Seismic Processing Techniques for Geohazard Identification and Risk Reduction in a Frontier Exploration Area

Abstract

Abstract The main objective of Geohazard Investigation is to reduce operational risk in Drilling and Developments. While this is paramount during all operations, it is especially so for exploration drilling in frontier areas where only sparse data are available. Geohazard analysis is often carried out using conventional exploration 3D seismic data on a standalone basis. As these data are primarily acquired and processed to image deeper targets, they do not contain the high frequency content in the shallow section that would be achieved by high-resolution 2D or 3D acquisition. To ensure operational integrity in areas where there is poor well control, and, or, where geologic complexity is high, it is necessary to pursue techniques beyond the traditional evaluation of available data to deliver high quality risk assessments. Application of processing and analysis techniques to gain additional insight to conditions, by extracting additional attributes from existing geophysical data are, therefore, attractive. These techniques can be used to build a more robust geologic model, to understand the complexities of the geological system, in the absence of direct sampling, and are even more useful when complemented by ground-truthing. This paper describes how exploration 3D seismic data were reprocessed into a "high-resolution" 3D seismic volume. The reprocessing was carried out to improve frequency content by focusing on the shallow section for use in site investigation. Work was undertaken to deliver improved understanding of the shallow velocity field by generating a Full Waveform Inversion velocity model. This was then used as the starting model for a pre-stack Kirchhoff depth migration which was able to provide further improved stratigraphic and structural imaging to allow an even more accurate interpretation. Having delivered an improved seismic volume, advanced coherency algorithms were applied to understand discontinuities, at multiple scales, and spectral decomposition analysis was performed to better understand the distribution of seafloor and subsurface lithologies. The combined effect of the application of these processing and analysis steps lead to a better understanding of the geologic complexities of the area and how these might translate to potential geohazards, allowing them to either be directly avoided, or mitigated, through engineering design prior to the start of drilling operations.