Fracture Characterization Estimating from Seismic Methods (Tomography & VSP) and Pressure Transient Test in the Hohi Geothermal

Abstract

Various seismic methods (crosswell tomography, VSP, reflection) and pressure transient test have been applied to evaluate geological and hydraulic characteristics of a fractured reservoir in the Hohi geothermal field, Japan. We have also developed a new three-component downhole receiver capable of operating at temperatures up to. The velocity tomogram derived from the crosswell survey has a much resolution than that obtained of reflection images from VSP and surface seismic data. Relatively low velocity zones were identified near the well in the velocity tomogram the low velocity regions are consistent with circulation loss zones. Pressure transient data analysis indicated a high permeability zone near the well and a low permeability zones beyond the high permeability zone. Not all of the fractures intercepted by individual wells extend very far beyond about 20 meter) into the formation. These results are consistent with the local low velocity zones near the well in crosswell tomography data. We believe that seismic tomography in concert with pressure transient data represents a promising technique for characterizing fractured reservoirs.