Journal of Applied Mathematics and Physics, 2014, 2, 1009-1021
Published Online October 2014 in SciRes. http://www.scirp.org/journal/jamp
http://dx.doi.org/10.4236/jamp.2014.211115
How to cite this paper: Fan, J.J., Guo, J.Q., Zhang, S.Q. and Ji, X.F. (2014) CO2 Geological Storage Suitability Assessment of
Sichuan Basin. Journal of Applied Mathematics and Physics, 2, 1009-1021. http://dx.doi.org/10.4236/jamp.2014.211115
CO2 Geological Storage Suitability
Assessment of Sichuan Basin
Jijiao Fan, Jianqiang Guo, Senqi Zhang, Xiaofeng Ji
Center fo r Hydrogeology an d Environmental Geology Su rvey , CGS, No.1305, Qiyi Middle Road, Baoding,
071051, Heb ei Province, Chin a
Received August 2014
Abstract
The paper choos es th e sec onda ry tecton ic u n its of Sichuan Basi n as th e e valua tion object , and con-
siders regional crust al s t ability condi tio ns, basic geol ogic al condi tions, reservoir and cap roc k
conditions , stora ge p ote n tial c onditio ns, geo the rmal co nditi ons, research d egree and po ten tial
resources condi tions, soci al and economi c co ndition s as fi rst-lev el indexes . B ased on collec ted da-
ta and a comprehensive a nalysis of 16 lev el-tw o ind exes and 9 level-three in dex es, and wi th th e
application of compreh ensive index m eth od , the co nclusions reg arding th e s uitabili ty p arti ti on of
the seco ndary tec tonic u n its of Sichuan Basi n a re as foll ows : Centr al Sichuan low-fla t stru ctu r al
belt is highly suitable f or c arb o n dioxide geologic al s tor ag e, W est Sichuan low- slope structu r al b elt
is relativel y suitabl e, and SW low-slope structur al bel t is unsui table f or carbon dioxide geological
stora ge, South Sichuan low-slope struc tur al bel t is relativ ely unsu ita ble, whereas E as t Sichuan
high-slope faulted fold b elt, and No rth Sichuan low-flat s tru ctu r al b elt are fa irly suitabl e for car-
bon dioxide geological stor age. Based on th e a bov e, with a compreh ensive analy sis of co rre s-
ponding hyd rog raph ic and geolog ical condit ions, and at the same time consid ering the non-c ov-
ered oil or g as res ou rce s and the bu ried s tru ctu re , si x CO2 ge ologi cal targe t fo rmati ons are iden ti-
fied, includ ing lowe r Jurassic Ziliujing Gr oup , upper Tri assic Xu j iah e Grou p , middle Triassic Lei-
koupo Group , low er Triassic Jialingji ang Grou p and Feixian guan Group , an d lo wer Permian Qixia
Group . Thi s paper provides an important guidance and referenc e for the selection crite ri a of CO2
geologi c s tora ge sites in Sichuan Basin.
Keywords
Suitability E valua tion, Sichuan Basin, Geologic al S to rag e of C ar bon D ioxide, Tectonic Un it
1. Introduction
With the establishment of operational targets regarding controlling greenhouse gas emissions, as well as the ap-
propriate policy measures and actions put forward by the State Council, Chinese enterprises with high energy
consumption and high carbon dioxide emissio ns are facing tremendous pressure to reduce emissi ons. To alle-
viate the pressure and to develop the green and low-carbon economy, some companies start to focus on carbon
dioxide capture and storage by taking so me actions.

J. J. Fan et al.
1010
China CO2 emissions are approximately 8 billion tonnes per year. Therefore Chines e govern ment and compa-
nies are playing an increasingly prominent role in assessment and development of CCS technologi es. The activi-
ties in Chi na include indigenous research and development, colla borative research with i nt ernational entitie s,
learning from other countrie s thr ough knowledge shar ing, and development of demonstration or full-scale
projects. Between 2010 and 2012, China has carried out ca rbon dioxide geological stor age potential evaluation
and suitabili ty assessment, and has finished CO2 geological storage suitabilit y assessment at both regional and
basin-scales [1]-[5]. Potential and suitability assessment of CO2 geological storage was divided into five sta ges,
with each stage focusing on a smaller scale area and increasing the level of precision for the storage capacity es-
timate (Figure 1). The first stage is re gi onal-scale, and the study object is individual basin, the second sta ge is
basin-scale, and the study object is the first or second tectonic units, and so on until completion of the inj ec-
tion-scale assessment. The “ta rget scale” ser ves as a transition between the basin-scale and site-scale stages. For
this article, t he basin scale research was based compilation of existing maps, devel op ment of some new maps,
and calculatio n of stor age capacities. In general, the capacit y assessment was conducted using methodologies
published under the Carbon Sequestration Leadership Forum (CSLF) as presented in [6]. The suitability assess-
ment was conducted by othe r professors work [7]-[10]. Based on technical requireme nts of the project “natio nal
CO2 geological stor age poten tial evaluation and suitability assessment” impleme nted between 2010 and 2012,
this paper carried out t he basin-scale assessment in Sichua n Basin.
