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International Journal of Greenhouse Gas Control 78 (2018) 62–72
Contents lists available at ScienceDirect
International Journal of Greenhouse Gas Control
journal homepage: www.elsevier.com/locate/ijggc
Evaluation of the potentiality and suitability for CO2 geological storage in
the Junggar Basin, northwestern China
T
⁎
Zhaoxu Mia, Fugang Wanga, , Yongzhi Yangb, Fang Wangb, Ting Hua, Hailong Tiana
a
b
Key Laboratory of Groundwater Resources and Environment, Ministry of Education, Jilin University, Changchun, 130012, China
PetroChina Research Institute of Petroleum Exploration & Development, Beijing, 100083, China
A R T I C LE I N FO
A B S T R A C T
Keywords:
Junggar Basin
CO2 geological storage
Analytic hierarchy process
Fuzzy comprehensive evaluation
Suitability evaluation
CO2 geological storage is one of the most important methods for reducing the emissions of anthropogenic
greenhouse gases into the atmosphere. Junggar Basin is an important energy base in China, with high CO2
emissions and geological storage potential. The evaluation of the suitability for CO2 geological storage is the
basis for screening CO2 geological storage sites, and a scientific and effective evaluation method is key. Using the
Junggar Basin as the study site, an indicator system consisting of 3 indicator layers and 27 indicators was
constructed. By combining the analytic hierarchy process and fuzzy comprehensive evaluation method, the
geological suitability for CO2 geological storage in 44 secondary tectonic units in the Junggar Basin was evaluated. The evaluation results provide a scientific basis for site selection and project construction for CO2 geological storage in the Junggar Basin.
1. Introduction
Global warming presents a serious threat to the environment.
Reducing the emissions of carbon dioxide (CO2) is a common challenge
for countries worldwide (Feng et al., 2017). The technology of CO2
geological storage has attracted the attention of governments and scientists around the world as a direct and effective emissions reduction
technology recognized by the international community (Wang et al.,
2016). CO2 geological storage is the injection of supercritical CO2 into a
safe target reservoir with competent caprock. CO2 is trapped in reservoirs by various mechanisms such as structural and stratigraphic
trapping, residual CO2 trapping, solubility trapping and mineral trapping. Suitable sequestration targets predominately include deep saline
aquifers, oil and gas reservoirs, and deep unmineable coalbeds (Zhang
and Huisingh, 2017). CO2 geological storage suitability assessment is
one of the decision-making tools for the consideration of a CO2 geological storage project. Choosing the right storage location is important
for improving the storage capacity and injectivity and reducing the risk
of CO2 leakage. The leakage of CO2 will pose a serious threat to the
environment and society. The reliability of the evaluation results will
also affect whether the expected goal can be achieved after the project
is implemented. As CO2 geological storage involves many aspects such
as the geology, engineering, society, economy and environment, CO2
geological storage becomes a complicated systematic project (Du et al.,
⁎
2016). Therefore, selecting safe and effective storage sites is the most
important issue before the construction of CO2 geological storage projects.
Bachu and Adams proposed a systematic theory and method of CO2
geological storage potential evaluation and built an evaluation indicator system including 15 basin-level indicators and evaluated the
storage potential of the main sedimentary basins in Canada (Bachu,
2003; Bachu and Shaw, 2003). The IPCC proposed an overarching
framework for the assessment of CO2 geological storage potential and
suitability (Coninck et al., 2005). Oldenburg comprehensively considered the health, safety and environmental risks of CO2 geological
storage and proposed a screening evaluation indicator system and
evaluation method for CO2 geological storage sites (Oldenburg et al.,
2010). Shen Pingping proposed a geological storage suitability evaluation system consisting of 25 indicators, using Daqingzijing Oilfield in
China as an example. Song Tiejun established an indicator system that
consists of 16 indicators by applying the gray relational analysis
method to the basin level suitability assessment of the 33 secondary
tectonic units of Songliao Basin (Song et al., 2017). In the meantime,
some countries and international organizations have implemented a
number of demonstration projects of CO2 geological storage, such as the
Sleipner project in Norway, the Quest and Aquistore project in Canada,
the Illinois Industrial Carbon Capture and Storage project in the United
States and the Shenhua Ordos CCS demonstration project in China
Corresponding author.
E-mail address: wangfugang@jlu.edu.cn (F. Wang).
https://doi.org/10.1016/j.ijggc.2018.07.024
Received 26 March 2018; Received in revised form 19 June 2018; Accepted 25 July 2018
1750-5836/ © 2018 Elsevier Ltd. All rights reserved.
International Journal of Greenhouse Gas Control 78 (2018) 62–72
Z. Mi et al.
3. Indicator system and method for evaluating CO2 geological
storage suitability
(Gaede and Meadowcroft, 2016; Rostron et al., 2015; Verdon et al.,
2013).
Compared with other basins that have been evaluated for the suitability of CO2 geological storage, the geology, hydrogeology and reservoir capillaries of the Junggar Basin have substantial differences.
The Junggar Basin is located in an arid area with scarce precipitation.
In an assessment of the potential and suitability for CO2 geological
storage in 390 continental sedimentary basins in China, the Junggar
Basin ranks seventh in storage potential and has good suitability.
