Evaluation of the potentiality and suitability for CO2 geological storage in the Junggar Basin, northwestern China

International Journal of Greenhouse Gas Control 78 (2018) 62–72

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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

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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.,

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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: [email protected] (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.

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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

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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

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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

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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. 66

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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

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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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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

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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

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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

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B D C C D D E E E E B B A B B B B A B B D C

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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.

183–193. Gaede, J., Meadowcroft, J., 2016. Carbon capture and storage demonstration and low-carbon energy transitions: explaining limited progress. The Palgrave Handbook of the International Political Economy of Energy. Palgrave Macmillan, London, pp. 319–340. Guo, J., Wen, D., Zhang, S., Xu, T., Li, X., Diao, Y., Jia, X., 2015. Potential and suitability evaluation of CO2 geological storage in major sedimentary basins of China, and the demonstration project in Ordos Basin. Acta Geol. Sin. 89, 1319–1332. He, D., Chen, X., Zhang, Y., Kuang, J., Shi, X., Zhang, L., 2004. Enrichment characteristics of oil and gas in Jungar Basin. Acta Petrolei Sinica 25, 1–10. Kuang, J., Qi, X.-f., 2006. The structural characteristics and oil-gas explorative direction in Junggar foreland basin. Xinjiang Pet. Geol. 27, 5–9. Li, D., He, D., Santosh, M., Ma, D., Tang, J., 2015. Tectonic framework of the northern Junggar Basin part I: the eastern Luliang uplift and its link with the East Junggar terrane. Gondwana Res. 27, 1089–1109. Oldenburg, C.M., Lewicki, J.L., Dobeck, L., Spangler, L., 2010. Modeling gas transport in the shallow subsurface during the ZERT CO2 release test. Transp. Porous Media 82, 77–92. Qu, G., Ma, Z., Zhang, N., Li, T., Tian, Y., 2008. Fault structures in and around Junggar Basin. Xinjiang Pet. Geol. 29, 290–295. Rao, S., Hu, S., Zhu, C., Tang, X., Li, W., Wang, J., 2013. The characteristics of heat flow and lithospheric thermal structure in Junggar Basin, northwest China. Chin. J. Geophys. 56, 2760–2770. Rostron, B., White, D., Chalaturnyk, R., Sorenson, J., Hawkes, C., Worth, K., Young, A., 2015. An overview of the aquistore project: Canada’s first CO2 storage project associated with a commercial-scale coal-fired power plant. International Conference Exhibition. Song, T., Wen, Y., Zhang, W., Rao, W., Meng, J., Fan, J., Gao, R., 2017. Suitability assessment of geological sequestration of CO2 in Songliao Basin based on gray relational analysis method. Geol. Bull. China 36, 1874–1883. Su, X., Xu, W., Du, S., 2013. Basin‐scale CO2 storage capacity assessment of deep saline aquifers in the Songliao Basin, northeast China. Greenh. Gases Sci. Technol. 3, 266–280. Verdon, J.P., Kendall, J.-M., Stork, A.L., Chadwick, R.A., White, D.J., Bissell, R.C., 2013. Comparison of geomechanical deformation induced by megatonne-scale CO2 storage at Sleipner, Weyburn, and in Salah. Proc. Natl. Acad. Sci. 110, E2762–E2771. Wang, S., Hu, S., Wang, J., 2000. The characteristics of heat flow and geothermal field in Junggar Basin. Chin. J. Geophys. 43, 816–824. Wang, F., Jing, J., Xu, T., Yang, Y., Jin, G., 2016. Impacts of stratum dip angle on CO2 geological storage amount and security. Greenh. Gases Sci. Technol. 6, 682–694. Yang, Z., 2009. Hydrocarbon Accumulation Mechanisms Near the Top Overpressured Surface in Central Junggar Basin, Northwest China. China University of Geosciences. Yang, H., Chen, L., Kong, Y., 2004. A novel classification of structural units in Junggar Basin. Xinjiang Pet. Geol. 25, 686–688. Yang, G., Su, X., Du, S., Xu, W., Meng, J., Gao, D., 2011a. Suitability assessment of geological sequestration of CO2 in Songliao Basin. Diqiu Xuebao 32, 570–580. Yang, Z., Wang, J., Lin, S., Wu, S., Liu, Y., Li, Q., Zhang, P., 2011b. Hydrocarbon accumulation mechanism near top overpressured surface in central Junggar Basin. J. China Univ. Pet. 3, 006. Zhang, Z., Huisingh, D., 2017. Carbon dioxide storage schemes: technology, assessment and deployment. J. Clean. Prod. 142, 1055–1064.

The evaluation indicator system, evaluation method and evaluation result will provide a scientific basis for further screening of the CO2 geological storage site in the Junggar Basin. 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. References Bachu, S., 2003. Screening and ranking of sedimentary basins for sequestration of CO2 in geological media in response to climate change. Environ. Geol. 44, 277–289. Bachu, S., Shaw, J., 2003. Evaluation of the CO2 sequestration capacity in Alberta’s oil and gas reservoirs at depletion and the effect of underlying aquifers. J. Can. Pet. Technol. 42, 51–61. Buckman, S., Aitchison, J.C., 2004. Tectonic Evolution of Palaeozoic Terranes in West Junggar, Xinjiang, NW China. Geological Society, London, pp. 101–129 Special Publications 226. Chen, X., Lu, H., Shu, L., Wang, H., Zhang, G., 2002. Study on tectonic evolution of Junggar Basin. Geol. J. China Univ. 8, 257–267. Coninck, H.D., Loos, M., Metz, B., Davidson, O., Meyer, L., 2005. IPCC Special Report on Carbon Dioxide Capture and Storage. Intergovernmental Panel on Climate Change. Diao, Y., Zhang, S., Guo, J., Li, X., Zhang, H., 2011. Geological safety evaluation method for CO2 geological storage in deep saline aquifer. Geol. China 38, 786–790. Diao, Y., Zhang, S., Guo, J., Li, X., Fan, J., Jia, X., 2012. Reservoir and caprock evaluation of CO2 geological storage site selection in deep saline aquifers. Rock Soil Mech. 33, 2422–2428. Du, S., Su, X., Xu, W., 2016. Assessment of CO2 geological storage capacity in the oilfields of the Songliao Basin, northeastern China. Geosci. J. 20, 247–257. Feng, G., Xu, T., Tian, H., Lu, M., Connell, L.D., Lei, H., Shi, Y., 2017. Three-phase non-isothermal flow behavior of CO2-brine leakage from wellbores. Int. J. Greenh. Gas Control. 64,

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