Geochemical assessment of a MgCl2 heat transport fluid to evaluate the feasibility of using geothermal energy from saline systems

Abstract:

Saline formations have heat conductivity, 2 to 4 times greater than most rocks. Therefore, higher temperatures can be found near salt formations. These higher temperatures create the potential for geothermal electrical energy production at shallower depths. A heat transport fluid is required to bring the geothermal heat to the surface. The heat transport fluid must demonstrate a low affinity for mineral dissolution and precipitation to avoid dissolving the formation and clogging the piping material. Our project aims to evaluate a geothermal system consisting of two boreholes within the geological setting of the Canadian part of the Williston Basin. A saturated MgCl₂-brine is used to transport heat.

Sophisticated numerical modelling with a reactive transport model is used to evaluate MgCl₂-brine as a heat exchange fluid in a halite dominated formation. Since solubility is temperature dependent, the model needs to simulate the dissolution and precipitation of salt minerals due to temperature change. Preliminary results, completed under equilibrium conditions suggest a 90°C range where dissolution and deposition will be slow. These temperatures fall within the 80 to 130°C range present in the salt formations.