Integrated Analysis of Well Logs and Seismic Data to Deduce the Possible Distribution in Depth of Gas Hydrate in Shenhu Area, South China Sea

Abstract

AbstractThe available geological and geophysical information indicates the presence of gas hydrate at Shenhu Area of Northern South China Sea. The drilling cores recovered in 2007 testify the expectation and reveal that the gas hydrate disseminates evenly within the hydrate stable zone (HSZ), but its regional distribution is inhomogeneous. However, the logging record length and coring depth coverage are limited, which causes the depth distribution of gas hydrate to be indeterminate. Logs at well site SH7 were used to link the information of physical properties of sediments to the coincident seismic data acquired in this area. According to the relation between physical properties of sediments and seismic reflection characteristics, three primary formations were calibrated and the pseudo‐well constrained impedance inversion was then applied on post‐stack seismic data. The results showed a high velocity zone below the interval bearing gas hydrate. To determine whether this high velocity zone is related to the occurrence of gas hydrate or not, the technique of AVO forward modeling was further used to analyze the reflecting characteristic of pre‐stack seismic data. The comparison between synthetic seismic models and real seismic data indicates that the HSZ was composed of thin interbeds of gas hydrate‐bearing sediments and water‐saturated sediments, which suggests that another gas hydrate deposit exists most likely below the depth where gas hydrate‐bearing sediments were cored in the hole.