Hideki Mizunaga

Reservoir monitoring by a 4-D electrical technique

An advanced geoelectrical technique for imaging potential fractures has been developed by Engineering Geophysics Laboratory of Kyushu University. The method, fluid‐flow tomography (FFT), has been applied to monitor fluid‐flow behaviors during massive water/steam injection operations through a borehole. Fluid‐flow behaviors in potential fractures could be continuously traced and visualized as a function of time by the FFT system. Potential fractures can be evaluated by 3-D inversion of self‐potential (SP) anomalies based on a potential theory similar to the hypocenter of the earthquakes. The FFT method has been applied to determine the location of fractures in a geothermal area in Japan.

Flash Flood Risk Assessment for Kyushu Island, Japan

Using advanced geospatial analysis technologies, flash flood risk is assessed for the island of Kyushu, Japan. In this study, the flash flood risk is redefined in terms of the flash flood potential index (FFPI) and the flash flood residential hazard (FFRH). The island experiences rainy weather, especially in the summer (June–August), when catastrophic flash flood events have historically occurred. Studies of the surface hydrological properties of the island are very rare and localized; hence, geospatial techniques are most appropriate for the assessment process. The Soil Conservation Service rainfall-runoff model was used to estimate hydrological responses on the island. Four factors were included in the flash flood assessment. A multi-criteria analysis was carried out to map the FFPI and FFRH from the evaluation factors. The results show that the highest flash flood risk occurs in the northern parts of the island, where the soil displays relatively low infiltration rates and relatively high curve numbers, despite the comparatively low precipitation rates that occur there. The results indicate that soil hydrological properties are the main driving forces of flash floods, especially in regions with low precipitation rates. The results of this research are consistent with previous in situ measurements of runoff made at several sites on the island. The results also show a strong geographic correlation with historical flash flood events on the island. This research validates the use of geospatial analysis for large geographic regions where in situ measurements cannot be taken due to time or cost constraints. The results of this study provide decision makers with the information needed to select a management strategy to address possible future flash flood events that considers safety and water harvesting.

Three-dimensional magnetotelluric inversion using a heterogeneous smoothness-constrained least-squares method

This paper presents a fast algorithm for electromagnetic data inversion to three-dimensional (3D) resistivity models. The algorithm is distinctive for the level of accuracy it attains while bypassing the sensitivity matrix update. A common sensitivity matrix for homogeneous half-space is used in all iterations. Instead of updating the sensitivity matrix, the smoothness filter coefficients at each model element are updated, based on the spatial variations in resistivity in the model derived from the latest iteration. This substitution is expected not only to reduce the computation time required for large-scale inversions, such as those for 3D surveys, but also to allow the resolution of sharp boundaries in resistivity structures. Our algorithm was applied to 3D magnetotelluric inversion in order to confirm its effectiveness. Using synthetic examples under several conditions, we demonstrated that the method can reduce the number of forward calculations required to reduce data misfits to noise level, and that the method is robust for constructing target models even with sharp boundaries without generating fatally false resistivity structures or boundaries under noisy conditions.

MAM and MT explorations in the Sibayak geothermal field

Summary Deep Magneto-Telluric (MT) and Mise-a-la-Masse (MAM) geophysical imaging methods provide valuable information on fundamental processes within a geothermal field. However, because of an inherent non-uniqueness problem during data processing, interpretation of each individual method sometime has no good agreement with a real geological structure in a geothermal field. As a result, the naive application of the methodology can lead to erroneous results. Therefore, to convince the interpretation result by decreasing non-uniqueness possibility, we have performed integrated inversion of MT and MAM data observed in the Sibayak geothermal field, Indonesia. The results were then correlated to borehole data. The final interpretation show a dome-shape structure of the low resistivity, indicating an up-flow zone around fractures in the southeast direction of the Sibayak Mountain. This geophysical information is useful for the task of selecting sites for the promising zone in the Sibayak geothermal field.

Fluid flow monitoring of EOR process by electrical prospecting

An advanced geophysical technique for reservoir monitoring by electrical prospecting has been developed by the joint research works of Kyushu University and JAPEX on the EOR Project in Canada. The method has been applied to monitor fluid-flow behaviors during steam injection operations. With an automatic recording system controlled by a personal computer, charged potentials and spontaneous potentials can be simultaneously measured as a function of time at multiple stations surrounding an operating borehole. Fluid-flow behavior in the subsurface was visualized as a function of time by means of contour maps of the residual potential and the relative changes of apparent resistivity during the thermally enhanced oil recovery process at Hangingstone test site in Fort McMurray, Alberta, Canada.

