the energy in the system is limited by both how much fluid you pump down and how hot the fluid is. Even for a static flow rate you can just keep increasing the temperature of the injected fluid to increase heat transfer. Even if the steam is supercritically heated, everything should still work.

Infact, supercritical steam is preferrable! It helps catalyze the conversion from CO2 gas to stable calcite minerals, opens up pore space at depth for more efficient heat transfer to the rock reservoir, and is much more thermally conductive than plain water or steam.