[H-DS30_29PM2] Submarine landslides and their consequences

[HDS30-02] Feature of slump and associated structure observed at Daini-Atsumi knoll, the gas production test site from gas-hydrate

*Kiyofumi SUZUKI¹, Tokujiro TAKAYAMA¹, Yoshinori SANADA², Tetsuya FUJII¹ (1.JOGMEC/TRC, 2.Japan Agency for Marine-Earth Science and Technology)

Keywords:Slump, 3D seismic profile, LWD, Over-consolidate, Gas hydrate, Low impedance

The Daini-Atsumi knoll became famous as the first offshore gas production test site from methane hydrate-bearing marine sediments, is one of outer ridges along northeast Nankai trough, near central Japan. Several slumps were found on seismic sections around Daini-Atsumi knoll. Fortunately, several wells had been penetrating slump deposits and logging data were measured. As a result of seismic profile observations, a strong negative-impedance seismic reflector (NISR) was found in the turbidite sequence beneath the slump deposits. A seismic reflector containing the NISR has good continuity with variable reflectivity from a bottom-simulating reflector (BSR) sequence; that is, the NISR does not indicate a slump basement or the boundary of a chaotic unit. Nevertheless, very normal thin-layer turbidites were found at the depth of NISR from LWD measurement and coring, however, fluid data could indicate difference between upper slump unit and beneath turbidites unit. It implies that NISR does not mean pressured fluid but some fluid stagnation.AcknowledgementThis research is conducted as a part of MH21 research and the authors would like to express their sincere appreciation to MH21 and the Ministry of Economy, Trade and Industry for disclosure permission for this research.