Geothermics 108 (2023) 102617
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Geothermics
journal homepage: www.elsevier.com/locate/geothermics
Conceptual model of supercritical geothermal system in Shiribeshi Region,
Hokkaido, Japan
Daisuke Oka a, *, Makoto Tamura a, Toru Mogi b, Mitsuhiro Nakagawa c, Hiroaki Takahashi d,
Mako Ohzono d, Masayoshi Ichiyanagi d
a
Research Institute of Energy, Environment and Geology, Hokkaido Research Organization, Sapporo, Japan
Volcanic Fluid Research Center, Tokyo Institute of Technology, Tokyo, Japan
Department of Earth and Planetary Sciences, Faculty of Science, Hokkaido University, Sapporo, Japan
d
Institute of Seismology and Volcanology, Faculty of Science, Hokkaido University, Sapporo, Japan
b
c
A R T I C L E I N F O
A B S T R A C T
Keywords:
Supercritical geothermal system
Shiribeshi
Niseko
Geothermal conceptual model
Supercritical geothermal systems (SGS) have the potential to significantly increase the amount of geothermal
power generation. Researches and studies on SGS are being conducted worldwide. In Japan, the New Energy and
Industrial Technology Development Organization (NEDO) has started to research and development of super­
critical geothermal power generation on SGS recently. Various studies have been conducted in and around the
Niseko Mountains in the Shiribeshi region of Hokkaido, Japan to detect supercritical geothermal systems in the
Niseko area including geological, electromagnetic, seismic and temperature analyses. Based on threedimensional structures obtained from these studies, we constructed a conceptual model of supercritical
geothermal systems in and around the Niseko Mountains. The shallowest part of the supercritical geothermal
systems in the Niseko area was detected at approximately -3 km a.s.l. below Mt. Iwao-nupuri and Mt. Chisenupuri.
1. Introduction
Supercritical geothermal systems (SGS) are high-temperature
geothermal assemblages that are located at depths near or below the
brittle–ductile transition zone in the crust, where the reservoir fluid is
assumed to be in the supercritical state; that is, for pure water, the
temperature and pressure are in excess of 374 ◦ C and 221 bar, respec­
tively (Reinsch et al., 2017). SGS, which originated from the subduction
of oceanic plates, have the potential to substantially increase the amount
of geothermal power generated by the year generation 2040 (New En­
ergy and Industrial Technology Development Organization (NEDO),
2022). However, these high-temperature and high-pressure conditions
inside and around the SGS make it difficult to extract thermal energy,
compared with that of conventional geothermal system which are
generally 150-300 ◦ C and a few 100 MPa. Research and development in
various science and technology fields must be conducted to realize
“supercritical geothermal power generation” (Dobson et al., 2017) using
SGS as a thermal source. We have performed a study to verify the
presence of SGS, as a base for SGS development. Studies on SGS have
been conducted in various parts of the world. In Iceland, IDDP (Iceland
Deep Drilling Project) drilled IDDP-1 between 2008 and 2012,
confirmed superheated steam fluid of 450◦ C, 0.4 - 14 MPa, and 36 MW
equivalent (Friðleifsson et al., 2015). Subsequently, in IDDP-2 from
2016 to 2017, 427◦ C and 34 MPa were confirmed at the well bottom.
These results suggest that geothermal fluids in these areas exist in a
supercritical state and form SGS. Reinsch et al. (2017) mentioned some
difficulty of supercritical geothermal development, which supercritical
fluids were very corrosive and abrasive from IDDP-1and said that
innovative drilling and well completion techniques were needed to deal
with the high temperatures and aggressive fluid chemistry compositions
of the supercritical geothermal systems. NEDO and project members
conducted field surveys and data collection at the three most likely sites
in Japan (Shiribeshi (Niseko), Sengan (Kakkonda), and Hohi (Kuju)) to
characterize SGS and to evaluate the potential for supercritical
geothermal power generation (New Energy and Industrial Technology
Development Organization (NEDO), 2022). The targets of this project as
determined by NEDO were (a) assuming that a considerable amount of
SGS exists in the shallow crust in the three locations., the location of a
* Corresponding author at: Hokkaido Research Organization, Kita19jo Nishi12chome, Kita-ku, Sapporo, Hokkaido, 060-0819 Japan
E-mail address: oka-daisuke@hro.or.jp (D. Oka).
https://doi.org/10.1016/j.geothermics.2022.102617
Received 2 February 2022; Received in revised form 30 September 2022; Accepted 17 November 2022
Available online 29 November 2022
0375-6505/© 2022 Elsevier Ltd. All rights reserved.
D. Oka et al.
Geothermics 108 (2023) 102617
Fig. 1. Map of research area, Niseko Shiribeshi, Hokkaido, Japan Areas surrounding dashed lines indicates volcanic groups. In the lower-right map, the grey square
indicates the map of research area. 100%
young magmatic body at a depth of less than 5 km would be identified,
and (b) demonstrating that more than 100 MW of power generation can
be achieved using the SGS at each site. In this project, three groups
surveyed the SGS in the three regions, and another group performed
numerical simulations of heat extraction from a supercritical geothermal
reservoir based on the survey results of the three regions. The authors
were responsible for studying SGS in the Shiribeshi region. In this paper,
we discussed the results of our surveys and reviewed existing data for
SGS in the Shiribeshi region, Hokkaido.
