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Carbon dioxide CO2could corrode the oil well cement paste matrix under agreeable moisture and pressure condition in deep oil wells, which could decrease the compressive strength and damage the annular seal reliability of cement paste matrix. The problem of oil well cement paste matrix corrosion by CO2was researched in the paper for obtain the feasible corrosion prevention technical measures. The microstructure and compressive strength of corroded cement paste matrix were examined by scanning electron microscopeSEMand strength test instrument etc. under different corrosion conditions. The mechanism and effect law of corrosion on oil well cement paste matrix by CO2were analyzed. And the suitable method to protect CO2corrosion in deep oil wells was explored. The results show that the corrosion mechanism of cement paste matrix by CO2was that the wetting phase CO2could generate chemical reaction with original hydration products produced from cement hydration, which CaCO3were developed and the original composition and microstructure of cement paste matrix were destroyed. The compressive strength of corrosion cement paste matrix always was lower than that of un-corrosion cement paste matrix. The compressive strength of corrosion cement paste matrix decreased with increase of curing temperature and differential pressure. The corroded degree of cement paste matrix was intimately related with the compositions of cement slurry. Developing and design anti-corrosive cement slurry should base on effectively improving the compact degree and original strength of cement paste matrix. The compounding additive R designed in the paper could effectively improve the anti-corrosive ability of cement slurry.

The compressive strength of oil well cement would be damaged by high temperature in deep oil wells, which was caused by the obvious change of the components and microstructure of cement hydration products. The adaptability of common oil well cement for cementing under higher temperatures was confined by above reasons. Characteristics of development and change of compressive strength of Class G oil well cement were studied under different temperatures by using Static Gel Strength Analyzer and High Temperature-High Pressure curing chamber. The influence law of temperature and silica sands on compressive strength was analyzed. The results showed that the critical temperatures at which the compressive strength begun to decline were about 110°C and 150°C respectively; The compressive strength increased with curing time during the initial period and would reduced after it reached a certain value when temperature exceeded 110°C; For cement with silica sands, the compressive strength development trend was in the shape of two-stage form with increase of curing time within the range of 110~150°C, but for 160~200°C temperature range the development form was in the shape of single stage; The reasonable amounts of silica sands which would be added to cement slurry to enhance the compressive strength of hardening paste were determined to be 30%~40%.