State‐of‐the‐art remote characterization of shallow marine sediments: the road to a fully integrated solution

Abstract

Current methods for characterizing near‐surface marine sediments rely on extensive coring/pene‐trometer testing and correlation to seismic facies. Little quantitative information is regularly derived from geophysical data beyond qualitative inferences of sediment characteristics based on seismic facies architecture. Even these fundamental seismostratigraphic interpretations can be difficult to correlate with lithostratigraphic data due to inaccuracies in the time‐to‐depth conversion of geophysical data and potential loss and/or compression of high‐porosity and under‐consolidated sea‐floor material during direct sampling. To complicate matters further, when quantitative information is derived from marine geophysical data, it often describes the sediments using terminology (e.g., acoustic impedance and seismic quality factor) that is impenetrable to geologists and engineers. In contrast, for hydrocarbon prospecting, reservoir characterization using quantitative inversion of geophysical data has developed enormously over the past 20 years or more. Impedance and amplitude‐versus‐angle inversion techniques are now commonplace, whereas computationally expensive waveform inversions are gaining traction, and there is a well‐developed interface between these geophysical and reservoir engineering fields via rock physics. In this paper, we collate and review the different published inversion methods for high‐resolution geophysical data. Using several case study examples spanning a broad range of depositional environments, we assess the current state of the art in remote characterization of shallow sediments from a multidisciplinary viewpoint, encompassing geophysical, geological, and geotechnical angles. By identifying the key parameters used to characterize the subsurface, a framework is developed whereby geological, geotechnical, and geophysical characterizations of the subsurface can be related in a less subjective manner. As part of this, we examine the sensitivity of commonly derived acoustic properties (e.g., acoustic impedance and seismic quality factor) to more fundamentally important soil properties (e.g., lithology, pore pressure, gas saturation, and undrained shear strength), thereby facilitating better integration between geological, geotechnical, and geophysical data for improved mapping of sediment properties. Ultimately, we present a number of ideas for future research activities in this field.

Characterization of seabed properties from Scholte waves acquired on floating ice on shallow water

“…Seismic data can provide estimates of in situ mechanical properties of the seabed sediments (Vardy et al . ). Reflection and refraction data can provide mechanical properties in case of deep water.…”

Near‐shore geophysical and geotechnical investigations in support of the Trieste Marine Terminal extension

“…Vardy et al . ; Holland et al . ; Reiche, Berkels and Weiß ), amplitude‐versus‐offset (AVO) analysis (e.g.…”

Characterization of shallow overpressure in consolidating submarine slopes via seismic full waveform inversion

“…During consolidation, relative volumetric changes of pore-space and solid grains modify the response of the multi-phase medium to mechanical wave propagation (e.g., Mavko et al, 2009). For non-lithified sediments, this is of greater extent than, for instance, the lithology of the solid grains (e.g., Vardy et al, 2017). In the absence of fluid-substitution and thermo-chemical effects, it is therefore sensible to use porosity (φ) as the parameter most directly affecting the acoustic properties of the subsurface.…”