Moreover, as an important energy base and industrial base in China, the
Junggar Basin has underwent rapid economic growth in recent years
and has become a major CO2 emission zone in northwestern China.
However, there are few studies on CO2 geological storage in the
Junggar Basin. In order to ensure the efficient and safe operation of
geological storage projects, it is necessary to evaluate the suitability of
the Junggar Basin. Based on the characteristics of the Junggar Basin,
this paper analyzes the influencing factors of CO2 geological storage
suitability and establishes a basin-level CO2 geological storage suitability assessment indicator system to evaluate the suitability for CO2
geological storage in each secondary tectonic unit in the Junggar Basin.
The results will provide a scientific basis for the screening of CO2
geological storage sites.
With reference to the domestic and international CO2 geological
storage suitability evaluation methods (Bachu and Shaw, 2003;
Oldenburg et al., 2010; Su et al., 2013), the analytic hierarchy process
and fuzzy comprehensive evaluation method were used to evaluate the
suitability of the secondary tectonic units in the Junggar Basin. The
evaluation results were normalized and the suitability was graded according to the normalized results.
3.1. Construction of the evaluation indicator system
The evaluation indicator system is based on a full analysis of the
features of the Junggar Basin, and the previous related research. The
main principles are as follows.
(1) Geological safety is the most important factor for the evaluation
indicators. The geological safety of CO2 geological storage is analyzed from the aspects of regional crustal stability, the sealing
capability of caprock and the hydrogeological conditions. The
higher the geological safety factor is, the more favorable a site is for
the geological storage of CO2.
(2) The storage capability is fully analyzed according to the scale of the
tectonic units, reservoirs, geothermal geological conditions, storage
potential and other factors. The larger the storage capability is, the
more conducive a site is to CO2geological storage.
(3) The evaluation process considers the principles of social environmental and economic conditions. The better the environmental and
economic conditions, the more conducive a site is to CO2 geological
storage.
2. Geological characteristics of the Junggar Basin
The Junggar Basin is located in the northern Xinjiang Uygur
Autonomous Region in China. The West Junggar Mountains are in the
northwest part of the basin, the Altai Mountains, the Qinggelidi
Mountains and the Kelameili Mountains are in the northeast part of the
basin, and the North Tianshan Mountain Range is in the south part of
the basin. The Junggar Basin is a triangular enclosed inland basin. The
geographical coordinates of the Junggar Basin have a range of
N43°20′∼46°50′ and E82°30′∼ 91°50′, with an east-west length of
approximately 700 km, a north-south width of approximately 379 km,
and a total area of approximately 135,000 km2.
According to the late Paleozoic tectonic characteristics, the Junggar
Basin is divided into six first-order tectonic units, namely, the Wulungu
Depression, Luliang Uplift, Western Uplift, Central Depression, Eastern
Uplift and North Tianshan thrust belt, and 44 secondary tectonic units
(Li et al., 2015; Yang et al., 2004). The division of tectonic units in the
Junggar Basin is shown in Fig. 1.
Junggar Basin is a compressional superimposed basin with late
Paleozoic, Mesozoic, and Cenozoic deposits and experienced the effects
of the Hercynian, Indosinian, Yanshannian and Himalayan orogenies,
resulting in a complex tectonic framework (Chen et al., 2002). The
stratigraphic system of the Junggar Basin is very complicated. The
strata in the northwestern, southern and central regions of the basin
vary widely. The basement of the basin consists of Ordovician, Silurian,
Devonian, and Carboniferous metamorphic and volcanic rocks. The
Carboniferous base is the most widely distributed (Buckman and
Aitchison, 2004). The main sedimentary strata are Permian, Triassic,
Jurassic, Cretaceous, Tertiary, and Quaternary strata, and the sedimentary rock total thickness is more than 15000 m.
Junggar Basin is an important energy base in China, rich in coal, oil,
natural gas and other resources. The northern slope of the Tianshan
Mountains in the southern part of the basin is one of the most developed
regions in modern industrialization, agriculture, transportation and
educational technology in Xinjiang, China. It is one of the key areas for
the development of western China. In the area, 83% of the heavy industry and 62% of the light industry are concentrated in Xinjian district. There is a large number of coal-fired power plants, steel mills and
coal chemical industries in Xinjian district, which are the major CO2
emission sources.
According to the above principles, combined with the actual conditions in the Junggar Basin, the CO2 geological storage suitability
evaluation indicator system was constructed, as shown in Table 1. The
evaluation system includes 3 indicator layers, 9 sub-indicator layers
and 27 indicators.
3.2. Determining the weight of the indicators by AHP
The analytic hierarchy process(AHP) is a systematic analysis
method developed on the basis of a qualitative method to quantitatively
determine the weight of the factors used in the assessment. This method
can quantify people's experience and help to achieve a quantitative
evaluation (Yang et al., 2011a).
The steps for calculating weights using the AHP are as follows:
(1) Analyze the relationships among various factors in the system and
establish the hierarchical structure of the system. In this study, the
system is divided into three levels: indicator layer, sub-indicator
layer, and indicator.
