Scholarly article on topic 'Evaluation of CO2 Aquifer storage capacity in the vicinity of a large emission area in Japan: Case history of Osaka Bay'

Evaluation of CO2 Aquifer storage capacity in the vicinity of a large emission area in Japan: Case history of Osaka Bay Academic research paper on "Earth and related environmental sciences"

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{"storage capacity" / "saline aquifers" / "storage model" / "storage aquifer" / "seal formation" / Japan}

Abstract of research paper on Earth and related environmental sciences, author of scientific article — Tsutomu Hashimoto, Shin-ichi Hiramatsu, Takashi Yamamoto, Hitoshi Takano, Manabu Mizuno, et al.

Abstract Possibility of CO2 geological sequestration was studied in the Osaka Bay, one of major CO2 emission sources in Japan. Based upon the facies distribution in thick formations of the Osaka Group, a geological model of CO2 sequestration was constructed and the aquifer structure and the storage effective of a possible storage aquifer were evaluated. It was made clear that the preliminary storage capacity in the Osaka Bay would be sufficient to store emitted CO2 in the area.

Academic research paper on topic "Evaluation of CO2 Aquifer storage capacity in the vicinity of a large emission area in Japan: Case history of Osaka Bay"

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Energy Procedia 1 (2009) 2701-2708

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GHGT-9

Evaluation of CO2 Aquifer storage capacity in the vicinity of a large emission area in Japan: Case history of Osaka Bay

Tsutomu Hashimoto3 *, Shin-ichi Hiramatsub, Takashi Yamamoto0, Hitoshi Takanod, Manabu Mizuno6, and Hideaki Miidaf

a Suncoh Consultants Co. Ltd., Tokyo, Japan (former Engineering Advancement Association of Japan (ENAA)) bOyo Corporation, Saitama,Japan "Kawasaki Geological Engineering Co. Ltd., Tokyo, Japan dDia Consultants Co. Ltd., Saitama, Japan ' Japan Petroleum Exploration Co., Ltd.,Tokyo, Japan (former Research Institute of Innovative Technology for the Earth (RITE)) Engineering Advancement Association of Japan (ENAA), Tokyo, Japan

Abstract

Possibility of C02 geological sequestration was studied in the Osaka Bay, one of major C02 emission sources in Japan. Based upon the facies distribution in thick formations of the Osaka Group, a geological model of C02 sequestration was constructed and the aquifer structure and the storage effective of a possible storage aquifer were evaluated. It was made clear that the preliminary storage capacity in the Osaka Bay would be sufficient to store emitted C02 in the area.

© 2009 Elsevier Ltd. All rights reserved.

Keywords: storage capacity; saline aquifers; storage model; storage aquifer; seal formation,Japan

1. Introduction

This paper describes a part of the results in a research project called "Research and Development of Underground Storage Technology for Carbon Dioxide [1]" which was funded by the Ministry of Economy, Trade and Industry of Japan, and carried out by the Research Institute of Innovative Technology for the Earth (RITE) in cooperation with the Engineering Advancement Association of Japan (ENAA) during fiscal years of2006 to 2008.

As a means of reducing global warming due to greenhouse gas effects, attention has been paid to a technology called CCS

(Carbon Dioxide Capture and Storage), and investigations and researches into candidate sites of C02 geological sequestration and their storage potentials have been recently conducted in many countries. In Japan, in a research project of "Research and Development of Underground Storage Technology for Carbon Dioxide", Takahashi et al. re-evaluated the storage capacity of C02 in deep saline aquifers [2]. This re-evaluation was, with additional geological data newly obtained in the exploatory seismic and wells and new findings, a review of the previously estimated storage capacity of about 90Gt-C02 calculated by Tanaka et al. [3] based on the geological data in fundamental oil and gas investigations. Takahashi et al. showed storage capacities of 30.1 Gt-C02 in saline aquifers with anticlinal structures, and the total amount of 146.1 Gt-C02 including deep saline aquifers with stratigraphic and structural traps.

On the other hand, when considering the economic side of the CCS technology, matching between C02 emission sources and storage sinks becomes important. It is known that in Japan transportation cost is comparatively high [1]. If storage potential can be identified in the vicinity of emission sources, it is very promising for CCS technology to materialize. However, most emission sources are concentrated in inland seas and coastal areas, and the exploatory seismic and wells for oil

* Corresponding author. Tel.: +81-3-3683-7101; fax: +81-3-3683-7222. E-mail address: t.hashimoto@suncoh.co.jp doi:10.1016/j.egypro.2009.02.039

and natural gas have not been carried out in these areas in the national scale. They were 'unexplored' areas in the reevaluation by Takahashi et al. [2].

