SEAFLOOR RESISITIVTYINVESTIGATION OF METHANE.HYDRATEDISTRIBUTION IN MISSISSIPPI CANYON; BLOCK 118, GULF OF MEXICO

摘要

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 deep-marine environments. Hydrate-bearing 'sediments have resistivities ranging from 1 to 100 Sim 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 Om, in contrast to resistivities between 0.6 and 1.0 Om 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.