Monitoring Sea-floor Instability Caused by the Presence of Gas Hydrate Using Ocean Acoustical and Geophysical Techniques in the Northern Gulf of Mexico

Abstract

The northern Gulf of Mexico is characterized by an extremely heterogeneous near-surface geology that makes the geophysical identification of subsurface gas hydrate challenging, and the interpretation of data is commonly ambiguous. This chapter describes a set of novel seismic experiments designed to characterize the subsurface hydrate distribution at Mississippi Canyon Block 798 (MC798) in the northern Gulf of Mexico. A vertical line array (VLA), specially designed for high resolution in shallow sediments, was deployed by the Center for Marine Resources and Environmental Technology (CMRET) with the general objectives of (1) acquiring very high-resolution seismic reflection profiles in 850 m (2789 ft) of water depth, (2) studying the acoustic character and features of the sea floor for evidence of sea-floor hazards, and (3) looking for evidence of subsurface gas hydrates and their properties. Comparisons were made of the results of several seismic experiments in the area of interest in MC798, including the prototype VLA test in 2003, and conventional multi- and single-channel seismic data from previous years. In this article, these data sets were integrated to show the improved resolution of the near-surface sediments in the VLA data. Two interpretations of the geology are given; the evidence for the presence of subsurface gas hydrate is ambiguous.