(2) Compare the importance of various factors on the same level and
construct a judgment matrix to compare the two factors.
(3) Calculate the weights of each indicator layer and sub-indicator
layer of the indicators (Table 1). Then, check the consistency of the
calculation results.
The consistency ratio of the comparison judgment matrix for the
indicator layer is 0.0088 (< 0.1), which has good consistency.
3.3. Comprehensive score for the suitability of the secondary tectonic units
Due to the complexity of CO2 geological storage, the fuzzy comprehensive evaluation method was used to evaluate the suitability of
the secondary tectonic units in the Junggar Basin.
The fuzzy comprehensive evaluation method is a synthetic
63
International Journal of Greenhouse Gas Control 78 (2018) 62–72
Z. Mi et al.
Fig. 1. Division of the tectonic units in the Junggar basin.
1-Hongyan fault zone; 2-Suosuoquan Depression; 3-Shiyingtan Uplift; 4-Yingxi Depression; 5-Sangequan Uplift; 6-Dibei Uplift; 7-Xiayan Uplift; 8-Sannan Depression;
9-Shixi Uplift; 10-Dishuiquan Depression; 11-Dinan Uplift; 12-Wucaiwan Depression; 13- Shazhang fault-fold belt; 14-Shishugou Depression; 15-Huangcaohu Uplift;
16-Shiqiantan Depression; 17-Heishan Uplift; 18-Wutongwozi Depression; 19-Qitai Uplift; 20-Beisantai Uplift; 21-Jimsar Depression; 22-Guxi Uplift; 23-Gucheng
Depression; 24-Gudong Uplift; 25-Mulei Depression; 26-Fukang Fault zone; 27-Huomatu anticline zone; 28-Qigu fault-fold belt; 29-Sikeshu Depression; 30-Chepaizi
Uplift; 31-Hongche fault zone; 32-Zhongguai Uplift; 33-Kebai Fault zone; 34-Wuxia fault zone; 35-Mahu Depression; 36-Dabasong Uplift; 37-Penyijingxi Depression;
38-Mobei Uplift; 39-Mosuowan Uplift; 40-Donghaidaozi Depression; 41-Baijiahai Uplift; 42-Fukang Depression; 43-Monan Uplift; 44-Shawan Depression.
Table 1
Weight of the evaluation indicators.
Indicator layer
Weight
Sub-indicator layer
Weight
Indicator
Weight
Geological safety
0.4579
Regional crustal stability
0.2471
Sealing capability of caprock
0.1360
Hydrogeological conditions
Tectonic unit size
0.0748
0.0968
Reservoir
0.1522
Geothermal condition
0.0515
Storage capacity
0.1156
Social environment
0.0420
Economic conditions
0.0840
Seismic peak ground acceleration
Historical seismic activity
Active faults
Burial depth of caprock
Caprock lithology
Caprock thickness
Continuity of caprock distribution
Permeability
Secondary sealing capacity above the main caprock
Hydrodynamic action
Area of tectonic unit
Sediment thickness
Resource potential
Burial depth of reservoir
Reservoir thickness
Reservoir lithology
Porosity
Permeability
Land surface temperature
Geothermal gradient
Terrestrial heat flow
Theoretical potential
Theoretical potential per unit area
Population density
Land use type
Quantity of carbon source
Distance to carbon source
0.0809
0.1020
0.0642
0.0228
0.0173
0.0171
0.0264
0.0329
0.0194
0.0748
0.0242
0.0242
0.0484
0.0296
0.0448
0.0196
0.0291
0.0291
0.0103
0.0206
0.0206
0.0578
0.0578
0.0210
0.0210
0.0560
0.0280
Storage capability
Environmental and economic conditions
0.4161
0.1260
64
International Journal of Greenhouse Gas Control 78 (2018) 62–72
Z. Mi et al.
cause substantial safety and environmental problems. The distribution
of active faults in the Junggar Basin is shown in Fig. 3 (Qu et al., 2008).
(2) Stable caprock ensures the geological safety of CO2 geological
storage, which largely determines the capability of CO2 geological
storage (Diao et al., 2012). An ideal caprock requires good integrity and
sealing ability to effectively prevent CO2 leakage from the reservoir.
CO2 geological storage in a supercritical state requires that the burial
depth of the caprock is over 800 m with a continuous spatial distribution, a relatively large thickness, no penetrative fractures and good
sealing ability. Therefore, when evaluating the caprock sealing ability,
it is necessary to consider the macroscopic characteristics of the caprock and the microscopic sealing capability. The sealing ability of
caprock is mainly evaluated by the burial depth of the caprock, caprock
lithology, caprock thickness, continuity of caprock distribution, permeability, secondary sealing capacity above the main caprock.
Based on the analysis of the historical structural and sedimentary
evolution of the Junggar Basin, the suitable caprocks for CO2 geological
storage are mainly distributed in the Jurassic, Cretaceous and Tertiary
strata. In addition, there are a few suitable caprocks distributed in the
Triassic, Permian and Carboniferous strata. For the horizontal distribution, the mudstone caprock in the Jurassic and Cretaceous strata
cover a large area and are relatively thick, which makes these the favorable caprock in the basin. The tertiary mudstone caprock are mainly
distributed in the piedmont fault zone area south of the Luliang Uplift.
