumed to be trapped within depleted hydrocarbon
reservoirswithout aquifer support (based on oil and gas production
testing;CNPA), or within migrating plumes associated with the
large-scaleflow systems present in shallower aquifers. The use of
both hydro-carbon and aquifer volumes in determining the available
porevolume for CO2 storage is outlined below.
4.2.1. Oil reservoirsOil reservoirs were assigned a baseline
storage efficiency of 7%
(following Bachu and Shaw, 2003, 2005; Haszeldine, 2006),
basedon general CO2Enhanced Oil Recovery (EOR) considerations
(listedby Holt et al., 1995), thereby yielding a theoretical
storage capacityMCO2 hydrocarbon as follows (Bachu et al., 2007;
CSLF, 2008):
MCO2 hydrocarbon =Ce CO2r Rf OOIP
Bf(3)
where Ce is the storage (sweep) efficiency factor, CO2r is the
aver-age CO2 density within the reservoir (assumed to be 620
kg/m3;Ennis-King and Lincoln, 2002; MIT, 2008), Rf is the recovery
factor,OOIP is oil originally in place, and Bf is a formation
volume fac-tor determined as the volume of oil extracted to the
surface fromthe reservoir multiplied by 1.5 (based on
Morton-Thompson andWoods, 1992; Satter et al., 2008).
4.2.2. AquifersA different estimation method was used for
aquifers, in which
the surface area (areal extent) of the sedimentary basin, the
averageporosity of the aquifer, and the gross thickness of the
aquifer wereused to determine storage potential (Koide et al.,
1992; Bradshawet al., 2007). The technique for estimating aquifer
CO2 storagecapacity used here is based on that of Hendriks et al.
(2004) andBachu et al. (1994), and includes both safety (Es) and
efficiencyfactors (Ee). As the CO2 is unlikely to fill an entire
aquifer, thetheoretical storage capacity MCO2 aquifer can be
calculated using:
MCO2 aquifer = CO2r A h (
N
G
) Ee Es (4)
where CO2r is the CO2 density within the reservoir, A is the
surface
area of the sedimentary basin, h is the gross thickness of the
aquifer,
is the average porosity across the entire aquifer, N/G is the
netsand thickness, Ee is the storage efficiency factor, and Es is
the safetyfactor. An average CO2 density of 620 kg/m3 (as assumed
in Section
-
2 f Greenhouse Gas Control 30 (2014) 1933
42
5
tttgbta
5
5
eGnaBtoKcawv1mruhtfst(eda
htipdbsf
5
rnctawlmbt
sin
scre
enin
g
for
CO
2st
orag
e
suit
abil
ity
in
Cam
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ia.
Kh
mer
Kam
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g
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Ton
le
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ng
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nd
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lan
d
Fore
lan
d
Fore
lan
d
Fore
lan
d
Fore
lan
d
Fore
lan
dte
nsi
ty
Lim
ited
fau
ltin
gan
d
frac
turi
ng
Lim
ited
fau
ltin
gan
d
frac
turi
ng
Mod
erat
ely
fau
lted
and
frac
ture
dEx
ten
sive
ly
fau
lted
and
frac
ture
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ten
sive
ly
fau
lted
and
frac
ture
dEx
ten
sive
ly
fau
lted
and
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ture
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ten
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ly
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lted
and
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ture
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eds
Bed
s
Bed
s
Non
e
Non
e
Non
e
Non
esi
n
Dee
p
Dee
p
Dee
p
Shal
low
Shal
low
Shal
low
Shal
low
nLa
rge
Larg
e
Larg
e
Med
ium
Smal
l
Med
ium
Med
ium
Ass
um
ed
regi
onal
flow
aqu
ifer
sA
ssu
med
regi
onal
flow
aqu
ifer
sA
ssu
med
regi
onal
flow
aqu
ifer
sA
ssu
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regi
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aqu
ifer
sA
ssu
med
shor
tfl
ow
aqu
ifer
sA
ssu
med
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aqu
ifer
sA
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sl r
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arm
basi
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Col
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Ass
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4 C. Mao et al. / International Journal o
.2.1) is considered across all the basins (following Koukouzas
et al.,009).