CPI constructed the first domestic 10,000 ton level “CO2 capture and liquefaction p l ant” for their coal-fir ed
power plant named Shuanghuai Plant in Hechuan Town (Figure 2) in November, 2009. The Hechuan Town lo-
cated in the Cho ngqing Province in Sichuan Basin.The primary objective is to deter min e the feasibilit y for sto-
rage of about 100,000 tons per year CO2. In addition, consideration is also given to the expansi on to about
1,000,000 tons per year as the future target [11]. During mid-2012, our team was selected by Battelle to assist
them in geolo gic st orage assessment.
2. Study Area and Carbon Emission
Sichuan Basin is located in Sichuan-Chongqing area, between 28˚ - 32˚40′ north latitude and 102˚30′ - 110˚ east
longitude , with a total area of 260,000 km2. Sichuan Basin, one of the four largest basins in China, is also called
Bashu Basin, Xinfeng Basin or Purple (Red) Basin. The outline of Sichuan Basin is of rhombus shape,
Fig ure 1. Stages of CO2 geological sto rage asses s ment in China.

J. J. Fan et al.
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Figure 2. Location of the Sic h uan Basin and carbon sources.
containing the east part of Sichuan Pr ovince, most of Chongqing and t he junction zone of three provinces: Hubei,
Guizhou and Yunnan. Cons i dering its geo graphical variations, Sic huan Basin can also be divided into three parts:
Chengdu Plain in the west of Sichuan, hilly areas in the middle, and parallel ridge-valley region in the eastern
Sichuan.
The Sichuan Basin is the most important gas-producing basin in China , the amounts of natural gas resources
are the largest in China, accounting for about one -fourth of The total national gas production. It is also one of
the most important hea vy industrial zones in China, having a large number of CO2 emissi on sources such as
power plants, cement production plants, and steelworks. The main sources of carbon emissions are the two pro-
vincial capitals (Chengdu and Chongqing) and the fourteen large cities (Ya’an, Meishan, Leshan, Ziyang, Zi-
gong, Luzhou, Yinbi , Suining, Nanchong, Guanga n, Mianyang, Bazho ng, Dazhou and Guangyuan). Four para-
meters (emission amount of power plants and cement production plants of Chen gdu and Chongqing) have been
collected to assess the amoun t of carbon emission in the Sichuan Basin. Chongqing and Sichuan’ results are of
the s ame order of 108 t magnitude according to China statis tic s yearbooks of 2008a (National Bureau of Statis-
tics of China, 2008). The economic circle can be divided into Chengdu centered Western Sic huan economic
zone (W estern Sichuan eco no mic belt), Chongqing centere d Chuanjiang eco no mic zone (Chuanjiang econo mic
belt) and Nanc hong centered North-Central Sichuan economic zone. Compared with the experi mental, the total
carbon emission is referring to the energy consumption related to economic development and GDP. Along with
economic growth and people’s energy co nsumption demand increase, the carbon emission amou nt must be a
rising tendency. It is one of the mos t rapidly developing areas with large energy consumption and CO2 emission,
carbon capture and storage is probable and urgently needed.
3. Evaluation Method
China’s CO2 geological stora ge suitability at basin scale could be classified as 7 first-level evaluation indexe s :

J. J. Fan et al.
1012
(1) regional crustal stability conditions, (2) basic geological conditions, (3) reservoir and cap-rock conditions, (4)
potential conditio ns of storage, (5) geothermal geological conditions, (6) research degree and resource potential
conditions, and (7) socio-economic conditions (Table 1). and 16 second-level indexes (Table 1) and 9 third-
level indexes (Table 2, Table 3), and as shown at with 5 levels for each index as 9, 7, 5, 3 and 1, representing
conditions of highly suitable, suitable, generally suitable, unsuitable and highly unsuitable (Tables 1-3). The
synthetic al index for each secondary tectonic unit co uld be calculated according to the following formula [12]:
1
n
ii
i
P PT
=
=∑
where, P represents the synthetical index of CO2 geological storage suitability within second-order tectonic units
in the basin;
i
P
represents a given index of the ith evaluation factor, and here
i
P
has values of 9, 7, 5, 3, or 1 as assigned
as a evaluation result of each index through comparing with ranking conditions listed in Table 1-3, as described
in chapter 4, that is, The indices of
i
P
is given by professors group according to existing infor matio n.
i
T
represents the weight of the ith index, which is given by professors group according to their experience
value.
Table 1. Carbon dioxide geological storage suitability evaluation system.