The caprocks in the Triassic, Permian and Carboniferous strata are
mainly distributed in the northeastern and northwestern parts of the
basin with limited extents.
(3) The hydrogeological conditions have a significant impact on the
CO2 storage potential and storage safety. The effects of the hydrogeological conditions on the CO2 fluid can be considered in three facets:
hydraulic seal, hydraulic jam-up and hydraulic migration-escape.
Hydraulic seal occurs in aquifers with stable barriers to water. The
groundwater flow in the aquifer is very slow and even stagnant, and the
CO2 migration is slow. This effect mainly exists in the Central
Depression of the basin. Hydraulic jam-up means that the direction that
CO2 is likely to leak is opposite to the direction of groundwater flow.
The groundwater prevents CO2 from moving upwards and leaking from
the reservoir. Hydraulic migration-escape often exists in an area with a
faulted structure, high water conductivity, and high groundwater flow.
During groundwater movement, the migration of CO2 may be accelerated and CO2 may leak to the surface. This effect may occur in the
southern margin of the Junggar Basin, where a large number of faults
exist.
Based on the related former studies (Guo et al., 2015) and combined
with the actual geological conditions in the basin, the grading standards
of each indicator for evaluating the geological safety suitability are
established (Table 2).
assessment method that applies fuzzy mathematical principles to evaluate factors and phenomena affected by a variety of factors. It applies
the fuzzy transformation theory and the maximum membership degree
law to a comprehensive evaluation to various factors. According to the
fuzzy evaluation result, the priority of various alternatives can be
achieved as a reference for decision makers.
The evaluation indicator of CO2 geological storage suitability is
divided into five levels, A, B, C, D and E, with a score of 9,7,5,3, and 1,
respectively. A indicates the most suitable site for CO2 geological storage and E indicates the least suitable site. The following models are
used to assess the comprehensive score of each unit.
n
x (i) =
∑ pn * An (i = 1,2, 3……44)
n=1
where x(i) is the comprehensive score of CO2 geological storage suitability for the i-th evaluation unit; n is the number of evaluation indicators; pn is the score of the n-th evaluation indicator; and An is the
weight of the n-th evaluation indicator.
3.4. The normalization of the comprehensive score
The comprehensive scores using the fuzzy comprehensive evaluation method are located in the [1,9] interval. To facilitate the suitability
classification, the comprehensive score is normalized by feature scaling
method so that the evaluation results are all between 0 and 1. The
formula is:
X (i) =
x (i)−min (x )
max (x )−min (x )
where X(i) is the normalized score of the i-th evaluation unit; x(i) is the
comprehensive score of the i-th evaluation unit; min (x ) is the minimum
score of all the comprehensive scores; and max (x ) is the maximum
score of all the comprehensive scores.
According to the normalized scores, the CO2 geological storage
suitability for each unit is divided into five levels, Grade A, Grade B,
Grade C, Grade D and Grade E.
4. Analysis of the suitability for CO2 geological storage in the
Junggar Basin
4.1. Evaluation of geological safety suitability
Geological safety is the primary factor that affects CO2 geological
storage and is a strong indicator of the CO2 geological storage (Diao
et al., 2011). The geological safety evaluation indicator layer includes
three sub-indicator layers, namely, regional crustal stability, sealing
capability of caprock and hydrogeological conditions. There is a total of
10 evaluation indicators.
(1) The regional crustal stability of the sedimentary basin directly
affects the geological safety of CO2 geological storage and is the most
important risk factor of CO2 geological storage. The regional crustal
stability is evaluated on the basis of three indicators, namely, seismic
peak ground acceleration, historical seismic activity and active faults.
Seismic peak ground acceleration and historical seismic activity
directly reflect the crustal stability of the secondary tectonic units in the
Junggar Basin. Among them, seismic peak ground acceleration refers to
the horizontal acceleration corresponding to the maximum earthquake
response spectrum of an earthquake. The distribution of the seismic
peak ground acceleration in Junggar Basin (Fig. 2) was constructed
based on the "China Ground Motion Parameter Zoning Map".
The active faults refer to the faults that have been active since the
late Pleistocene, especially since the Holocene, and have the ability to
produce moderate-strong earthquakes. The active faults can cause CO2
to escape into the atmosphere and enhance the risk of CO2 leaking from
the reservoir. Once the CO2 in the reservoir leaks through faults, it will
4.2. Evaluation of storage capability suitability
The evaluation indicator of storage capability includes four sublayers, the tectonic unit size, reservoir conditions, geothermal geological conditions and storage potential. There are 13 evaluation indicators for this indicator layer.
(1) Tectonic unit size is a direct factor affecting CO2 storage. The
sub-indicator includes the area of tectonic unit, sedimentary formation
thickness and resource potential.
The area of the tectonic unit directly affects the reservoir system
scale, thus affecting the CO2 storage potential. The Junggar Basin is
divided into six primary tectonic units and 44 secondary tectonic units,
with a total area of approximately 135,000 km2. The tectonic unit size
is graded according to the area of each secondary tectonic unit.
