Geothermal resource is a clean and efficient unconventional energy source. It is crucial to reduce heat loss along shallow interval around non-net for efficient use of geothermal energy. One potential method is to create a cement sheath with good mechanical and insulation properties through well cementing. However, there are few relevant studies. In this paper, the foamed cement slurry with good thermal insulation performance was prepared by a new nitrogen gas generating reactant, and the properties of cement slurry were further optimized by nano oxide and expanded vermiculite. The results show that: the foam distribution in self-generating nitrogen foamed cement is uniform and stable, which is beneficial to ensure the mechanical strength and thermal insulation ability of cement stone; The thermal conductivity of the cement stone with 5–8% expanded vermiculite can be reduced to 0.3719 W/m·k after curing for 48 h at 120 °C, and there is no adverse effects on the compressive strength of cement stone; Nano oxide can improve the mechanical properties and temperature resistance of the cement stone; The compressive strength of foamed cement composite remains above 18 MPa after curing for 48 h at 120 °C, without obvious deterioration of the cement performance. This research can provide reliable technical means for efficient exploration of geothermal energy.

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