Distributions of BSR and underlying free gas zones and related controlling factors

Bottom Simulating Reflector (BSR) is the seismic reflection marker of the base of gas hydrates. The blanking zones above represent hydrate-bearing sediments and the abnormally high amplitude zones below represent free gas zones (FGZs) sealed by hydrates. In this paper, high resolution 3D seismic data from offshore Mauritania are used to characte-rize in detail the seismic reflection characters of BSR and underlying FGZs, as well as their relations with nearby structural units. The BSR upwarps in the upper part of the diapir and deepens rapidly near canyon walls. In the diapir zone, the thermal flow migrating along the fault system during dipirism changed the hydrate stability conditions, causing the shallowing of the stable bottom boundary of BSR. The cooling of the surrounding deposits by the canyon, on the contrary, caused the deepening of the stable bottom boundary of BSR. Additionally, research shows that the BSR and FGZs are prone to form in areas with well-developed fluid migration conduits such as faults and chimneys, indicating that the fluid migration system is critical for the formation of gas hydrate and FGZs and may provide gas source for the hydratesystem.