Application principles of seismic depositional in ultra-deep layers: A case study of the Hutubi anticline belt

This study focuses on the lower assemblage of the Hutubi anticline belt on the southern margin of the Junggar Basin (burial depth > 7 300 m) to address challenges in ultra-deep oil and gas exploration, such as thin reservoirs, limited drilling data, and low seismic resolution. Based on seismic sedimentology, we propose methodological principles for identifying depositional patterns in such settings. By integrating well-logging data, lithofacies analysis, and sedimentary structure interpretation, we determined the depositional systems as braided-river deltas (Qingshuihe Formation) and fan deltas (Kalazha Formation). Seismic waveform classification, amplitude attributes, and well-seismic calibration were employed to delineate sedimentary facies boundaries. The results reveal that delta-front subfacies dominate the anticline's high and southern sections, while pro-delta to delta front transition zones are distributed in the northern part. Waveform classification proved to be effective in complex structural areas, and combining well-derived lithofacies with seismic characteristics reduced errors caused by structural and lithological variations. This research provides a methodological framework for sedimentary facies prediction and exploration strategy optimization in ultra-deep hydrocarbon reservoirs.