| CPC C04B 7/02 (2013.01) [C04B 7/32 (2013.01); E21B 33/13 (2013.01); C04B 2103/20 (2013.01); C04B 2111/70 (2013.01); C04B 2201/32 (2013.01)] | 19 Claims |

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1. A high-thermal conductivity grout composition for heat transfer from a hot rock formation into a working fluid of a geothermal heat harvesting system for electrical or thermal energy generation, comprising:
a grout mixture comprising a cementitious material, a retarder, and a high-thermal k material;
wherein the retarder is present in an amount effective that delays setting of the grout mixture at a target location having a geostatic target temperature of at least 300° F. for at least two hours; and
wherein the high-thermal k material is present in an amount effective such that the grout mixture has, upon setting at the target location, a thermal conductivity of at least 10 W/m° K.
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