Based on data from oil exploration wells in the Junggar Basin, the
stratigraphic deposition of secondary the tectonic units was interpreted.
Each secondary tectonic unit was evaluated and graded according to
the depth that suitable for the CO2 geological storage. The Junggar
65
International Journal of Greenhouse Gas Control 78 (2018) 62–72
Z. Mi et al.
Fig. 2. Distribution of the seismic peak ground acceleration.
exploitation. It is also one of the important standards for the maturity of
sedimentary basins. The potential for oil and gas resources can reflect
whether the sedimentary basin has good CO2 geological storage reservoirs, storage space and tectonic stratigraphic trapping ability. To a
Basin geological cross sections are shown in Fig. 4 (Yang et al., 2011b),
and the locations of the section lines are shown in Fig. 1.
The potential for oil and gas resources is an important evaluation
indicator of oil and gas geological reserves and the prospect of
Fig. 3. Distribution of the main active faults in the Junggar Basin.
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International Journal of Greenhouse Gas Control 78 (2018) 62–72
Hydraulic migration-escape
Hydraulic migration-escape
Hydraulic seal
Hydrogeological condition
Permeability (mD)
Secondary sealing capacity above
the main caprock
Hydrodynamic action
< 0.0001
Multiple groups, good quality
(50, 100)
Relatively continuous, relatively
stable
(0.0001, 0.001)
Multiple groups, moderate
quality
Hydraulic jam-up
Caprock thickness (m)
Continuity of caprock distribution
Burial depth of caprock (m)
Caprock lithology
Sealing capability of
caprock
certain extent, it also determines the CO2 geological storage potential.
In general, the amount of petroleum resources in the Junggar Basin
gradually decreases from the Jurassic to the Permian, Triassic,
Carboniferous, Cretaceous, Paleogene and Neogene lines. The petroleum resources are most abundant in the Permian, Triassic and Jurassic
strata. Similarly, natural gas resources are also distributed in the
Permian, Triassic and Jurassic strata. In the northwestern marginal step
zone, Luliang Uplift, Mosuowan-Mobei Uplift, Dabasong Uplift, and
Cheguai Uplift, there are large accumulations of oil and gas. These areas
are important sites for the formation of large-scale oil and gas fields.
Based on the related studies in the Junggar Basin (He et al., 2004;
Kuang and Qi, 2006), the distribution of the reservoirs within each
tectonic unit in the study area is plotted (Fig. 5).
(2) The evaluation indicators of the sub-indicator layer of reservoir
evaluation is composed of the depth, lithology, thickness, porosity and
permeability of the reservoir rock. The theoretical depth of supercritical
CO2 geological storage is more than 800 m, but the excessive depth will
increase the difficulty and cost of project implementation. The rock
properties have a significant effect on the size of the reservoir space.
The major reservoir lithology consists of clastic rocks and carbonate
rocks. Reservoir thickness is also an important parameter affecting the
storage capacity. The larger the reservoir thickness is, the higher the
storage capacity. Porosity and permeability are important parameters
for reservoir evaluation. The higher the porosity and permeability are,
the more conducive the reservoir is to CO2 geological storage.
The reservoirs in the basin are mainly concentrated in the Jurassic
strata. The thickness distribution of the Cretaceous reservoirs is small,
and these reservoirs are thinner than the Jurassic reservoirs. The
Tertiary reservoirs are only distributed in the southern basin with very
limited areas. The favorable CO2 reservoirs are mainly the Jurassic
reservoirs, followed by the Cretaceous reservoirs, and the Tertiary reservoirs are unfavorable. The Jurassic reservoirs are divided into five
formation groups, Badaowan Formation, Sangonghe Formation,
Xishanyao Formation, Toutunhe Formation and Qigu Formation, all of
which are sandstone reservoirs. The CO2 storage capacities of the
Jurassic and Cretaceous reservoirs account for approximately 80% of
the total basin reserves.
(3) Geothermal geological condition indicators include land surface
temperature, geothermal gradient and terrestrial heat flow. These indicators have a significant impact on the CO2 storage capacity, storage
safety and engineering costs.
Under normal conditions, the ideal CO2 geological storage state is a
supercritical fluid state. The pressure and temperature of the reservoir
are the direct factors controlling the state of CO2 in the reservoir.
It is difficult to obtain the temperature data of the deep reservoir in
the actual evaluation work. Therefore, the reservoir temperature is
generally calculated according to the formula Ts = Tc + G × D (where
Ts is the reservoir temperature(°C), Tc is the temperature of the land
constant temperature layer(°C), G is the geothermal gradient(°C/
1000 m) (Fig. 6), and D is the reservoir depth(m)) (Rao et al., 2013).
However, in the actual area evaluation, the temperature of the constant
temperature layer is also difficult to obtain. However, the land surface
temperature is easy to obtain and close to the temperature of the constant temperature layer. Therefore, the land surface temperature is used
instead of the temperature of the constant temperature layer. CO2
density increases with increasing pressure and decreasing temperature.
The lower the ground temperature gradient and the land surface temperature are, the lower the reservoir temperature is, which is favorable
for CO2 geological storage.
