Editorial: The state-of-the-art techniques of seismic imaging for deep and ultra-deep hydrocarbon reservoirs, volume III

With the rapid development of the global oil and gas industry over the past half century, exploration targets have progressively shifted from shallow and mediumdepth formations to deep and ultra-deep reservoirs. These reservoirs, typically buried at depths greater than 5 km, have become increasingly important contributors to global hydrocarbon resources. Compared with conventional shallow-to-mid-depth reservoirs, deep and ultra-deep petroleum systems exhibit distinct geological characteristics, including complex hydrocarbon generation processes, unique accumulation mechanisms, and heterogeneous sweet-spot distribution patterns. Understanding these characteristics is essential for effective exploration and development.Seismic imaging plays a fundamental role in subsurface exploration. It provides threedimensional structural information about impedance interfaces and, increasingly, valuable insights into rock and fluid properties through advanced inversion and attribute analysis. Over the past decades, seismic imaging technologies have contributed to numerous major discoveries worldwide, including in regions such as the Middle East, the Gulf of Mexico, the North Sea, and western China. Nevertheless, the application of seismic methods to deep and ultra-deep hydrocarbon reservoirs remains highly challenging. The great burial depths often lead to weak reflection signals, severe attenuation, and strong noise contamination, resulting in low signal-tonoise ratios in seismic data. Furthermore, complex geological settings frequently cause difficulties in velocity model building, which in turn degrades imaging accuracy and resolution. The contributions collected in this volume cover a broad spectrum of topics related to seismic imaging and reservoir characterization. Several papers focus on improving seismic data quality through advanced preprocessing and noise suppression techniques. For example, one study presents a combined identification and attenuation strategy for anomalous amplitude noise in nodal land seismic data, demonstrating improved signal preservation and data reliability. Another contribution discusses the challenges of reservoir prediction under sparse well conditions in offshore fields, providing perspectives on integrating seismic data with limited well information.Another group of papers addresses advances in seismic modeling and numerical simulation. One contribution proposes an elastic-wave-equation numerical simulation method based on a time-space domain dispersion-relation-based staggered-grid finitedifference scheme, which improves computational accuracy and efficiency in simulating complex wave propagation phenomena. Such developments are crucial for both forward modeling and inversion in complex geological settings.Velocity model building and inversion techniques also receive considerable attention in this volume. Several studies explore advanced full-waveform inversion approaches, including methods based on Hessian operator preprocessing and wavefield reconstruction strategies designed to enhance inversion stability when dealing with noisy data. These techniques contribute to more accurate subsurface velocity models, which are essential for high-resolution seismic imaging.Migration and imaging methodologies constitute another key theme of this Research Topic. Contributions include studies on reverse time migration (RTM) with improved imaging conditions, such as a local Nyquist cross-correlation imaging condition with accurate first-arrival traveltime correction. In addition, full-azimuth angle-domain RTM approaches are presented to better illuminate complex subsurface structures.Ray-based approaches are also represented through work on Gaussian beam migration, which discusses methodological developments, practical advantages, and implementation considerations for exploration seismology.Beyond imaging algorithms, several papers highlight the integration of seismic methods with rock physics and reservoir characterization techniques. For instance, wide-azimuth anisotropic inversion based on rock physics models is applied to fractured reservoir prediction in tight sandy conglomerate formations, illustrating how seismic data can be linked to geological and petrophysical interpretations.Together, these studies demonstrate the rapid progress being made in seismic imaging technologies for deep and ultra-deep hydrocarbon exploration. They address key challenges including noise suppression, accurate wavefield modeling, robust velocity inversion, and advanced migration algorithms. The methodological innovations and practical case studies presented in this volume provide valuable insights and tools for improving subsurface imaging and reservoir characterization in complex deep geological environments.As guest editor, I would like to express our sincere gratitude to all authors who contributed their valuable research to this Research Topic. I also thank the reviewers for their constructive comments and the editorial staff for their professional support throughout the publication process. I hope that the contributions presented in this volume will stimulate further research and collaboration in the field of seismic imaging and promote continued advancements in the exploration of deep and ultradeep hydrocarbon resources.