ADVECTIVE HEAT TRANSPORT AND THE SALT CHIMNEY EFFECT: A NUMERICAL ANALYSIS

It has long been recognized that there is a significant thermal anomaly associated with the high thermal conductivity of salt rocks as compared to other sedimentary rocks. Although the so-called “salt chimney effect” has been widely recognized in models of conductive heat transport near salt structures, recent studies have shown that advective heat transport could exert an even greater influence on the temperature distribution near salt. We conducted numerical simulations of coupled fluid and heat transport in a salt dome environment to determine the effects of advective heat transport in different scenarios. Model sets were designed to investigate (1) salt geometry, (2) depth dependent permeability, (3) geologic heterogeneity, and (4) a combined simulation to assess the relative influence of each of these factors. Decreasing the dip of the diapir induces advective heat transfer up the side of the diapir, elevating temperatures in the basin. The resulting fluid circulation causes flow up the diapir flank. Depth dependent permeability causes upwelling of warm waters in the basin. Heat is advected up the diapir in a narrower zone of upward-flowing warm water, and cold waters are advected deeper into the basin. The resulting fluid circulation pattern causes increased discharge at the diapir margin and fluid flow downward, above the crest of the diapir. Geologic heterogeneity decreases the overall effects of advective heat transfer. Sealing horizons reduce the vertical extent of convective cells and fluid flow is dominantly up the diapir flank. The combined effects of depth dependent permeability coupled with geologic heterogeneity provide the most realistic model. Conductive heat transfer dominates in the basal units, whereas advection of heat begins to affect the middle layers of the model and dominates the upper units. Convection cells split by sealing layers develop within the upper units. Overall, our results indicate that fluid flow and the associated thermal advection is strongly controlled by salt geometry, aquifer thickness, and permeability. Advection likely dominates in shallow sediments with relatively high permeability. Further modeling is necessary to assess the relative influence of these factors in the presence of salt dissolution.