Neural net detection of seismic features related to gas hydrates and free gas accumulations on the northern U.S. Atlantic margin

Abstract

Bottom simulating reflections that sometimes mark the base of the gas hydrate stability zone in marine sediments are often identified based on reverse polarity reflections that cut across stratigraphic layering in seismic amplitude data. On the northern U.S. Atlantic margin between Cape Hatteras and Hudson Canyon, legacy seismic data have revealed pronounced bottom simulating reflections south of the deepwater extension of Hudson Canyon but more subtle ones from offshore Delaware south to Cape Hatteras, where the reflections sometimes follow stratigraphic layering. Using high-resolution seismic data acquired during the 2018 Mid-Atlantic Resource Imaging Experiment and a supervised neural net, we identify seismic features associated with gas hydrates and/or the top of gas between Hudson Canyon and Cape Hatteras. Using seismic attributes sensitive especially to the presence of gas, we train a neural network algorithm on seismic data from an area with strong bottom simulating reflections and then apply the model to the rest of the data set. The results indicate that gas hydrate and/or shallow free gas are far more widespread on the northern part of the U.S. Atlantic margin than previously known. Seismic indicators of gas extend landward from the 2000 m isobath to the upper continental slope in sectors with (offshore Virginia) and, to a lesser extent, without (offshore New Jersey) pervasive upper slope methane seeps. Higher sand content and intermediate sediment thickness, factors related to the container size and gas charge in a petroleum systems framework, are associated with more robust gas indicators.