In Hokkaido, there are many volcanoes that form the volcanic front
of Japan Islands; therefore the geothermal potential of this region is
relatively high (Geological Survey of Japan, 2009). The Shiribeshi re­
gion is located in the south western part of Hokkaido, and includes the
Niseko Mountains containing the Niseko Volcanic Group and the Raiden
Volcanic Group. The Niseko Volcanic Group is situated in the eastern
part of Niseko Mountains, and includes Mt. Nisekoan-nupuri, Mt.
Iwao-nupuri, and Mt. Chise-nupuri (Fig. 1). Mt. Yotei, a stratovolcano, is
located on the eastern extension of the Niseko Mountains. There are two
major rivers around the Niseko Mountains: the Horikappu and the
Shiribetsu. The Horikappu River runs on the northern side of the
mountains, and the Shiribetsu River runs on the southern side.
The Niseko Volcanic Group has many wells which are used to pro­
duce geothermal fluid for spas, and fumaroles were previously identified
in Iwao-nupuri (Geological Survey of Hokkaido et al., 2020) as
geothermal phenomena (Fig. 2). In the 1980s, NEDO conducted surveys
of geothermal resources, whereby a well was drilled in the northern part
Fig. 2. Location of hot spring wells, Niseko Shiribeshi, Hokkaido, Japan Diamond shapes indicate hot spring wells. 100%
2
D. Oka et al.
Geothermics 108 (2023) 102617
Fig. 3. Temporal and spatial changes in volcanism in the Niseko-Raiden Volcanic Group. Red rectangle is the indicated target of this geological survey. White circles
are from NEDO (1985), black circles are from Hokkaido Disaster Prevention Council (2005), blue diamonds are from Hokkaido Disaster Prevention Council (2018),
and red squares and yellow triangles are from this study. 67%
of the Niseko Volcanic Group to explore the geothermal structure of the
area, NS-61-1 (New Energy Development Organization (NEDO), 1986).
Geothermal surveys and development in this area were suspended due to
the halting of geothermal development in Japan. However, since the
Great East Japan Earthquake in 2011, geothermal energy has once again
attracted attention in Japan, and a survey for geothermal development
was reinstated in this area in 2015. Since 2015, the Japan Oil, Gas and
Metals National Corporation (JOGMEC) has conducted extensive,
high-precision surveys using airborne geophysical technology by heli­
copter to narrow down prospective areas for efficient geothermal
resource development in the Niseko area. Since 2017, the Hokkaido
Research Organization, Hokkaido University, and Hokkaido Institute of
Public Health have researched geothermal structure and estimated the
geothermal potential in and around the Niseko area (Geological Survey
of Hokkaido et al., 2020). The Geological Survey of Hokkaido et al.
(2020) used geophysical, electromagnetic (magnetotelluric method),
and gravity-survey, as well as geochemical research of borehole fluid to
detect geothermal reservoirs beneath Mt. Iwao-nupuri in the Niseko
Volcanic Group. In this project, we choice the Niseko area as a research
target because the Niseko area contains relatively young volcanoes, high
temperature zone may be located relatively shallow part, which high
temperature zone can be developed up to approximately 5 km depth.
Based on these research results a geothermal reservoir containing su­
percritical fluid may exist in the deep part of the Niseko Mountains
beneath the Niseko Volcanic Group. Therefore, we initiated a survey for
SGS in 2018, focusing on the Niseko Volcanic Group from the NEDO
project. We conducted geological surveys, detailed electromagnetic
surveys (Tamura et al., 2022), seismic observation (Ichiyanagi et al.,
2021), and underground temperature research in and around the Niseko
Mountains. A geological survey was performed to recompile the volcanic
activity in the research area. Electromagnetic surveys and seismic
observations were conducted to determine the structure of the deep part
and the temperature structure was estimated using a temperature
analysis. Combining our results with existing researches, we constructed
a conceptual model of SGS in the Niseko Mountains.
2. Materials and Methods
2.1. Surveys for Supercritical Geothermal System in the Niseko Volcanic
Group
2.1.1. Geology
The Niseko Mountains were formed as a chain of volcanoes by the
invasion of the horseshoe-shaped Miocene-Pliocene basin from the
western coastal area. Before the volcanic activity (approximately 2.0 Ma
or earlier), volcanic groups which formed on the Neogene basement
were deposited in this sedimentary basin (Geological Survey of Hok­
kaido et al., 2020). NEDO summarized the volcanic history of the Niseko
Mountains (New Energy Development Organization (NEDO), 1986);
however, the age of the rocks in their research is inaccurate because the
survey is outdated, and there are gaps in the ages of rocks between some
data (New Energy Development Organization (NEDO), 1985) (Fig. 3).
Fig.3 show the age of the rocks of each volcanoes have gaps between the
age from NEDO (1985) and Hokkaido Disaster Prevention Council 2005
as references. Volcanic activity in the Niseko Mountains started in the
west and moves to the east, while the activity of the Weisshorn and Mt.
