Study on Thermal Insulation Cement and Its Thermal Insulation Charateristics for Geothermal Wells

Geothermal energy is a clean, efficient and plentiful unconventional energy, and reducing the heat loss in wellbore is the key for efficient development of geothermal resource. It is a reliable solution to establish a long-term stable wellbore with good thermal insulation effect through cementing, which requires hardened cement with good mechanical and thermal insulation properties. However, there is little research in this regard at present. In this paper, a multi-material and multi-structure hollow cement slurry is developed, and a thermal-conductivity prediction method is proposed correspondingly based on Maxwell model. Nitrogen-filled foam and hollow glass beads were employed to reduce the heat conduction path, and their effects on the thermal conductivity, mechanical properties of hardened cement are analyzed. Results shows that: the distribution of self-generating nitrogen foam in foamed cement is uniform and stable, which is benefit for the mechanical strength and thermal insulation effect of hardened cement; 10 ~ 13% hollow glass beads can significantly reduce the thermal conductivity of hardened cement, without significant adverse effects on the rheology and strength of foamed cement; The prediction error of the newly established model is within 2%, which can be used to guide the optimization of thermal insulation cement. This research can provide technical support for efficient development of geothermal resources.