DIRECT IMAGING FRACTURES BY A 4-D GEOELECTRICAL TECHNIQUEAT SUMIKAWA GEOTHERMAL FIELD, JAPAN

摘要

The Sumikawa geothermal field is located in theHachimantai volcanic region of northeastern Japan,where the Sumikawa geothermal power station hasbeen operated since 1995. An advanced geophysicaltechnique has been applied to image major fracturedistributions at the Sumikawa area. The 4-Dtechnique named as the FFT method (Fluid FlowTomography) has been developed by EngineeringGeophysics Laboratory of Kyushu University forimaging transient phenomena as a function of time.Subsurface resistivity structures could be determinedfrom 3-D inversion of the mise-a-la-masse data,while fracture distributions could be estimated from3-D inversion of SP (Self Potential) data using timeseries data obtained by the FFT method. It isconcluded that distribution of potential fractures inthe Sumikawa geothermal field were delineated anddrilling programs were proposed for furtherdevelopments of production and reinjection wellsbased on the joint interpretation of apparentresistivity and SP data obtained from the 4-Dgeoelectrical technique.