R&D Activities ● CO2 Storage Research GroupRITE Today 2021

CO2 Storage Research Group
Members (As of Dec.2020)
Ziqiu Xue, Group Leader, Chief Researcher
Kenji Uchida, Deputy Group Leader, Chief Researcher
Satoru Yokoi, Chief Researcher
Makoto Nomura, Chief Researcher
Nobuo Takasu, Associate Chief Researcher
Takahiro Nakajima, Associate Chief Researcher
Takeshi Myoi, Associate Chief Researcher
Ryozo Tanaka, Associate Chief Researcher
Tsutomu Hashimoto, Senior Researcher
Saeko Mito, Senior Researcher
Yasuhiro Okabayashi, Senior Researcher
Tetsuma Toshioka, Senior Researcher
Osamu Takano, Senior Researcher
Keisuke Uchimoto, Senior Researcher
Hironobu Komaki, Senior Researcher
Atsushi Ibusuki, Senior Researcher
Nobutoshi Shimizu, Senior Researcher
Tsutomu Soejima, Senior Researcher
Yuji Watanabe, Senior Researcher

Yi Zhang, Senior Researcher
Hyuck Park, Senior Researcher
Jiro Suekuni, Senior Researcher
Satoko Fuchikami, Chief
Kimiko Nakanishi, Chief
Yankun Sun, Researcher
Takayuki Miyoshi, Researcher
Masafumi Kotani, Researcher
Takeya Nagata, Researcher
Rasha Amer, Researcher
Hiroto Yoshikawa, Researcher
Junko Hirai, Research AssistantShiori Tsuji, Research AssistantYuko Himi, Research AssistantAkemi Nishide, Research Assistant
Megumi Okumichi, Research Assistant
Megumi Sasaki, Research Assistant
Tokio Sasai, Research AssistantResearch and Development on Geological CO2 Storage for Safe CCSOperation
1. Introduction

large scale CO2 reservoirs.

In terms of capturing and sequestrating of CO2 from

Our development up to now has moved a number oflarge scale emission sources geological CO2 storage istechnologies into a stage of demonstration in theone of the most important options for achieving ambi-

fields: safety management systems for injection, as-tious net zero CO2 emission goals.

sessment/monitoring technologies for the stability of

The CO2 Storage Research Group as a member of theGeological Carbon Dioxide Storage Technology Re-

geological formations and an efficient injection technology.

search Association has conducted a project funded by

To contribute to large-scale CO2 storage, it is critical

the New Energy and Industrial Technology Develop-

to prove these technologies applicable for an actual

ment Organization (NEDO), called “Research and De-site at scale. The CO2 Storage Research Group has beenvelopment of CO2 Storage Technology to implement

working closely with universities and research institutes

safe CCS”.

internationally to move forward with technical demon-The project is in a technology development phasestration at large sites overseas.

for large-scale CO2 storage, which is qualified with safe

Highlighted in the following sections are our out-injection and storage of more than 1 Mt CO2/y understanding achievements in 2020: a microbubble CO 2

the ground. To achieve the goal, our group has been

injection technology, a safety management system fordeveloping technologies for safety management, effi-

CO2 storage (ATLS: Advanced Traffic Light System) andcient injection and effective resource utilization forsystems for CO2 leakage detection and marine envi-50

R&D Activities ● CO2 Storage Research GroupRITE Today 2021

ronmental impact assessment. We have developedcontour. The two core samples are comparable inthese technologies as systems with high practicability

terms of their pore space volume. Microbubble CO2 fills

and applicability. The microbubble CO2 injection tech-

the space more densely (upper panel of Figure 1) andnology will be applied to multiple overseas geologicalis injected and dissolved more (lower panel) than con-

CO2 storage sites, including that in North Dakota, USAventionally-injected CO2, so called normal bubble.

