Shinsuke Nakao

National Institute of Advanced Industrial Science and Technology

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Julie Najita

Lawrence Berkeley National Laboratory

Kenzi Karasaki

Lawrence Berkeley National Laboratory

Tsuneo Kikuchi

National Institute of Advanced Industrial Science and Technology

Tsuneo Ishido

Geological Survey of Japan

Toshiyuki Tosha

Tokyo University of Marine Science and Technology

T. Ishido

National Institute of Advanced Industrial Science and Technology

Hiroki Goto

Juntendo University

Yuji Nishi

Geological Survey of Japan

Mituhiko Sugihara

Geological Survey of Japan

D. g. Zorin

Cooperative Institutions

National Institute of Advanced Industrial Science and Technology

Geological Survey of Japan

Photonics Electronics Technology Research Association

Lawrence Berkeley National Laboratory

Juntendo University

The University of Tokyo

Japan Research Institute

National Institute for Land and Infrastructure Management

NASA Earth Science

University of California, Berkeley

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Repeated Self-Potential Profiling of Izu-Oshima Volcano, Japan

Journal of geomagnetism and geoelectricity (1997)

Tsuneo Ishido Tsuneo Kikuchi Nobuo Matsushima Yusaku Yano Shinsuke Nakao

Between March 1989 and March 1994, annual self-potential (SP) surveys were carried out on Izu-Oshima, a small volcanic island. A terrain-related SP distribution of about -1 mV per meter of elevation was observed outside the caldera in all five surveys. Inside the caldera, SP increases from about -350 mV to near 0 mV (relative to the coastline) as the summit crater is approached, although negative anomalies of small spatial extent are manifest. Self-potential inside the caldera decreased by about 100 mV between the March 1989 and the March 1990 surveys, which appears to be correlated with a significant decline in the degassing rate from the summit crater. After 1990, the SP distribution is quite steady along the entire survey line which extends from the west coast through the southern part of the caldera, and ends east of Ura-sabaku. Recently a postprocessor has been developed to calculate space/time distributions of electrokinetic potentials resulting from histories of underground conditions (pressure, temperature, salt concentration, flowrate etc.) computed by multiphase multi-component unsteady geothermal reservoir simulations (Ishido and Pritchett, 1996). We applied this postprocessor to a simple two-dimensional model of hydrothermal activity in a volcanic island. The low potentials in areas of high elevation are reproduced in the model, and are caused by downflow of meteoric waters. The high potential centered at the summit crater is found to be produced by upflows of volcanic gas and vapor which diminish meteoric water downflow near the volcanic conduit.

Caldera

Fumarole

10.5636/jgg.49.1267

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Hydraulic well testing inversion for modeling fluid flow in fractured rocks using simulated annealing: a case study at Raymond field site, California

Journal of Applied Geophysics (2000)

Shinsuke Nakao Julie Najita Kenzi Karasaki

10.1016/s0926-9851(00)00029-x

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Citations (14)

Sensitivity Study on Hydraulic Well Testing Inversion Using Simulated Annealing

Ground Water (1999)

Shinsuke Nakao Julie Najita Kenzi Karasaki

Abstract Cluster variable aperture (CVA) simulated annealing has been used as an inversion technique to construct fluid flow models of fractured formations based on transient pressure data from hydraulic tests. A two‐dimensional fracture network system is represented as a filled regular lattice of fracture elements. The algorithm iteratively changes element apertures for a cluster of fracture elements in order to improve the match to observed pressure transients. Aperture size is chosen randomly from a list of discrete apertures. The cluster size is held constant throughout the iterations. Since hydraulic inversion is inherently nonunique, it is important to use additional information. We investigated the relationship between the scale of heterogeneity and the optimal cluster size and shape to enhance convergence of the inversion and improve the results. In a spatially correlated transmissivity field, a cluster size corresponding to about 20 % to 40 % of the practical range of the spatial correlation is optimal. Inversion results of the Raymond test site data are also presented and based on an optimal cluster size; the practical range of the spatial correlation is estimated to be 5 to 10 m.

