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JAMSTEC-R IFREE Special Issue, November 2009
― Report ―
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Masataka Kinoshita1*, Keizo Sayanagi2, Takafumi Kasaya1(LLFKLUR$UDNL3, Hisao Ito4
Spatio-temporal distribution of temperature beneath the seafloor provides essential information on the thermal and
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southern Mariana Trough and in the western Sagami Bay, and thermistor array system was tested in two onland boreholes in
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were commonly observed in boreholes. These variations would result from convection or any kind of flow within the hole.
Such variation can be as large as any signal from the formation, so more careful assessment is necessary for the deep-borehole
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Masataka Kinoshita
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+81-46-867-9323
[email protected]
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89
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1. Introduction
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It is now widely accepted that numerous geological
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phenomena are controlled by the physical environment,
release) in the seismogenic zones. Thus we need to achieve
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accurate (to the order of ~mK) and in-situ temperature
more about the events occurring under the ground or
monitoring system. This paper presents a progress report on
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what we learned so far on the temperature measurement in
situ temperature structure and its variation. The best way to
boreholes.
know the temperature at depth is to drill a hole and directly
measure temperature there. However, the number of deep
2. Factors affecting formation temperatures
drill holes is not enough and their depths are limited. Thus,
The formation temperature under the ground (or
in most cases we have to derive it from measurements of
below seafloor), basically determined from the tectonics
surface heat flow and sub-seafloor thermal conductivity
(age of the plate, etc.) or volcanism in the region, is distorted
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by several factors. First, temperature variation at surface,
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caused by millennium-scale climate change to daily variation
global scale, because some of them are affected by local
due to sunshine or tidal modulation, propagates down
effects such as advective heat transfer at hydrothermal
to the formation through thermal diffusion. Nagao and
systems. Other indirect way is to derive temperature from
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temperature-sensitive parameters (deeper limit of seismicity,
measurements at several boreholes, with their depth ~100m
Curie-point depth, seismic velocity, electric conductivity,
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etc.).
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linear and stable temperature profiles for intervals deeper
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than ~30 m below surface. Nonlinear profiles above this
boreholes reveal that the long-term, in-situ temperature
depth are attributed to the seasonal change in surface
monitoring can be a useful tool for detecting transient
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has been carried out by penetrating a lance with multiple
through thermal inversion from time-series borehole
thermistors inside in the sediment (e. g. Kinoshita et al.,
WHPSHUDWXUHHJ&KDSPDQDQG+DUULV:DQJ
1996; Hamamoto et al., 2005). Hamamoto et al. (2005)
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showed that the seasonal changes of temperature above the
diffusivity can be estimated by comparing temperature
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variation between at surface and in borehole (e. g. Kinoshita
Second, drilling operations largely disturb the
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formation temperature; cutting a hole will heat up the
applied to remove the effect of surface temperature variation,
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and to estimate true formation temperatures (e. g. Hamamoto
in-situ temperature. Temperature logging with wireline tools
et al., 2005). From the engineering point of view, the true
is the simplest way to take downhole temperature profile,
temperature is necessary for planning of drilling operations
but the drilling effect must be removed through repeated
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ORJJLQJUXQVE\VWDWLVWLFDOO\H[WUDSRODWLQJWHPSHUDWXUHXVLQJ
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or through fault zones.
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method is +/- 5 K or worse, which is not accurate enough
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Fuca Ridge or in some accretionary prisms (CORK; Becker
accurate enough formation temperatures is to make long-
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term, in-situ measurements.
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Even if we install temperature sensors in the
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borehole, there is intra-hole convection. Cermak et al.
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(2008a; 2008b) monitored temperature at two boreholes
deep borehole observatory system, in which temperature
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90
JAMSTEC-R IFREE Special Issue, November 2009, 89 í102
M. Kinoshita et al.,
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column just above the seafloor for some time, because the
of the hole) displayed intermittent, non-periodic oscillations
water column in the deep sea is often in a thermally very
of temperature of up to several hundredths of degrees, which
stable condition.
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There are two ways in assembling the borehole
temperature measurement system. One is to set the
3. Downhole temperature measurement techniques
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advantages for thermistor against other elements are that it is
need ROV or even drillship to install the system, but once it
easier to measure (resistance), that it has a higher sensitivity
is installed the data is easily downloaded or we can even get
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the data on a real-time basis if the data logger is connected to
response time because of its small dimension, etc. On the
the shore through deep-sea cables.
other hand, disadvantages are that the resistance-temperature
The other is to install a set of stand-alone modules in
relation is non-linear, that its applicable range is narrow (-50
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The accuracy of thermistors depends also on how
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geo.de) (Fig. 1). This is a stand-alone measurement system
for temperature. The isothermal bath have a stability and
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accuracy of 0.01 K or worse. They were actually recorded
memory and battery. The resolution is ~1 mK.
in the temperature data even in the sensors to be calibrated.
