Seismic exploration technologies with distributed acoustic sensing (DAS) are investigated to acquire seismic waves in high-temperature environments and locate supercritical geothermal reservoirs deeper than the brittle-ductile transition... more
Seismic exploration technologies with distributed acoustic sensing (DAS) are investigated to acquire seismic waves in high-temperature environments and locate supercritical geothermal reservoirs deeper than the brittle-ductile transition boundary in Japan. We conducted a seismic reflection survey in the Mori-Nigorikawa geothermal field in the Nigorikawa caldera basin. An optical fiber system and an array of geophones were installed to 2100 m depth in F-01, a little-deviated high-temperature geothermal production well, and along a road for about 1.2 km on the surface. Numerous reflectors appear to gather at a depth between 2000 and 3000 m, corresponding to the production zone of the well. Although the production zone is located mainly within the Nigorikawa volcanic conduit estimated in the past geothermal analysis, the reflectors are also distributed outside the conduit. The DAS waveforms show distinct traveltime discontinuity at 1060 m depth. Our traveltime tomography and forward-si...
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Research Interests: Geology and Precipitation
SUMMARY Time-lapse-studies of the CCS, CO2-EOR and fractured zones of shale gas production is now one of very important technologies. The seismic-ACROSS (Accurately Controlled and Routinely Operated Signal System) can generate very stable... more
SUMMARY Time-lapse-studies of the CCS, CO2-EOR and fractured zones of shale gas production is now one of very important technologies. The seismic-ACROSS (Accurately Controlled and Routinely Operated Signal System) can generate very stable and continuous seismic waves for long time, it might be one of the most suitable methods for the time lapse works. Assuming a single ACROSS source and a multi-geophone array, we have made simulation at the Ketzin pilot site for CO2 storage in Germany. At Ketzin, CO2 has been injected since July, 2008. About 62 ktons of super-critical CO2 have been injected to date at about 630-650 m depth, and injection will continue into 2013. To monitor how the injected CO2 behaves after injection is extremely important for studying the long term behavior of a storage site. The objectives of this study are to find the most suitable locations for an ACROSS-source and receivers at the Ketzin site given infrastructure constraints. Results using the velocity-density structure site model show that a rectangular injection zone 200 m wide and 10 m thick at 665 m depth is well imaged. We also made 3D simulation in Ketzin. The result suggests that large aperture is very important to obtain better image. This result encourages us to plan for using an ACROSS-source for time-lapse-studies to monitor the migration of injected CO2 at Ketzin, even after injection has finished.
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Abstract To examine the effectiveness of our time-lapse method for oil and gas reservoir and carbon-dioxide capture and storage (CCS) monitoring, we carried out an air-injection field test in Japan using the Accurately Controlled and... more
Abstract To examine the effectiveness of our time-lapse method for oil and gas reservoir and carbon-dioxide capture and storage (CCS) monitoring, we carried out an air-injection field test in Japan using the Accurately Controlled and Routinely Operated Signal System (ACROSS) seismic source. We injected 80 t of air at a depth of 100 m for 5 days. Thirty-one 3C seismometers on the ground surface and one 3C borehole seismometer at a depth of 800 m were deployed. We calculated the transfer functions from the seismic source to every seismometer for all observed records. Their residual waveforms, that is, the difference in transfer functions to each seismometer before and after the injection, were calculated. The residual waveforms indicate very large travel time and waveform changes due to the migration of the injected air. Distinct time delays were observed at half of the seismic stations after starting the air injection. The air and water spread very fast (0.2 cm/s). We imaged the migration of air from west to east for 5 days using the reverse-time method for residual waveforms.
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Abstract A field study to assess the practicability of Accurately Controlled and Routinely Operated Signal System (ACROSS) time lapse was carried out in a desert area of the Kingdom of Saudi Arabia from 2011 to 2015. Because the test... more
Abstract A field study to assess the practicability of Accurately Controlled and Routinely Operated Signal System (ACROSS) time lapse was carried out in a desert area of the Kingdom of Saudi Arabia from 2011 to 2015. Because the test field was located at a water pumping site, temporal variation associated with water pumping was expected to be detected in a time-lapse seismic observation using the ACROSS system. An ACROSS seismic source and a three-component seismometer network were used to obtain time-lapse seismic records. The time-lapse records show significant temporal changes in the surface waveforms due to water pumping and weather conditions that change the state of near-surface materials in time. The results suggest the importance of eliminating near-surface effects. In addition, the ambient noise of the acquired ACROSS observation data was analyzed. These results indicate the possibility of the ACROSS system being used simultaneously for both active and passive time-lapse seismic recordings.
