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

(A)实地研究：在东北大学东-八马台油田进行井间地震测量。利用井下气枪作为震源，记录了通过人工加压裂缝传输的信号。改变加压状态、光源和探测器的位置。(2)TFC/3DTFC方法分析：采用时频相干(TFC)和3D-TFC方法对现场实验记录的信号进行分析。区分了一些相干分量，包括直达波、反射相位波和未知相干波。(C)解释：利用弹性波理论研究了从受压裂隙中产生相干波的可能性。结果表明，沿裂缝传播的泄漏导波是探测到的低速相干波的最可能来源，且与加压高度相关。

(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.