Moiwa located on the east but are older than other eastern Niseko vol­
canoes. An attempt to reconsider the eruption history of the Niseko
volcano group is needed. Therefore, based on conventional research,
new samples were collected, and the age of the rocks was determined by
radiometric dating. The analysis methods adopted in this research were
K-Ar and 40Ar-39Ar dating methods (Dalrymple and Lanphere, 1971)
3
19NIS-16
19NIS-9
70
19NIS-13
19NIS-11
19NIS-12
139
19NIS-8-1
NI-1
NI-2
NI-3_1
NI-4
NI-5
NI-6
NI-7
NI-9
Mt. Iwanai-dake
Chise-nupuri
Chise-nupuri
Nito-nupuri
Nito-nupuri
Mt. Moiwa
Nisekoan-nupuri
Weisshorn
Unit
peak lava
dome lava
S lava
dome lava
Flat lava
peak lava
peak lava
NE lava
Occurrence
42.9283
42.8934
42.8462
42.8881
42.8662
42.8631
42.8709
42.9272
Lat(N)
140.5148
140.6055
140.6057
140.6104
140.6175
140.6334
140.6624
140.6754
Lng(E)
1.412±0.028
1.934±0.039
1.837±0.037
1.983±0.04
2.021±0.04
1.213±0.024
1.288±0.026
1.47±0.029
K wt.%
5.44±1.53
4.25±3.59
4.73±3.11
3.14±2.63
3.16±3.11
3.02±0.17
0.89±0.13
8.43±0.45
Rad. 40Ar (10− 8cc STP/g)
4
19NIS-16
70
NI-8
NI-3_2
100%
Field No.
No.
Chise-nupuri
Nisekoan-nupuri
Unit
S lava
NE lava
Occurrence
Table 2
40
Ar-39Ar dating of the Niseko volcano group.
42.8462
42.8787
Lat (N)
140.6057
140.6772
Lng (E)
64.8 ± 0.9
203.4 ± 30.5
Plateau age (ka) (± 2σ)
Ar (%)
85
39
202.6
± 128.7
64.9
± 1.0
Isochron age (ka)
Ar/36Ar
298.57
± 2.05
291.95
± 4.11
40
0.82
MS WD
* The rock samples were fresh and showed no evidence of alteration, so it was possible that the eruption dates were too young. 100%
Field No.
No.
Table 1
K-Ar dating of the Niseko-Raiden volcano group.
65.2 ±1.0
202.9 ±88.3
Ar/36Ar
298.58
± 2.06
291.8
± 4.3
40
94.0
98.2
97.6
98.2
98.4
75.7
89.8
74.4
1.02
MS WD
Non rad. 40Ar (%)
Inv. Isochron age (ka)
0.99±0.28
0.57±0.48
0.66±0.44
0.41±0.34
0.4±0.4
0.64±0.04
0.18±0.03
1.48±0.08
K-Ar age (Ma)
353.5
± 34.0
167.3
± 36.2
Total fusion age (ka)
Not determined
Remarks
Too young No evidence of alteration*
Too young No evidence of alteration*
Too young No evidence of alteration*
Too young No evidence of alteration*
Remarks
D. Oka et al.
Geothermics 108 (2023) 102617
D. Oka et al.
Geothermics 108 (2023) 102617
Fig. 4. Distribution of volcanic activity in last 1Ma for the Niseko Volcanic Group. Yellow circles show sampling points of rocks; the name of each point is shown in
Tables 1 and 2. 67%
(Tables 1 and 2).
The activity of the Niseko-Raiden Volcanic Group occurs from the
western to the eastern side of the Niseko Mountains (Figs. 3 and 4). Mt.
Raiden, Mt. Weisshorn, and Mt. Iwanai-dake, which were formed in an
early stage of volcanic activity in the Raiden-Niseko Volcanic Group,
have been eroded and have clear valley topographies. In contrast, Mt.
Chise-nupuri, Mt. Nito-nupuri, and Mt. Iwao-nupuri are newer vol­
canoes with less erosion from climatic conditions; therefore, they have
formed clearer terrains, such as lava flows, pyroclastic, and explosion
craters.
The activities of Mt. Weisshorn and Mt. Moiwa of the Niseko Vol­
canic Group are well established, while Mt. Nisekoan-nupuri, Mt. Iwaonupuri, and Mt. Chise-nupuri were formed by newer volcanic activities.
Mt. Iwao-nupuri is the newest volcano, with volcanic activity beginning
in the Holocene.
