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SUMMARY Resolving thin layers and accurate delineation of layer boundaries are very important for reservoir characterization. Many seismic inversion methods based on a least-squares optimization approach with Tikhonov-type regularization can intrinsically lead to unfocused transitions between adjacent layers. A basis pursuit inversion algorithm (BPI) based on L1 norm optimization method can, however, resolve sharp boundaries between appropriate layers. Here we formulate a BPI algorithm for amplitude-versus-angle (AVA) inversion and investigate its potential to improve contrasts between layers. Like the BPI for post-stack case (Zhang and Castagna, 2011), we use an L1 norm optimization framework that estimates three reflectivities, namely, Rp, Rs and R?. High resolution velocities (Vp, Vs) and density (?) can be derived from these parameters by incorporating initial models. Tests on synthetic and field data show that the BPI algorithm can indeed detect and enhance layer boundaries by effectively removing the wavelet interference.
- Geophysics > Seismic Surveying > Seismic Modeling > Velocity Modeling > Seismic Inversion (1.00)
- Geophysics > Seismic Surveying > Seismic Interpretation (1.00)
Summary The spectral element method (SEM) is a very powerful method for seismic modeling. This method is well established in the 2D case with quadrilateral elements due to its accuracy and computational efficiency. However, an implementation of SEM with triangular elements (TSEM) is preferable for meshing complex structures, but it has additional challenges of obtaining the interpolation polynomial and quadrature rules. In this work, we describe a second-order TSEM scheme using the Cohen nodes, and demonstrate how to circumvent the difficulties in triangular elements. After that, we study the grid dispersion and stability using plane-wave analysis. The analysis shows that the TSEM scheme is more accurate than the classical finite element method (FEM) scheme. Furthermore, the second-order TSEM has a larger stability condition than the third-order FEM. A numerical experiment is presented to compare TSEM and FEM; the results confirm our analysis.