Seismic Identification and Prediction of Granitic Weathering Crust Reservoirs in the Baiyun Sag, Northern South China Sea

The granitic weathering crust reservoir is an important target for deep hydrocarbon exploration. However, effective prediction of the thickness and distribution of granitic weathering crust reservoirs remains difficult in offshore areas with sparse boreholes. The Baiyun Sag, the largest hydrocarbon‐rich sag in the northern South China Sea, provides an ideal study area due to newly acquired 3D seismic data. By integrating limited borehole and seismic data, this study identifies and predicts granitic weathering crust reservoirs. One‐dimensional forward modelling simulated seismic responses for various combinations of overburden and weathering crust. Results show that troughs below the T g interface delineate the weathering crust extent, with stronger amplitude corresponding to greater thickness. Weathering crust thickness correlates with seismic responses as follows: < 32 m: indistinguishable; 32–64 m: enhanced trough amplitude below the T g interface; 64–128 m: broad and dim troughs and > 128 m: dual sub‐peak troughs. The modelling further reveals that relatively thick weathering crust is distributed on the structural highs of the Yundong, southern Yunli, western Yunkai and southern Panyu Low Uplifts. Amplitude attributes demonstrate that the weathering crust thickness is directly related to structural positions. The thickest weathering crust occurs atop uplifts, thinning towards slopes, with detrital deposits at the uplift edges. Reservoir evolution involved four stages: basement formation; development of fracture networks and weathering crust; reactivation of Late Mesozoic fractures and formation of Cenozoic fracture systems; and reservoir reformation by Cenozoic magmatic activities. This study provides a quantitative methodology for predicting granitic weathering crust reservoirs in offshore areas with limited boreholes.