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<p>To mitigate strength retrogression in Class G oil-well cement and enhance its thermal conductivity under high-temperature geothermal conditions, a metakaolin/graphite-modified cement composite was developed. Metakaolin was incorporated to densify the cement matrix and offset the strength reduction associated with graphite addition, whereas graphite acted as a thermally conductive phase. Under simulated geothermal curing conditions (240 ℃), the composite containing 15% metakaolin exhibited the highest compressive strength of 42.4&#xa0;MPa, representing a 236.5% increase compared with plain cement. With the further addition of 5% graphite, the thermal conductivity increased by 31.9%. Microstructural analyses showed that metakaolin promoted the formation of tobermorite and gel products, reduced the total porosity by 9.66%, and refined the pore structure by increasing the fraction of pores smaller than 50&#xa0;nm, thereby contributing to a dense and thermally stable matrix. Meanwhile, well-dispersed graphite flakes established effective heat-transfer pathways, facilitating phonon transport and enhancing thermal conductivity. This study provides a practical strategy for designing cement-based materials that combine high mechanical strength with improved thermal conductivity for deep geothermal well applications.</p>

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Metakaolin/graphite-modified oil-well cement composites with enhanced high-temperature strength and thermal conductivity for geothermal applications

  • 期刊论文

  • 发表日期：

    2026年7月27日

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  • Cen Guo,
  • Huiting Liu,
  • Xiujian Xia,
  • Yukun Yang,
  • Ming Li

摘要

To mitigate strength retrogression in Class G oil-well cement and enhance its thermal conductivity under high-temperature geothermal conditions, a metakaolin/graphite-modified cement composite was developed. Metakaolin was incorporated to densify the cement matrix and offset the strength reduction associated with graphite addition, whereas graphite acted as a thermally conductive phase. Under simulated geothermal curing conditions (240 ℃), the composite containing 15% metakaolin exhibited the highest compressive strength of 42.4 MPa, representing a 236.5% increase compared with plain cement. With the further addition of 5% graphite, the thermal conductivity increased by 31.9%. Microstructural analyses showed that metakaolin promoted the formation of tobermorite and gel products, reduced the total porosity by 9.66%, and refined the pore structure by increasing the fraction of pores smaller than 50 nm, thereby contributing to a dense and thermally stable matrix. Meanwhile, well-dispersed graphite flakes established effective heat-transfer pathways, facilitating phonon transport and enhancing thermal conductivity. This study provides a practical strategy for designing cement-based materials that combine high mechanical strength with improved thermal conductivity for deep geothermal well applications.