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We present a general framework for selecting optimal measurement locations for applications. This framework incorporates the basic ingredients that are usually part of an inversion process: choice of regularisation scheme, nature and size... more
We present a general framework for selecting optimal measurement locations for applications. This framework incorporates the basic ingredients that are usually part of an inversion process: choice of regularisation scheme, nature and size of measurement error, and use of prior knowledge to constrain solutions. The basic idea of the framework is to minimise errors associated with the reconstruction of a given quantity of interest. We introduce five functional layers which reflect the structure of the framework. Further, with framework adaption we formulate an iterative algorithm which finds optimal measurement locations at each iteration step to obtain improved reconstructions of the inverse problem. Using initial reconstructions as input, framework adaption does not require prior knowledge of the source distribution. We illustrate the feasibility of framework adaption by solving an acoustic source problem. Numerical examples are given.
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Research Interests: Geology and Seismology
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Seismic ACROSS (Accurately-Controlled Routinely-Operated Signal System) enables us to continuously monitor the temporal change of the amplitude and/or travel-time of particular seismic reflectors or diffractctors from a time-variant... more
Seismic ACROSS (Accurately-Controlled Routinely-Operated Signal System) enables us to continuously monitor the temporal change of the amplitude and/or travel-time of particular seismic reflectors or diffractctors from a time-variant region (e.g., oil-gas /CO2/aquifer reservoirs and a focal region) because of very accurate-and-stable seismic signals. The seismic ACROSS controlled by GPS clock is fixed type source which can generate 10-50Hz and 40 ton-f at 50Hz. To evaluate the seismic characteristics before and after the change and optimized source-receiver array design and to image the time-variant target region, we investigated the following cases with a velocity change of (i) 10 % in a CO2 reservoir with a 300-m-wide and 100-m-thick at 200m-depth, and (ii)~30 % in a deep-slip zone with a 10-km-long and 200-m-thick at 30-km-depth, by applying a imaging method using FDM back-propagating residual waveforms. We can robustly obtain the location and shape of the targets by using the vel...
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We carried out a long-duration seismic time-lapse experiment consisting of two periods in 2012-2013 and 2015 in a water pumping field in the Kingdom of Saudi Arabia using an ultra-stable ACROSS seismic source and a geophone array. The... more
We carried out a long-duration seismic time-lapse experiment consisting of two periods in 2012-2013 and 2015 in a water pumping field in the Kingdom of Saudi Arabia using an ultra-stable ACROSS seismic source and a geophone array. The comparison of travel times and amplitudes of P waves show quite small but distinct temporal variation with time. The maximum change is approximately 1.5 ms during two months both in the first and the second periods. Because the total travel time is 0.2 s, the change of 1.5 ms corresponds to 0.75%. The resolution of travel-time change is ~0.1 ms and it is good resolution to detect the change of subsurface caused by CO2 or high-temperature H2O injection to the heavy oil reservoir. We also discuss the NRMS repeatability of the observation system using the first arrivals at the stations within 700 m from the source and found that the NRMS repeatability was better than 5% during 2 month periods. The source itself might have roughly 2% NRMS repeatability. Th...
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We propose a seismic approach on active seismic sources using a distributed acoustic sensor (DAS) and a distributed temperature sensor (DTS) (Hartog, 2017) to develop the most effective tools for obtaining the characteristics of... more
We propose a seismic approach on active seismic sources using a distributed acoustic sensor (DAS) and a distributed temperature sensor (DTS) (Hartog, 2017) to develop the most effective tools for obtaining the characteristics of geothermal fields. Our approach employs fibre optics and full waveform inversion (FWI) methods. The New Energy and Industrial Technology Development Organization (NEDO) in Japan has, in its project called ‘Research and Development of Supercritical Geothermal Resources,’ promoted the use of these resources for geothermal power generation. As a part of this programme, we have focussed our efforts on studying seismological approaches using DAS in the geothermal field since 2017. In 2018 and 2019, we conducted a DAS seismic survey using one of the boreholes in the Medipolis geothermal field on Kyushu Island, Japan (Kasahara et al., 2019a, b, 2020). We obtained excellent DAS seismic records for both natural earthquakes and seismic vibrator activations. Because the geological setting of the geothermal field is heterogeneous and the scattering attenuation due to heterogeneity is high, we stacked the DAS data 480–960 times to enhance the S/N ratio with source signature correction. We observed a significant seismic reflection at a depth of 3.8 km. The zone at approximately 3.8 km shows high Vp/Vs, suggesting the possibility of supercritical water (Kasahara et al., 2020).