Mt. Iwanai involved of the Raiden Volcanic Group was formed at
approximately 1 Ma, whereas Mt. Weisshorn and Mt. Moiwa of the
Niseko Volcanic Group developed at approximately 1.5 Ma and 0.64 Ma,
respectively, and Mt. Nisekoan-nupuri close to 0.2 Ma. It can be esti­
mated that the hot rock body, which is the heat source of the current
geothermal activity in the Niseko volcanic group, exists in the deep parts
under Mt. Chise-nupuri, Mt. Nito-nupuri, and Mt. Iwao-nupuri.
from wells and hot springs with, a sampling number of 62 (Fig. 5,
Table 3). Ion chromatography analysis, using hydrogen and oxygen
isotopic ratios revealed that geothermal fluid is formed from a mixture
of meteoric water, magmatic water, and fossil salt water. From the
Giggenbach diagram (Giggenbach, 1988) by the Geological Survey of
Hokkaido et al. (2020) (Fig. 6), most of the geothermal water from the
wells was relatively new, and the reaction between rock and water had
yet to be established. No distinct regional characteristics were observed,
as all samples were immature. The temperature estimated from the
Na-K-Ca geochemical thermometer was approximately 250 – 300 ◦ C
(Geological Survey of Hokkaido, Hokkaido Research Organization,
Hokkaido University, Hokkaido Institute of Public Health 2020). What
Geological Survey of Hokkaido, Hokkaido Research Organization,
Hokkaido University, Hokkaido Institute of Public Health 2020 obtained
from the geothermometers was that the shallow hot water has experi­
enced that temperature at deep part.
2.1.3. Resistivity structure
An electromagnetic survey was conducted using the magnetotelluric
method to estimate the resistivity structure of the Niseko area (Tamura
et al., 2022). Tamura et al. (2022) measured the resistivity at 61 ob­
servations in this project, and added existing data from previous surveys
at 55 locations (Fig. 7) (Geological Survey of Hokkaido et al., 2020). The
authors estimated 3-D resistivity structure using 116 observations with
WSINV3DMT (Siripunvaraporn and Egbert, 2009).
Results of the 3-D resistivity analysis (Figs. 8 and 9), revealed
intrusion from the deep part, which indicates a lower resistivity, beneath
Mt. Iwao-nupuri and Mt. Chise-nupuri.
2.1.2. Geochemical research of hot springs
In and around the Niseko area, New Energy Development Organi­
zation (NEDO) (1986) researched on geochemistry of geothermal fluid
from natural discharge hot springs and borehole wells. Many new
borehole wells for spas and hot spring resorts have been drilled over the
past 30 years, creating a greater number of boreholes for spas (from 100
to 180). Based on a survey of the present state, Geological Survey of
Hokkaido et al. (2020) geochemical analysis was performed of hot water
2.1.4. Gravity survey
Gravity surveys had been previously conducted around the Niseko
5
D. Oka et al.
Geothermics 108 (2023) 102617
Fig 5. Distribution of sampling hot springs for geochemical research based on Geological Survey of Hokkaido et al.(2020). Blue squares and red circles indicate
natural springs and drilling wells respectively. The numbers reflect the sampling number. Black rectangles denote mountains. White shaded areas indicate hot spring
groups. 100%
area (New Energy Development Organization (NEDO), 1986). To update
the rock density structure, the Geological Survey of Hokkaido et al.
(2020) re-surveyed the gravity of the area. A Bouguer anomaly map was
constructed using data correction (Fig. 10) and anomaly ranges of from
approximately 40 to 80 μgals were found around the Niseko area.
High-gravity zones were located under the Niseko Mountains. The
gravity anomaly in the Raiden Volcanic Group was higher than that in
the Niseko Volcanic Group. The gravity anomaly surrounding the Niseko
Mountains is relatively low, while the high-gravity zone is located in the
eastward section, which indicates intrusive rock formation in the Niseko
Mountains (Geological Survey of Hokkaido et al., 2020). NEDO (1986)
explained that Niseko mountains were formed by intrusive rock from
deep part, through basin, from geological survey and existing gravity
survey. We agree this geological explanation, and density analysis by
Geological Survey of Hokkaido et al. (2020) revealed same result.
wells stopping production. Fig. 11 reveal the 85 well data, NS61-1 was
drilled at high elevation area compared with other wells, and the ther­
mal gradient of NS61-1 is higher than almost of the other wells. The
deepest of these wells reached 140 ◦ C at a depth of 1300 m. However,
this well is located in Iwanai town, NW area of the Niseko Mountains. In
this area, there are some high temperature wells, but in Raiden Volcanic
Group, whose rock age was old, from geochemical survey, the origin of
the fluid is mixture of meteoric water and fossil salt water.
The Activity Index (AI; Hayashi et al., 1981) was adopted for wells
without well logging data, to estimate the underground thermal struc­
ture (Fig. 12).
(
)
Tb − Tm
Activity Index = 1 −
× 100
Tb + Tg
where Tm is the maximum temperature measured or estimated using
various methods, we used fluid temperature on wellhead in this study.
