Characterization of subsurface artificial fracture by the TFC/3DTFC method

（a）实地研究：在东北大学东八幡台油田进行了井间地震测量。采用井下气枪作为震源，记录了通过人工加压裂缝传播的信号。改变了加压状态、源和探测器的位置。（B）通过TFC/3DTFC方法的分析：通过时间-频率相干（TFC）和通过3D-TFC方法分析现场实验中记录的信号。对直达波、反射波和未知相干波等相干分量进行了识别。（c）解释：利用弹性波理论研究了从加压裂缝产生相干波的可能物理学。结果表明，沿沿着裂缝传播的漏导波是最有可能探测到的低速相干波的来源，且与压力高度相关。

(a)Field Studies: Crosshole seismic measurement at Tohoku University Higashi-Hachimantai Field was carried out. Downhole airgun was used as a seismic source and signals transmitted through artificially pressurized fracture was recorded. The state of pressurization, location of source and detector were changed.(b)Analysis by the TFC/3DTFC method: The recorded signals in the field experiment were analyzed by the time-frequency coherency (TFC) and by the 3D-TFC methods. Some coherent components including direct arrivals, reflected phase and unknown coherent waves were discriminated.(c)Interpretation: Possible physics to generate coherent waves from pressurised fracture was investigated using theory of elastic wave. It has been concluded that leaky guided waves propagating along fracture is the most possible origin of detected coherent waves with lower velocity and highly correlated to pressurization.