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MCS reflection records in the western Pacific Ocean show wide variations of seismological characteristics of the Moho from no reflections to strong and continuous reflections (Kasahara et al., this meeting). In order to find the relation... more
MCS reflection records in the western Pacific Ocean show wide variations of seismological characteristics of the Moho from no reflections to strong and continuous reflections (Kasahara et al., this meeting). In order to find the relation of such wide variation of characteristics and the nature of the Moho Transition Zone (MTZ), we examined the characteristics of the Moho reflections using
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To quantify the temporal and spatial changes of underground geophysical state, we require an integrated mapping and monitoring system (Kasahara et al., in this meeting). A mapping of the crustal structure has been suggested by seismic... more
To quantify the temporal and spatial changes of underground geophysical state, we require an integrated mapping and monitoring system (Kasahara et al., in this meeting). A mapping of the crustal structure has been suggested by seismic reflection and refraction experiments by chemical explosive sources, other artificial sources and natural earthquakes. For example, across the central Japan the strong PxP reflection
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Abstract To examine the usefulness of the accurately controlled routinely operated signal system (ACROSS) for the detection of the temporal change of scattering or reflection signatures, we conducted a 9-month experiment using a seismic... more
Abstract To examine the usefulness of the accurately controlled routinely operated signal system (ACROSS) for the detection of the temporal change of scattering or reflection signatures, we conducted a 9-month experiment using a seismic ACROSS source in Toki City, Japan, and a temporal linear seismic array extending from Toki City toward the south. The seismic experiment was carried out from December 2005 to September 2006. The observations show that the 8-day stacking at ~60 km of offset distances is characterized by prominent arrivals similar to that of the 30-day stacking. This suggests that 1-week stacking is sufficient to detect prominent arrivals up to ~60 km offset distances. We calculated theoretical travel times and synthetic seismograms using the reanalyzed crustal structural model and compared the observed seismograms with theoretical travel times and synthetic seismograms. The synthetic and observed records match well with each other. However, the phases reflected from the subducting plate boundary could not be identified for the offset range of receivers used in this study. Nevertheless, the 8-day stacking of the data received at station “OSD” at an offset distance of 61.2 km provides a sufficient signal-to-noise ratio to identify Pg, which is a refracted wave in the crust, and shallow reflected arrivals.
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ABSTRACT ACROSS (Accurately Controlled and Routinely Operated Signal System) is effective in monitoring temporary changes of Earth's interior. A long-term operation experiment near Nojima fault [Ikuta et al.,2004] detected small... more
ABSTRACT ACROSS (Accurately Controlled and Routinely Operated Signal System) is effective in monitoring temporary changes of Earth's interior. A long-term operation experiment near Nojima fault [Ikuta et al.,2004] detected small temporary changes of travel time of P and S waves at tele-seismic events. Toward Tokai monitoring plan to detect the reflected phases from the top of Philippine Sea Plate and monitor its temporal changes, a mid-term continuous experiment was conducted using ACROSS source and a seismic array. The experiment was operated for the period from Dec. 2004 to Sep.2005 in the Tokai area, Pacific side of the central part of Japan. In this region, the expected Tokai earthquake is a serious concern. In addition, slow slip events and low-frequency tremors are observed in this area. A strong reflected phase from the plate boundary was found by the seismic observation using artificial sources [Iidaka et al.,2003]. The purpose of the experiment is to establish a method to detect and monitor the reflection from the plate boundary using ACROSS. The ACROSS source is located in Toki city and operated by Tono Geoscience Center. The ACROSS source continuously transmits precisely-controlled frequency-modulated signals whose frequency band ranges from 10 to 20 Hz with an interval of 50 seconds. We deployed a short-span seismic array at the distance of 55 km from the ACROSS source. The cross-shaped seismic array spanning 2 km consists of 12 seismometers equipped with an offline data logger, amplifier and solarpanel. We stacked the received signal for a month with an interval of 200 seconds in order to improve signal noise ratio. We extracted a series of line spectrum of ACROSS signal. Transfer function can be obtained by dividing spectrum by the source. Applying inverse Fourier transform, we can obtain the transfer function in time-domain. We identified direct P and S phases by comparing with the standard travel time table by JMA. We also found some coherent later phases. By comparing the travel-time of these phases with the travel-time calculated by ray-tracing with a given structure model, these phases may include the reflection waves from the top of Philippine Sea plate, the Mohorovicic discontinuity and some other physical discontinuities. We calculated the semblance of the later phases to estimate the slowness and the incident angle. A later phase with a low slowness can be found after the direct P phase. We also try to evaluate the temporal change of travel time and waveform. The detail results will be presented in the conference.
