Abstract
A two-dimensional high-resolution seismic survey was conducted in 2001 for exploration of methane hydrate in the eastern part of Nankai Trough area, where a huge amount of methane gas hydrate has been suggested by many researchers. Seismic survey lines were settled with coverage of four types of BSR (Bottom Simulating Reflector) distribution, which is a significant indicator of free gas existed below the methane hydrate stability zone. Interval of each seismic survey line was approximately 5km, and total survey length was 2, 800km.
Tuned air gun array with total volume of 1, 060 cubic inch (17.37 liters) was used as an energy source, and two types of field data were acquired through whole survey lines using two streamer cables towed with water depths of 3m and 6m. High continuity of seismic events could be obtained by usage of the depth of 6m, which is a quite conventional method, but resolution of seismic events is not so high especially at BSR with this depth. Using the towing depth of 3m, a high-resolution seismic data was acquired along whole survey lines. Combination of these types of seismic data including deep-tow seismics with well log data to be obtained in 2003 is expected as an effective geophysical indicator for exploration of methane hydrate and free gas in the Nankai Trough area.
