Study on the improvement of geothermal cement properties by nanofluid composed of deep eutectic solvent and graphene oxide

Guided by the goal of improving the heat transfer efficiency of geothermal cement, the development of high thermal conductivity fillers is urgently needed. Considering the drawbacks of carbon-based fillers in deteriorating the strength and fluidity of cement, this study proposes the use of green and low-cost deep eutectic solvents (DES) loaded with graphene oxide to form nanofluids (GONF) to improve the connection between graphene oxide and cement. The thermal conductivity and basic properties of GONF-cement under thermal storage conditions (60-100 °C, 0-36%NaCl) were reported, and the influence mechanism of nanofluids was analyzed. The following interesting conclusions were found: (1) The oxygen-containing functional groups on the surface of graphene oxide were connected to active sites of DES through the formation of the hydrogen bond network, forming thermal stable nanofluids. (2) Nanofluids was proven to be a low-cost (reduce material costs of graphene oxide by 90%) and effective material for enhancing the thermal conductivity and mechanical properties of geothermal cement while maintaining appropriate fluidity and low variation of density. (3) The synergistic mechanism between nanofluids and cement is due to the fact that nanofluids promotes hydration process by providing stable reaction sites, significantly reducing the porosity and pore size of cement. The dense structure enhances compressive strength and shortens the heat transfer path. This study enriches geothermal cementing technology and provides support for the low-cost application of graphene oxide in exploration engineering.