Research Interests: Geology and Seismology
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ABSTRACT We have developed a method to extract “events” localized in a time domain from a transfer function in the frequency domain, which is a part of the basic analysis in ACROSS (Accurately-Controlled Routinely-Operated Signal System).... more
ABSTRACT We have developed a method to extract “events” localized in a time domain from a transfer function in the frequency domain, which is a part of the basic analysis in ACROSS (Accurately-Controlled Routinely-Operated Signal System). In response to the limitations with respect to the practical application shown in the previous procedure, we designed a revised version of this method, based on maximum likelihood estimation. The basic theory, including the revision, is presented here, along with a practical procedure for automatic travel time determination. We then submitted this revised version to a numerical test, the results of which supported the validity of this method for analysis of transfer functions involving plural “events” in the time domain.
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Recently, in order to determine crustal structure in the oceanic region, a huge amount of seismic data has been collected using a set of digital OBSs and a large volume (e.g., ~8,040 cubic inches) tuned airgun-array. Such survey can... more
Recently, in order to determine crustal structure in the oceanic region, a huge amount of seismic data has been collected using a set of digital OBSs and a large volume (e.g., ~8,040 cubic inches) tuned airgun-array. Such survey can provide full-waveform data of wide-angle reflected and refracted arrivals. Most of previous analyses using OBS data have commonly been carried out
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Research Interests: Geology and Seismology
We present a method for interpreting seismic records with arrivals and waveforms having characteristics which could be generated by extremely inhomogeneous velocity structures, such as non-typical oceanic crust, decollement at subduction... more
We present a method for interpreting seismic records with arrivals and waveforms having characteristics which could be generated by extremely inhomogeneous velocity structures, such as non-typical oceanic crust, decollement at subduction zones, and seamounts in oceanic regions, by comparing them with synthetic waveforms. Recent extensive refraction and wide-angle reflection surveys in oceanic regions have provided us with a huge number of high-resolution and high-quality seismic records containing characteristic arrivals and waveforms, besides first arrivals and major reflected phases such as PmP. Some characteristic waveforms, with significant later reflected phases or anomalous amplitude decay with offset distance, are difficult to interpret using only a conventional interpretation method such as the traveltime tomographic inversion method. We find the best process for investigating such characteristic phases is to use an interactive interpretation method to compare observed data with synthetic waveforms, and calculate raypaths and traveltimes. This approach enables us to construct a reasonable structural model that includes all of the major characteristics of the observed waveforms. We present results here with some actual observed examples that might be of great help in the interpretation of such problematic phases. Our approach to the analysis of waveform characteristics is endorsed as an innovative method for constructing high-resolution and high-quality crustal structure models, not only in oceanic regions, but also in the continental regions.
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ABSTRACT Recently, a very strong reflected PP phase from the subducting plate boundary was found beneath the aseismic forearc slope of the Japan Trench (Fujie et al., 2003, Kasahara et al., 2003). This strong PP reflection is interpreted... more
ABSTRACT Recently, a very strong reflected PP phase from the subducting plate boundary was found beneath the aseismic forearc slope of the Japan Trench (Fujie et al., 2003, Kasahara et al., 2003). This strong PP reflection is interpreted as a reflection from the non-asperity region along the plate boundary caused by the presence of low-Vp material. Similar strong PP reflection phase was observed near the plate boundary of the subducting Philippine Sea Plate and the Eurasian Plate, in the western part of Shizuoka Prefecture along the NS seismic survey line across the central part of Japan using explosive sources (Iidaka et al., 2003, Kodaira et al., 2004). This region is match to the aseismic slip zone since 2000 observed by GPS (Ozawa et al., 2002). This region is supposed to the lower edge of future Tokai or Tonankai earthquake along the Nankai Trough. The "ACROSS" (Accurately Controlled and Routinely Operated Signal System) (Kunitomo and Kumazawa, 2004) can continuously transmit accurately-controlled seismic waves in amplitude, frequency and phase. Using continuous transmission of seismic waves from the ACROSS source located in Toki City, Japan and /or the new ACROSS source under planning in the western part of Shizuoka Prefecture and the high sensitivity seismometers along the NS traverse line, we can delineate the temporal variation of seismic wave properties of the anomalously reflected PP phase along the boundary of subducting Philippine Sea Plate. This observation can give information on variation of the physical state of frictional slip and clues for the earthquake generation. It is also very useful for the monitoring of precursory slip and/or after-slip of the future Tokai and Tonankai earthquakes (or any large earthquakes) with sources along the Philippine Sea Plate.
