Numerical simulation of shear wave attenuation in borehole inserted by a horizontal fracture
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RESEARCH ARTICLE - APPLIED GEOPHYSICS
Numerical simulation of shear wave attenuation in borehole inserted by a horizontal fracture Binpeng Yan1 · Weiming Ou2 · Xingguo Huang3 · Nuno Vieira da Silva4,5 Received: 28 May 2020 / Accepted: 13 October 2020 © Institute of Geophysics, Polish Academy of Sciences & Polish Academy of Sciences 2020
Abstract The amplitude of shear waves is attenuated when passing through horizontal fractures crossing a borehole. In this study, we investigate the amplitude attenuation of shear waves throughout simulation of full-wave acoustic logging with the finitedifference method. As the fracture aperture is very small, it needs to be represented in a very fine gird when carrying out finite-difference simulation. Therefore, the variable-grids finite-difference method is adopted to avoid over-sampling in the non-fracture regions, yielding substantial savings in computational cost. We demonstrate the accuracy of waveform modeling with the variable-grid finite-difference by benchmarking against that obtained with the real-axis integrating method. We investigated the effects of several important parameters including fracture aperture, distance from receiver to fracture, borehole radius and extended distance utilizing that benchmarked variable-grid finite difference code. We determined a good linear relationship between the attenuation coefficient of shear wave amplitude and the fracture aperture. Then, the effects of distance from receiver to fracture, the borehole radius and the extended distance of fracture on shear wave attenuation are also studied. The attenuation coefficient of shear wave becomes smaller with the increasing borehole radius. While, it increases as the distance from receiver to fracture and the extended distance of fracture increase. These effect characteristics are conducive to the use of shear wave to evaluate fractures. Keywords Horizontal fracture · Shear wave attenuation · Variable grids · Acoustic logging · Finite-difference
Introduction Fractured reservoirs are widely distributed in various geological formations, such as carbonate rocks, hard sandstones, igneous rocks and shales. Fractures play a crucial role as migration channels of petroleum from the source rock to the reservoir, and as storage space of petroleum. In addition, the * Binpeng Yan [email protected] 1
China University of Petroleum-Beijing At Karamay, Xinjiang, China
2
The 54th Research Institute of China Electronics Technology Group, Shijiazhuang, China
3
Department of Earth Sciences, University of Bergen, Allegaten 41, 5020 Bergen, Norway
4
Department of Earth Science and Engineering, Imperial College London, South Kensington Campus, London SW7 2AZ, UK
5
Present Address: Total E&P UK, Tarland Road, Westhill, Aberdeen AB32 6JZ, UK
existence of fractures changes substantially the shape of the waveforms recorded in well-logging. Thus, mastering the effects of fractures on acoustic waveforms is beneficial to the detection and evaluation of fractures. P-wave, S-wave, Stoneley wave
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