We observed traveltime delays of transmitted waves during pressurization of a subsurface artificial fracture at Higashi Hachimantai geothermal field, Iwate Prefecture, Japan. The transmitted waves generated by a downhole air gun were observed by the downhole triaxial seismic detector during pressurization. Traveltime delay was detected by the cross-spectrum method with a resolution of 0.01 ms. There is a strong correlation between the wellhead pressure and traveltime of P- and S-waves. The P- and S- wave traveltime delays of about 0.2 ms to 0.3 ms maximum were observed when the fracture was pressurized up to 3.4 MPa. We discuss the mechanism of this phenomenon using a model of a fracture with micro-cracks in the vicinity of the main fracture which are hydraulically connected with each other.
|ジャーナル||Geothermal Science and Technology|
|出版ステータス||出版済み - 1999|