Sensitivity analysis of seismic attributes parametrization to reduce misinterpretations: Applications to deepwater channel complexes

Abstract

Geoscientists apply algorithms such as seismic attributes to better interpret depositional systems that enhance various aspects of the seismic data. However, they are limited by the original seismic amplitude or frequency content, data quality, and algorithm parameters considered.Additionally, our capacity to interpret depositional system architecture is limited by seismic resolution, which results in potential misinterpretations associated with the correct position of stratigraphic features. Resolution also sets a minimum thickness that can be observed in seismic data. This is particularly important as mapping reservoir architecture (geobody size, shape, and stacking patterns) in the subsurface is critical for exploring and producing hydrocarbons, CO2 storage, and geothermal resource development since it can define connectivity or compartmentalization of flow zones.To address these concerns, we investigated five synthetic seismic volumes from low to high-dominant frequencies of 15 Hz, 30 Hz, 60 Hz, 90 Hz, and 180 Hz based on an architectural model of an outcropping deepwater channelized slope system in the Magallanes Basin, Chile. We analyzed 1) how seismic bandwidth affects the resolution of stacked stratigraphic features (i.e., deepwater channel elements and Mass Transport Deposits (MTDs)) and their subsequent seismic interpretation, and 2) the effect of different seismic attributes commonly employed in channel interpretation on our data to understand the “mixing” or “vertical smearing” of stratigraphic features by comparing the seismic with the true geological model 3) we explored how the attributes’ parametrization affects the imaging of differently sized features by modifying the analysis window in each case from ± 2ms to ± 50 ms. Finally, 4) we evaluated the effect of different noise levels in the sensitivity analysis. Resultsshow that the “mixing” of events occurs mainly as a result of 1) the seismic bandwidth, 2) the algorithm used for each seismic attribute calculation, 3) the attribute vertical analysis window, and 4) the signal-to-noise ratio of the data. Broadband, higher frequency data, and small analysis windows provide clearer images of the stacked channels. In contrast, low-frequency data and larger analysis windows result in more mixing or “composite” appearances, affecting interpretations and net-to-gross estimates, especially in small-size stratigraphic features such as individual channel elements and Mass Transport Deposits (MTDs). Our observations warn of potential misinterpretations in applying default attributes to actual seismic data, especially in geometrical attributes and window-dependent ones. Recognizing these misinterpretations is paramount for reconstructing deepwater architecture (this study), sedimentary and structural studies for drilling locations, reserves estimation, and overall uncertainty assessment.