Feasibility study of seismic monitoring for gas hydrate production in the Ulleung Basin in the East Sea

Abstract

During gas hydrate production, the upper parts of the gas hydrate-bearing layer (GHBL) behave as a seal. If parts of the upper gas hydrates are dissociated, free methane gas present in the lower parts of GHBL may leak into the upper parts of the layer. Therefore, the dissociation of methane gas in the GHBL must be monitored to ensure strong stability during gas production. To investigate the feasibility of monitoring the dissociation of gas hydrates with a seismic survey, we established a rock physics model incorporating the geological characteristics of the region around the UBGH 2-6 well in the Ulleung Basin based on LWD data and core analysis data. We performed fluid substitution modeling to build a velocity model with the dissociated parts of the gas hydrates, and generated synthetic data. Diffractions from the edges of the dissociated parts allowed detection of gas hydrate dissociations, and the dissociated locations could be identified in the migrated image. In addition, sensitivity testing showed that the dissociated part was recognizable in the migrated image, even at a width of half the wavelength. Therefore, we conclude that the stability of gas hydrates during production can be monitored using a time-lapse seismic survey.