High-precision 3D acquisition technology and its application for deep subsalt structure in Yingxiongling, Qaidam Basin

Although the Yingxiongling Area in the Qaidam Basin is rich in hydrocarbon resources and holds significant exploration potential, it was once regarded as a “forbidden zone” for seismic exploration due to its complex and harsh seismic geological conditions, which posed substantial challenges to exploration efforts. Following the high-fold, high-density 3D seismic survey conducted in the area between 2011 and 2013, the data quality achieved a breakthrough from scratch. However, despite multiple rounds of processing and interpretation research, the improvement in deep subsalt structural imaging remained limited. To address these challenges, a secondary 3D acquisition was carried out in the favorable southern region of Yingxiongling, targeting the following key issues: 1) severe deformation and transformation of deep subsalt structures, along with inaccurate imaging of high and steep strata on the lower wall of faults; 2) significant absorption and attenuation of seismic waves in the thick, dry, and loose near-surface layers, coupled with strong noise interference and extremely low signal-tonoise ratio (S/N) in raw data; and 3) the considerable difficulty in constructing a high-precision velocity model for the thick, loose surface layers. To tackle these problems, this paper proposes a targeted acquisition solution: “Wide azimuth + large offset geometry for deep layer imaging, combined with small array and high-fidelity shooting and receiving, supported by step-by-step constrained true surface modeling”. The application of this method has significantly improved subsalt imaging in the newly acquired 3D data. The results reveal clear small faults, excellent well-tie accuracy with break points and formation occurrences, and high fidelity with preserved amplitudes. These advancements have played a crucial role in supporting the major shale oil exploration breakthrough in the Yingxiongling Area.