. Basin screening
The Cambodian sedimentary basins were evaluated accordingo the
screening method presented above. The limited informa-ion available
means that the screening procedure focuses onhe location,
geological setting, size and depth, faulting intensity,eothermal
regime, and paired reservoirseal systems of theseasins. The
criteria are discussed below, and Table 3 summarizeshe results of
the basin suitability screening for geological CO2 stor-ge in terms
of containment, storage capacity, and feasibility.
.1. Khmer Basin
.1.1. Geological setting and reservoirseal systemsThe Khmer
Basin is thought to be a foreland basin (Vysotsky
t al., 1994; Fyhn et al., 2010). The basin is located in the
easternulf of Thailand and covers an area of 8600 km2. The basin
trendsorthsouth and is bounded to the east by the Khmer Fold Beltnd
to the west by the Khmer Ridge, which separates the Khmerasin from
the Pattani Basin in Thailand (Fig. 3). This basin con-ains
>6000 m of MesozoicCenozoic sediments including 2000 mf
TriassicCretaceous basement. Cenozoic sediments within thehmer
Trough are dominated by sandstones interbedded withlays, shale,
silts, and coals (Fig. 4). Lower Miocene sandstonesre the most
effective reservoirs for hydrocarbon accumulationsithin the central
trough. These lower Miocene sandstone reser-
oirs were charged vertically by upper Oligocene shales (Okui et
al.,997), although there is a lack of vertical connections
betweeniddleupper Miocene sandstones and upper Oligocene source
ocks, so because these are thermally immature the majority
ofppermost middle to upper Miocene reservoirs are depleted
inydrocarbons and therefore can be treated as aquifers. The water
ofhe aquifer is brackish according to chloride content (data
sourcedrom CNPA). Abundant coal seams are also present within
Mioceneediments. These coals are black to very dark brown, vary
from
-
C. Mao et al. / International Journal of Greenhouse Gas Control
30 (2014) 1933 25
Fig. 3. Simplified geological cross-section of the offshore
Cenozoic Khmer Basin (based on a CNPA internal technical report),
showing potential reservoirs and cap rocksf withini olor i
ctF
Modsag3aCsaSb(gpCaitethtaW4so
or CO2 storage within the Khmer Trough. Suitable storage
lithologies are located njection target for CO2 storage in
aquifers. (For interpretation of the references to c
losure with depth, and this would not regionally
compartmen-alize the shallower aquifer formation (data sourced from
CNPA;ig. 3).
Economic oil and gas reservoirs have been discovered
withiniocene sediments in the Khmer Trough, and are at various
stages
f development (data sourced from CNPA). The reservoir
formation,iscussed in Section 5.1.1 above, consists of interbedded
thin sand-tones and clays with minor coal beds. The sandstone
reservoirsre thought to be present as a stacked sandstone sequence
with aross thickness of 5001000 m, and an average net thickness
of00 m; these reservoirs may have been both oil and gas chargednd
sealed by interbedded shale source rocks (data sourced fromNPA).
The reservoirs could potentially be used for geological CO2torage
once they are depleted. Other opportunities for CO2 stor-ge may
also exist in saline aquifers within Miocene successions.aline
aquifers with high potential for CO2 storage are assumed toe
present in the uppermost middle to upper Miocene sedimentsFigs. 3
and 4); these saline aquifers have large lateral extents, aross
thickness of 400 m, and a net sand thickness of 80 m. Aetrophysical
interpretation established as part of a table review ofNPA
exploration documents estimates that these reservoirs haven average
porosity of 26% and a permeability of 250 md, indicat-ng that they
may be good targets for CO2 injection. These indicatehat injected
CO2 would migrate horizontally as a plume over sev-ral kilometers
laterally and hundreds of meters vertically, to berapped by
uppermost Miocene seals (Fig. 3). In reality, this largeorizontal
CO2 plume may be trapped within hydrodynamic sys-ems, with
structural traps (measuring 1020 km2) providing andditional safety
net for CO2 storage (data sourced from CNPA).
ell data show that the basin has a geothermal gradient of between
5 C/km and 55 C/km with a sea-bed temperature of 22 C
(dataourced from CNPA), indicating that in terms of geothermal
effectsn CO2 storage, this is a warm basin.
the lowermiddle Miocene successions. The hatched area indicates
the primaryn this figure legend, the reader is referred to the web
version of the article.)