The terrestrial heat flow is a direct indication of the heat in the
earth, reflecting the overall geothermal condition in the region and
controlling the overall thermal environment of the reservoir (Wang
et al., 2000). The smaller the value of terrestrial heat flow is, the
smaller the heat exchange is in reservoirs, resulting in a small temperature variation. These conditions keep the reservoir temperature
stable with a high CO2 density, which is conducive to CO2 geological
Hydraulic jam-up
> 0.1
No
M >7
Located in a large active fault zone;
fracture activity is strong
< 800 or > 3500
Cracked limestone, clastic
sandstone
< 10
Not continuous, unstable
5∼6
Small-scale active fracture;
activity is weak
(800, 1000)
Argillaceous siltstone,
argillaceous sandstone
(10, 30)
Relatively discontinuous,
relatively unstable
(0.01, 0.1)
One group, moderate quality
M<5
Close to the active fracture; no
active fracture penetration
(2000, 2700)
Sandy mudstone, sandy siltstone
Earthquake gap
Away from the active fault zone;
no active fault penetration
(1000, 2000)
Gypsum, mudstone, calcareous
mudstone
> 100
Continuous and stable
5-6
Active fracture penetration,
but weak activity
(2700, 3500)
Silty mudstone, sandy
mudstone
(30, 50)
Continuous and stable in
general
(0.001, 0.01)
One group, good quality
> 0.20
0.15-0.20
0.10-0.15
0.05-0.10
Seismic peak ground acceleration
(g)
Historical seismic activity
Active faults
Regional crustal stability
< 0.05
Indicator
Sub-indicator layer
Table 2
Grading standards for the geological safety suitability.
A
B
C
D
E
Z. Mi et al.
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Z. Mi et al.
Fig. 4. Geological cross section of the Junggar Basin (Yang, 2009).
Fig. 5. Distribution of the main oil and gas reservoirs in the Junggar Basin.
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International Journal of Greenhouse Gas Control 78 (2018) 62–72
Z. Mi et al.
Fig. 6. Distribution of the geothermal gradient in the Junggar Basin (°C / 1 km).
(1) Social environmental condition indicators include population
density and land use type.
A CO2 geological storage project has potential risks and impacts on
safety of the ecological environment and personal health., It will cause
extremely serious consequences that once a large-scale CO2 leaks from
reservoir in a short time in densely populated areas and the areas not
conducive to the CO2 diffusion. To minimize the potential risks of CO2
geological storage, nontechnical factors such as population density and
land use type require special consideration. CO2 geological storage sites
should be selected as far away as possible from densely populated areas
and areas with high levels of land use. The areas with low population
densities (Fig. 7) and land use are more suitable for CO2 geological
storage.
(2) Economic conditions include the quantity of the carbon source
and the distance between the carbon source and the storage site.
The technical difficulty and economic cost of carbon capture have
important impacts on the implementation of a CO2 geological storage
project. A dense area of carbon release sources is favorable for reducing
the technical difficulty and economic cost of carbon capture. Due to the
particularity of the carbon source, the scale of the carbon source per
unit area is used as the evaluation indicator for the carbon source scale.
At the same time, the distribution of some large carbon release sources
such as thermal power plants and steel works are considered.
There is a distance between the storage site and the carbon source,
which also has an impact on the implementation of CO2 geological
storage. The closer the carbon source is to the storage site, the lower the
cost of transporting the CO2.
Referencing previous studies (Guo et al., 2015) and combining the
actual geological conditions, the grading standards of the evaluation
indicator for environmental and economic conditions are established
(Table 4).
storage.
(4) The storage capacity evaluation layer includes the theoretical
potential and the theoretical potential per unit area.
According to the working level and accuracy requirement, the assessment of CO2 geological storage potential in China is divided into
five level grades, the regional level, the basin level, the target zone
level, the site level, and the engineering injection level. Different grades
correspond to different CO2 storage potential evaluation methods (Guo
et al., 2015). This paper focuses on the basin-level storage potential
assessment. The storage potential is the theoretical total amount of CO2
that can be stored in the secondary tectonic units. The theoretical potential per unit area is the amount of CO2 stored per unit area of the
secondary tectonic units. The greater the theoretical potential and the
theoretical potential per unit area, the more favorable the unit is for
CO2 geological storage.
The reservoirs suitable for the geological storage of CO2 in the
Junggar Basin are oil reservoirs, gas reservoirs, deep saline aquifers and
coal seams. The total theoretical storage potential is approximately
21,200 × 106t. The first-level tectonic units with the greatest potential
for storage in the Junggar Basin are in the Central Depression, accounting for 46.29% of the total storage potential. In particular, there is
substantial storage potential in the northwestern region, followed by
the Luliang Uplift and Wulungu Depression, accounting for 30.62% and
11.75% of the total storage potential, respectively. The Eastern Uplift
and North Tianshan thrust belt have very little storage potential, accounting for only 1.52% and 0.91% of the total storage potential.
Based on the previous studies (Guo et al., 2015) and combined with
the actual geological conditions, the grading standards of each indicator
for Storage capability suitability are established (Table 3).
4.3. Evaluation of Environmental and economic condition suitability
The evaluation indicator layer of the environmental and economic
conditions includes the social environment and economic conditions,
with a total of 4 indicators.