For this reason, investigations on storage potential near major emission sources were conducted as part of the project "Research and Development of Underground Storage Technology for Carbon Dioxide." Based on the published geological data, the existence of aquifer formations and seal formations, their distributions and the storage properties were studied in 4 representative areas with large emission sources, viz. in Tokyo Bay, Ise Bay, Osaka Bay, and northern part of Kyushu, and preliminary storage capacities at each area were calculated. Of the 4 areas studied, a case history of the Osaka Bay is introduced here.

2. General view of Osaka Bay and possibility of C02 sequestration

2.1. General view of Osaka Bay

Osaka Bay is an oval sea with an area of about 1,400 km2, surrounded by 500 to 1,000m high mountains such as Rokko, Ikoma, Kongo, and Izumi mountain chains, as well as by hills, highlands, lowland like Osaka Plane and Awaji Island. Osaka Bay area is the second largest urban area in Japan, next to Tokyo metropolitan area, and is one of the large CO2 emission areas. Along the coastline, there are oil power generating stations and steel plants, emitting about 5Mt-C02 annually.

2.2. Possibility of CO2 sequestration in Osaka Bay

For a safe subsurface CO2 sequestration, it is imperative to have a saline aquifer with a high porosity, overlain by a formation of sedimentary rock which possesses sufficient sealing effective. For the Japan Islands located in the mobile belt of the Pacific Rim, this requirement may be satisfied by sedimentary rocks younger than Neocene epoch. While unlike stable geology found in North American or European countries, sedimentary rocks older than the Neocene epoch in Japan generally form complicated geological structures with high compactions and fissures, and are not suitable for geological sequestration of

A geological structural map around the Osaka Bay is shown in Figure 1. Thick formations of Tertiary Pliocene to Quaternary Pleistocene distribute in the subsurface of the Osaka bay. They are called the Osaka Group, and are composed of half- cemented to uncemented sediments of mainly clay, silt, sand and gravel. It is expected that they can be target aquifers for C02 sequestration.

Figure 1 Geological map around the Osaka Bay [4]

2.3. CO2 storage model based on the fades distribution in Osaka Group

A geological model of C02 sequestration based on the facies distribution in the Osaka Group is shown in Figure 2. The sedimentation sequence of the group has been extensively studied by Ichihara [5] and Kansai Geotechnical Information Usage Council [6]. According to their research results, the Osaka Group is divided into three (lowermost, lower and upper) parts with intercalated key beds of volcanic ash and marine clay (Ma-l to Ma 12). Their facies distribution changes, depending upon whether it is above or below the Ma-l (bottom marine clay) layer. The formations below Ma-l consist of fluvial deposits with a mixture of sandy gravel, sand and silt, while those above Ma-l are composed of alternating layers of thick

marine clay and fluvial sandy gravel and sand. Judging from the facies distributions, the fluvial deposits below Ma-l may be considered as aquifer formation, whereas the layers with frequent occurrence of thick marine clay above Ma-l may be considered as seal formation. It is considered here that multiple sealing layers act as a seal formation.

Figure 2 C02 storage model based on the facies of Osaka Group (added to [6])

3. Calculation of preliminary storage capacity

3.1. Procedure taken to calculate storage capacity

The procedure of storage capacity calculation in the Osaka Bay is shown in Figure 3. For the storage capacity estimation, mainly the following two studies were performed, taking the storage model shown in Figure 2 into consideration:

The first study was an evaluation of the Osaka Group as an aquifer structure. Collecting and sorting out the published geological maps, deep borehole data, and analysed cross sections from the reflective seismic surveys, geological assessment was carried out, evaluating the thicknesses of aquifer formation and seal formation, and their distributions. The other study was an evaluation of the storage effective of the Osaka Group. Using published deep borehole data as well as newly obtained laboratory test data, parameters such as sand to clay ratio and porosity were evaluated.

