Predicting and Controlling the Thermal Conductivity of Portland Cement for Underground Conditions

In low-temperature geothermal development (typically <150 °C), significant heat loss through the wellbore─especially across the cement sheath─reduces produced fluid temperature and system efficiency. Conventional oil well cement, with high thermal conductivity (0.8–1.5 W/(m·K)), offers poor insulation, undermining geothermal project economics. To address this, we investigate prediction and control strategies for the thermal conductivity of concrete under subsurface conditions. Systematic experiments reveal that, within practical ranges, thermal conductivity positively correlates with moisture content, curing temperature, and age but negatively with porosity, permeability, and water-to-cement ratio. A regression model for Jiahua G-grade cement accurately predicts thermal conductivity based on these parameters, identifying moisture content as the dominant factor. Crucially, incorporating impermeable insulating additives to maintain low internal moisture─by preserving air-filled, uninvaded pores─emerges as the most effective approach to enhance insulation. This strategy enables tailored cement formulations with thermal conductivity below 0.4 W/(m·K) while ensuring mechanical integrity. The findings provide a robust technical foundation for designing high-performance insulating cement systems that minimize wellbore heat loss, improve geothermal efficiency, and support sustainable utilization of low-temperature geothermal resources.