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Sub-surface precipitation of salts in supercritical seawater |
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| Authors: | Martin Hovland Tatyana Kuznetsova† Håkon Rueslåtten‡ Bjørn Kvamme† Hans Konrad Johnsen¶ Gunnar E Fladmark§ Andreas Hebach† |
| Institution: | Statoil, Stavanger, Norway; Department of Physics and Technology, University of Bergen, Bergen, Norway; NumericalRocks, Trondheim, Norway; Statoil, R&D Department, Rotvoll, Trondheim, Norway; Department of Mathematics, University of Bergen, Bergen, Norway |
| Abstract: | Extremely low solubility of typical seawater salts within certain supercritical sections of their pressure–temperature composition space is a proven experimental fact. Its consequences are often referred to as either 'shock crystallization' or 'out-salting'. Our alternative model for the formation of salt deposits hypothesizes that high temperatures and pressures characteristic for the high heat-flow zones of tectonically active basins may bring submarine brines into the out-salting regions and result in the accumulation of geological-scale salt depositions. To confirm the laboratory observations, molecular-scale simulations (molecular dynamics) have been employed to study structural changes in a model seawater system where temperature increased from ambient to near-critical and supercritical. Fluid properties and phase transition regions extracted from the simulations were then used as input parameters for a reservoir simulator program to model out-salting in a simple hydrothermal geological system. Both numerical simulations and laboratory experiments confirm that supercritical out-salting is a viable process of geological significance for the formation and accumulation of evaporites. We suggest two regions where hydrothermally associated salts may be depositing today: Atlantis II Deep, in the Red Sea, and Lake Asale, Ethiopia. |
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