Effect of mullite whiskers and graphite flakes blending on the mechanical properties of oil well cement

• Adjust the dosage of mullite whiskers and graphite flakes in cement slurry. • The influence of mullite whiskers and graphite flakes composite materials on the mechanical properties such as strength of cement paste was studied. • Analyzed the mechanism of action of mullite whiskers and graphite flakes composite materials in cement stone. • Emphasis was placed on the importance of composite materials in achieving ideal cementing results. In the process of heavy oil thermal recovery, the cement ring used for well consolidation is prone to cracking under high-temperature conditions, which reduces the strength of the cement stone and may further lead to sealing failure and safety accidents in oil and gas extraction. This study explores the impact of the combined action of mullite whiskers and graphite flakes on the performance of cement stone, and reveals its mechanism of action through testing and analysis of microstructure. The results show that the addition of mullite whisker/ graphite flakes significantly enhances the early strength and deformation resistance of cement stone under 90 °C conditions. In particular, after adding 0.7 % mullite whiskers and 1 % graphite flakes, the compressive strength of the cement stone at 3 days and 7 days increased by 76.57 % and 57.72 %, respectively. The microstructure indicates that mullite whiskers can promote the formation of hydration products, while graphite flakes plays a role in filling pores and reducing cracks in the cement stone, maintaining the integrity of the cement stone through a "crack bridging" mechanism. This study provides theoretical support and new directions for the improvement of cement slurry systems in heavy oil thermal recovery.