Research Interests: Geology and Seismology
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Abstract We have developed a technology for active monitoring of seismogenic zones and/or volcanic areas. The technology utilizes Accurately-Controlled Routinely-Operated Signal System (ACROSS) and is capable to detect subtle changes in... more
Abstract We have developed a technology for active monitoring of seismogenic zones and/or volcanic areas. The technology utilizes Accurately-Controlled Routinely-Operated Signal System (ACROSS) and is capable to detect subtle changes in physical properties. It also requires optimal placement of source and receiver arrays containing many easy-to-use seismometers. However, any current calibration method determining a frequency response of the ground motions for such seismometers is not accurate enough. We developed a secondary calibration method for easy-to-use seismometers by utilizing seismic ACROSS signals, a vibration table and reference accelerometers. We present the basic concept together with technical steps, and demonstrate the experimental results for 52 target uni-axial sensors by using the more reliable accelerometers as reference. Despite the average accuracy of the frequency responses for the reference sensors, we could easily obtain a precise enough frequency response for each tested sensor using the Maximum Likelihood method. In experimental results, the accuracies of frequency response for sensors were approximately 10 2 -10 3 . Although these values are not accurate enough for active monitoring of the Earth’s interior, we can conclude that this method is useful enough to provide a simultaneous and precisely-determined frequency response for a large array of easy-to-use seismometers.
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Recent studies revealed that large earthquakes at the subducting plate boundary repeatedly occur in asperities. On the other hand, the rest of plate boundary zone is called non-asperities and releases strain by slow slip. The subducting... more
Recent studies revealed that large earthquakes at the subducting plate boundary repeatedly occur in asperities. On the other hand, the rest of plate boundary zone is called non-asperities and releases strain by slow slip. The subducting plate interface in two regions show strong seismic reflections (bright interface) from the nonasperity interface. If we can map the nonasperities by intensity of PP reflections, we can map the distribution of asperity on the plate boundary. It can give quantitative data for the estimation of ongoing subduction process. The EARS (Exploration of Asperities-Reflectors System) intends to integrate necessary research components for the estimation of on-going plate subduction. Major component of EARS are: mapping active and continuous monitoring, real time data telemetry and study of physical properties. In the geophysical exploration technologies such as 2D, 3D seismic surveys on land and offshore wide-angle reflection-refraction survey using OBS-airguns are essential technologies to map the nature of the subuducting plate boundary. The second component is active and continuous monitoring. The ACROSS (Accurately and Routinely Operated Signal System) is a unique seismic and/or electromagnetic survey method to use active and continuous signal sources. It can be used for time-lapse geophysical survey. Using an ACROSS seismic source and temporary seismic array across the central Japan, we carried out feasibility study to characterize seismic arrivals through slow slip region where one of strong reflections has been observed in the NE region of Lake Hamana and large aseismic slip has been also detected by GPS. By comparison of synthetic seismogram and observed records, we identified refracted phases and some reflected phases. Although, the observational offset was not full enough to identify the reflected phase from the plate boundary, the results showed high potential to use ACROSS for the time-lapse and EARS studies.
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Recently, our seismological knowledge about source mechanisms of plate-boundary earthquakes has revealed the possibility in the detection of spatiotemporal changes in physical properties that may occur at interplate boundaries.... more
Recently, our seismological knowledge about source mechanisms of plate-boundary earthquakes has revealed the possibility in the detection of spatiotemporal changes in physical properties that may occur at interplate boundaries. Seismological interest is identified to be in seismogenic zones that are deeper than several kilometers from the surface.