5.2. Kampong Saom Basin
5.2.1. Geological setting and reservoirseal systemsThe Kampong
Saom Basin is thought to be a foreland basin
(Vysotsky et al., 1994; Fyhn et al., 2010) that formed in
responseto the Sundaland Accretion. This basin is approximately 100
kmwide, and is flanked to the east by the Kampong Saom Fold Beltand
to the west by the Khmer Fold Belt (Figs. 2 and 5). TheKampong Saom
Basin extends northsouth from the southernboundary of the Tonle Sap
Basin to the central part of the Gulfof Thailand (Figs. 1 and 2;
Fyhn et al., 2010). The basin coversa total area of 28,000 km2
offshore and 12,000 km2 onshore.The Kampong Saom Trough, in the
center of the basin, consistsof deformed Paleozoic complex basement
material and overlyingUpper TriassicCretaceous orogenic complex
sediments (Fig. 6).These Mesozoic sediments are dominated by
terrigenous sand-stones with widespread silt and clay horizons that
were depositedduring the development of the trough. Upper
JurassicCretaceoussuccessions within the trough have just entered
the main stage ofoil generation (Vysotsky et al., 1994), suggesting
that gas generationmay already have taken place in this section.
Gas and condensatesmay also have been generated within upper
Carboniferous to Tri-assic successions (Fig. 6), although the most
promising targets forhydrocarbon exploration are Upper Triassic to
Middle Jurassic, andUpper Jurassic to Cretaceous sequences within
the trough (Fyhnet al., 2010). The Kampong Saom Trough also
contains Middle Juras-sic and Cretaceous coals at depths of 250 and
2000 m (Vysotskyet al., 1994).
5.2.2. CO2 storage potentialThe sedimentary succession within
the Kampong Saom Trough
ranges in age from late Paleozoic to Recent and is up to 5 km
thick.A Carboniferous to Middle Triassic rift forms the basement of
the
-
26 C. Mao et al. / International Journal of Gree
Fig. 4. Generalized stratigraphy of the Khmer Trough with CO2
injection targets andpotential cap rocks (based on Vysotsky et al.,
1994; CNPA internal technical report).The stratigraphic positions
of suitable storage reservoirs and associated cap rocksare given in
the descriptions within the figure. (For interpretation of the
referencesto color in this figure legend, the reader is referred to
the web version of the article.)
nhouse Gas Control 30 (2014) 1933
basin, overlain by younger sedimentary cover that consists of
UpperTriassic to Cretaceous Indosinian orogenic complexes. The
base-ment successions are moderately faulted, but the overlying
UpperJurassic to Cretaceous successions have undergone minimal
faul-ting (Vysotsky et al., 1994). Previous seismic activity is
limited(Giardini et al., 1999) in both onshore and offshore areas,
suggestingthat the basin is relatively tectonically stable at
present.
This basin is interpreted to be immature but is currently
under-going hydrocarbon exploration. It is assumed that the
majority of oiland gas is trapped in structural closures formed
within Upper Tri-assic to Middle Jurassic sandstones that are
regionally intercalatedwith clay-rich lithologies, which act as
seals for the hydrocarbonaccumulations (Vysotsky et al., 1994).
