Xinjiang Petroleum Geology ›› 2024, Vol. 45 ›› Issue (5): 604-610.doi: 10.7657/XJPG20240513

• APPLICATION OF TECHNOLOGY • Previous Articles     Next Articles

A Method of Anisotropic Velocity Modeling for HTI Medium in the Surface of Piedmont Gravel Zone

KONG Fanyong1a(), XIE An2, XIA Jianjun1a, ZHANG Lulu1a, WANG Liye1a, WANG Wei1b, YU Jinlin1a, WEI Jianbo1a   

  1. 1. CNPC BGP, a. Xinjiang Geophysical Prospecting Department; b. Urumqi Branch of Research Institute of Geology, Urumqi, Xinjiang 830016, China
    2. Xinjiang Research Institute, Huairou Laboratory, Urumqi 830000, China
  • Received:2024-03-19 Revised:2024-04-02 Online:2024-10-01 Published:2024-10-09

Abstract:

There are widespread alluvial fans with extremely thick gravel deposits in the surface of the piedmont zones in western China. These fans exhibit strong azimuth anisotropy. The tomographic inversion velocity differs greatly from the vertical velocity, severely impacting the accuracy of static correction value of 3D seismic data and the imaging of shallow-to-medium layer in pre-stack depth migration. Based on the HTI medium theory, a method for determining the symmetry axis and constructing an anisotropic model through azimuthal tomography fitting using first-arrival forward modeling was proposed. First, based on anisotropy, the first-arrival time from both micro-logging forward modeling and actual data is examined and compared to identify the symmetry axis characteristics. Then, elliptical fitting is performed on the azimuthal first-arrival tomography inversion model to derive the initial fast and slow velocities and the symmetry axis orientation. Next, by using 2D VTI anisotropic forward modeling and tomography inversion, the correction coefficients of the velocity in the direction of the symmetry axis are obtained. Finally, an anisotropic velocity model is established for the piedmont gravel zone.

Key words: piedmont zone, nearsurface, anisotropy, azimuthal tomography, forward modeling, modeling method

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