Seismic Inversion for Site Characterization: When, Where and Why Should We Use It?

Abstract

Abstract The application of seismic inversion techniques to the foundation and drilling top hole zones has garnered significant interest in recent years. The shift towards more geologically complex and deeper water sites, combined with the global economic climate, has driven a requirement for more cost-effective site characterisation. More often used by the exploration industry, seismic inversion has been touted as a potentially valuable tool for quantifying the spatial and depth variability in sediment properties. In doing so, this approach can reduce the risk of encountering unforeseen ground conditions and the need for excessive over-design. Despite its potential, the inversion of high-resolution seismic data has yet to see widespread use, leaving unanswered questions regarding how and where this tool can best fit into the site characterization work flow. We test the potential usefulness of seismic inversion using a range of existing site investigation data sets. We apply several different inversion methods, including acoustic impedance and seismic quality factor inversion, as well as artificial neural network multi-attribute regression, to tackle end-member potential uses. First, explore early-phase potential uses, showing how seismic quality factor and acoustic impedance inversion can be used to capture the spatial variability in facies architecture and bulk sediment properties that could be used in appraisal and pre-FEED studies to optimize borehole and penetrometer (CPT) depths/locations and to ensure effective site-wide characterization. Second, we apply a combined acoustic impedance and artificial neural network workflow to link seismic properties with CPT profiles. These results demonstrate the potential late-phase use of seismic inversion for short-range interpolation/extrapolation of more complex geotechnical properties through the generation of synthetic CPT profiles useful for infrastructure design and micro-siting late in the development cycle. While not a comprehensive list of applications, together these examples illustrate how seismic inversion can be utilized throughout the development cycle. If the required objectives are clearly defined and an appropriate inversion workflow developed, seismic inversion can help to reduce uncertainty in site-wide characterization and drive efficiencies in layout and design studies throughout a project lifetime.