| The oil and gas fields in China generally contain large amounts of CO2 and H2S, and carbon dioxide flooding also introduces CO2 to the formation. Such acidic gas in the formation leads to increase of the permeability rate of cement sheath, reduce of the compressive strength and bonding strength, which will fail to isolate inter-layer fluid. What's worse, it will cause the engineering problem of fluid channeling. Therefore, it has very important significance to prevent the acid gas corrosion of cement stone.The anti-corrosive ability of cement stone can be improved by solidified membrane, filling and cementation of resin. A water-soluble resin HY-1 was selected as the main preservative and the formula of resin cement slurry was obtained by adjusting the dosage of resin, curing agent, dispersant, fluid loss additives, the kind and dosage of retarder under the condition of 90??150?. The basic properties of resin cement slurry system are as follows:the density is 1.88 g/cm3, API water loss is 43mL, the compressive strength of 24h is 18.3MPa, and thickening time can be adjusted, the flowability of cement slurry perform well. The corruption law of resin cement slurry was researched after the change of compressive strength, permeability, corrosion depth and corrosion rate were studied before and after corrosion under different corrosion conditions. Under the corrosion condition of 60?×3MPa×90d, the loss rate of cement strength of the formula of cement slurry, the micro silicon cement slurry, the resin cement slurry are the 34.6%?25.9%?-9.09%, the anticorrosion rate of the micro silicon cement slurry, the resin cement slurry are the 54.8%?72.5%; Under the corrosion condition of 110?×3MPa×90d, the loss rate of cement strength are the 55.6%?40.5%?14.7%, the anticorrosion rate are the 44.6%,66.4%; Under the corrosion condition of 80?×3MPa×90d, the loss rate of cement strength are the 54.8%?39.4%?-8.33%, the anticorrosion rate are the 50.6%?71.3%; Under the corrosion condition of 80?×2MPa X 90d, the loss rate of cement strength are the 41.7%-. 33.3%?-10.3%, the anticorrosion rate are the 53.2%?74.0%; Under the corrosion condition of 80?×4MPa×90d, the loss rate of cement strength are the 65.0%?54.6%?-6.25%, the anticorrosion rate are the 40.9%?65.7%. After 5 days of the corrosion condition in the liquid H2S and gaseous H2S, the loss rate of cement strength of the formula of cement slurry are the 31.7% and 43.3%, the anticorrosion rate of the formula of cement slurry are the 25.4% and 29.9%; the loss rate of cement strength of the resin cement slurry are the 8.33% and 10.4%, the anticorrosion rate of the resin cement slurry are the 6.70%and 9.15%.The experiments show that the resin cement slurry has good anti-corrosive ability.The corrosion mechanism of the resin cement slurry was analyzed through X-ray diffraction, scanning electron microscopy. The experimental results show that the Ca(OH)2 and the membranous organic matter can be seen inside the water-soluble resin cement stone after corrosion. The water-soluble resin will solidify along with the solidification of cement, which will attach to the surface and pore of the cement stone in the form of organic membrane and the diffusion of the acid medium to the internal of cement stone is prevented. Besides, a part of solidified water-soluble resin will fill in the pore of cement stone, which leads to decrease of the permeability of cement stone, reduce strength loss rate and permeability growth rate and improve the anticorrosion rate.In conclusion, the water soluble resin cement slurry system studied in this paper could effectively improve the acid gases corrosion resistance ability and has strong practical significance in the anti-corrosion of oil-gas field. |
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