Index
lay er s Wei gh t
Evaluation
Index sub-lay er s Wei g h t
Highly
suitable Relatively suitable Fairly suitable Relatively unsuitable unsuita ble
Crustal Stability 0.37 Crustal Stability 0.370 Stab le Basically stable Slightly unstable Less stable unstable
Bas ic
Geologic al
Condition of
tectonic unit
0.07
Ar e a/km2 0.033 S > 10000 5000 < S ≤ 10000 500 < S ≤ 5000 1 00 < S ≤ 500 S < 100
Sedimentary
Depth/m 0.033 H > 3500 2500 < H ≤ 3500 2 500 < H ≤ 1500
1500 < H ≤ 800 H < 800
Seal and
Reser voi r
0.22
Seal 0.078 highly suitable suit ab le p oss ible unlikely unsuitable
Reservoir stratum 0.078 highly suitable
suit ab le p oss ible unlikely unsuitable
Comb ination 0.067 Regional seal, Independent
seal
Regional seal,
self-reserv oi r
and self-sea l
Local seal,
Independent
seal
Local seal,
self-reserv oi r
and self-sea l NO
Predicted
potential 0.16
Pred i c t ed
pot enti a l/10 8t 0.094 M > 50 25 < M ≤ 50 0.5 < M ≤ 25 0.02 < M ≤ 0.5 M < 0.02
Predicted potential
per area/(10 4t·km −2) 0.063 m > 200 100 < m ≤ 200 50 < m ≤ 100 1 < m ≤ 50 m < 1
Geoth er ma l
Geology
0.12
Geothermal gradient/
[˚C·(100 m) −1] 0.049 G < 2.0 2.0 < G ≤ 3.0 3.0 < G ≤ 4.0 4.0 < G ≤ 5.0 G > 5
Geothermal heat flow
value(mW·m−2) 0.049 q < 54.5 54.5 < q ≤ 65 65 < q ≤ 75 75 < q ≤ 85 q > 85
Land Surface
Tempera t ure/ ˚C 0.025 t < −2 −2 < t ≤ 3 3 < t ≤ 10 10 < t ≤ 25 t > 25
Research
Degree
and
Resources
Potential
0.04
Exploration Degree 0.022 Devel o p men t High G en era l Low No
Data supply 0.011 Full, reliable
dat a Less full dat a General full data Not sufficient
dat a No data
Resources potential 0.004 large Relatively
large G en era l Relatively less less
Social &
Econ omic
Condi tion 0.02
Population density
(Person/k m2) 0.013 P < 50 50 < P ≤ 100 100 < P ≤ 200 200 < P ≤ 1000
P > 1000
Land use types 0.009 Desert , lan d
no using Grassland Woodland Arable land Sett lem en t s waterbody
Score 9 7 5 3 1

J. J. Fan et al.
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Table 2. Reservoir ran ks.
Reservoir Evalu ati on Index Weigh t Highly suitable Relatively suitable Fairly suitable Relatively unsuitable Unsu ita b le
First
reservoir
lith olog y 0.25 Clastic rocks Mixed clastic
and carbonate carbonate
Magmatic rock,
metamorphic rocks,
salt dome etc.
Special reservoir
No
depth 0.15 1500 ≤ H ≤ 2000 2000 < H ≤ 2500 2500 < H ≤ 3000 3000 < H ≤ 3500 H > 3500
Porosity (%) 0.3 φ ≥ 25 20 ≤ φ < 25 10 ≤ φ < 20 5 ≤ φ < 10 φ < 5
Permeability
(×10
−3
μm
2
)
0.3 K ≥ 1000 500 ≤ K < 1000 50 ≤ K < 500 1 ≤ K < 50 K < 1
Secon d r eser voi r
stra tu m
Same to First reservoir
…
Table 3. Seal ranks.
Seal Evaluation Index Weigh t Highly suitable Relatively suitable Fairly suitable Relatively unsuitable Unsui tab le
First
seal
Lithology 0.2 Gypsum, mudst on e,
calc i lut ite
Mudstone
conta in
aleurite, sand
Arena c eo u s,
siltstone
mudst on e
Argillaceous
sandstone,
Argillaceous siltstone
Sha le, com pact
limestone
The distribution
of continuity 0.25 continu ou s, stea d y more continuous, more steady Midd le Poorer
conti nu ou s,
poorer steady discontinuous
thickness of
single layer 0 .1 h ≥ 20 10 ≤ h < 20 5 ≤ h < 10 2.5 ≤ h < 5 h < 2.5
gross thickness 0.2 h ≥ 300 150 ≤ h < 300 100 ≤ h < 150 50 ≤ h < 100 h < 50
permeability 0.25 K < 0.001 0.001 ≤ K < 0.01 0.01 ≤ K < 0.1 0.1 ≤ K < 1 K > 1
Secon d
seal
Same to First seal
…
i
T
of every level indexes satisfy the condition:
1
1
n
i
i
T
=
=∑
n
represents the total number of evaluation factors, and here n = 9 for third-level indexes, n = 16 for second-
level indexes and n = 7 for first-level evaluation indexes.
The results of synthet i cal index scores P of individual are in the ran ge of [1] [9], to make the results distri-
butes mo re aver age between [0, 1], the synthetic al index scores P are normalized according to:
, 1~6,1~6
, 1~6, 1~6,1~6
min
max min
ii ii
ii ii ii
PP
PPP
= =
=
= =
−
=−
As a result of this process, each second-order tectonic units in Sichuan basin being screened and ranked by
Table 4.
