Study On The Composite Cement System Of Phosphoaluminate And Silicate

Silicate cement commonly used for cementing, but there are still many defects, its mechanical strength is not high, carbon dioxide corrosion resistance and high temperature resistance are bad. Phosphoaluminate cement is a new high-performance special cement. In order to adapt to more complex well conditions. Combined phosphoaluminate cement with silicate cement is expected to improve the performance of cement slurry.Combining with the characteristics of phosphoaluminate cement and silicate cement and from the view of material science and cementing operation requirements, suspension stabilizer, retarder and loss reduction agent for compound system are selected. The compressive strength and tensile strength of cement slurry are investigated. The high temperature property and carbon dioxide corrosion resistance are analyzed. Using the XRD and SEM, the mineral composition and microstructure of cement are analyzed and the impact mechanism of high temperature resistance and corrosion resistance of cement system are revealed.The compound cement system has good mobility, good stability and small fluid loss. Adding phosphoaluminate cement3%-40%, mechanical properties of the composite cement system is higher than other proportion cement system, even the single-phase composition. The high temperature resistance of pure phosphoaluminate cement is significantly higher than silicate cement. However, C2SH and C3A2SH4lead to the compound cement system without high temperature resistance. Corrosion products of phosphoaluminate cement are Ca10(PO4)(CO3)3(OH)2, Al(OH)3, C5P3H and calcium silicoaluminate hydrate instead of CaCO3. The corrosion resistance of composite cement system G+40%PALC is the best. Corrosion products of it are Ca1.5SiO3.5·xH2O, C5P3H, Al(OH)3and bits of CaCO3, which formed a protective barrier of cement paste to prevent the carbon dioxide into cement paste. So, it has good corrosion resistance.