Resource estimates and thevolumetric density of hydrocarbon within
the basin (Vysotsky et al.,1994) indicate that the oil provinces
within the Kampong SaomTrough may be less economically significant
than those withinother basins, but these provinces may be suitable
for CO2 storageafter hydrocarbon depletion. Reservoirseal pairs
within the troughthat may be suitable for CO2 storage are plentiful
within uppermostTriassicMiddle Jurassic and Upper Jurassiclowermost
Cretaceoussuccessions (Fig. 5). In addition, the saline aquifer
with the highestpotential for CO2 storage is most likely present
within Upper Juras-sic sediments (Figs. 5 and 6); this saline
aquifer has a gross thicknessof 450 m and a net sand thickness of
about 90 m.
The Upper Jurassic sediments in this trough are equivalent
to,although named differently from, sediments along the
southeastThailandwestern Cambodia border (Meesook, 2011; Meesook
andSaengsrichan, 2011; Ridd et al., 2011; Ridd and Morley, 2011).
Thismeans that regionally, these aquifer intervals can be assumed
tohave an average porosity of 10.8% (no permeability data
wereavailable) (Canham et al., 1996; Racey et al., 1996; El Tabakh
et al.,1999; Racey, 2011), indicating that they have fair CO2
storagepotential. Extrapolation of data from the Khmer and Tonle
Sapbasins suggests that the Kampong Saom Basin is a warm basin.
5.3. Tonle Sap Basin
5.3.1. Geological setting and reservoirseal systemsThe foreland
Tonle Sap Basin covers an onshore area of 23,
800 km2 and, in central Cambodia, is bordered to the north by
aregional orogenic uplift (Vysotsky et al., 1994) that is
comparable tothe transpression zone of the
northwestsoutheast-trending MaePing Fault Zone (Fig. 2; Fyhn et
al., 2010), and farther to the northby the southernmost monocline
of the Khorat Basin. The Tonle SapBasin is bordered to the south by
the onshore Kampong Saom Basin(Figs. 1 and 2). The basement of the
Tonle Sap Basin is a com-plex Paleozoic graben that is dominated by
metamorphic rocks.This graben may have developed between the late
Carboniferousand the Middle Triassic, and is filled with sediments
dominatedby terrigenous sandstones and carbonates, with a total
thicknessof >1000 m. These horizons may have potential for both
gas gen-eration and hydrocarbon reservoirs. The overlying Upper
Triassicto Middle Jurassic strata have an average thickness of 2000
m andhave entered the oil window, indicating that these strata are
a pos-sible source rock for liquid hydrocarbons. Other possible
reservoirsand seals may also be present within Upper JurassicLower
Cre-taceous intervals, which have a total thickness of 2000 m;
theseintervals are collectively termed the Bokor Formation (Fyhn et
al.,2010). The Tonle Sap Trough also contains
CarboniferousPermianand Upper TriassicMiddle Jurassic coals, with
the Middle Jurassiccoals (Vysotsky et al., 1994).
5.3.2. CO2 storage potentialThe sedimentary fill within the
central trough consists of more
than 4 km of sediments that mirror the Kampong Saom sedimen-tary
successions. The burial and hydrocarbon generation histories
-
C. Mao et al. / International Journal of Greenhouse Gas Control
30 (2014) 1933 27
Fig. 5. Simplified geological cross-section of the Kampong Saom
Basin (based on Vysotsky et al., 1994 and a CNPA internal technical
report), showing potential formationsfor CO2 storage located within
the Kampong Saom Trough. Suitable formations are located within the
uppermost TriassicMiddle Jurassic and Upper Jurassic successions.T
(For it
(abs2hUiaZeq1
esaunrT>pofbb2
5
5
n(
he hatched area indicates the primary injection target for CO2
storage in aquifers.o the web version of the article.)
Vysotsky et al., 1994) of the Tonle Sap and Kampong Saom
basinsre also similar. The syn-rift portion of the basin fill
(i.e., upper Car-oniferous to lower Permian and lower Permian to
Middle Triassicediments) within the Tonle Sap Trough has undergone
intense and
extensive faulting, leading to the development of many
complexalf-grabens. The intensity of faulting decreases within the
post-riftpper Triassic to Middle Jurassic sediments, and is least
intensive
n the overlying Upper Jurassic to Cretaceous sequences (Fig. 7).
