Estimation of motion of subsurface fracture by using proximity AE doublets analysis

点击翻译按钮获取中文摘要

Proximity Acoustic Emission (AE) doublets analysis is used for subsurface fracture measurement. AE is a microseismic event. Location and shape of subsurface fracture is estimated from distribution of AE sources. Measurement of subsurface fracture is important in many areas of human activities associating with the Earth. Geothermal energy is extracted from subsurface fracture reservoirs in which steam and hot water are stored. Carbon dioxide is stored in tiny spaces of subsurface fracture.Proximity AE doublet analysis is a new method in which both fine structures of subsurface fracture and their motion can be estimated. Proximity AE doublets have a similar waveform, and they occur in a succession with an interval that is less than 1 s. Accurate relative location between AE sources can be realized because a medium, in which AE waves propagate, does not change during the interval. Intervals of P-wave and S-wave between proximity AE doublets are detected in cepstrum analysis. Proximity AE doublets have one or two peaks at their internals in their cepstrum. In proximity AE doublets, a second event with a similar waveform arrives before attenuation of the first event. Conventionally, it is difficult to estimate similarity between the two waveforms and their interval. I made time-quefrency analysis that can determine interval of P-wave when there are two peaks of the interval in the cepstrum. Data after the second S-wave arrival are replaced with zeros and the peak that represents S-wave interval decrease in the time-quefrency analysis. This analysis can show the interval of P-wave between proximity AE doublets. I estimated relative locations between AE sources of proximity AE doublets, which were measured in Soultz geothermal field.