Effect of thermally conductive filler on thermal conductivity of cementing materials in geothermal wells

Adding heat-conducting filler to the cement of the geothermal well could significantly improve the thermal conductivity of the cement stone and enhance the heat extraction effect of the geothermal well. In this study, on the basis of summarizing the heat conduction path theory and concept of high packing density, the effects of different filler types, particle sizes and dosages on the thermal conductivity of cementing cement were investigated through experiments. The test results showed that graphite had the best effect on improving the thermal conductivity of cement stone compared to other types of filler; the larger the graphite particle size, the higher the thermal conductivity of cement stone. The mixing of graphite with different particle sizes had a better effect on improving the thermal conductivity of cement stone than graphite with a single particle size. The optimal mixing formula was: graphite particle size was 150 μm and 100 μm, and the mass ratio was 2：1. With the increase of graphite content, the thermal conductivity of cementing materials increased, and the fluidity and compressive strength of 48 h gradually decreased. According to the relevant cementing specifications, the graphite content in the cementing materials should be controlled at about 9%. The research will provide references for the preparation of high thermal conductivity cementing materials for geothermal wells.