4. The Analys is of Suitable Conditions
4.1. Geologic Structure
The interior Sichuan Basin is divided into six second-level tectonic units, includ i ng East Sichuan high -slope
faulted fold belt, So uth Sichuan low-slope structural belt, Central Sichuan low-fla t struc tura l belt, SW low-slope
struc tura l b elt, Nor th S ichuan low-flat structural belt, Nor th Sichuan low-flat struct ural belt and West Sichua n
low-slope structural belt, with corresponding area and deposition thickness shown in Table 5 [13].

J. J. Fan et al.
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Table 4. Comparison table of number range of P valu e and evaluation result.
Evaluation Result Highly suitable Relatively suitable Fairly suitable Relatively unsuitable unsuitable
Number Range of P 0.8, 1 0.6, 0.8 0.4, 0.6 0.2, 0.4 0, 0.2
Table 5. Tectonics units in Sichuan Basin.
No Secon d -level tectonic units Area (km2) Deposition thickness (m)
I1 East Sichuan high-slope faulted fold belt 50,000 10,000
I2 South Sichuan low-slope structural belt 26,000 8000
II1 Central Sichuan low-flat structural belt 37,000 9000
II2 Southwestern low-steep fold belt 21,000 7000
III1 North Sichuan low-flat structural belt 34,000 12,000
III2 West Sichuan low-slope structural belt 32,000 10,000
4.2. Regional Crustal Stability
According to Yang X.’s resea rch results [14], for the a vailable seismic network r ecord between1970 a nd 2010,
the number of earthqua kes with ML ≥ 2.0 in Sichuan Basin and its periphery is 33646, and the number of earth-
quake s with ML ≥ 2.0 in Sic huan Basin is 9058. The number of earthq uakes with focal depth record and with
ML ≥ 2.0 in this basin is 4271, where in the shallowest one is 1 km, the deepest one is 60 km and the majority is
within the range of 5 - 30 km, belonging to shallo w-focus eart hquake. According to the research of Zhang J. et
al., the occurrence of the next ea rthqua kes with eight ma gnit udes in Sichua n should be between 2041 and 2042
[15], and it is substantially sufficient for the car bo n dioxide storage field to run for 30 years.
According to GB18306-2001 [16], the ma p of Chinese seismic peak acceleration, it can be seen that seismic
peak acceleration values from eastern high and steep fold belt are less tha n or equal to 0.05 g, values fr om
southern low-steep fold belt are 0.05 g, va lues from middle gentle fold belt are less than 0.05 g, values from
southwestern low-steep fold belt are within the range of 0.05 g and 0.1 g, values from nort hern low-steep fold
belt was 0.05 g, and val ues from western low-steep fold belt are within the ran ge of 0.1 g and 0.2 g. Overall, t he
central and eastern basin area has the highest stability level.
The large-ma gnitud e earthqua ke wit h magni tude 8.0 occurred in Sichuan Wenchuan on May 12, 2008, with
its significant influence along the Yingxiu-Bei chuan fault zone to Ningq i ang County in Shaanxi of Qingch uan
fault zo ne [17].
A comprehe nsive analysis s howed that the crust stability conditio ns for carbo n dioxid e geological storage in
Sichuan Basin is relatively high in Central S i chuan low-fla t s t ruct ural be lt, but the rest area, including East Si-
chua n high-slope faulted fold belt, South Sic huan low-slope structural belt, North Sichuan low-flat structural
belt, SW low-slope structural belt and West Sichuan low-slope structural belt is unsuitable for carbon dioxi de
geological storage.
4.3. Reservoir-Cap Combination of CO2 Geological Storage
Sichuan Basin is an Artesian Basin consisting of Permian and T riassic strata. The first set of regional seal cov-
ering the whole basin is Jurassic Shaximiao Group, whereas the second set is Suining Group and Penglaizhen
Group. According to field sur vey, shale cont ent in Shaximiao Group is mor e than 50%. The S uinin g Group
mainly consis ts of b rown-red mudstone a nd sandy mudstone with siltstone thin layer. Pengl aizhen mainly con-
sists of gray a nd sandy mudstone , as well as multiple la yers of marl and siltsto ne. These two sets of covering
caps are relatively stable [18].
Jurass ic is distributed in southeast platea u area, middle gentle uplif t, and northwest dep ressions of Sichuan
Basin. Some strata are mis sing in East Sichuan high -slope faulted fold belt, South Sichuan low-slope structur al
belt and SW low-slope structural belt except for the middle and lower part. Considering the risk of leakage , only
the lower part of Jurassic Ziliujing Group is considered as carbon dioxide geological stor age site. Specifically,

J. J. Fan et al.
1015
the lenticular sand body of lower part of Jurassic Ziliujing Group is considered as the exact site for carbon dio-
xide geological storage.
Water alternating phenomenon is strong around mountains at the edge of the basin or at the eastern separated
file fold anticline area. Since it is the infiltration type of fresh wate r in these places, they are not appropriate for
carbon dioxide storage. By contrast, the anci ent sealed water with sedimentary origin is found in the d eep p art of
Triassic strata, and this is the right place for carbon dioxide geological storage [19].
