Potentially large subsurface gas hydrate bodies in the Mexican Ridges, Southwestern Gulf of Mexico

Abstract

Because rising ocean temperatures can destabilize gas hydrate, identifying and characterizing large shallow hydrate bodies is increasingly important to understanding their hazard potential. In the southwestern Gulf of Mexico, reanalysis of 3D seismic reflection data reveals evidence for the presence of six potentially large gas hydrate bodies located at shallow depths below the seafloor. We originally interpreted these bodies as salt because they share common visual characteristics on seismic data with shallow allochthonous salt bodies, including high-impedance boundaries and homogeneous interiors with very little acoustic reflectivity. However, when seismic images are constructed using acoustic velocities associated with salt, the resulting images were of poor quality containing excessive moveout in common-reflection point offset image gathers. Further investigation reveals that using lower valued acoustic velocities results in higher quality images with little or no moveout. We believe that these lower acoustic values are representative of gas hydrate and not of salt. Directly underneath these bodies lies a zone of poor reflectivity, which is typical and expected under hydrate. Observations of gas in a nearby well, other indicators of hydrate in the vicinity, and the regional geologic context support the interpretation that these large bodies are composed of hydrate. The total equivalent volume of gas within these bodies is estimated to potentially be as large as 1.5 gigatons or 10.5 trillion cubic feet, considering uncertainty for estimates of porosity and saturation, comparable with the entire proven natural gas reserves of Trinidad and Tobago in 2019.