Paper submitted to EAGE Annual 2026
Summary
The Ana and Doina gas fields are located within the Ana-Doina-Bianca (ADB) area of the XV Midia Shallow Block in the Romanian Black Sea. Both fields produce dry biogenic gas from late MioceneDacian shallow-marine sandstones at approximately 1100 m depth. The ADB area lies beneath a complex near-surface regime dominated by Quaternary paleo-Danube submarine channels and shallow gas accumulations. These features introduce severe seismic imaging challenges, including frequency-dependent attenuation (amplitude loss and phase dispersion) and structural “push-down” of deeper reflectors. Such issues have long been recognized in the region: dimmed reservoir reflectors and sagged structures beneath channels were evident in early seismic interpretations (Duley & Fogg, 2009). Over the past decade, imaging approaches have evolved to address these challenges. The 2016-2018 benchmark processing (Costriiciuc et al., 2018) integrated Full Waveform Inversion (FWI) and preliminary Q-compensation, yielding improved images but continued to struggle beneath the largest Danube channel.
In 2024-2025, a full 3D seismic reprocessing program (577 km²) covering the ADB area was undertaken to achieve a step-change in image quality using Q-compensated Pre-stack Depth Migration (Q-KPSDM). The workflow incorporated industry advances in attenuation handling (e.g., spatially variable Q models as described by Matta et al., 2021), while being tailored to the specific data characteristics and project constraints. Although a formal Q-tomography inversion was not applied, the Q model was data-driven, derived from spectral analyses and iterative calibration tests on the seismic data, including 1D Q-tomography-style trials and reference-frequency sensitivity studies. The outcome is a state-of-the-art, depth-migrated seismic volume that provides significantly enhanced imaging beneath the Danube channel and shallow gas features, resulting in improved clarity for leads located below this complex overburden.