According to the researc h of Wang J. [20] the average porosity of reservoir mat rix of fractured sand stone in
Sichuan Basin is about 4%, the average porosity of carbonate matrix is less than 2%, a nd the average porosity of
the porous carbonate reservoir is within the ran ge of 4% and 6%, with permeability mo re than 1 md. By contrast,
sandstone porosity is approximately 4.5%, with per meability less than 0.01 md. Therefore, it could be concluded
that t he distribution of the porosity and permeability in Sichuan Basin is 5 ≤ φ < 10 and K < 1, which represents
less suitab le and unsuitable conditions, respectively.
According to Zhang K. [21], based on thickness values of stora ge reservoirs in Sichuan Basin derived from
corresponding contour maps and the areas of different tectonic unit, t he volume of secondary tectonic units coul d
be obtained, among which eastern high and steep fold belt accounts fo r 25.21%, northern low-steep fold belt ac-
counts for 21.25%, western low-steep fold belt accounts for 17.09%, southern low-steep fold belt accounts for
7.56%, southwestern low-steep fol d belt accounts fo r 8.99%, and middle gentle fo ld belt acco unts fo r 19.9%.
A compr ehensive analysis of reservoir-cap in Sichuan basin shows tha t East Sichuan hi gh-slope faulted fold
belt is relatively unsuitable for carbon dioxide geological sto rage. By contrast, Nor th Sichuan low-flat structur al
belt, West Sichuan low-slope structural be lt, S outh Si chuan low-slope struc tura l b elt a nd SW lo w-slope struc-
tural belt are relatively suitable, and Centra l Sichuan low-flat structur al belt is the best place for carbon dioxide
geological storage.
4.4. Geothermal and Geological Conditions
Geothermal gradient between middle ge ntle fol d belt and SW low-slope structural belt in Sichuan Basin is rela-
tively high, ranging from 24 to 30˚C/km. The ge otherma l gr adie nt of Weiyuan tecto nic zone is more than
30˚C/km. The geothermal gradie nt b et ween East Sichua n high-slope faulted fold belt and North Sichuan low-flat
struc tura l b elt gradually decreases to 20˚C/km. Also, the geothermal grad ient of the outer edge of the northe as-
tern Sichuan is as low as 16˚C/km. On both sides of Central Sich uan low-flat s t ruct ural belt and West Sichuan
low-slope structural belt, the geothermal gradient is maintained a round 20˚C/km. The piedmont fractured de-
veloped in northeastern Sichuan could lead to the downward infiltration of gro undwater, which would future
cause the reduction of local geothermal gradient so that it is much lower than the ave rage level.
Terrestrial heat flow values in Sichuan Basin are within the range of 35.4 and 68.8 mw/m2, with the ave rage
value as 53.2 mw/m2, which is similar with low heat flow character istics of other typical cratonic basins all over
the word. As to the aspect of regional distribution, terrestrial heat flow is obviously affected by the base struc-
ture. Terrestrial heat flow values of uplift area are within the ran ge of 60 and 70 mw/m2, val ues of depression
area are below 60 mw/m2, a nd value s could be even less than 40 mw/m2 near the leading edge of the fold belt of
Daba Mo unt ain, which is located in the northeastern Sichuan [22].
According to annual average temperature statis tics of the Si chuan Basin, Chongqing, Yibin and Chengdu be-
tween 1997 a nd 2005, the derived average temperature in Sichuan Basin is 17.9˚C. Specifically, t he ave rage
temperature in East Sichuan high-slope faulted fold belt or South Sic huan low-slope structural belt is 18.6˚C, the
average temperature in Centr al Sichuan low-flat structural be lt or southwestern lo w-steep fold belt is 18. 3˚C,
and the a verage temperature in North Sichuan low-flat structural belt or western low-ste e p fold be lt is 16.8˚C
[23].
A comprehe nsive ana lysis of geothermal geological co nditions in Sichuan basin shows that East Sichuan
high-slope faulted fold belt, Sout h Sichua n low-slope struc tura l belt, Central Sichuan low-flat structural belt and
West S i chuan low-slope structural be lt is relat ively suitable for carbon dioxide geologic al storage. By contrast,
SW low-slope structura l belt and North Sich uan low-flat structural belt are not suitable for carbon dioxide sto-
rage purpose.
4.5. Storage Potential Conditions
When CO2 geological storage potentials in deep saline aquifers are calculated, it is necessary to consider the vo-

J. J. Fan et al.
1016
lume of the aquifer, satura tion of CO2 trapped after formation water countercurrent, porosity of saline aquifer,
densi ty of CO2 under the conditions of formation water, th e density of the initial formation water and the solu-
bility of CO2 in saline aq uifers [6].
According to the distributed a rea and thickne ss of the reservoir described in 4.3, the reservoir volume of every
reservoir located 800 m depth below in every secondary tectonic unit could be calculated, and the eval uation of
D grade inferred potential of CO2 geological storage in deep saline aquifers of secondary tectonic units in Si-
chua n Basi n is shown in Table 6.
