Exploration of Potential Fractures by Water Injecting Operations

Abstract

An advanced geoelectrical method for fracture imaging has been developed for monitoring of fracture creations and propagation in related to the Hot Dry Rock geothermal power project at the Ogachi area by the Exploration Geophysics Laboratory in Kyushu University. The method named as Fluid Flow Tomography (FFT) utilizes a casing pipe itself as a charged current electrode instead of a buried point source used for the mise-a-la-masse method. The method has been applied to monitor fluid flow behavior during massive hydraulic fracturing operations for direct imaging of potential fractures. In the Hatchobaru geothermal field, a large amount of poisonous gas (H2S) was blowing out around the depth of kick off point of a directional borehole. Therefore, two sidetracks were examined for deviating from the fracture, however the results were unsuccessful and drilling operations were stopped. Finally, the FFT survey was applied to determine the strike and dip of major fractures from 3D inversion of SP data in order to design a casing program. This paper presents a case study of the FFT survey applied to an exploratory drilling at a virgin area in the Hatchobaru geothermal field, Oita, Japan.