Near-future perspective of CO2 aquifer storage in Japan: Site selection and capacity

Energy 30 (2005) 2360–2369 www.elsevier.com/locate/energy

Near-future perspective of CO2 aquifer storage in Japan: Site selection and capacity Xiaochun Lia,*, Takashi Ohsumia, Hitoshi Koidea, Keigo Akimotob, Hironori Kotsubob a

CO2 Sequestration Research Group, Research Institute of Innovative Technology for the Earth, 9-2 Kizugawadai, Kizu-cho, Kyoto 619-0292, Japan b System Analysis Group, Research Institute of Innovative Technology for the Earth, 9-2 Kizugawadai, Kizu-cho, Kyoto 619-0292, Japan

Abstract Japan has started a 5-year national R&D project titled ‘Underground Storage of Carbon Dioxide’ to reduce CO2 emissions into the atmosphere. One of the targets of the project is to select a few preferred storage sites as candidates for large-scale demonstration tests in the next phase, and for commercial use in the near future. For this purpose, we have ranked the sites in terms of capacity potential and CO2 supply potential, both of which significantly affect the storage economics. Here, the supply potential for a storage site is characterized by the annual amount of the stationary emission sources and the site–source distance; that is, how much CO2 is available and how far away it is. In total, 69 sites on land and offshore and 113 fossil fuel fired power plants are being considered. Finally, using the data on capacities and supply potentials, the sites are graded into three ranks. As a result, a map that shows the rankings of each site has been made. The sites in rank 1 are recommended as nearfuture candidate sites. These sites have a comparatively large capacity and can obtain a reasonable amount of CO2 from nearby sources without requiring a main pipeline. q 2004 Elsevier Ltd. All rights reserved.

1. Introduction The potential impact of the rising concentration of carbon dioxide (CO2) in the atmosphere has become a global concern. The technical feasibility of CO2 aquifer storage has been proven by successful experiences in numerous underground natural gas storage projects, EOR schemes, and the commercial practice in Sleipner [1]. Encouraged by these facts and a huge potential storage capacity of 91.5 Btonnes * Corresponding author. Fax: C81 774 752 313. E-mail address: [email protected] (X. Li). 0360-5442/$ - see front matter q 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.energy.2004.08.026

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[2], Japan has started a 5-year national R&D project titled ‘Underground Storage of Carbon Dioxide’ [3]. One of the targets of this project is to select a few preferred storage sites as the candidates for large-scale demonstration tests and then for commercial implementation in the near future. The selection is based on economic and safety viewpoints. Here, we rank the potential sites in terms of their capacities and CO2 supply potential, both of which have a significant effect on storage economics. In particular, the supply potential with respect to a storage site is characterized by the annual amount of emissions and the site– source distance; that is, how much CO2 is available and how far away it is. Previously, Tanaka et al. [2] calculated the storage capacities of 69 sites. In this study, by adding some new sites and dividing the basins more finely, 82 sites are recognized. Then, the capacities of some sites are calculated as done by Tanaka et al. [2]. Based on the data of the CO2 annual emissions and locations of 113 fossil-fuel fired power plants, the supply potential for each site is also estimated. Then, we use the data of capacities and supply potential to grade the sites into three ranks and put them on a site-ranking map. The sites in rank 1 are recommended as near-future candidate sites. These sites have a relatively large capacity and can obtain a reasonable amount of CO2 supply from nearby sources nearly without building a main pipeline.