Tb is the boiling temperature at the measured depth (Haas, 1971). Tg is
the assumed temperature at the above depth calculated using the normal
geothermal gradient of 0.03 ◦ C/m. By utilizing Activity Index (AI),
vertical distributions of temperature at the well location can be deter­
mined from the temperature data of hot water pumped up without well
logging data (Hayashi, 1982, Geological Survey of Japan, 2009). Ac­
tivity Index (AI) is calculated from the percentage of the pure boiling
curve and the normal ground temperature gradient (0.03 ◦ C/m), and the
temperature profile has an upward convexity. Therefore, the Activity
Index (AI) has a larger error than the temperature profiles of the thermal
conduction, which show linear profiles, or lateral flow type, which show
the inflection point in the geothermal profiles. However, it can estimate
profiles from the temperatures of hot water even in areas where well
2.1.5. Temperature structure
To comprehend the underground temperature distribution and
detect high temperature zones over 380 ◦ C, the Geological Survey of
Hokkaido et al. (2020) collected and compiled temperature data of
wells. As mentioned previously, there are few deep wells intended for
geothermal development in the Niseko area, although many wells have
been drilled for ski and spa resorts in the region. The drilling depths of
these wells were shallow, because the required temperature of the fluid
produced from these wells is 50 – 100 ◦ C for bathing. In this research,
169 temperature data points with hot water pumped up from the deep
part of wells and 85 well-logging data points were selected and compiled
(Fig. 11) (Geological Survey of Hokkaido, 2008). These well logging
data involve both of wells producing hot water for spa and abandoned
6
Geothermics 108 (2023) 102617
D. Oka et al.
Table 3
Trace elements in hot spring water (Geological Survey of Hokkaido et al., 2020). Sample numbers are as per Figure 5. 100%
Sample
No.
Type
Fe
mg/L
Mn
Al
Si
B
As
DOC
H2S
CO2
Hg
μg/L
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
Mg-SO4
Mg-SO4
Mg-SO4
Mg-SO4
Mg-SO4
Mg-SO4
Mg-SO4
Ca-SO4
Ca-SO4
Ca-SO4
Na-HCO3
Ca-SO4
Na-Cl ⋅ HCO3
Na-Cl ⋅ HCO3
Na-Cl ⋅ HCO3
Na-Cl ⋅ HCO3
Na-Cl
Na-Cl ⋅ HCO3
Na-Cl ⋅ HCO3
Na-Cl ⋅ HCO3
Na-Cl ⋅ HCO3
Na-Cl
Na-Cl ⋅ HCO3
Na-HCO3 ⋅ SO4
Na-Cl ⋅ HCO3
Na-HCO3 ⋅ SO4
Na-Cl ⋅ SO4
Na-Cl ⋅ HCO3
Na-Cl ⋅ HCO3
Na-Cl ⋅ HCO3
Na-Cl ⋅ HCO3
Na-Cl ⋅ HCO3
Na-HCO3
Na-Cl
Na-Cl ⋅ HCO3
Na-Cl
Na-Cl ⋅ HCO3
Na-Cl ⋅ HCO3
Na-Cl ⋅ HCO3
Na-Cl
Na-HCO3 ⋅ SO4
Ca-SO4
Na-Cl ⋅ HCO3
Na-Cl ⋅ HCO3
Na-Cl ⋅ HCO3
Na-Cl ⋅ HCO3
Na-Cl ⋅ HCO3
Na-Cl
Na-HCO3
Na-Cl
Na-Cl
Na-Cl
Na-Cl
Na-HCO3
Na-Cl
Na-Cl
Ca-SO4
Ca-SO4
Ca-SO4
Na-Cl
Na-Cl
Ca ⋅ Na-Cl
0.7
8.7
0.8
1.0
0.1
0.4
1.1
0.7
0.7
5.0
7.3
7.5
1.6
6.1
1.9
0.4
0.0
0.5
1.8
0.1
0.1
1.7
1.8
2.1
0.5
0.9
0.6
6.0
0.5
0.1
2.4
0.1
0.0
4.2
2.1
0.1
0.1
0.0
56.1
1.7
5.8
1.2
0.3
1.0
0.1
0.0
0.0
0.0
0.0
14.9
10.3
0.2
0.2
1.3
6.2
0.0
0.0
0.0
0.7
0.1
0.2
0.0
0.2
0.0
0.2
0.6
0.1
0.2
2.1
0.0
0.3
0.3
0.4
0.0
1.5
0.4
2.4
1.3
2.6
0.2
1.2
0.9
0.5
0.0
0.0
0.0
0.0
1.6
1.0
0.0
0.2
0.2
0.0
0.0
0.0
27.6
73.6
1.2
0.1
0.0
0.0
0.0
0.0
0.0
0.0
0.0
3.9
0.0
0.0
0.0
0.4
0.3
0.2
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.3
0.0
0.0
0.0
0.0
0.0
9.0
0.0
0.0
26.6
34.5
10.3
22.5
15.8
46.1
35.8
78.4
66.3
49.9
69.4
63.4
88.5
90.4
80.3
54.6
17.0
53.6
60.5
56.0
36.6
78.8
79.1
68.9
53.9
58.0
45.2
49.9
46.4
41.7
79.0
17.8
23.9
25.1
37.3
39.6
32.3
16.0
47.5
31.9
76.4
63.0
37.0
85.1
43.8
35.4
20.3
9.9
28.2
6.6
18.6
2.1
4.1
2.0
10.4
17.2
14.6
11.5
20.8
16.2
12.1
12.8
32.6
2.7
8.3
2.3
4.9
4.7
10.9
3.8
20.8
19.0
18.2
4.1
21.2
19.4
17.0
7.1
14.4
20.3
3.3
20.6
3.6
5.4
1.9
2.8
2.6
13.5
5.9
10.9
7.2
1.7
3.2
32.3
2.1
7.8
4.1
16.4
0.0
0.0
0.0
0.1
0.1
0.0
0.1
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.1
0.0
0.0
0.0
0.0
0.1
0.1
0.0
0.1
0.0
0.0
0.3
0.0
0.2
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.2
0.7
2.5
2.4
0.5
0.6
2.0
1.7
3.6
1.6
0.0
0.0
0.0
0.0
0.0
0.0
11.2
0.8
1.0
1.1
0.2
