Three-dimensional in-situ stress prediction in shale gas reservoirs using a seismic-FEM physics-guided fourier surrogate

Reliable three-dimensional in-situ stress prediction is a key requirement for safe and efficient development of deep shale gas reservoirs, where stress heterogeneity controls hydraulic-fracture containment, wellbore stability, casing-deformation risk, and stimulation design. Empirical stress transforms are computationally efficient, but they are commonly limited by one-dimensional calibration and simplified geological assumptions. Finite-element modeling (FEM) accounts for three-dimensional structure and heterogeneous mechanical properties, but it remains too expensive for frequent operational updating. We develop a seismic-FEM physics-guided Fourier surrogate (PG-FNO) to predict the minimum and maximum horizontal stresses ( σ h and σ H ) in the Longmaxi-Wufeng shale gas reservoir of the Sichuan Basin. The workflow integrates seismic-derived elastic, pore pressure, overburden, and structural-curvature volumes with FEM stress simulation. A poroelastic analytical branch provides a mechanically interpretable baseline, while a Fourier neural branch learns spatial residual corrections to the baseline stress field. Under spatial holdout evaluation, PG-FNO achieves an overall test R 2 of 0.9835, RMSE of 3.236 MPa, and MAE of 0.515 MPa. These results demonstrate improved predictive performance relative to the PG-CNN and PG-UNet baselines under the same spatial holdout protocol. After training, full-volume inference requires only about 1 min, compared with approximately 4.5 d for the FEM simulation. Error diagnostics show that larger deviations are concentrated near faults and high-curvature zones, identifying structurally complex areas where additional calibration or monitoring would be most beneficial for engineering reliability. The proposed workflow provides a practical route for integrating seismic interpretation, numerical geomechanics, and deep learning into rapid 3D stress characterization for deep shale gas development.