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temperature monitoring
precision) to be a few mK. To secure better relative accuracy
Since 2001, we have developed temperature
among multiple sensors, we put the sensors in the water
monitoring instruments for deep-sea environment, and have
Thus, we describe the accuracy for absolute temperature as
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JAMSTEC-R IFREE Special Issue, November 2009, 89 í102
91
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carried out temperature measurements in both onland and
deployment at other sites, and we decided to conduct a long-
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obtained data through these measurements.
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4.1. 1300m-deep borehole at Matsukawa geothermal
more for production was selected for this purpose. It is
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In 2000, we made a 1000m-long thermistor array
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string with 20 thermistors and a data logger to be deployed
3). Its total depth is 1298m below the ground level, and its
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upper 710m is a cased section. The upper 200m consists of
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Matsukawa dacite layer, underlain by Tamagawa welded tuff
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Table 1. Specifications of the temperature monitoring system designed for
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Fig. 4. Vertical section of temperature measurement system at
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92
JAMSTEC-R IFREE Special Issue, November 2009, 89 í102
M. Kinoshita et al.,
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protected by Kevlar coat (arrow), being inserted into the hole, with the other cable for self-potential monitoring.
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temperature with large variation was recorded on the ground (depth=0m).
Fig. 7. Temperature versus depth profile at
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period in 2003.
JAMSTEC-R IFREE Special Issue, November 2009, 89 í102
93
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their amplitude is largest at deepest interval, these diurnal
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variations are not caused by the variation in the surface
2003 for 19 months (Sayanagi et al., 2005).
temperatures.
Fig. 4 shows the schematic section of sensor
Temperature logging data measured in 1992 and 1995
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LQGLFDWHGWKDWWKHZDWHUKHDGLQWKHERUHKROH7*ZDV
system specification. Sampling interval is programmable
m and 138 m, respectively. Thus our temperature data at T8
between 1 second and 1 hour, and was set as 1 minute for
and T9 (50 m and 100 m below the ground, respectively)
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should be watching air temperatures.
mK). Each thermistor was independently coated with poly-
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apparently random temperature variations for all sensors (Fig.
to work up to 6000m water depth.
9). Spiky variations for T1-T7, with their amplitude of ~50
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mK and period of 10-30 minutes, would be caused by water
stable with its variation less than 1 K. Temperature at 270m
circulation or movement in the borehole. Lack of such spiky
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variations at 50 m and 100 m depths (i.e. temperature above
is estimated as 220K/km, which is affected by the local
the water table in the borehole) may support this inference,
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Fig. 8 shows a week-long record of temperature
due to much higher Rayleigh number than that of air under
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this condition.
overlaps). Surface temperature is shown for comparison on
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4.2. Mini-borehole at a hydrothermal site in the southern
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Mariana Trough (March 2004)
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deeper section of the hole.
94
JAMSTEC-R IFREE Special Issue, November 2009, 89 í102
M. Kinoshita et al.,
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bar and the thermistor string went down, lots of soft material
(March 15 to 27, 2004), an intensive survey was carried out
(probably hydrothermal deposits precipitated in the casing)
at several hydrothermal sites in the southern Mariana Trough
came out of the hole. The string stopped falling at ~1.7m.
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Several trials to insert the thermistor string deeper by moving
was prepared to be installed into one of the boreholes drilled
the string back and forth ended in vein. The mission ended
using BMS (Benthic Multi-coring System, chartered from
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during dive #780 on March 25.
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the hole, or to detect any transients or tidal modulation.
in Fig. 12. Four thermistors were in the casing below sea
The thermistor string consists of a data logger,
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thermistor string including 10 thermistors, tension member
a gradual decrease in the hydrothermal venting rate through
wire and a steel sinker bar (Fig. 10). Sampling interval was
the casing. Temperature scattering with their amplitude of
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4.3. Mini-borehole in the western Sagami Bay (2006)
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dive #776. First a sinker bar, temporarily used as a pull-pin,
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was pulled out successfully. Then the sinker bar was inserted
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YHU\VPRRWKO\LQWRWKHFDVLQJDW$30DWWKH)U\HUVLWHƒ
into the sediment, this outer casing pipe is released from the
1ƒ
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corer and stays in the sediment. Mud inside the casing is
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is shown for comparison on the bottom panel. Spiky variations for T1-T7, with their typical period of 10-30 minutes,
may be caused by water circulation or movement in the borehole.