1.2
1.0
1.3
1.8
0.6
0.7
0.7
1.2
0.5
0.4
8.0
0.5
0.2
2.2
1.1
3.3
1.7
1.8
0.4
0.5
1.1
0.6
0.4
1.2
159.9
0.3
0.4
0.2
3.9
14.7
4.1
23.4
0.3
25.8
0.6
0.0
0.2
0.0
1.7
0.0
0.0
0.0
0.0
0.0
0.2
0.0
0.0
0.0
2.0
0.0
0.0
0.0
0.0
0.0
0.1
0.3
0.0
30.4
0.0
0.0
0.0
0.1
0.0
0.0
0.0
0.0
0.0
4.3
0.0
0.0
0.0
0.0
0.0
0.7
0.0
0.0
0.0
0.0
658.7
560.2
261.3
91.6
563.7
384.9
267.4
206.3
151.3
139.0
342.9
230.8
172.0
354.9
229.7
64.6
69.2
80.4
44.4
321.8
13.8
169.3
99.9
185.4
71.5
508.8
328.4
567.8
1310.
594.8
99.4
11.7
5.5
78.5
124.0
0.0
7.4
253.6
566.1
157.4
149.3
24.7
13.8
0.0
13.8
4.8
0.7
0.7
20.4
0.0
0.0
0.9
0.1
0.0
0.0
0.0
0.1
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.1
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.1
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Geothermics 108 (2023) 102617
Fig 6. diagram in and around the Niseko mountains based on Geological Survey of Hokkaido et al.(2020) .67%
logging data are not available, and it was used to calculate geothermal
potentials for all of Japan (Geological Survey of Japan, 2009).
The development of resort facilities is unevenly distributed and
concentrated in the eastern and southern parts of the Niseko Mountains;
therefore, most bore holes for spas are situated in the eastern and
southeastern parts. Since areas around the summits of the Niseko
Mountains are within the range of Niseko-Shakotan-Otaru Kaigan QuasiNational Park, few wells are is located around the summits.
All wells did not reach a supercritical geothermal reservoir, and the
deep temperature structure was estimated by linear extrapolation (New
Energy and Industrial Technology Development Organization (NEDO),
2019). First, the temperature data processed at each 50 m depth from
the well logging data and the temperature profile estimated using the
method of Hayashi et al.(1981) is interpolated using approach of NEDO
(2019) (Fig. 13). The temperature at each depth of 50 m in each well was
obtained from Hayashi (1982). Hayashi (1982) show the Tb, in case
Activity Index (AI) is 100, and Tg, in case Activity Index (AI) is 0, with
depth. Using this data, we calculated the temperature profile by interior
division with Tb and Tg. The thermal gradient for interpolation was
calculated using the temperature data at the bottom 500 m in each
borehole and well by using linear regression. As a result of this study, a
high- temperature zone (>380 ◦ C) was detected in the central region
under Mt. Iwao-nupuri at a depth of 2000–3000 m (Fig. 14).
temporal seismic observations with seismographs in the Niseko Moun­
tains (Fig. 15). The Japan Meteorological Agency certified the Niseko
Mountains as active volcanos in 2003, but because seismic activity
around the Niseko Mountains is little, no permanent seismograph is
installed in the Niseko Mountains. Ninety earthquakes were detected
during the temporary observation period using the VELEST program
(Kissling et al., 1994; Ichiyanagi et al., 2021). However, during the same
period, the number of earthquakes listed in the Japan Meteorological
Agency’s unified earthquake catalogue was 3.
A one-dimensional velocity structure using travel-time data was
obtained from temporal observations founded by Ichiyanagi et al.
(2021), and basic seismic observation points (NIED Hi-net; National
Research Institute for Earth Science and Disaster Resilience (2019)) in
the surrounding Niseko Mountains (Ichiyanagi et al., 2021). The
earthquakes occurred beneath the ridgeline between Mt. Shirakaba and
Mt. Nisekoan-Nupuri. They occurred relatively frequently on the
northern side, and their depth was less than 5 km (Fig. 15). In the
Kutchan City area, which is located east of the Niseko Mountains, the
earthquakes were deeper than those beneath the Niseko Mountains.
Ichiyanagi et al. (2021) suggested the spatial inhomogeneity of the
earthquake zone in this area. In addition, the shallow P wave velocity
was recorded as 4.0 km/s up to a depth of 5 km (Fig. 16).
