Influence of rock fractures on the amplitude of dipole-source reflected shear wave*
Wang Hao, Li Ning, Wang Cai-Zhi, Wu Hong-Liang, Liu Peng, Li Yu-Sheng, Liu Ying-Ming, and Yuan Ye
1. Research Institute of Petroleum Exploration & Development, Beijing 100083, China.
2. Yangtze University, Wuhan, Hubei 430100, China.
3. School of Earth and Space Sciences, Peking University, Beijing 100871, China.
Abstract：
To identify reflector fractures near borehole by using dipole-source reflected-shearwave logging, we need to understand the relation between the amplitude of the reflected shear wave and the source radiation, borehole conditions, and attenuation owing to the surrounding formations. To assess the effect of these factors on the amplitude of the reflected waves, we first studied the radiation performance and radiation direction of the dipole source in fast, medium, and slow formations by using the asymptotic solution in the far field of the borehole. Then, the relation between the fracture parameters, and the reflected-shear-wave amplitude as well as the ratio of the reflected-shear-wave amplitude to the direct-wave amplitude (relative amplitude, RA) was evaluated by the three-dimensional finite-difference (3D FDTD) method. Finally, the fracture detection capability of the dipole reflected-shear-wave logging tool in different formations was analyzed by using the RA. The results suggest that the radiation amplitude of the SH-wave in the slow formation is weaker than those in the fast and medium formations, and the amplitude of the reflected shear wave is lower. However, the RA in the slow formation is close to or even greater than in the fast and medium formations, which means that dipole-source shear-wave logging has the same or even better fracture detection capability in the slow formation as in the fast and medium formations. In addition, when RA is small, there is a good correlation between the RA and the various fracture parameters in the different types of formation, which can be used in determining the lower limit of the fracture parameters identified by reflection logging.
Xiong Sheng-Qing,Tong Jing,Ding Yan-Yun et al. Influence of rock fractures on the amplitude of dipole-source reflected shear wave*[J]. APPLIED GEOPHYSICS, 2019, 16(1): 1-14.
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2019, Vol. 16 
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