Controls on gas hydrate system evolution in a region of active fluid flow in the SW Barents Sea

Abstract

The location and stability of gas hydrates in the SW Barents Sea is poorly constrained due to complex geological, geochemical, and geophysical conditions, including poor controls on regional heat flow and gas chemistry. Understanding the stability of gas hydrates in this region is important, as recent studies suggest destabilizing hydrates may lead to methane discharge into the ocean and possibly in to the atmosphere. Here, we use high-resolution 3D P-Cable seismic data, combined with 3D heat flow and fluid flow models to place new constraints on gas hydrate stability in this region. The 3D P-Cable seismic data, acquired in 2009 west of Loppa High, show cross-cutting, reverse polarity, high-amplitude reflectors interpreted as the base of gas hydrate stability. To constrain heat flow, fluid flow, and gas hydrate stability within the 3D seismic volume, we use a 3D steady-state, finite difference diffusive thermal model that incorporates regional bottom water temperature from CTD casts, expected geothermal gradients, and gas composition derived from well data. In general, modelled bottom simulating reflectors are deeper than observed BSRs. Our analysis weighs multiple factors that might explain the discrepancy between observed and modelled bottom simulating reflector depths. From this analysis, we propose that the most significant discrepancies in BSR depth are likely related to changes in regional fluid/heat flow and fluid geochemistry. The anomalously shallow bottom simulating reflectors can be explained via vertical fluid flow that might include ensuing potential effects on gas composition, pore water salinity and temperature. Our estimate suggest that a maximum vertical fluid flux of approximately 12 mm/y is necessary to explain the most significant anomalies. Our study provides new insight into regional heat flow, geochemistry, and endmember vertical fluid flux rates in the Barents Sea. Moreover, it documents that the fluid flow system is active and most likely, very dynamic.