69
International Journal of Greenhouse Gas Control 78 (2018) 62–72
Z. Mi et al.
Table 3
Grading standards for the suitability of storage capability.
Sub-indicator layer
Tectonic unit size
Reservoir
conditions
Geothermal conditions
Storage potential
Indicator
A
B
C
D
E
Area of tectonic unit (km )
Sediment thickness (m)
Resource potential
Burial depth of reservoir (m)
Reservoir thickness (m)
Reservoir lithology
> 5000
> 3500
Large
(800, 1700)
> 100
Clastic rock
(500, 1000)
(2500, 2500)
Moderate
(2700, 3500)
20-50
Carbonate rocks
> 25
> 50
<2
< 20
30-50
> 5000
> 150
(200, 500)
(800, 1600)
Relatively small
> 3500
10-20
Magmatic rocks, metamorphic rocks,
etc.
5–10
0.1–1
10–25
40–50
90–150
2–50
1–50
< 200
< 800
Small
< 800
< 10
Mudstone
Porosity
Permeability (mD)
Land surface temperature (°C)
Geothermal gradient (°C/1 km)
Terrestrial heat flow (mW/m2)
Theoretical potential (106t)
Theoretical potential per unit
area
(106t/100 km2)
(1000, 5000)
(1600, 2500)
Relatively large
(1700, 2700)
(50, 80)
Mixed clastic rocks and carbonate
rocks
20–25
10–50
2–3
20–30
50–70
2500-5000
100–150
2
5. Results of the suitability evaluation for CO2 geological storage
in the Junggar Basin
10–20
1–10
3–10
30–40
70–90
50–2500
50–100
<5
< 0.1
> 25
> 50
> 150
<2
<1
Formation and Xishanyao Formation all have good caprock. In addition
the Badaowan Formation has a good caprock in the basin with a large
thickness and distribution area. The caprocks of the other formations in
the basin are thin, the distribution areas are small, and the sealing
capabilities are poor. The Badaowan Formation, Sangonghe Formation
and Xishanyao Formation have large thicknesses and distribution areas
and are mainly composed of sandstone reservoirs. The porosities of
these three formations are between 12% and 22%, and their thicknesses
are generally over 100 m, making them favorable reservoirs for CO2
storage. Toutunhe Formation, Qigu Formation and Kelazha Formation
have small reservoir distribution areas, lack good caprocks and have
limited CO2 storage capacities. The Jurassic reservoirs are the main
reservoirs for CO2 storage in the basin.
From the bottom up, the Cretaceous strata are divided into four
reservoir-caprock combinations: the Qingshuihe Formation, the Hutubi
Formation, the Shengjinkou Formation, and the Lianmuqin Formation.
Based on the analysis results of each indicator of geologic safety,
storage capability and environmental and economic conditions for each
secondary tectonic unit, the comprehensive score of the suitability of
each secondary tectonic unit is obtained. Then, the comprehensive
score is normalized by the feature scaling method. According to the
normalized score, the suitability is divided into Grade A, Grade B,
Grade C, Grade D and Grade E. Table 5 shows the range of standards for
each suitability level. The suitability assessment results for all the secondary tectonic units are listed in Table 6, and the suitability zoning
map is shown in Fig. 8.
The best reservoir-caprock assemblages in the basin are mainly
Jurassic and Cretaceous formations.
In the Jurassic reservoir-caprock assemblage, the Sangonghe
Fig. 7. Distribution of the population density in the Junggar Basin.
70
International Journal of Greenhouse Gas Control 78 (2018) 62–72
Z. Mi et al.
Table 4
Grading standards of Environmental and economic conditions suitability.
Sub-indicator layer
Indicator
A
B
C
D
E
Social environment
Population density
(person/km2)
Land use type
< 25
25–50
50–100
100–200
> 200
Desert and other unused
land
> 20000
Grassland
Woodland
Arable land
10000–20000
1000-10000
100–1000
Residential areas and mining land, transport
land, water
< 100
Close
Relatively close
Moderate
Relatively far
Far
Economic conditions
Quantity of carbon source
(104t)
Distance to carbon source
6. Conclusions and suggestions
Table 5
Grading standards of the normalized score.
Suitability level
Grade E
Grade D
Grade C
Grade B
Grade A
Normalized score
0–0.2
0.2–0.4
0.4–0.6
0.6–0.8
0.8–1.0
This study evaluates the suitability for CO2 geological storage in the
secondary tectonic units of the Junggar Basin by establishing a CO2
storage suitability assessment indicator system. The main conclusions
are as follows:
There are four sets of caprock layers, including two sets in the
Qingshuihe Formation, one set in the Hutubi Formation and one set in
the Lianmuqin Formation. The caprocks in the other strata are thin. The
Qingshuihe Formation sandstone reservoirs are mainly distributed in
the northwestern and eastern parts of the Central Depression and have
sedimentary thicknesses of greater than 10 m up to tens of meters. The
Hutubi Formation sandstone reservoir is mainly distributed in the
Luliang Uplift and the eastern part of the Central Depression, with a
small distribution area. The Shengjinkou-Lianmuqin Formation reservoir is widely distributed in the Central Depression and Luliang
Uplift. These four formations are favorable reservoirs for CO2 storage in
the Cretaceous. The reservoir caprock assemblages in the Cretaceous
are poorer than those in the Jurassic in terms of distribution area and
thickness.