3.2. Existing geological data used in the evaluations

The following are main existing geological data in the Osaka Bay. Collecting and sorting out these data, detailed evaluations were carried out:

3.2.1. Reflective seismic survey

The locations of main seismic survey lines in the Osaka Bay are shown in Figure 4. In the offshore area, reflective seismic surveys have been carried out by the National Institute of Advanced Industrial Science and Technology (AIST, formerly Geological Survey of Japan) and the Hydrographie and Oceanographic Department of Japan (formerly Hydrographie Department of Japan). The research council on the Osaka Bay geotechnical information [7] and Inoue & Nakagawa [8] performed comprehensive interpretation of the analysed cross sections. Comparing the sections from different research institute with the gravity mapping data and so on, they reviewed inconsistencies among the results, and drew consistent cross sections.

3.2.2. Deep borehole

A typical deep borehole is the GS-K1 Higashinada borehole (1,700 m), which penetrates through the Osaka Group to basement rock. There are other deep borehole data available in coastal areas and onshore: GS-K2 (354m), GS-K3 (680m), GS-K4 (545m), YU (603m), OD-1 (667m), and OD-2 (667.5m). No offshore deep boreholes are available.

Figure 3 Flow chart of CO2 storage capacity estimation in the Osaka Bay area

134.9 E 135.0 Ê 135.1 E 135.2 E 135.3 E 135.4 E 135.5 E

Longitude (deg.)

Figure 4 Locations of main seismic lines in the Osaka Bay[7]

3.3. Evaluation of aquifer structure: thickness and area of aquifer

3.3.1. Aquifer thickness

To evaluate the aquifer thickness, multiple numbers of geological cross sections were constructed, linking the onshore area to the offshore area in the Osaka Bay. The geological cross sections of the Osaka Bay are shown in Figure 5. In the offshore area, the analysed cross sections of reflective seismic survey by the research council on Osaka Bay geotechnical information [7] were referred to, while in the onshore area geological cross sections by Ichihara [5] were connected. There are no geological data existing at the boundary between the offshore and onshore areas. Comparing the geology between offshore and onshore areas at the boundary of the lowermost part and the lower part, and the horizon of the Ma-1 layer, the data were then interpolated in such a way that geology would be consistent in the offshore and onshore areas.

Since CO2 is supposed to be sequestered in supercritical condition, the depth of the storage formation should be larger than 800m. To describe this, a contour line corresponding to -800m was marked in the constructed geological cross section, and the intersection points were obtained. In the formations locating below Ma-1, the portions lying deeper than the intersection correspond to targeted storage aquifer. The thickness of this portion may be read in the geological cross section as 1,000 to 1,500 m (1,200 m on average).

3.3.2. Aquifer area

Based on the constructed geological cross section and the geology map by Ichihara [5], a horizontal geological cross section was created at -800 m, straddling both offshore and onshore areas. The distribution extent of Ma-1, boundary between aquifer formation and seal formation, was then evaluated. Thus determined horizontal cross section at -800 m is shown in Figure 6.

It may be seen in the figure that at -800 m level formations above Ma-1 distribute approximately in the middle of the bay in an oval shape, with the west side boundary cut off by the Osaka Bay Fault. It is in this area that seal formation confines C02 in supercritical condition. The area covered by the seal formation (i.e., area surrounded by Ma-1) is about 400 km2. It may be noted that there is a region on the west side of the Osaka Bay Fault where the level of Ma-1 layer is deeper than -800 m, but it is not accounted for in the current evaluation.

3.4. Evaluation of storage effective: sand to clay ratio and porosity

3.4.1. Sand to clay ratio

Geological columns of borehole GS-K1 Higashinada to a depth of 1,700m are shown in Figure 7. Below Ma-1, there are alternating layers of silt and clay that are not suitable for C02 storage, and they must be excluded from the thickness of the entire aquifer formation. Since there are no deep boreholes available in the offshore area of the Osaka Bay, ratio of sand to clay (ratio of sand and gravel to clay and silt) was evaluated using the geological columns of GS-K1 Higashinada. As a result, coarse materials (sand and gravel) amounted to 57.8% of the total volume at depths between 692 and 1,546m. For storage capacity estimation the ratio was assumed as 50 %, and the effective thickness of aquifer formation was calculated to be 600 m (= average aquifer thickness 1,200 m x 0.5).

3.4.2. Porosity

In the borehole data from the GS-K1 Higashinada, porosity information, say from the Neutron log, were not obtained. Instead, laboratory core tests were carried out, and the porosity of cores corresponding to aquifer formation depth was determined to be 25 to 35%. In addition, laboratory tests on samples of the lowermost part of Osaka Group retrieved from a surface outcrop showed that the porosity was 33 to 35%. The latter values were considered overestimated due to the effect of weathering, and the lowest value (25%) was adopted for the storage capacity calculation.

