TRAPS IN GAS HYDRATE DATA INTERPRETATION GAUSED BY MASS TRANSPORT DEPOSITS: EXAMPLES FROM SHENHU AREA, SOUTH CHINA SEA

The bottom simulating reflector (BSR) is considered as the most important indicator of gas hydrates, but it is not a indespensable indicator since there is no strict correspondent relationship between gas hydrate and the BSR. The bottom of the mass transport deposits may have similar features to gas hydrate-related BSR in seismic profiles. The MTD is often mis-interpretated as gas hydrate, and may become a trap in seismic data interpretation. In order to effectively differentiate the MTD-related BSR from the gas hydrate-related BSR, seismic attribute analysis and fine logging interpretation technology are both used for interpretation of the 3D seismic data and logging curves acquired from the Shenhu Area of the South China Sea. The results show that MTD are characterized by strong relative acoustic impedance, cut-crossing, low-similarity, and chaotic reflection on seismic profiles and high velocity and high resistance on logging curves, which are hard to be differentiated from hydrate caused BSR. However, MTD usually have higher clay content, lower resistivity increment, and lower water saturation, indicating that the abnormal log responses to the beds overlying the BSR are related to the process of compaction of sediments. The data from the Well 2 is carefully studied in this paper. Considering the facts that BSR is consistent with the bottom of the MTD, and there is no evidence to prove the occurrence of free gas in the underlying layer, phase-boundary or geotectonic difference, we conclude that the BSR there may indicate the bottom of a MTD.