Focal mechanism inversion with single-well microseismic wave energy
Zhao Wei1, Xin Wei2, Mao Zhonghua3, Zhai Shang1, Hu Tianyue1, He Chuan1
1. Institute of Oil & Gas, School of Earth and Space Sciences, Peking University, Beijing 100871, China; 2. Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China; 3. Shengli Branch, Geophysical Company, SINOPEC, Dongying, Shandong 257086, China
Abstract:The microseismic focal mechanism contains important information about reservoirs and fractures,which makes it critical to evaluate the reservoir production.Conventional methods that utilize S/P amplitude ratios to determine the focal mechanism are not applicable for the cases where the observation aperture is limited.Studies have shown that the wave energy is sensitive to the focal mechanism.For this reason,we propose a method to invert the focal mechanism with wave energy.Before the inversion,the velocity model,source location,and scalar seismic moment are calculated in advance.We select P-and S-wave windows to calculate wave energy for waveforms after the seismic moment normalization.Using the weighted K nearest neighbor prediction method,the strike,dip,and rake of fault plane are resolved.Synthetic data test shows that the accuracy of inversion results is greater than 97% under the noise free condition.Tests with different noise levels indicate that the proposed method is more stable than the amplitude ratio method and can improve the inversion accuracy.Finally,real data tests in an oil field show that the proposed method achieves good results in application.
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