2. Capacity calculations 2.1. Potential storage sites Japan has a large area of sedimentary basins surrounding its numerous islands [4]. However, its stationary anthropogenic CO2 emission sources, including fossil fuel fired power plants and general industries, are mostly on four main islands: Hokkaido, Honshu, Shikoku and Kyushu [5]. Thus, the economically promising storage sites may be selected from the sedimentary basins on the land or offshore of these four islands. Fig. 1 shows the location of the 113 fossil fuel fired power plants in operation and under construction, and some of the major potential storage sites. The previous study by Tanaka et al. [2] classified the storage sites into four categories based on each site’s geologic structural features and estimated their storage capacities (Table 1). We follow their classification, but add some sites. Category 1: oil and gas reservoirs and neighboring aquifers. Thirteen sites were examined by Tanaka et al. [2], the locations of which are not shown in Fig. 1. Twelve of them are situated on land near the Japan Sea and close to sites IV-18 to IV-21 and the other one is offshore, just inside the site IV-21. These oil/gas reservoirs fields are not expected to become CO2 storage sites in the near future, because they are still active and might continue to be productive in the future with help of improvements in EOR technologies. Moreover, even if they are depleted, they can be used for natural gas storage, as pointed out by Tanaka et al. [2]. Thus, we exclude them from the sites to be ranked. Category 2: aquifers in anticlinal structures. Tanaka et al. [2,6] examined 16 sites on land and 13 sites offshore. All of them are in our site list for ranking, but only nine of them are marked in Fig. 1. Each of these nine sites has a capacity exceeding 50 Mtonnes that corresponds to 20 years of CO2 emissions from a medium-scale power plant. They are numbered II-1 to II-9 in the figure; the rest are labeled II-10 to II-29. Category 3: aquifers in monoclinal structures on land. Tanaka et al. [2] included in this category three currently operating natural gas fields of dissolved-in water type. They are marked as sites III-8, III-9, and

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Fig. 1. Location map of fossil fuel fired power plants and potential storage sites made by synthesizing fuel resource map of Japan [4] and location map of thermal power plants [5]. The storage sites of categories II, III and IV are indicated. Table 1 Numbers and capacity of the sites examined Categories

I II III IV a

Tanaka et al. [2]

Present

Numbers

Capacitya

Numbers

Capacitya

13 29 3 15

2.0 1.5 16.0 72.0

– 29 12 28

–

Capacity in Btonnes-CO2.

1.5 48.1 102.2

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III-12 in Fig. 1. We add nine sites to this category based on the fuel resources map of Japan in Ref. [5]. The added sites are bounded by coastlines, the 1000-m sedimentary isopaches and basin boundaries. Category 4: aquifers in monoclinal structures offshore. Tanaka et al. [2] divided the offshore basins into 15 areas based on a distribution map of sedimentary basins surrounding Japan with a scale of about 1:10,000,000 [7]; here, we divide the offshore basins into 28 sites based on the fuel resources map of Japan with a scale of 1:5,000,000. This map has more information on basin distribution and thickness, enabling a finer division than that in Tanaka et al., and also has sea depth isograms. In our map, the sites of this category are bounded by coastlines, 1000-m sedimentary isopaches, and 500-m sea depth isograms. 2.2. Storage capacity calculations For the sites in category II, Tanaka et al. [2] calculated the capacity based on the assumption that they had an ability to trap supercritical CO2 (called supercritical-based storage). In the present study, we follow their storage estimates without recalculation. The capacities of sites III-8, III-9 and III-12, are also cited from Tanaka et al. [2,6] without recalculations. The capacities of the other nine sites of category III and all sites in category IV are calculated in the same way as Tanaka et al. [2], but we use different parameters as follows. Fig. 2 shows the geometry of a site. A site is bounded on the sides by vertical surfaces through coastline, the 1000-m sedimentary isopach, and/or the 500-m sea-depth isogram. At its top is the 500-m isopachous surface, and at the bottom are the 3000-m sedimentary isopachous surface and/or basement. Because the aquifers in monoclinal structures cannot constrain gaseous or supercritical CO2, we assume that the stored CO2 is all dissolved in the formation water (called dissolution-based storage). Its capacity can be estimated using S Z AhhFEf Rr

Fig. 2. Dividing a site into blocks. The blocks shadowed are considered to contribute to the storage.