3. Results and Discussion
2.1.6. Seismicity
As survey was conducted to determine current seismic activity and
estimate the seismic wave velocity structure around the Niseko Moun­
tains (Ichiyanagi et al., 2021). Ichiyanagi et al. (2021) found Tthree new
3.1. Estimation of supercritical geothermal reservoir
Based on the above data, we estimated the supercritical geothermal
8
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Geothermics 108 (2023) 102617
Fig 7. Distribution of observations for electromagnetic surveys in Tamura et al. (2022). Red and yellow circles show the stations observed by the Geological Survey
of Hokkaido et al. (2020). The circles with numbers denote the new stations in this research project. 67%
reservoir in the Niseko area. As a result of the underground thermal
structure from well data and resistivity structure, a high-temperature (>
380 ◦ C) and low resistivity (< 30 Ω ⋅ m) zone was detected at a depth of
3000 m around Mt. Chise-nupuri and Mt. Iwao-nupuri in the Niseko
Volcanic Group (Fig. 17). Assumed rock is granite–porphyry system
(Tsuchiya et al., 2016). It was concluded that this zone contains a
magma chamber, and the upper surface of this zone corresponds to the
upper surface of the supercritical geothermal reservoir, considering the
geology and seismicity (Tsuchiya et al., 2016). Tomiya (2016) defined
magma reservoir was composed of outer crystal mush and innner
magma chamber based on Bachmann and Bergantz (2008). Then this
NEDO project defined supercritical geothermal reservoir, which was
target of geothermal development, as most out of crystal mush and
discrete magma based on Tomiya (2016) andBachmann and Bergantz
(2008).
From the resistivity structure of the Niseko volcanic group, a lowresistivity zone from the deep part to 2-3 km depth was detected
around Mt. Chise-nupuri and Mt. Iwao-nupuri. The underground ther­
mal structure of the Niseko Volcanic Group showed a high-temperature
zone around the Kombu area, Mt. Iwao-nupuri, and Mt. Nisekoannupuri. This low resistivity zone is situated a few kilometers west of
the high-temperature zone, but as previously mentioned, no well is
located around the summits of the Niseko Mountains, and most wells are
located in the eastern and southern regions. Therefore, we cannot
evaluate the extension of this high-temperature zone to the westward
direction or the temperature upward from this low resistivity zone.
3.2. Geothermal conceptual model
We made the conceptual model of SGS beneath Niseko volcanic
group. The modeling was conducted using the conceptual model in
Tsuchiya (2021) as a base from which to integrate the information about
the Niseko region. Tsuchiya (2021) characterized potential of super­
critical geothermal resources into the following four categories, 1: sur­
face geothermal manifestation and shallow high temperature, 2: high
geothermal gradient, 3: Aseismic zone which indicates an existence of
melt, 4: low velocity zone which indicates magma input. In Niseko, the
shallow high temperature and relative high geothermal gradient were
obtained from geothermal structure. Seismic observation estimate the
velocity structure model and hypocenter distribution show the active
seismic zone beneath Niseko volcanic group (Ichiyanagi et al., 2021).
Fig. 18 shows the conceptual model of the supercritical geothermal
system, which was considered in these studies in the Niseko Volcanic
Group. The magma chamber was situated at a depth of approximately 3
km under Mt. Iwao-nupuri and Mt. Chise-nupuri, and was detected as a
low resistivity zone. Discrete magma, which penetrates the deep part of
the magma chamber, is found under Mt. Iwao-nupuri, and may supply
geothermal fluid to the active volcano, which forms the Niseko Volcanic
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Geothermics 108 (2023) 102617
Fig. 8. Plan view of the resistivity structure by three-dimensional resistivity analysis in the Niseko area (Tamura et al., 2022). Black dots indicate the observed
stations. 100%
Group, and the discrete magma formed a shallow geothermal reservoir.
The volcanic activity near Mt. Iwao-nupuri was caused by this discrete
magma, which is consistent with the conceptual model of NEDO (1986)
regarding discrete magma as a shallow part of the geothermal reservoir.
Ichiyanagi et al. (2021) reported indicate that the number of earth­
quakes was low and the magnitude of these earthquakes was not large
(< 3) from observations of earthquakes in the Niseko mountains, but
seismic events were detected at the end of the low resistivity zone. These
seismic and resistivity structure overlay may indicate the presence of a
ridge or boundary in the magma chamber.
The upper surface of the geothermal reservoir had a temperature is
380 ◦ C and resistivity of 30 Ω ⋅ m. We defined geothermal reservoir in
this study as the zone where the temperature was over 380 ◦ C and the
resistivity was less 30 Ω ⋅ m. The thickness of the supercritical
geothermal reservoir was assumed to be 500 m (Watanabe et al., 2017).
To stack resistivity, temperature, and topography, we used the Leapfrog
Geothermal software (Fig. 19) (Seequent, 2021).
zone beneath or around Mt. Iwao-nupuri. The underground temperature
structure was compiled from well data, and there was high- temperature
anomalies beneath Mt. Chise-nupuri and Mt. Iwao-nupuri. Based on the
three-dimensional structures obtained from geological survey, the re­
sistivity structure, seismicity observation and the thermal structure, we
constructed a conceptual model of supercritical geothermal systems in
and around the Niseko Mountains. The shallowest part of the super­
critical geothermal systems in the Niseko area was estimated at
approximately -3 km a.s.l. below Mt. Iwao-nupuri and Mt. Chise-nupuri.
