Vibroseis is widely used in land surveys, but source-ground coupling and equipment nonlinearities generate second- and higher-order harmonics as well as narrowband resonance lines. These source-related interferences overlap the target reflection band, markedly degrading the signal-to-noise ratio (SNR) and masking weak reflections. We propose a dual-branch wavelet-fusion U-Net (DW-U-Net) for harmonic noise attenuation. The backbone operates in the time domain, while a wavelet side branch explicitly represents low-frequency background and high-frequency details. A differentiable inverse discrete wavelet transform (IDWT) injects the reconstructed wavelet features into the decoder to structurally suppress harmonic streaks while preserving reflections. Training data are generated by adding higher-order harmonics to a reference sweep and then simulating shot records through forward modeling. On the Marmousi2 model under strong harmonic noise, DW-U-Net increases the whole-shot average SNR from 9.92 dB to 29.29 dB, and achieves residual energy 2.44 × 10⁻³, root mean square error (RMSE) 4.51 × 10⁻⁵, and multiscale structural similarity (MS-SSIM) 0.9959. Experiments on the Marmousi2 model and the public Utah FORGE field data demonstrate that DW-U-Net attenuates coherent harmonic streaks and suppresses narrowband resonance lines in shot records. Compared with DnCNN, a standard U-Net, dual residual network (DURN), and multi-input multi-output U-Net (MIMO-U-Net) trained under the same protocol, DW-U-Net delivers consistently higher SNR under strong noise levels. Time-frequency analyses further show that the main reflection band is well preserved in amplitude and bandwidth, while coherent harmonic remnants are substantially reduced.

Predictions of fluid distribution, stress field, and natural fracture are essential for exploiting unconventional shale gas reservoirs. Given the high likelihood of tilted fractures in subsurface formations, this study focuses on simultaneous seismic inversion to estimate fluid bulk modulus, effective stress parameter, and fracture density in the tilted transversely isotropic (TTI) medium. In this article, a novel PP-wave reflection coefficient approximation equation is first derived based on the constructed TTI stiffness matrix incorporating fracture density, effective stress parameter, and fluid bulk modulus. The high accuracy of the proposed equation has been demonstrated using an anisotropic two-layer model. Furthermore, a stepwise seismic inversion strategy with the L_P quasi-norm sparsity constraint is implemented to obtain the anisotropic and isotropic parameters. Three synthetic model tests with varying signal-to-noise ratios (SNRs) confirm the method's feasibility and noise robustness. Ultimately, the proposed method is applied to a 3D fractured shale gas reservoir in the Sichuan Basin, China. The results have effectively characterized shale gas distribution, stress fields, and tilted natural fractures, with validation from geological structures, well logs, and microseismic events. These findings can provide valuable guidance for hydraulic fracturing development, enabling more reliable predictions of reservoir heterogeneity and completion quality.

The main objective is to optimize the development of shale gas-rich areas by predicting seismic sweet spot parameters in shale reservoirs. We systematically assessed the fracture development, fracture gas content, and rock brittleness in fractured gas-bearing shale reservoirs. To better characterize gas-bearing shale reservoirs with tilted fractures, we optimized the petrophysical modeling based on the equivalent medium theory. Based on the advantages of shale petrophysical modeling, we not only considered the brittle mineral fraction but also the combined effect of shale porosity, gas saturation, and total organic carbon (TOC) when optimizing the brittleness index. Due to fractures generally functioning as essential channels for fluid storage and movement, fracture density and fracture fluid identification factors are critical geophysical parameters for fractured reservoir prediction. We defined a new fracture gas indication factor (GFI) to detect fracture-effective gas content. A new linear PP-wave reflection coefficient equation for a tilted transversely isotropic (TTI) medium was rederived, realizing the direct prediction of anisotropic fracture parameters and the isotropic elasticity parameters from offset vector tile (OVT)-domain seismic data. Synthetic seismic data experiments demonstrated that the inversion algorithm based on the L_P quasinorm sparsity constraint and the split-component inversion strategy exhibits high stability and noise resistance. Finally, we applied our new prediction method to evaluate fractured gas-bearing shale reservoirs in the Sichuan Basin of China, demonstrating its effectiveness.