Based on parameters of CO2 geological storage potentials in deep saline aquifers, gr ade D constructive poten-
tials of CO2 geological storage in every secondary tectonic unit of Sichuan Basin could be calculated, among
which stora ge potentials of East Sichuan high-slope faulted fold belt reach the ma ximum value and account for
27.55% of the total stor age capacity of deep saline aquifers. Also, stora ge potentials of West Sic huan low-slope
struc tura l belt account for 15.62% of the total storage capacity. Storage potentials of Central Sichuan low-flat
structural belt account for 20.33% of the total storage capacity. Storage potentials of SW low-slope structural
belt account for 7.48% of the total storage capacity. Storage potentials of North Sichuan low-flat structural belt
account for 22.30% of the total storage capacity. By contrast, storage potentials of South Sichuan low-slope
struc tura l belt have the minimum value and account for 6.72% of the total storage capacity. Storage potentials
and per unit area storage potentials of the secondary tectonic units of Sichuan Basin are 0.5 < M ≤ 25 and 1 < m
≤ 50, respectively.
A comprehensive analysis indicates that storage potential conditions of the secondary tectonic units in Si-
chuan Basin are generally suitable.
Table 6. Evaluation of D grade inferred potential of CO2 geological storage in deep saline aquifers of secondary tectonic
units in Sichuan Basin.
Type of storage
Tectonic unit Saline aquifers
East Sichuan
high -slop e
fau lt ed fold belt
South Sichuan
low-slop e
structural belt
Cen t ra l Sichuan
low-fla t
structural belt
SW low-sl ope
structura l
belt
North Sichuan
low-fla t
structural belt
West Sichuan
low-slop e
structural belt
D grade
inferred
potential of
residual gas
mech an i s m
(×106t)
Jurassic Ziliujing
Formation 383.97 175.95 219 .77 128.80 227.79 208.00
The Upper Triassic
Xujiahe Formation 455.83 226.34 276 .64 135.26 280.94 312.00
The Middle Triassic
Leikoupo Formation 939.60 0.00 2433.17 988.01 1556.56 2273.52
The Middle Triassic
Jialing River Formation 5972.84 1144.29 2852.89 864.51 3097.99 2614.89
The lower Triassic
Feixianguan Formation 3127.35 1144.29 2093.66 864.51 3769.42 796.26
Lower Permian
Qixia Formation - - - - - 142.10
total 10879.58 2690.86 7876.14 2981.10 8932.70 6346.77
Grade inferred
potential of
dissolution
mech an i s m
(×106t)
Jurassic Ziliujing
Formation 28.49 14. 70 14. 76 11. 83 8.95 8.93
the Upper Triassic
Xujiahe Formation 19.04 10.64 15. 50 6.99 11.04 13.40
The Middle Triassic
Leikoupo Formation 18.12 0.00 293.64 51.09 2 8.26 57. 43
The Middle Triassic
Jia lin g River Formation 443.16 53. 81 222 .78 44. 71 121.79 1 12.31
The lower Triassic
Feixianguan Formation 182.02 5 3.81 117 .31 44. 71 263.27 15.79
Lower Permian
Qixia Formation - - - - - 3.59
total 690.82 132.97 663.98 159.34 433.31 211.45
Total (×106 t) 11570. 40 2823.83 8540.12 3140.43 9366.01 6558.22

J. J. Fan et al.
1017
4.6. Research Levels and Resource Potentials
The exploration of Sichuan basin co uld be considered as under a developmental state. Each secondary tectonic
unit has its own drilling well control system so that the suit a b ility assessment could be done based on the infor-
mation of local resource potentials. According to the latest resource evaluation results of 2002, oil resources are
only founded in the middle, eastern and nort hern blocks of Sichuan basin, among which the middle block of the
basin has the highest level of oil sto rage, accounting for 48% of total oil storage. By contrast, the eastern a nd
nort hern blocks of Sichuan basin have 29% and 23% of total oil storage, respectively. By contrast, gas resources
are found in all six blocks of the basin, among which the eastern block has the highe s t leve l of gas storage, ac-
counting for 43.26% of total gas storage. For other blocks, ga s storage from the highest to the lowest level is in
the order of western block (23.46%), middle block (12.43%), northern block (9.65%), southwestern block
(6.22%) and southern block (4.98%) [24].
A compr ehensive anal ysis reveals that both the Centr al Si chuan low-flat structural be lt and the East Sichuan
high-slope faulted fold belt are highly suitable in terms of research levels and resource potentials of the second-
ary tectonic units. Similarly, North Sichuan low-flat structural belt is relative ly suitable, and West Sichua n
low-slope structural belt is fairly OK. By contrast, South Sichuan low-slope structural beltand SW lo w-slope
struc tura l belt are unsuitable.
4.7. Social and Economic Conditions
According to the natio nal standard Land Use Classification [25], remot e sensin g t echnique has been app lie d to
Sichuan basin in order to better understand current land use status, with land use status of six secondary tectonic
units shown in Table 7.
According to relevant report [26], the statistics of population density within different secondary tectonic units
could be derived. The density of eastern high and steep fold belt is 350 persom/km2, the density of southern
low-steep fold belt is 335 person/km2, the density of middle gentle fold belt is 490 person/km2, the density of
southwestern low-steep fold belt is 418 person/km2, the density of North Sichuan low-flat structural belt is 275
person/km2, and the density of West Sichuan low-slope structural belt is 591 person/km2.