CRediT authorship contribution statement
Daisuke Oka: Conceptualization, Methodology, Software, Investi­
gation, Writing – original draft, Visualization. Makoto Tamura:
Conceptualization, Methodology, Investigation, Writing – review &
editing. Toru Mogi: Conceptualization, Methodology, Writing – review
& editing. Mitsuhiro Nakagawa: Conceptualization, Methodology,
Investigation, Writing – review & editing. Hiroaki Takahashi:
Conceptualization, Methodology, Investigation, Writing – review &
editing. Mako Ohzono: Methodology, Investigation, Writing – review &
editing. Masayoshi Ichiyanagi: Methodology, Investigation, Writing –
review & editing.
4. Conclusion
To detect supercritical geothermal systems in the Niseko area, in the
Shiribeshi region of Hokkaido, Japan, we conducted various surveys in
and around the Niseko Mountains. In this project, a geological survey
could reveal the new volcanic activity history of the Niseko Volcanic
Group using new rock samples. It can be estimated that a hot rock body
exists in the deep part under Mt. Chise-nupuri, Mt. Nito-nupuri and Mt.
Iwao-nupuri. The resistivity structure from MT showed a low-resistivity
Declaration of competing interest
The authors have no conflicts of interest directly relevant to the
content of this article.
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Geothermics 108 (2023) 102617
Fig. 9. Examples of N-S cross sections of resistivity structure by three-dimensional resistivity analysis in the Niseko area (Tamura et al., 2022). Latitude (X=0) and
longitude (Y=0) of origin for the analysis are 42˚60ʹ, 140˚38ʹ, respectively. 100%
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Geothermics 108 (2023) 102617
Fig. 10. Bouguer anomaly map in and around the Niseko area with correction density of 2300 kg/m3 (Geological Survey of Hokkaido et al., 2020). Gravity stations
(GSH2017-2018 and GSH2011) were measured by the Geological Survey of Hokkaido (Geological Survey of Hokkaido et al., 2020); gravity stations (AIST2013) are
included in Geological Survey of Japan (2013). The red square shows the research area of the Geological Survey of Hokkaido et al.(2020). 100%
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Geothermics 108 (2023) 102617
Fig. 11. Vertical distribution of well logging data of temperature in the Niseko area. 67%
13
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Geothermics 108 (2023) 102617
Fig. 12. Geothermal vertical temperature profile based on Activity Index (Hayashi et al., 1981). 67%
14
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Geothermics 108 (2023) 102617
Fig. 13. Well logging temperature profile around Niseko area from NEDO(1987). Solid and dashed lines show the temperature profile obtained by well logging and
estimated from the well logging data, respectively. Well codes were recorded from Geological Survey of Hokkaido (2008). 67%
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Geothermics 108 (2023) 102617
Fig. 14. Distribution of underground temperature estimated at -2000m a.s.l, -3000m a.s.l., and inwells. 67%
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Geothermics 108 (2023) 102617
Fig. 15. Hypocenter distribution from 13 November 2019 to 13 October 2020 calculated by the VELEST program using more than four seismic stations based on
Ichiyanagi et a l. (2021). Open triangles and squares are temporal and Hi-net stations, respectively. Solid lines represent active faults. 100%
17
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Geothermics 108 (2023) 102617
Fig. 16. Estimated 1-D velocity structure model. Blue and red lines are P-wave and S-wave velocities respectively. Green line is a P-wave velocity model used for
routine hypocenter determination in Hokkaido University (Ichiyanagi et al., 2021). 50%
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Geothermics 108 (2023) 102617
Fig. 17. Resistivity colour map and temperature distribution contour line. a)-4000 m a.s.l. b) -5000 m a.s.l. 50%
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Geothermics 108 (2023) 102617
Fig. 18. Conceptual model of the geology and thermal structure of SGS in the Niseko Volcanic Group. 100%
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Geothermics 108 (2023) 102617
Fig. 19. a) Cross section of supercritical geothermal reservoir. The line A-A’ relates to X=467,424 m (UTM54N), which is also shown in b). b) Distribution of
resistivity and temperature at -4000 m a.s.l.
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Data Availability
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Magnetotelluric survey and three-dimensional resistivity structure in and around the
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Watanabe, N., Numakura, T., Sakaguchi, K., Saishu, H., Okamoto, A., Ingebritsen, S.E.,
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The data that has been used is confidential.
Funding
This work is supported by Ministry of Economy, Trade and Industry
(METI) (Project of evaluate supercritical geothermal resources and
design detailed specifications for exploration wells), and New Energy
and Industrial Technology Development Organization (NEDO), Poten­
tial survey and estimation of power generation of supercritical
geothermal resources in East Japan and Kyushu, Japan.
Acknowledgment
We are greatly indebted to the landowners for their permission for
any surveys and observations. Parts of the figures in this study were
drawn using the QGIS (QGIS Project, 2019). We would like to thank
Editage (www.editage.com) for English language editing.
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