EXPERIMENTAL STUDY ON TOUGHENING CEMENT SLURRY WITH CARBON-BASED CARBON NANOTUBES

The horizontal wells in shale oil and gas reservoirs generally need large-scale fracturing to achieve economic and effective reservoir development. The fracturing process puts forward higher requirements on the mechanical properties of the cement ring. In this regard, the use of carboxylated carbon nanotubes to toughen cement slurry cementing technology is proposed to improve the toughness and other mechanical properties of cement paste. Aiming at the problems of poor dispersibility of carbon nanotubes, easy agglomeration, and unknown tensile effect of cement stone, this article discusses pure carbon nanotubes, pure carboxylated carbon nanotubes, urea modified carboxylated carbon nanotubes, and ethanolamine modified carboxylated carbon nanotubes. The dispersibility and cement stone performance of glycine modified carboxylated carbon nanotubes were compared indoors. Finally, the technical solution of using glycine to modify the carboxylated carbon nanotubes is selected, and its dispersion effect and mechanical properties are the most favorable. On this basis, laboratory experiments were carried out to analyze the micro-dispersion state, mechanical properties, porosity and permeability of cement paste, and engineering characteristics of glycine-modified carboxylated carbon nanotube cement slurry. Experiments have confirmed that carbon nanotubes coexist with a single bridging inside the cement stone. In some areas, the carbon nanotubes are obviously bridged and formed into a network. After the bridge is formed into a network, the bonding force between the cement paste is improved, and the impermeability and mechanical properties of the cement stone have been significantly improved. The permeability and porosity of the matrix have decreased by 22.9% and 25.5%, respectively. 0.03% addition amount is the best. The engineering characteristics of cement slurry, such as water separation, fluid loss, and thickening time, have no obvious influence below 0.03% addition amount. A high-toughness cement slurry cementing technology based on carboxylated carbon nanotubes has been formed, providing a new way to improve the toughness of cement stone under large-scale fracturing operations and ensure the integrity of the cement ring.