Spatial correlation

10.1111/j.1745-6584.1999.tb01166.x

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Citations (6)

Current status of regional hydrogeological studies and numerical simulations on geological disposal.

BULLETIN OF THE GEOLOGICAL SURVEY OF JAPAN (2004)

Shinsuke Nakao Tsuneo Kikuchi Tsuneo Ishido

地層処分に関する広域地下水流動系の研究動向を，数値シミュレータを用いた地下水流動モデリングの動向を含めて調べた．日本の研究動向については主に，東濃地域において核燃料サイクル開発機構(JNC)により実施されている広域地下水流動研究プロジェクトの結果から，数値モデル構築に必要なモデル域の規模，物性分布，境界条件等を考察した．また，淡水と塩水の遷移帯の挙動を解明することは，沿岸地域の広域流動系モデリングにおいて重要な研究事項であり，近年の研究動向を述べるとともに，地熱の貯留層モデリング用ツールとして使われている数値シミュレータの技術的特徴を述べた．

10.9795/bullgsj.55.409

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Sensitivity study on hydraulic well testing inversion using simulated annealing

Shinsuke Nakao Julie Najita Kenzi Karasaki

For environmental remediation, management of nuclear waste disposal, or geothermal reservoir engineering, it is very important to evaluate the permeabilities, spacing, and sizes of the subsurface fractures which control ground water flow. Cluster variable aperture (CVA) simulated annealing has been used as an inversion technique to construct fluid flow models of fractured formations based on transient pressure data from hydraulic tests. A two-dimensional fracture network system is represented as a filled regular lattice of fracture elements. The algorithm iteratively changes an aperture of cluster of fracture elements, which are chosen randomly from a list of discrete apertures, to improve the match to observed pressure transients. The size of the clusters is held constant throughout the iterations. Sensitivity studies using simple fracture models with eight wells show that, in general, it is necessary to conduct interference tests using at least three different wells as pumping well in order to reconstruct the fracture network with a transmissivity contrast of one order of magnitude, particularly when the cluster size is not known a priori. Because hydraulic inversion is inherently non-unique, it is important to utilize additional information. The authors investigated the relationship between the scale of heterogeneity and the optimum cluster size (and its shape) to enhance the reliability and convergence of the inversion. It appears that the cluster size corresponding to about 20--40 % of the practical range of the spatial correlation is optimal. Inversion results of the Raymond test site data are also presented and the practical range of spatial correlation is evaluated to be about 5--10 m from the optimal cluster size in the inversion.

Spatial correlation

10.2172/658166

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Operation Strategy of Continuous Gravity Measurement as Complementary to Seismic Survey on Geological CO<sub>2</sub> Storage

Journal of MMIJ (2021)

Masao Sorai Hiroki Goto Mitsuhiko Sugihara Yuji Nishi Shinsuke Nakao

Toward the implementation of geological CO2 storage, cost reduction of CO2 monitoring during and after injection into targeted reservoirs is the key issue. The continuous gravity measurement using a superconducting gravimeter, which has been applied to the demonstration project site in Japan ahead of the rest of the world, has a potential to resolve the issue from the viewpoint of a complement to the high-cost seismic survey. The concept is such that the continuous gravity measurement is substituted for constant monitoring and that the use of seismic survey could be limited only when any anomaly is detected. The comparison of the monitoring cost after the completion of CO2 injection indicated that applying gravity measurement can reduce costs by up to 15 to 50% of the seismic cost. The current detection limit of gravity change is around 1 μGal based on the application result in the coastal area in Japan. However, the time series analysis using pseudo gravity data suggested the possibility of anomaly detection even below the detection limit. Further improvement of analysis precision would lead not only to more rapid and more reliable anomaly detection but also to contribution to the cost reduction during the CO2 injection period.

Gravimeter

Anomaly (physics)

Seismic survey

10.2473/journalofmmij.137.46

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Production Tests and Long-term Pressure Observation at the Mutnovsky Geothermal Area, Kamchatska, Russia

日本地熱学会学術講演会講演要旨集 (1996)

Yasukatsu Yano Shinsuke Nakao Nobuo Matsushima Toshiyuki Tosha T. Ishido

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