and that of the Junlun Petroleum Company in China.
Other technologies of ours being demonstrated at a
CO2 storage site include Distributed Fiber OpticalSensing (DFOS). We have created our own method tomeasure strains of geological formations and integrated it into multi-sensor systems capable of concurrent measurements of temperature, pressure, acoustic
wave, and strain of geological formations. That system
is also being implemented and demonstrated at an
overseas site.
Through improving our technologies and implementing them in the fields, our group continues toFig. 1

Evaluation for storage efficiency of microbubble
CO2 using core samples

contribute to CCUS deployment.
For the field tests of microbubble injection in 2020,
2. Major Research Topics and Outcomes

we used the Sarukawa oil field owned by JAPEX in Oga,

2.1. Microbubble CO2 Injection technology

Akita, where we did previous tests last year. The tar-

Microbubble CO2 injection technology is to turn CO2

geted formation for injection there was a low permea-

into microbubbles through a special ceramic filter andble sandstone layer at a depth of around 800 m. Inthen to inject the microbubble CO2 under the ground.

order to improve efficiency in installation of our mi-

Microbubble CO2 has the following advantages in in-

crobubble CO2 generator, we have designed a smaller

jection for geological CO2 storage:

system, length of which below the packer is 14 m, 1/6- To easily enter gaps (pore throat) of sandstone that isin comparison with the last year one, 84 m (Figure 2).

composed of reservoir,- To access more pore space than where CO2 injectedby a conventional way, andThanks to the design change, time for installment andde-installment was reduced to about 1/3 from 15hours to 4 hours.

- To easily dissolve in saline water.
The CO2 Storage Research Group has demonstrated
these advantages in lab and field tests. In the lab tests,
we used core samples of rock in an X-ray CT scanner.
The upper panel of Figure 1 shows a result from a series of tests. The panel illustrates CO2 distribution at atime when CO2 injected at the left edge reached apoint 82mm away from the edge with warm color

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R&D Activities ● CO2 Storage Research GroupRITE Today 2021The field tests demonstrated the validity of thesmaller microbubble generator and the improvementof its installing work successfully. This will contribute tocost saving in the production, installation andde-installation of the microbubble injection system.
Our development of the microbubble CO2 generation technology was initiated by a fundamental study
in collaboration with Tokyo Gas. We have acquired apatent of the technology (registered patent No.
5399436), titled “storage device and storage method
for stored substances”. Through various lab tests andfield demonstration, we have completed its development phase. At present, we are attempting to deploy
the technology globally, applying it to actual projects,
Fig. 2

Overview of the microbubble CO2 injection tools
settings in a borehole

The system downsizing also reduced the size of themicrobubble generator from 18m to 4.5m. These

including those in North Dakota in the USA and inJunlun Petroleum Company’s field in China.

2.2. Development of Advanced Traffic Light System(ATLS) for the Safety Management of CO2 Injectionchanges resulted in shallower microbubble generation

In various underground fluid injection projects, there(Figure 2b), whereas it was at a depth of the formation

are concerns that an increase of formation pressure

targeted for injection in 2019 (Figure 2a). Microbubble

induces earthquakes. Operation in waste water injec-

injection tests were conducted to verify whether thetion and enhanced geothermal systems (EGS), is

new configurations can still exploit the advantages oftherefore, managed in a way that prevents induced

microbubble CO2 by comparing the performance inseismicity around its site with Traffic Light Systems

2019. The injection rate was set out at 1.5 tonnes per(TLS). According to reports at CO2 storage sites to date,day, the same as last year. The wellhead pressure wasmicroseismicity observed there have been limited to a

8.4 MPa, whereas the bottom-hole pressure was risen

magnitude of 1.1 or less. However, we should deeply

from 8.8 MPa to 14.9 MPa and then was kept at theconsider and implement risk management at a CO2level. The CO2 injection index, which is an injection rate

storage site, taking the possibility of the seismicity intoper MPa, was 0.25 tonnes/day/MPa. This is comparable

account.

