Investigation on thermal conductivity property and hydration mechanism of graphene-composite cement for geothermal exploitation

Abstract

In the process of geothermal exploitation, the thermal conductivity of casing cement affects the heat exchange efficiency of geothermal wells to a great extent. Because of this, combining with theoretical analysis and experimental study, this paper documented the development of a graphene-composite cement material for geothermal exploitation, based on the evaluation of thermal conductivity property and its hydration mechanism. Cement additives, including NS-600 and 1200 mesh silicon carbide (SiC) as basic thermal conductive fillers, graphene nanosheets (GNSs) aqueous solution for synergistic thermal conduction, and early strength agent (ZQ-4), structural stabilizer (FL-5), defoamer (MC-6) were utilized. The rheological properties, stability, compressive strength, and thermal conductivity of cement slurry were evaluated by laboratory instruments. X-ray diffraction (XRD) and environmental scanning electron microscope (ESEM) were used to analyze the phase composition and micro morphology of the optimized formulas, and the hydration and thermal conductivity mechanism of the graphene-composite cement was obtained. The thermal conductivity of the two optimized formulas obtained in the experiment were 2.141 W/(m · K) and 1.862 W/(m · K) respectively. The study results provide a new method to improve the properties of potential casing cement for enhancing the heat exchange efficiency of deep geothermal exploitation.