(1)

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where S A h h F Ef R r

storage capacity (g-CO2) area (m2) stratum thickness (m) effective aquifer ratio (fraction), defined as the ratio of effective aquifer thickness to h porosity (fraction) sweep efficiency (fraction) CO2 solubility in water (N m3/m3) density of CO2 at 0 8C and 1 atm (g/N m3)

The calculation procedures are outlined as follows. A site is divided into blocks as shown in Fig. 2. The capacity of each block is then calculated using its temperature and pressure, the summation of which is the capacity of the site S Z S1 C S2 C S3

(2)

S1 Z A1 hFEf r500½R500 C 0:75R1000 C 0:25R1500 

(3)

S2 Z A2 hFEf r500½R500 C R1000 C R1500 C 0:75R2000 C 0:25R2500 

(4)

S3 Z A3 hFEf r500½R500 C R1000 C R1500 C R2000 C R2500 

(5)

where A1 area between 1000 and 2000-m isopaches A2 area between 2000 and 3000-m isopaches A3 area corresponding to a depth of 3000 m or more R500 CO2 solubility under the pressure, temperature, and salinity of the ocean at 500-m depth. The information on the aquifer characteristics is very limited. The above parameters for each site are evaluated based on the data from a few nearby wells, if available. The effective aquifer ratio h ranges from 0.075 to 0.1 and porosity F ranges within 0.15–0.25. Following Tanaka et al. [2], the sweep efficiency Ef is designated as 0.5 for all sites. Evaluation of the solubility requires data on the temperature, pressure, and salinity in the subsurface for each site. The subsurface temperature is estimated from the annual average temperature data of ground surface released by JODC [8] and a ground temperature gradient map [9]. The pressure in the subsurface is assumed to increase normally with depth. Following Tanaka et al. [2], we assume a salinity of 29,800 ppm for all sites. With these data and referring to the results on CO2 solubility measured under various temperatures, pressures, and salinities [10], the solubility for each site at different depths is obtained. The total capacities for each category are tabulated in Table 1 together with those by Tanaka et al. [2] for comparison. For category III, the total capacity includes those of the three sites examined by Tanaka et al. [2]. Our capacity data are apparently larger, mainly due to more sites included in our calculations and partially due to the difference in the value of the parameters.

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Fig. 3. CO2 supply potential for the sites of category II. The dotted line (A–B) and broken line (B–C) indicated the emission criteria.

2.3. Supply potential statistics We compiled the supply potential statistics for 69 sites. For a site, the distances to all emission sources within 100 km were estimated. Here, the site–source distance is defined as the shortest distance between the source and the boundary of the site. With these data and the annual emissions known, we can determine how much emission is available within different distances. Then, we determine the emission– distance curve for each site (Fig. 3).

3. Site ranking With a huge storage potential in comparison to the annual emission of 587 Mtonnes in 1999 from stationary sources, aquifer storage should be a promising option for CO2 emission control. However, this does not mean that all sites examined can be used immediately; this is because the cost efficiency is highly site-specific. The factors affecting storage economics of a site include its injectivity, its capacity, and the supply potential, among other factors. Because we lack sufficient geologic information, we exclude the injectivity from our discussions at this stage in spite of its importance. However, the capacity and supply potential are considered in the site ranking. In total, 69 sites are evaluated, and their capacities range widely from 1.0 Mtonnes to 24.5 Btonnes. Forty-nine of them have a capacity exceeding 50 Mtonnes, which equals the emission from a mediumscale power plant over 20–25 years. With so many larger sites available, the 20 smaller sites might not be considered as storage candidates in the near future, because storage in them could lead to a higher unit cost and contribute less to emissions reduction. In view of these considerations, the sites with a capacity smaller than 50 Mtonnes are put in rank 3 with lowest priority as near-future candidates (Table 2).

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Table 2 Ranking criteria Criteria Capacity

a

Emissionb

Categories

Rank 1

Rank 2

Rank 3

II, III, IV

R50 and E50R2

R50 and E50!2 and E100R2

!50 or E100!2

E0R2

E0!2 and E50 R2

E50!2

II III IV

a

In Mtonnes-CO2. In Mtonnes-CO2/year. Ed is the annual emission from the sources within a distance of d. E0 is that inside or on the boundary of a site. b

Table 3 Capacities and supply potentials of the sites in rank 1 No.

Capacitya (Mtonnes)

Supply potentials (Mtonnes/year) E0

II-4 II-5 II-6 Sum

E50

E100 15.4 5.6 15.4

67.0 141.0 81.0 289.0

0.0 0.0 1.9

3.7 3.7 11.7

III-4 III-8 III-9 III-11 Sum

6785.2 2877.0 12351.0 967.6 22980.8

4.3 9.8 51.0 7.5

5.3 17.3 51.0 7.5

IV-5 IV-14 IV-18 IV-19 Sum

5412.6 10044.0 1196.2 7111.4 23764.2

2.2 27.4 4.7 15.4

4.3 36.6 9.4 17.1

a

Total capacity is 47.0 Btonnes.