with the last year performance of 0.36 tonnes/day/MPa

Our group has been developing a microseismicity

and higher than the performance of conventional in-management system for CO2 storage in Japan, calledjection of 0.09 tonnes/day/MPa. These results proved

ATLS (Advanced TLS). The requirements for the systemthat microbubble injection with the new configuration

suitable for Japan are:is also capable of injecting more CO2 than the conven-- Capability to extract microseismic events fromtional one. The CO2 storage efficiency was high enoughground motion data that include data of a number

at 82.9%, equivalent to the last year rate.

of natural earthquakes and high-level environmental

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R&D Activities ● CO2 Storage Research Groupnoise caused by human activities,- Function to determine the hypocenters of microseismic events, and- Capability to process data in real time automatically.

RITE Today 2021

plicable to various sites. An example is to support
seismic observation planning which, using a layout ofseismometers and an event location as input, calculates an event location to be estimated by ATLS. Comparison the actual event location with the estimatedIn order to build a management system that meets

one makes it possible to assess the adequacy ofthese requirements, we have been conducting R&D forplanned seismometer locations and an expected ac-ATLS using data from the Tomakomai Demonstration

curacy of event positioning beforehand from theSite, where microseismicity has been monitored at its

viewpoint of ATLS operation.

CO2 storage site. Figure 3 illustrates a schematic viewof the workflow of ATLS. After obtaining ground motion data, the extraction of seismic events and theidentification of their locations are automatically carried out. In parallel, a latest hypocenter catalog is obtained from the Japan Methodological Agency (JMA),
which is used to exclude natural earthquakes from thecatalog generated in ATLS.

Fig. 4

An example of the output from ATLS

Another example is a tool for the conversion of input
data formats. ATLS had initially been designed only for
the SEGD format, which is used in the Tomakomai testsite. With the developed tool, ATLS is now capable ofFig. 3

Flow diagram of ATLS

handling min-SEED and ASCII formats, which arewidely used in natural seismic observation.

Using the continuous observation data for 2 years orThe validation of ATLS by applying it to the actual

more in Tomakomai, it was demonstrated that ATLS has

CO2 storage site in Tomakomai and the expansion of

the capability to automatically analyze ground motion

applicable sites with additional tools has completed

data and to locate each of the detected microseismic

our development of ATLS.

events near at the injection point. Figure 4 shows animage of the output report of ATLS. This presents the2.3. Integrated system of CO2 leakage detection andfrequency and locations of micro- and natural earth-marine environmental impact assessment

quakes in the monitoring area and the colors of traffic
light determined by the ATLS.

Since CO2 storage sites are deliberately selected tostore CO2 stably and safely, it is considered that CO2

In addition to the main system, we have developed

leakage from the geological reservoirs is remotely

auxiliary tools to support this system to be more ap-possible. Monitoring a CO2 behavior is, however, still53

R&D Activities ● CO2 Storage Research GroupRITE Today 2021

essential as there are public concerns about CO2 leak-constructed a database, with which we can extractage. In addition, when storing CO2 in the sub-seabedcorrelation between values of ΔpCO2 and their impacts

geological formation in Japan, it is mandated to assess

easily. By given features of organisms (e.g. taxonomic

marine environmental impacts based on the supposi-groups, habitats), the database selects organisms thattion of CO2 leakage and to monitor to verify that there

meet the conditions and outputs data on how they

are no signs of CO2 leakage or migration from the res-could be affected by different levels of ΔpCO2. Com-ervoir. Hence, our group has studied and developedbining the output data from the database and themethods of the marine environmental impact assess-simulated distribution of ΔpCO2, we can deduce what

ment and those of the monitoring for several years.

kinds of marine organisms could be how affected inThis year, we have combined our developed methods

which areas.

into an integrated system. Here, we outline the methods that we have developed.