In general, the North Tianshan thrust belt and the eastern part of the
Eastern Uplift are the most unsuitable areas for CO2 geological storage.
The suitability of the Western Uplift, the western part of the Eastern
Uplift and the Wulungu Depression is low to moderate. The suitability
of CO2 geological storage in the Luliang Uplift and Central Depression is
good. Among them, the best suited areas are distributed in the southwestern part of the Luliang Uplift and the southeastern part of the
Central Depression.
(1) By referring to the domestic and international CO2 geological storage suitability evaluation methods, we construct an indicator
system for the CO2 geological storage suitability assessment with
three indicator layers and 27 indicators. In addition, the evaluation
criterion of each indicator was determined on the basis of the
geological conditions in the Junggar Basin. The evaluation method
for the suitability of CO2 geological storage in the basin combined
the analytic hierarchy process and fuzzy comprehensive evaluation.
(2) Based on the constructed evaluation indicator system and evaluation method, the Junggar Basin was selected as the research object,
and the suitability of all the secondary tectonic units in the Junggar
Basin are evaluated. According to the evaluation results, the Luliang
Uplift and the Central Depression area are favorable for CO2 geological storage. The southwestern part of the Luliang Uplift and the
southeastern part of the Central Depression have the most favorable
suitability.
(3) According to the evaluation results, the better reservoir-caprock
assemblages in the Junggar Basin are mainly in the Jurassic and
Cretaceous strata. The Jurassic Badaowan Formation, Sangonghe
Formation and Xishanyao Formation have the best storage suitability and are the main storage reservoirs in the Junggar Basin. The
Cretaceous Qingshuihe Formation, Hutubi Formation, Shengjinkou
Table 6
Results of suitability evaluation for the secondary tectonic units in Junggar Basin.
Secondary
construction unit
Normalized
score
Suitability level
Secondary
construction unit
Normalized
score
Suitability level
Wucaiwan Depression
Shazhang fault-fold belt
Beisantai Uplift
Jimsar Depression
Guxi Uplift
Gucheng Depression
Gudong Uplift
Mulei Depression
Qitai Uplift
Wutongwozi Depression
Heishan Uplift
Huangcaohu Uplift
Huangcaohu Uplift
Shishugou Depression
Dinan Uplift
Dishuiquan Depression
Shixi Uplift
Dibei Uplift
Sannan Depression
Xiayan Uplift
Sangequan Uplift
Yingxi Depression
0.693
0.532
0.603
0.640
0.274
0.274
0.389
0.200
0.124
0.194
0.193
0.390
0.294
0.354
0.690
0.659
0.810
0.777
0.810
0.810
0.756
0.662
Grade
Grade
Grade
Grade
Grade
Grade
Grade
Grade
Grade
Grade
Grade
Grade
Grade
Grade
Grade
Grade
Grade
Grade
Grade
Grade
Grade
Grade
Shiyingtan Uplift
Chepaizi Uplift
Hongche fault zone
Zhongguai Uplift
Wuxia fault zone
Kebai Fault zone
Sikeshu Depression
Qigu fault-fold belt
Huomatu anticline zone
Fukang fault zone
Shawan Depression
Monan Uplift
Fukang Depression
Penyijingxi Depression
Mosuowan Uplift
Mobei Uplift
Donghaidaozi Depression
Mahu Depression
Dabasong Uplift
Baijiahai Uplift
Hongyan fault zone
Suosuoquan Depression
0.614
0.385
0.420
0.409
0.347
0.318
0.151
0.000
0.199
0.177
0.715
0.779
0.966
0.778
0.800
0.790
0.754
1.000
0.765
0.750
0.268
0.429
Grade
Grade
Grade
Grade
Grade
Grade
Grade
Grade
Grade
Grade
Grade
Grade
Grade
Grade
Grade
Grade
Grade
Grade
Grade
Grade
Grade
Grade
B
C
B
B
D
D
D
E
E
E
E
D
D
D
B
B
A
B
A
A
B
B
71
B
D
C
C
D
D
E
E
E
E
B
B
A
B
B
B
B
A
B
B
D
C
International Journal of Greenhouse Gas Control 78 (2018) 62–72
Z. Mi et al.
Fig. 8. Evaluation results of the suitability for CO2 geological storage in the Junggar Basin.
Formation and Lianmuqin Formation are also favorable reservoirs
for CO2 storage.
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The evaluation indicator system, evaluation method and evaluation
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Acknowledgement
This work was financially supported by National Science and
Technology Major Project of China (grant No. 2016ZX05016-005), by
National Key Research and Development Project of China (No.
2016YFB0600804), and by a geological survey project (grant No.
121201012000150010). The paper also supported by Key Laboratory of
Groundwater Resources and Environment, Ministry of Education, Jilin
University; and by Key Laboratory of Water Resources and Aquatic
Environment of Jilin Province, Jilin University.
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