At the 2013 Stanford Geothermal Workshop, a new geothermal concept for downhole heat exchange was presented, called the ‘boiler’. Water is injected from surface via the wellbore annulus space between production casing and tubing, without pumping. At a selected depth, the heated water enters the boiler via a flash evaporation valve that reduces its saturation point. If the flash evaporation leads to 100% steam, then the steam can become superheated as it travels further through the boiler. On the other hand, if the flash into steam is only partial, then the remaining liquid can gain heat as it travels through the boiler, with associated flow boiling. Following the preliminary assessment calculations presented last year, more detailed investigations on the feasibility of the artificial Geyser concept were carried out, leading to a better understanding of the dependency of overall system efficiency on boiler’s entry conditions and its design, for both vertical and horizontal well sections. The inclusion of distributed fluid pressure drop and heat transfer along the boiler provides better insights into the relationship between the enthalpy of the fluid entering the boiler, the enthalpy downstream of the valve and the heat transfer required along the boiler to ensure exiting conditions capable of minimizing the re-condensation risk. The new calculations also allow to better assess when and where this concept may have a better chance of success, based on different reservoir parameter and constructive options.

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