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Microseismic analysis plays a key role in hydraulic fracture monitoring for developing shale plays and avoiding unwanted fracture development. Meanwhile, active seismic (or 4D seismic) monitoring is widely used for delineating temporal... more
Microseismic analysis plays a key role in hydraulic fracture monitoring for developing shale plays and avoiding unwanted fracture development. Meanwhile, active seismic (or 4D seismic) monitoring is widely used for delineating temporal change associated with fluid injection and production. For continuous analysis of both passive and active seismic at the same time, we introduce an approach to simultaneously aquire seismic signals from microseismic and from active seismic sources ACROSS (Accurately Controlled, Routinely Operated Signal System). We perform test data acquisition with two ACROSS sources in Kashiwazaki, Japan to obtain high signal-to-noise ratio (S/N) of ACROSS data and passive seismic signals after the suppression of ACROSS data. The ACROSS source was operated with sweep cycle of exactly 200 seconds and with frequencies ranging between 5 and 50 Hz. Permanent geophone data at 1.5 km and 5.5 km from the ACROSS sources confirmed highly repeatable ACROSS signals with 2 hour stack and 1 day stack, respectively. The results indicated that the transmittability of ACROSS signal is sufficient enough for daily-basis active-seismic analysis. On the other hand, motions related to ACROSS source were clearly suppressed by subtracting "weight-averaged" ACROSS data, and subtle motions from passive seismic were uncovered. The ground motions of lower than 50 micro kines (5 X 10-7 m/s) were extracted at just 70 m away from the ACROSS source. Since continuous microseismic observation is possible at most of the receiver locations, our proposed technicque should provide opportunities for passive and active seismic surveys at the same time and may be highly beneficial for shale or other tight reservoir characterization.
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In order to examine the validity of the Accurately-Controlled Routinely-Operated Signal System (ACROSS) to detect temporal changes of reflective signatures, we conducted a nine-month experiment using a seismic ACROSS in Toki city and a... more
In order to examine the validity of the Accurately-Controlled Routinely-Operated Signal System (ACROSS) to detect temporal changes of reflective signatures, we conducted a nine-month experiment using a seismic ACROSS in Toki city and a temporal linear seismic array extending toward the south from Toki city. The seismic experiment was carried out from December 2005 to September 2006.The observations show that
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We carried out a long-duration seismic time-lapse experiment consisting of two periods in 2012-2013 and 2015 in a water pumping field in the Kingdom of Saudi Arabia using an ultra-stable ACROSS seismic source and a geophone array. The... more
We carried out a long-duration seismic time-lapse experiment consisting of two periods in 2012-2013 and 2015 in a water pumping field in the Kingdom of Saudi Arabia using an ultra-stable ACROSS seismic source and a geophone array. The comparison of travel times and amplitudes of P waves show quite small but distinct temporal variation with time. The maximum change is approximately 1.5 ms during two months both in the first and the second periods. Because the total travel time is 0.2 s, the change of 1.5 ms corresponds to 0.75%. The resolution of travel-time change is ~0.1 ms and it is good resolution to detect the change of subsurface caused by CO2 or high-temperature H2O injection to the heavy oil reservoir. We also discuss the NRMS repeatability of the observation system using the first arrivals at the stations within 700 m from the source and found that the NRMS repeatability was better than 5% during 2 month periods. The source itself might have roughly 2% NRMS repeatability. The NRMS repeatability is based on the waveform change. The present result supports that the ACROSS source has excellent repeatability well enough to discuss the time lapse of the subsurface.
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超臨界地熱開発には未知の部分が多い。必要な地学的情報として超臨界地熱域の深さ、場所、流体の状態、鉱物組成と粒界状態と超臨界水量と化学的活性度、延性度などがある。玄武岩質岩石に比べ花崗岩質石はより低い温度、圧力条件で延性的になる。また変形速度も重要な要素である。過去幾多の変形実験が有る。葛根田など花崗岩質の領域はより浅い場所で延性的になりそれにより空隙が減少し流体循環による温度勾配の下がり超臨界状態になりやすいと考えられる。超臨界地熱域の地学的状態がある程度わかったとしてそこか... more
超臨界地熱開発には未知の部分が多い。必要な地学的情報として超臨界地熱域の深さ、場所、流体の状態、鉱物組成と粒界状態と超臨界水量と化学的活性度、延性度などがある。玄武岩質岩石に比べ花崗岩質石はより低い温度、圧力条件で延性的になる。また変形速度も重要な要素である。過去幾多の変形実験が有る。葛根田など花崗岩質の領域はより浅い場所で延性的になりそれにより空隙が減少し流体循環による温度勾配の下がり超臨界状態になりやすいと考えられる。超臨界地熱域の地学的状態がある程度わかったとしてそこから地熱を得る時、熱回収法、掘削技術、超臨界水によっても劣化しにくいケーシングとセメントの素材、超臨界状態でかつ延性領域の破砕帯を作る方法、コスト評価がある。本研究では超臨界地熱開発を円滑に推進する上で重要なモニタリングとシミュレーションに重点を置き実現可能性の調査検討を実施する。