4. Calculated storage capacity

Storage capacity was estimated using the following equation by Takahashi et al. [2]:

SfX-A x-h x 0 xSgï-BgC02 x/j

where S/ storage factor

A: aquifer area h: effective aquifer thickness 0 : porosity

Sg: saturation of supercritical C02 BgC02: volume factor of C02 p: C02 density at standard condition 0.001976 t/mJ

----------------------------------- (!)

0.25 400 km2

600 m (total thickness1,200m X sand to clay ratio 0.5)

0.00353

Storage factor, Sf, is the ratio of stored supercritical C02 volume to the total pore volume of the deep saline aquifer. Taking the effect of C02 buoyancy and heterogeneity of facies in the horizontal direction, Sf is assumed to be 25 % here. Saturation of supercritical C02 was assumed 50 %. Volume coefficient of C02, BgC02, was calculated using the average depth of aquifer formation(1,400 m) and average temperature of 60°C (from temperature log in GS-K1).

Using the evaluated parameters from the published geological data, and assumed parameters, a preliminary storage capacity of the Osaka Bay was calculated to be 4.2Gt- C02.

5. Conclusion

Possibility of C02 geological sequestration was studied in the Osaka Bay, one of major C02 emission sources in Japan. Based upon the facies distribution in thick formations of the Osaka Group, a geological model of C02 sequestration was constructed and the aquifer structure and the storage effective of a possible storage aquifer were evaluated. It was made clear that the preliminary storage capacity in the Osaka Bay would be sufficient to store emitted C02 in the area.

This study was performed based on the published seismic and deep borehole data, and the estimated capacity was preliminary. To obtain a practical storage capacity in the Osaka Bay, additional field investigation must be carried out. It is necessary to perform a series of comprehensive geological investigations (such as reflective seismic survey and deep borehole) in the area, obtaining missing information on facies in the aquifer formation and seal formation and property data. In addition, though not studied at the present time, an existing active fault called the Osaka Bay Fault on the West boundary of the assumed storage aquifer may affect the storage effective, exhibiting possible formation of leakage path. In the future, the way to treat the effect of the faults must be well studied in terms of evaluation method and offset distance.

In other countries than Japan, researches into CCS and demonstration tests are progressed, considering mainly sequestration in depleted oil and gas wells and into saline aquifers with anticlinal structures. In Japan, however, these structures do not exist in the vicinity of C02 emission sources, or are very small if they do. For CCS to become one of the promising options in reducing C02, sequestration in monoclinal saline aquifers near emission sources too have to be considered. It is necessary to build an unprecedented C02 sequestration model where C02 is stored safely in monoclinal saline aquifers as soon as possible, considering Japanese complicated geological conditions.

Figure S Geological cross section, taking C02 storage model into account

Figure 6 Sliced geological cross section at -800m, taking C02 storage model into account

Figure 7 Geological columns of borehole GS-K1 Higashinada to a depth of 1,700m [6]

References

1. The Research Institute of Innovative Technology for the Earth (RITE), Report on Research and Development of Underground Storage Technology for Carbon Dioxide, 2006,2007,2008.

2. Toshihiro Takahashi, Takashi Ohsumi, Kazuo Nakayama, Kazuo Koide, Hideaki Miida, Estimation of CO2 Aquifer Storage Potential in Japan, Proceedings of GHGT-9,2008.

3. Tanaka S., Koide H. and Sasagawa A., Possibility of underground C02 sequestration in Japan, Energy Convers. Mgmt.36, 527-530.1995.

4. Ichihara, M (editor), The Osaka Group, published by Sogensha,340pages, 1993 (in Japanese).

5. Ichihara, M. Osaka and surrounding areas in 1:125,000 Quaternary map, Urban Kubota, No.30, 1991 (in Japanese).

6. Kansai Geotechnical Information Usage Council, New Ground in Kansai area - between Kobe and Hanshin, 270 pages, 1988 (in Japanese).

7. The research council on the Osaka Bay geotechnical information, Ground in bay area and construction - Osaka Bay as anexample, 505 pages, 2002 (in Japanese).

8. Inoue, N. and Nakagawa, K. Modeling of the underground structure in the Osaka sedimentary based on geological interpretation of gravity anomalies and seismic profile, Jour.Geosci Osaka City Univ, 43, pp.97-110,2000.