SEAFLOOR RESISITIVTY INVESTIGATION OF METHANE HYDRATE DISTRIBUTION IN MISSISSIPPI CANYON, BLOCK 118, GULF OF MEXICO

We test the applicability of the direct current resistivity method for marine methane hydrate investigations. Methane hydrate is an ice-like compound found in near-bottom sediments in deepmarine environments. Hydrate-bearing sediments have resistivities ranging from 1 to 100 Ωm for saturation increasing from zero to 100%. The seafloor resistivity system used in the study is based on an existing engineering-scale land system. It consists of electronic components mounted in a pressure housing and a 1.1 km long, 56-electrode array constructed using graphite electrodes and high-pressure cable and connectors. For continuous resistivity profiling, the system is attached to a remotely operated underwater vehicle, which provides power, remote control functions, and navigational data. In June 2009, the system was towed along the seafloor across a known hydrate mound in 1 km water in Mississippi Canyon, Block 118. Seven profiles, totaling 26 km in length were collected. Inversions of the resistivity profiles were performed using a fixed seawater resistivity. Areas within the mound are underlain by resistivity anomalies ranging from 3 to 100 Ωm, in contrast to resistivities between 0.6 and 1.0 Ωm in areas adjacent to the mound. The 100 Ωm resistivity anomalies, likely associated with massive hydrate, occur where deep-seated normal faults intersect the seafloor.