To identify signs of CO2 leakage, the scope of monitoring should cover a wide range from deep geological

For marine environmental impact assessment, weformations, including CO2 reservoir, to the sea. Thefocus on increase of pCO2 (ΔpCO2; pCO2 is an index ofreservoir is at a depth of around 1 kilometer or deeper

CO2 concentration in seawater). Firstly the distribution

under the seabed. According to a simulation that weof the elevation of pCO2 is estimated based on sup-conducted previously, the amount of time that CO2

posed CO2 leakage, and then it is projected how themigrates from a reservoir to the seabed right aboveestimated ΔpCO2 could impact which organisms. Aswould be more than 5 years. Since the pathway of thethe leaked CO2 is dispersed by ocean currents, the dis-

CO2 migration would depend on the characteristics oftribution of ΔpCO2 is computed with currents in the sea

the formations between the reservoir and the seabed,calculated by an ocean model. The calculation of theCO2 would not necessarily leak into the sea in the area

distribution of ΔpCO2 requires a relatively small area,

right above the reservoir. Taking these into considera-

whose sides are smaller than a hundred kilometers. Ontion, we propose the following strategy for the moni-

the other hand, the calculation of the ocean currents

toring. Initially, we should put the focus on the deepneeds a much wider area because they are driven un-formations including the reservoir to detect signs of

der the influence of meteorological conditions andCO2 migration from the reservoir. Then, if detect, weocean topography over several hundred kilometers. In

move to in-depth investigation, targeting at overbur-our method, realistic currents oceanic data are calcu-den, to narrow the potential area for CO2 to leak out.

lated in a larger area model with a lower resolution andLastly, we prove the narrowed area to detect signals ofthen we obtain the calculated current data as theleaked CO2 in water column.

boundary conditions for a simulation of ΔpCO2 distri-Regarding the monitoring in the water column, webution which is simulated in the smaller area with ahave explored and developed methods to detect sig-

higher resolution.

nals of CO2 leakage. There are 2 kinds of signals of theThe simulated ΔpCO2 are used to assess what im-leakage: one is CO2 bubbles and the other is elevatedpacts they could make on which organisms. The rela-

CO2 concentration. Considering that a promising op-tion between ΔpCO2 and its impacts on a marine or-tion for detection of CO2 bubbles is side-scan sonar

ganism have been reported in many studies, but those(SSS, a kind of sonar system), we conducted an in-situ

data were not compiled into one. We have, hence,experiment to investigate the capability of SSS to de-54R&D Activities ● CO2 Storage Research GroupRITE Today 2021

tect CO2 bubbles in the sea. The experiment was to test

be given by the pCO2-DO threshold can be varied,whether SSS can detect CO2 bubbles released on thedepending on seasons. We have also found out that inseabed in various conditions. Our findings include thatevaluating the covariance of pCO2 and DO, it is neces-

SSS is capable of detecting bubbles released at a ratesary to take account of a difference in the responseof higher than 2-4 tonnes per annum and that the dis-times of the sensors. As has been stated, we havetance between the neighboring observation lines in theproposed the pCO2-DO threshold to detect signs ofmonitoring should be shorter than the altitude of SSS

CO2 leakage and clarified its various features, which(i.e. the distance between SSS and the seabed beneathwould be important in actual monitoring operation. Itit). The 4 tonnes of CO2 are remarkably small quantities;

should be, however, highlighted that to detect anoma-

they are comparable to CO2 that 10 people breathe out

lies in pCO2 caused by CO2 leakage at a small leakage

in a year.

rate, it is essential to observe in sea at high resolution

As to detection of CO2 concentration elevated byboth spatially and temporally. This is because dissolved

CO2 leakage, we have studied identification of anoma-

CO2 is easily dispersed by currents and because evenlously high values of pCO2 caused by CO2 leakage if

though the leak point is the same, the area where pCO2

any. CO2 is naturally contained in seawater, and its

becomes anomalous is varied depending on flow di-concentration naturally fluctuates. This makes it chal-rection and strength and leakage rate. We, therefore,

lenging to determine whether high pCO2 values aresuggest that indexes of CO2 concentration such asderived from CO2 leakage or from natural variability,

pCO2 and pH be monitored not for detection of CO2

and to define a threshold for the judgement (Fig. 5).

