Abstract: A method includes flowing, in a closed loop geothermal well residing in a target subterranean zone, a first heat transfer working fluid and flowing, in the geothermal well, a second working fluid from the surface inlet to the downhole location of the geothermal well. The second working fluid resides upstream of the first heat transfer working fluid. The second working fluid includes a fluid density greater than a fluid density of the first heat transfer working fluid. The method also includes circulating, in the geothermal well, the second working fluid pushing, with the second working fluid, the first heat transfer working fluid toward a surface outlet of the geothermal well. The method also includes collecting energy from the mobilized first heat transfer working fluid received at the surface outlet of the geothermal well.