Impact of Sub-Gas Hydrate Sediment Thermal Conductivity on Hydrate-Based Heat Flow Derivations

Studies of crustal heat flow are important not only for tectonophysics investigations (e.g., crustal structure, composition, and age—which carry significant societal implications, including seismic hazard assessment), but are also critical to energy resource assessment, including geothermal potential and petroleum occurrence. Along the marine elements of continental margins, heat flow estimates are typically made using borehole temperatures, heat probe measurements, and analysis of core from near the seafloor. In sedimentary basins hosting gas hydrate, the basal gas hydrate phase boundary may be expressed as a bottom-simulating reflector (BSR) in reflection seismic data. Because hydrate stability is controlled by well-defined pressure and temperature conditions, the BSR is frequently employed as a calibration point to estimate present-day heat flow in marine sediments. The BSR method has been particularly useful when paired with other constraints, including heat probe and oceanographic data, but when used alone, uncertainties and errors in calculated heat flows can be significant. Limitations resulting in such uncertainties have been detailed to some degree, and range from local controls such as seafloor topography to basin-wide controls such as sedimentation rate. Here, we explore one such limitation: potential thermal conductivity variations of basin fill (e.g., sediment and rock) beneath the BSR. We perform finite difference numerical modeling in conjunction with basin and petroleum system modeling to evaluate the hypothesis that even under different basal heat flow scenarios, BSR depths may be identical due to differences in sub-BSR thermal conductivities (and that, conversely, in areas with identical basal heat flows, BSR depths may be different due to differences in sub-BSR thermal conductivities). We recommend that sub-hydrate thermal conductivities be considered to avoid potential pitfalls (i.e., nonunique heat flow solutions) in estimated basin thermal regimes.