Inddition, both left- and right-lateral faults (e.g., the Mae Ping
Faultone) have been active during the Tertiary (Morley, 2002; Fyhnt
al., 2010). However, the low magnitudes of more recent earth-uakes
suggest that this basin is tectonically stable (Giardini et
al.,999).
The Tonle Sap basin has also been subjected to
hydrocarbonxploration, with oil and gas reservoirs being identified
in Jurassicedimentary sequences that may have postdepletion CO2
stor-ge potential. The basin also contains deep saline aquifers
withinppermost Jurassiclowermost Cretaceous sediments that
containumerous volcanogenic clastic sediments; these are
good-qualityeservoir formations, and have an aggregate thickness of
500 m.he reservoir intervals have an average porosity of 10%
(locally20%) and an assumed net value of 20%, indicating good CO2
storageotential. These reservoirs are sealed by Lower Cretaceous
evap-rites and claystones, both of which would make good cap
rocksor CO2 storage (Figs. 7 and 8). The geothermal gradient of
theasin is 35 C/km (Vysotsky et al., 1994), meaning that this is a
coldasin in terms of the geothermal effects on CO2 storage
(Bachu,003).
.4. Khorat Basin
.4.1. Geological setting and reservoirseal systemsThe southern
monocline of the Thai Khorat Basin flanks the
orthern part of Cambodia and covers an area of 12,400 km2
Figs. 1 and 2). This onshore foreland basin is thought to be
nterpretation of the references to color in this figure legend,
the reader is referred
associated with regional uplift comparable to the Mae Ping
trans-pression zone (Fyhn et al., 2010). The uppermost part of
thebasin in Thailand consists of Upper JurassicLower Cretaceous
andUpper Cretaceouslower Paleogene sediments (Racey et al., 1996;El
Tabakh et al., 1999), dominated by sandstones of variable
reser-voir quality and by nonreservoir mudstones and siltstones
(Canhamet al., 1996). In comparison, the majority of the upper
Mesozoicsection of the basin in Cambodia has been eroded as a
result ofminor basin inversion associated with the earliest stages
of theHimalayan Orogeny (Racey et al., 1996), leaving scattered
out-crops of Upper JurassicLower Cretaceous sediments, in
additionto older sediments that are considered to have formed
during theLate TriassicMiddle Jurassic and Permian (Vysotsky et
al., 1994).Sediment thickness modeling by Heine (2007) suggests
that thedepth to the base of the basin varies from 36 m at the
southernmargin to 500 m in northern Cambodia. The lower section of
thebasin, which contains Upper TriassicMiddle Jurassic and
Permiansediments, may be prospective for gas accumulations,
especiallywithin Permian limestones (Vysotsky et al., 1994; Canham
et al.,1996; Racey et al., 1996; El Tabakh et al., 1999).
5.4.2. CO2 storage potentialThe Khorat Basin in Cambodia extends
from the northern
CambodiaThailand border to the area north of the Tonle Sap
Basin.This area is thought to be generally tectonically stable
judging fromrecent seismicity (Morley, 2002) and from the current
tectonicsetting of the region (Giardini et al., 1999). Upper
TriassicUpperJurassic sandstones and associated saline aquifers
within the basinhave a gross thickness of 300 m, and reservoir
intervals within theseunits have an average porosity of 15% (Canham
et al., 1996; ElTabakh et al., 1999). Very little is known about
the productivity
of Permian limestone gas reservoirs within this basin, although
itis possible that these reservoirs may be suitable for storing
CO2gas. However, the graben shallows significantly toward the
south-ern margin of the basin, meaning that both Permian
limestone
-
28 C. Mao et al. / International Journal of Gree
Fig. 6. Generalized stratigraphy of the Kampong Saom Trough
(based on Vysotskyet al., 1994) showing CO2 injection targets and
potential cap rocks. The stratigraphicpositions of suitable storage
reservoirs and associated cap rocks are given in thedfi
a
