| Title | Ogachi HDR Reservoir Evaluation by Ae and Geophysical Methods |
|---|---|
| Authors | Hideshi Kaieda, Robert H. Jones, Hirokazu Moriya, Shunji Sasaki and Keisuke Ushijima |
| Year | 2000 |
| Conference | World Geothermal Congress |
| Keywords | Hot Dry Rock, AE, Ogachi, Fracture, Reservoir |
| Abstract | Fractures were created as a Hot Dry Rock reservoir by hydraulic fracturing from a 1,000 m depth well at Ogachi, northern Japan. The fracture location and extension were evaluated by the microearthquake (AE) event observation and the electrical methods. Recently a three-dimensional underground structure model was constructed by compiling the seismic reflection results and the electric resistivity results. Using this model, AE locations were re-calculated and determined more precisely. In order to obtain some significant structures in the reservoir, the collapsing method was applied to the relocated AE data. From this result, some structures trending to NNE and NE were found in the reservoir. These trends agreed with the electrical measurement results and the natural joints system. Therefore, the obtained structures are considered to reflect the locations of the main flow paths. Stress condition in the reservoir was also estimated by using the stress inversion method with the fault plane solutions of the relocated AE data. From this analysis, the maximum compressive principal stress direction is estimated to be in WNW nearly horizontal. But the stress ratio showed that the values of the maximum stress and the intermediate stress which direction is estimated to be in SSW are close. Many measurements for estimating stress condition have been applied for the Ogachi site. However, the results obtained by different methods have not necessary been consistent each other. The maximum stress locates in NE-SW in one result, for example core tests, but the maximum stress locates in SE-NW in the other result, for example stress inversion result of this study and BTHV survey. Therefore, more analysis for stress condition is needed. |