A novel concept of circulating molten salt (CMS) through a subsurface formation has been developed for the purpose of in- situ upgrading (IUP) of heavy oils into lighter transportation fuels, in pursuit of its potential to substantially reduce power expenditures and CO2 emissions during the IUP process. The CMS system can utilize molten nitrate salt to transfer heat from a surface heat source down to the hydrocarbon (HC) bearing reservoir via a system of underground pipes, essentially creating a subsurface heat exchanger. Nitrate salts are known to be strong oxidizers and can react exothermally with various hydrocarbon constituents in the subsurface under certain conditions. Detailed Computational Fluid Dynamics (CFD) simulations were carried out to evaluate the consequences of an accidental release of molten nitrate salt from a failed pipe and into the surrounding formation rock. Modeling results have been used to assess: (1) the temperature and pressure build up in the near wellbore region; and (2) the propagation of a reaction front in the formation and its impact on neighboring heater/producer wells. Extensive sensitivity analyses on salt temperature, reaction rate constants, and time of occurrence were performed. The simulation results indicate that the reaction progress is likely to be mass-transfer controlled rather than kinetically controlled under subsurface conditions. Both pressure and temperature build up are likely to be moderate in the event of a large release of molten salt. The damage that a moving burning front in the formation may cause to neighboring heater pipes appears to be manageable as long as sufficient flow rate is maintained in these pipes.
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