5. A Comprehensive Evaluation
The partition evaluation results of Sichuan Basin seco nd-grade structural units’ suitability is as shown in F igure
3, Table 8 and Table 9. The subsurface reservoirs are Lower Jurassic Ziliujing Formation, Upper Triassic Xu-
jiahe Formation, Middle Triassic system Leikoupo Formation, Lower Triassic system Jialingjiang Formation
and Feixianguan Formation, and the Qixia Formation in the lower part of Permian System. There is a risk of
leakage in Huanyin fault zone in the reservoir of Lower Jurassic Ziliujing Formation, Upper Triassic systems
Xujiahe Formation and Triassic system Leikoupo formation, but due to the impact of the Longmenshan and
Huanyin thrust fault smearing, the reservoir of Lower Triassic Jialingjiang Formation, Feixianguan For mation and
the lower part of Permian Qixia Formation have a sealing effect for the goal reservoir to some extent (Figure 4).
Table 7. Descriptions of land use area in Sichuan Basin.
Tectonic units Agricultural acre age
(km 2) Settlement (km 2) Woodland (km 2) Water body (km 2) Bare land (km 2)
East Sichu an high-slo p e fa u lt ed fold belt 2712 4. 3 152.5 21518 742.7
South S ic hu an low-sl ope st ruct ural b elt 1 4945. 8 3 2.9 1 160 0.8 515.1 162.5
Cen t ra l S ich ua n low -flat structural belt 35242.9 4 9.6 335.1 1268.9
SW low-slope st ructu ral bel t 1 4928 8 0.2 5926 .4 371.5 133.5
North S ic hu an lo w-flat structural belt 2 278 2.7 2 7. 8 1076 1. 4 392.4
West Si ch u an low-slop e st ruc tura l belt 1 744 5.9 250.2 12869.9 1699 .8 902.3

J. J. Fan et al.
1018
Figure 3. Map showing of a comprehensive evaluatio n r esu lt .
Table 8. P value and Evaluation result table.
Tectonic units P value Normalization result Evaluation result
West Sichuan low-slope structural belt 5.24 0.079 Relatively suitable
SW low-slope structural belt 5.06 0.000 Un sui ta b le
South Sichuan low-slope structural belt 5.79 0.320 Relatively unsuitable
East Sichuan high-slope faulted fold belt 6.03 0.425 Fairly suitable
North Sichuan low-flat structural belt 6.42 0.596 Fairly suitable
Central Sichuan low-flat structural belt 7.34 1.000 Highly suitable
Fractured water-bearing formation of Carbonate rock is mainly developed in the east side of hanging wall in the
Huanyin mountains fault, and the carbonate rock fissure cave water outcrops in the form of spring. The leaking
of the fault spring in the west side are mainly far away from the fault, having nothing to do with the deep fault;
and west side part which is near the fault, have no spring water dew point [27] [2 8 ] . It can be inferred that the
footwall of the west side of Huanyin mountains fault has good water-blocking properties, and can produce fault
sealing effect, so it is good for deep saline aquifers geological storage of carbon dioxide. Therefore, it can be
determined that as for reservoir of the Lower Triassic Jialingjiang Formation, Feixianguan Formation

J. J. Fan et al.
1019
Table 9. Sichuan Basin geological storage of carbon dioxide suitability evaluation results.
Weight
of first
level Index layer Indicator Weight
of Second
level
East Sichuan high-slope
faulted fold belt
South Sichuan low-slope
structural belt
Central Sichuan
low-flat structural belt
Decription Assignment
Index
value
Decription Assignment
Index
value
Decription Assignment
Index
value
0.33
stability
stability
1
Less
3
0.99
Less
3
0.99
stable
7
2.31
0.27 Basic
geology
Area (km2)
0.5
50000
9
1.22
26000
9
1.22
37000
9
1.22
sediment
depth (m)
0.5 10000 9 1.22 8000 9 1.22 9 000 9 1.22
0.04
research
degree and
resource
potential
exploration
degree
0.75 developin g 9 0.27 developing 9 0.27 deve loping 9 0.27
Data support 0.13
Completed,
reliable
7 0.04
Completed,
reliable
7 0.04
Completed,
reliable
7 0.04
coal/oil gas
resource
0.12 plenty 3 0.01 plent y 3 0.0 1 plenty 3 0.01
0.02 socio-econom y
population
density 0.86 transition
region 5 0.09
Core
densely
district
1 0.02
Core
densely
district
1 0.02
condition
of land use
0.14
Woodland,
farmland
5 0.01
Residential
& Transport
1 0.00
Residential
& Transport
1 0.00
0.06 Thermal
geology
Surface
temperature (˚C)
0.14 18.6 3 0.03 18.6 3 0.03 18.3 3 0.03
Terrestrial heat
flow (mW·m
−2
)
0.14 50 9 0.08 50 9 0.08 70 5 0.04
Geothermal
gradient
[˚C·100 m
−1
]
0.71 2-2.5 7 0.30 2.5-3 7 0.30 2.5-3 7 0.30
0.1
Inferred
storage
potential
Total (108 t)
0.83
115.7
9.0
0.75
28.2
7.0
0.58
85.4
9.0
0.75
