1994 Volume 16 Issue 1 Pages 85-108
We describe a downhole AE measurement performed at Ogachi Hot Dry Rock field in Akita prefecture during a hydraulic fracturing. Two types of AE signals, i.e., high frequency events and low frequency events containing of both P-and S-waves, were measured. Kaiser effect was clearly observed when total flow exceeded that of a previous experiment. The AE sources located by the triaxial hologram analysis show dynamic extention of the created subsurface fracture. Moreover, precise AE source location of AE doublets reveals a subsurface fracture plane on which the propaga-tion of the AE sources are concentrated. Differences of distribution of the AE sources and the AE activity between the two AE types suggest that two types of the subsurface extention occured during the hydraulic fracturing. The AE source location employing the downhole AE measurement well agrees with a result located by a microseismic surface network (which monitored AE in a following large scale hydraulic fracturing.) The high frequency events were too small to detect by the surface network.