JAMSTEC-R IFREE Special Issue, November 2009, 89 í102
95
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data logger (bottom) used at the Fryer site in
the southern Mariana Trough.
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96
JAMSTEC-R IFREE Special Issue, November 2009, 89 í102
M. Kinoshita et al.,
removed as a core sample.
temperature data was obtained at eight depths for 1 year until
The same thermistor string system that was used in
LWZDVUHFRYHUHGRQ'HF7KHVDPSOLQJLQWHUYDO
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was 10 min.
for a spherical-shell shape lid attached to the string in order
The bottom-water temperature variation was
to isolate the hole from sea water (Fig. 13).
identified in the hole for the first 9 days but it disappeared
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depth 1250m) during the KY05-14 cruise, using the heavy-
days) remained in the hole, and its amplitude was ~10%
duty ROV, or ‘Navigable Sampling System’ (NSS) of
of that in the water, and its phase delay was ~1 day (Fig.
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difference.
The average temperature gradient was calculated as
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(Kinoshita et al., 1992).
Fig. 15 shows a blowup of temperature record for
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their amplitude 10-20 mK and their period 0.5-1 hours.
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but it is likely that these variations are caused by intra-hole
convection of seawater.
4.4. Borehole GF-2 near Lake Tazawa (2008)
Fig. 12. Temperature in the casing (Tnorm10 is located at the lowest
point).
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western Sagami Bay.
JAMSTEC-R IFREE Special Issue, November 2009, 89 í102
97
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Fig. 15. Blowup of temperature record of the temperature array in the piston-core casing in the western Sagami Bay. Note that all temperature curves are
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98
JAMSTEC-R IFREE Special Issue, November 2009, 89 í102
M. Kinoshita et al.,
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their period 1 to 10 minutes (Fig. 17). No clear correlation
we carried out a system integration test for the tiltmeter using
between sensors is seen, but some variations seem to be
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described in the previous sections, these may be indicatives
1854 (Fig. 1).
of intra-hole convection or vertical migration of water due to
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4.5. Effect of intra-hole fluid circulation on geodetic
hole was cut to 800m depth in the welded tuff formation, and
measurements
the upper 300m is a cased section (Ito and Kikuchi, 1987). So
Through monitoring in above boreholes, we observed
far some temperature and stress measurements were carried
VRPHW\SHVRIWHPSHUDWXUHÀXFWXDWLRQV6HDVRQDOYDULDWLRQV
out, and the hole condition is well known.
are caused by the change in ground temperature (up to 30 K
The tiltmeter assembly was lowered with a standard
peak to peak), and they are attenuated at depth of a few tens
logging wire with seven conductors inside. Temperature
of meters below ground, depending on the thermal diffusivity
loggers were attached to the tiltmeter or to the wire (Fig. 16),
of formation material. Temperature variations with semi-
XVLQJYLQ\OWDSHVDQGFDEOHWLHV³WLHZUDS´7KHH[SHULPHQW
GLXUQDOSHULRGDUHREVHUYHGEHQHDWKWKHVHDÀRRU7KH\DOVR
was conducted from Sep.9 to Oct. 18, 2008, and the
attenuate with depth, so that they can be distinguished from
temperature monitoring with seven data loggers distributed
RWKHUÀXFWXDWLRQV
from surface to 200m depth was carried out just for one night
:HREVHUYHGWHPSHUDWXUHIOXFWXDWLRQLQPRVWRIWKH
(Sep. 12).