Unit (104 t/km2) 0.17 23.1 3 0.05 10.9 3 0.05 23.1 3 0.05
0.17 Reservoir
and cap-rock
Reservoir
condition
0.43 20.9 5 0.37 21.2 5 0.37 17 3 0.22
cap-rock
conditions
0.43 6.7 7 0.51 6.7 7 0.51 8.2 9 0.66
Reservoir and
cap-rock
conditions
0.14
regional,
mainly
independent
5 0.12
regional,
mainly
independent
5 0.12 re gional 9 0.21
comprehensive index
6.03
5.79
7.34
Weight
of first
level Index layer indicator weight
of Second
level
SW low-slope structural belt
North Sichuan low-flat
structural belt
West Sichuan low-slope
structural belt
Decription
assignment
Index
value
Decription assignment
Index
value
Decription
assignment
Index
value
0.33
stability
stability
1
Not stable
1
0.33
Less
3
0.99
Not stable
1
0.33
0.27 basic
geology
Area (km2)
0.5
21000
9
1.22
34000
9
1.22
32000
9
1.22
sediment
depth (m)
0.5 7000 9 1.22 12000 9 1.22 10000 9 1.22
0.04
research
degree and
resource
potential
exploration
degree
0.75 de veloping 9 0.27 developing 9 0.27 developing 9 0.27
Data support 0.13
Completed,
reliable
7 0.04
Completed,
reliable
7 0.04
Completed,
reliable
7 0.04
coal/oil gas
resource
0.12 ple nty 3 0.01 less 1 0.00 plent y 3 0.01
0.02 socio-economy
Population
density
0.86
Core densely
district
1 0.02 sparsely 9 0.15
Core densely
district
1 0.02
condition of
land use
0.14
Residential
& Transport
1 0.00
Woodland,
farmland
5 0.01
Residential
& Transport
1 0.00
0.06 Thermal
geology
Surface
temperature (˚C)
0.14 18.3 3 0.03 16.8 3 0.03 16.8 3 0.03
Terrestrial heat
flow (mW·m
−2
)
0.14 70 5 0.04 50 9 0.08 70 9 0.08
Geothermal
gradient
[˚C·100 m
−1
]
0.71 3 - 3.5 5 0.21 1.5 - 2 9 0.38 2 - 2.5 7 0.30
0.1
Inferred storage
potential
Total (108 t)
0.83
31.4
3.0
0.25
93.7
9.0
0.75
65.6
9.0
0.75
Unit (104 t/km2)
0.17
15.0
3
0.05
27.5
3
0.05
20.5
3
0.05
0.17 R eservoir and
cap-rock
Reservoir condition
0.43
26.8
9
0.66
24.7
7
0.51
17.6
3
0.22
cap-rock conditions
0.43
6.7
7
0.51
6.7
7
0.51
5.8
7
0.51
Reservoir and
cap-rock conditions
0.14 r egional 9 0.21 regiona l 9 0.21 regiona l 9 0.21
comprehensive index
5.06
6.42
5.24

J. J. Fan et al.
1020
Figure 4. Geological profile across the basin along the line A-B in Figure 2 (Blue formations indicate the saline aquifers and
red formation are the caprock seal).
and Lower Permian Qixia Formation, the gently fold belt reservoir in the middle part of Sichuan can be used as
geological goal targets. As for the reservoir of Lower Jurassic Ziliujing formation, Upper Triassic Xujiahe for-
mation, and Triassic system Leikoupo Formation, where exists the risk of leakage in Huanyin mountains fault
zone, the furthest areas from structure unit boundary faults zone should be selected for the best.
6. Discussion
Since the secondar y tectonic uni ts within the basin are considered as research objects, the scope of correspond-
ing evaluati on objects are narrowed to some extent. However, to achieve the goal tha t the storage of carbon dio-
xide reaches the ultimate state, i.e., t he mineralized storage state, a completely enclosed space is required strictly.
Regarding the closed space issues, the s mearing effect displayed by the fault rupture of Huan yin mounta in just
has a sealing function theoretically for the lower Triassic Jialing group, Feixianguan and lower P ermian Qixia
Formation reservoir, b ut its closed fracture feature is very complex and deserves more in-depth analysi s .
For the six geological targets determined preliminarily, borehole data should be used to analyze the sedimen-
tary microfacies of these six targets located at different geological laye rs. For area with less borehole data
available, microfacies analysis sho ul d be applied in order to establish the physical model of geological targets
and carry out corresponding numerical simulation work.
7. Conclusions
The suitability assessment of the secondary tectonic units in Sichuan Basis sho ws that middle gentle fold belt is
relatively suitable. Eastern high and steep fold belt, southwestern low-steep fold belt and North Sichua n low-flat
struc tura l belt are quite unsuitable, and western and southwestern low-steep fold be lts are unsuitable.
The underground reservoirs of six geological targets inc l ude lower Jurassic Ziliujing Group , upper Triassic
Xujiahe Group, middle Triassic Leikoupo Group, lower Triassic Jialingjiang Group, lower Triassic Fei xi an guan
Group and lower Permian Qixia Group.
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