The remaining sites are further ranked in terms of their supply potential. A site with a larger amount of CO2 emissions that can be supplied from nearer sources could rank higher. We designate the sites as rank 3 if they have a larger capacity (R50 Mtonnes), but do not have any medium-scale emission sources within 100-km distance for the sites of category II (E100!2 Mtonnes) and 50-km distance for sites of categories III and IV. Here, the sites of category II are treated differently from categories III and IV, because the category II sites can store supercritical CO2 and thus have better injectivity, which leads to a lower injection cost. The criteria for ranks 2 and 3 are decided following same ideas as the above (Table 2). As a result, 11 sites are in rank 1, 12 sites are in rank 2, and 46 are in rank 3. Table 3 lists the sites in rank 1, with a total capacity of 47 Btonnes, and Fig. 4 shows the distribution of the sites in all three ranks.

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Fig. 4. Map of site ranking.

4. Conclusions The concept of CO2 aquifer storage has been generally confirmed. However, Japan needs to refine the concept further based on the particular natural and industrial situations. This should be done in the coming years to fulfill the obligations in the Kyoto Protocol. The refinement of the concept depends on the extent to which we can answer (1) how much, (2) where, (3) in what way, (4) at what cost, and (5) how safe can CO2 can be stored in Japan. The investigations here should help to answer the first three questions and also should reveal some important issues. We will constrain the discussions to the nearfuture issues. Therefore, our discussions will be based on the data associated with the sites in rank 1. Fig. 4 shows that the 11 sites in rank 1 are distributed in five regions that are listed in Table 4. For each region, the total capacity, CO2 supply potential within different distances, and the ratio of the capacity to the supply potential are also given in the table. These data suggest the following: (1) Japan has a huge storage potential that is economical due to low transportation costs. For example, Japan can store the CO2 emitted from nearby sources in this century, and even beyond. In the near

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Regions

Sites

Capacity (S)

(Mtonnes) Southwest Hokkaido Niigata

Joban Toyama Kanto Sum

Source amounts

Annual CO2 supply (Mtonnes/year)

E0

E10

III-4, IV-5

12197.8

5

4.3

II-4, II-5, II-6, III-8, IV-19 IV-14 III-11, IV-18 III-9 11

10277.4

4

1.9

10044.0 2163.8

9 4

27 7.5

12351.0 47034.0

13 25

51 92

E20 4.3

E30 4.3

E00 5.3

S/E ratios (years)

E50 5.3

S/E0 5.3

15

15

15

15

17

27 7.5

27 7.5

37 7.5

37 7.5

37 7.5

51 106

51 106

51 116

51 116

51 118

S/E10

S/E20

S/E30

S/E40

S/E50

2837

2837

2837

2301

2301

2301

5409

667

667

667

667

601

367 289

367 289

367 289

274 289

274 289

274 289

242 511

242 445

242 445

242 406

242 406

242 400

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Table 4 Capacities and emissions in major regions

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future, the amount of storage, with a low transportation cost, could be around 100 Mtonnes. This amount exceeds the 70 Mtonnes that is 6% of 1990s emission of Japan, the CO2 cutting target in the Kyoto Protocol. (2) The Niigata–Toyama and the Joban–Kanto regions could have priority over the others, because they have huge capacities and also better CO2 supply potentials (Fig. 4, Table 4). (3) The sites of categories III and IV are associated with the dissolution-based storage, whereas the sites in category II are supercritical-based storage. In total, the three sites of category II in rank 1 only has a capacity of 289 Mtonnes, which is just 0.6% of the total capacity of all sites in rank 1 (Table 3). Thus, dissolution-based storage could be a major storage method in the near future and could later develop into the primary method. However, compared with supercritical storage, dissolution-based storage has not been well studied in laboratory and in the field. More attention should be paid to dissolution-based storage to decrease the gaps between theory, simulation, and practical implementations.

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