Geothermal exploration in difficult areas

According to the “Sunshine Project”, various gee. physical survey have been conducted in many geotherma: areas in Japan, In this Project, geophysical data har been interpreted as layered earth structures. However! there are often inherent difficulties in determining layer thickness and resistivities from one geophysical method alone in difficult areas. In order to combat this problem, numerical modeling for 2D or 3D models are usually conducted and the observed data has been carefully checked in order to get the best fitted model in a geothermal area. In the present paper, procedures for interpretation of geophysical data are carefully checked with well log data and an optimum method for geothermal exploration are derived in difficult area from the success case history of Hatchobaru geothermal field ( 55 MW, unit II ) by KEPCO in Japan.

Radiogenic heat production in Rudeis Formation, Lower Miocene, Belayim marine oil field, Gulf of Suez, Egypt

This study describes radiogenic heat production (RHP) estimated from two sets of well logging data recorded in Rudeis Formation, Belayim marine oil field. Subsurface total count gamma-ray (GR) data were recorded in nine wells, seven of which possessed spectrometric data (eU, eTh, and K). The data show that RHP estimated from GR logs (ABR) varies from 0.13 to 1.73 µW/m3, with an average of 0.7 µW/m3 and a standard deviation of 0.26 µW/m3. In addition, 72.9% of RHP values fall within the range of 0.6–1.0 µW/m3. RHP estimated from the concentrations of radioactive elements (AR) vary from 0.13 to 2.1 µW/m3, with an average 0.71 µW/m3 and a standard deviation of 0.38 µW/m3. 50% of these RHP values fall within the range of 0.6–1.0 µW/m3. Cross-correlation of ABR and AR calculations yielded a moderate fit of 0.75. The three-dimensional (3D)-slicing of the reservoir shows that the northern and north-western parts of the study area have higher RHP compared to other parts. The estimated RHP can produce enough heat which has an effect on the hydrocarbon potential in Rudeis Formation. This study describes radiogenic heat production (RHP) estimated from two sets of well logging data recorded in Rudeis Formation, Belayim marine oil field. Cross-correlation of the estimated RHP (AR and ABR) yielded a moderate fit of 0.75. The three-dimensional (3D)-slicing of the reservoir shows that the northern and north-western parts of the study area have higher RHP compared to other parts.

The education and human resource development for earth resources in Kyushu University

The various human resource development programs with a focus on fieldwork for earth resources engineering have been carried out in Kyushu University. The traditional internship subject of Kyushu University, that began over 90 years ago, brings in a great educational effect for human resource development. More than 2000 students took the internship program and more than 100 students went abroad to accomplish the internship subject. However, Kyushu University cannot carry out the internship subject alone. Kyushu University is supported by a lot of companies related to earth resources and energy. Although the internship subject requires great care by both teachers and companies, it is necessary for human resource development to bring up “Earth system engineers in the 21st century”.

3D Imaging Archaeological Tomb By Vertical Electric Soundings

Application of geophysical methods has increased to investigate near-surface horizons of interests in related to environmental and engineering geophysics because geophysical methods are cost-effective and large areas can be quickly surveyed at relatively low cost without borings and trench excavations. The most productive geophysical methods are Ground Penetrating Radar and Electrical Resistivity methods for which the target exhibits the greatest physical contrast with respect to the surrounding formations. However, the geoelectrical geophysics is very difficult to predict the sub-surface using conventional techniques because of the shortage of the resolution. These geophysical techniques have required upgrading of data acquisition accuracy of the methods using a multichannel resistivity tool such as Handy Archaeological Resistivity Meter developed by the joint research of Kyushu University and OYO Corporation in Japan. Geoelectrical methods have the economic advantages to solve various archaeological problems. However, there was no successful 3D computer program required for interpreting observed apparent resistivity data. In the present paper, a robust 3D computer program was developed and applied to archaeological prospection. Results of 3D inversion of VES data are compared with the results of GPR method and evaluated with archaeologists of Archaeological Society of Japan.