The Effect Of Nano-silica And Graphite Oxide On The Performance And Hydration Process Of Cementing Cement Slurry

The effect of nano-silica and graphite oxide on the properties of cementing slurry was experimentally studied, aiming at the zonal isolation failure in oil and gas wells due to the brittleness of cement stone. The experimental results showed that:1)the fluid loss decreased significantly, cement slurry stability was improved obviously, with the incorporation of nano-silica; the thickening time of cement slurry containing 2.5% nano-silica gradually shortened, compared with the control group, decreasing from 738min to 581min, shortening 21.3 percent of the time; static gelling strength transition time of cement slurry was short, which indicated that the cement slurry with nano-silica has a good anti gas channeling properties; 2)nano-silica could significantly improve the cement early strength (curing time less than or equal to 7 days), and the late strength (curing for 28 days) was also improved significantly; when nano-silica dosage was 2%, the compressive strength, flexural strength and splitting tensile strength of cement stone curing for 36 hours were increased by 78.9%, 137.5% and 69.8% compared to the control group; when nano-silica dosage was 1.5%, the compressive strength, flexural strength and splitting tensile strength of cement stone curing for 28 days were increased by 26.1%,18.7% and 100.98% respectively, compared to the control group; the porosity of the cement stone decreased obviously with the addition of nano-silica; when the dosage of nano-silica was 1.5%, the cement stone porosity decreased by 4.77% compared with the control group; 3)graphite oxide could significantly enhance the mechanical properties of cement stone, and the 28d compressive, flexural and splitting tensile strength of cement stone containing 0.05% graphite oxide were increased by 68.63%,17.44% and 159.12% respectively, compared to the control samples; graphite oxide had no bad effect on the application properties of cement slurry, but was helpful to improve the stability of cement slurry and reduce the fluid loss.The mechanism analysis results showed that:1) nano-silica could react rapidly with Ca(OH)2 produced in the process of cement hydration, generating C-S-H gel with strength, which coule fill pores and optimize the microstructure of cement stone, making it more compact and uniform; under low temperature conditions, there would be more needle, columnar like hydration product AFt in cement stone, which could play a "bridging" role and form a spatial network structure with the C-S-H gel, optimizating the microstructure and increasing the strength of cement stone; nano-silica played a role in filling the pores and compacting the structure of the cement stone; these three effects led to the improvement of early strength and late strength of cement stone under low temperature conditions; 2) the inter-layer and intra-layer of graphite oxide were both damaged, when the cement stone was destroyed by external force; on the one hand, when damage occured within graphite oxide layer, chemical bonds of graphite oxide must have been broken, leading to a large amount of energy consumption, on the other hand, the force between the layers of graphite oxide must have been overcome when interlaminar peeling happened, which would lead large amounts of energy consumption as well, the mechanical properties of the cement stone were mainly enhanced by this two aspects. The study of effect of nano-silica and graphite oxide on the properties of cementing slurry is of great importance, for improving the mechanical performance of cement stone, ensuring the safety of cementing operation, and improving the cementing quality.