boreholes as described above. Their amplitude ranges 10-50
$WDSUHOLPLQDU\ORRNZHFOHDUO\UHFRJQL]HWKDWDOO
P.DQGSHULRGPLQXWHVWRKRXU$OWKRXJKZHQHHGPRUH
temperatures fluctuates with their amplitudes ~50 mK and
careful analysis, they are probably caused by the intra-hole
)LJ/HIW%RUHKROHWLOWPHWHUDVVHPEO\EHLQJLQVHUWHGLQWR*)KROH&HQWHU7HPSHUDWXUHGDWDORJJHUDWWDFKHGWRWKHZLUHZKLWHFLUFOH5LJKW
'HSWKRIWHPSHUDWXUHGDWDORJJHULQWKHKROH
JAMSTEC-R IFREE Special Issue, November 2009, 89 í102
99
/RQJWHUPWHPSHUDWXUHVPHDVXUHPHQWVDWVRPHRQODQGDQGVXEVHDÀRRUERUHKROHV
ÀXLGFLUFXODWLRQ,WFDQVLJQL¿FDQWO\DIIHFWWKHSHUIRUPDQFH
RI WR ƒ& IRU PRUH WKDQ RQH \HDU:H DOVR IRXQG WKDW
of other instruments in the borehole, such as tiltmeter (section
WHPSHUDWXUHVÀXFWXDWHDWDSHULRGRIPLQXWHVZLWKWKHLU
$VLPSOHFDOFXODWLRQGHPRQVWUDWHVWKDWDWHPSHUDWXUH
DPSOLWXGH.IRUDOOVLWHV7KHH[LVWHQFHRILQWUD
difference of 0.1K between both ends of the metal housing
hole fluid circulation may be the cause of these variations.
of tiltmeter (length ~ 1 m) can cause its internal tilt of 10
-6
UDGLDQ DVVXPLQJ KRXVLQJ¶V WKHUPDO H[SDQVLRQ FRHIILFLHQW
-5
$EHWWHUNQRZOHGJHRIWKHLQWUDKROHDGYHFWLRQLVDEVROXWHO\
necessary to achieve the goal of borehole observatories.
-1
is 10 K ) and calculated by multiplying the length and
WHPSHUDWXUHGLIIHUHQFHZKLFKLVHTXLYDOHQWRUHYHQODUJHU
Acknowledgments
WKDQWKHIRUPDWLRQWLOWH[SHFWHGIRUWKHVHLVPRJHQLF]RQHV
7KHH[SHULPHQWVLQWKHUHSRUWDUHSULPDULO\IXQGHG
$ EHWWHU NQRZOHGJH RI WKH KROH FRQGLWLRQ LV DEVROXWHO\
E\ -DSDQ 0DULQH 6FLHQFH DQG7HFKQRORJ\ &HQWHU necessary to achieve the overall scientific goal of borehole
DQG LWV VXFFHVVRU -DSDQ DJHQF\ IRU 0DULQH(DUWK
observatories.
6FLHQFHDQG7HFKQRORJ\:HDUHJUDWHIXOIRURWKHUIXQGLQJ
sources, the Special Coordination Funds of MEXT (Ministry
5. Summary
of Education, Culture, Sports, Science and Technology) of
Since 2001, we have carried out the temperature
-DSDQ DV WKH $UFKDHDQ 3DUN 3URMHFW 3URMHFW DQG *UDQW
PRQLWRULQJEHQHDWKWKHVHDÀRRURUDWRQODQGERUHKROHV)RXU
LQ$LG IRU &UHDWLYH 6FLHQWLILF 5HVHDUFK *67KH
H[DPSOHV ZHUH SUHVHQWHG KHUH WZR LQ RQODQG ERUHKROHV
GDWDORJJHUXVHGLQ0DWVXNDZD7*VLWHZDVSXUFKDVHGE\
DQGWZRLQWKHGHHSVHDLQVLGHDIHZPKROHEHORZVHDÀRRU
(DUWKTXDNH5HVHDUFK,QVWLWXWH8QLYHUVLW\RI7RN\R:HDUH
:HIRXQGWKDWWKHWKHUPLVWRUHOHPHQWVFRDWHGZLWKµ7HÀRQ¶
JUDWHIXOWRWKHRSHUDWLRQWHDPRI52952326DQG166IRU
proved to be stable and reliable in a temperature range
the successful operations of deployment and recovery of
)LJ7HPSHUDWXUHUHFRUGHGLQ*)KROHIURPPWRPGHSWK$QQRWDWLRQVLQWKHJUDSKLQGLFDWHWKHVHQVRUQXPEHUDQGLWVGHSWKPHJµ7B¶
stands for sensor T5 set at 195m below surface). Note the data is vertically offset to avoid overlaps, so the absolute value of temperature is
meaningless.
100
JAMSTEC-R IFREE Special Issue, November 2009, 89 í102
M. Kinoshita et al.,
PDULQHWHPSHUDWXUHV\VWHPV:HWKDQNWKHVWDIIRI,)5((
-$067(&SURPRWLRQRI¿FHIRUWKHORJLVWLFVKDQGOLQJ
Planetary Interiors, 152, 314-325.
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Thermal response of sediment with vertical
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$UDNL(0.LQRVKLWD7.DVD\D7*RWR<+DPDQR
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JAMSTEC-R IFREE Special Issue, November 2009, 89 í102