leakage but for confirmation that marine environment

The threshold that we put forward is based on covari-remains unchanged after commencement of CO2

ance between dissolved oxygen (DO) and pCO2 (re-storage.

ferred to as the pCO2-DO threshold, hereafter). First,

We will incorporate these outcomes into the best

we have examined its validity through an analysis ofpractice manual that we have been compiling, hoping

natural fluctuation in quarterly data of its kind acquiredthat they are used in full-scale offshore CO2 storage

in Osaka Bay, an enclosed bay in Japan, over 9 years.

operation.

Our conclusions include that, in the identification of
anomalous pCO2 due to CO2 leakage in summer, whennatural variability in pCO2 is large, or in areas where sois it, the proposed pCO2-DO threshold is superior to athreshold simply based on pCO2, and that the threshold should be set out based on data for at least 5 years.
As a next step, we have carried out a continuous observation of pCO2, DO and so on in Osaka Bay morethan a year and analyzed their natural fluctuation. This
has revealed that pCO2 in the innermost part of the bay
in summer fluctuates largely and that pCO2 occasionally changes significantly within a few hours. The dataover 1 year has revealed that a rate of false-positives toFig. 5

The relation between the threshold andfalse-positives and -negatives

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R&D Activities ● CO2 Storage Research GroupRITE Today 2021

2.4. Contribution to the world by cutting-edge tech-Center (EERC), the University of North Dakota, USA. We

nology development

have built mutually beneficial relationships in this pro-

There are a number of large-scale geological CO2

ject: the US side is to be able to monitor the stability ofstorage projects in operation worldwide, including

the geological CO2 storage site and CO2 plume behav-

Snøhvit in Norway, Quest in Canada, Gorgon in Aus-iors, and our side has got an opportunity to demon-tralia. All these projects have successfully injected andstrate our DFOS system and to improve techniques forstored CO2 at about 1Mt/y.

its installation at their site.

Such large-scale CO2 storage has unfortunately not

Our optic-sensing technology will have more andyet been implemented in Japan. Nevertheless, ourmore opportunities to be demonstrated and deployedgroup intends to contribute to global CCS deployment

around the world. It will be, for example, applied tothrough international cooperation by providing ourmonitor deformation of seabed surface in a European

core competency technologies for large scale geolog-

project called SENSE, which is probing the stability ofical CO2 storage.

offshore CO2 storage. There also can be chances for

One of our core technologies is the aforementioned
microbubble CO2 injection technology which improves

our system to be implemented in CO2 storage projects
being planned in Asian countries.

CO2 storage efficiency even for low permeability for-The promotion of CCS by collaborating internation-mations. This will enable to use, for example, a CO 2

ally is crucial for Japan to achieve our ambitious zero

storage site closer to a CO2 source, giving more flexi-emission goal in 2050. Please keep your eye on thebility in site selection. This is a pivotal contributor for

activities of the CO2 Storage Research Group, RITE. We

CCS promotion in the world. Moreover, we will also

continue to contribute to CCS deployment by devel-strengthen our contribution to CO2-EOR by demon-

oping innovative technologies and consulting for theirstrating increased oil production in low-permeability

applications.

fields in China, which we have been jointly researchingwith Junlun Petroleum Company since 2018.
Another example is Distributed Fiber Optical Sensing(DFOS). In addition to functions of fiber optical sensing
to monitor pressure, temperature and so forth under
the ground that have already been used in the oil industry, our group has created our own method tomeasure strains of geological formations and has integrated and demonstrated them as a multi-sensor system that enables concurrent measurements of temperature, pressure, seismicity and strain of geologicalformations.
Our DFOS system draws attention not only domestically but also internationally. We have been conducting its demonstration at a commercial CCS site in collaboration with the Energy & Environmental Research56