Design And Property Study Of Corrosion Resistance Cement System To Co₂/h₂s

H₂S and CO₂ attack to oil well cement causes great dangers, which leads to the reduction of service life and the destruction of construction as well as production. According to this scientific problem, the micro-morphology and phase composition of cement attacked by H₂S and CO₂ was analyzed through SEM and XRD to ascertain the corrosion causes and the ways to improve H₂S and CO₂ corrosion resistance of cement. Then mineral admixture and organic matter were introduced into cement as addition materials for sulfate attack test and the optimum proportion of addition materials was obtained through orthogonal test. Finally, the corrosion resistance of designed cement and the effect of addition materials on corrosion resistance were studied. The results showes that:The corrosion products of H₂S and CO₂ were mainly CaCO₃, CaSO₄·2H₂O and amorphous SiO2. They could all lead to expansion cracks and eluviation. Then lowering the alkalinity of cement and improving the pore structure would be the two effective measures. The mineral admixture was beneficial to the decrease of Ca(OH)2 and the improvement of pore structure. When the ratio of mineral admixture to cement was 5:5, slag to fly ash was 4:6 and activator ( LBR ) to mineral admixture was 7:100, the corrosion resistance coefficient reached 1.227, which far exceeded that of pure cement in the same corrosive condition.In the basis of the cement above, bitumen was introduced with different admixture amounts. And the effects of bitumen on corrosion resistance were different under different temperature. The corrosion resistance coefficient of cement without bitumen was 1.19 under room temperature, and then decreased to 0.77 under 90℃. The corrosion resistance coefficient of cement with bitumen decreased under room temperature, and then increased under 90℃. Especially, the corrosion resistance coefficient reached 1.18 when mixing amount of bitumen was 10%.Then the cement combined with mineral admixture, bitumen or latex ( SBR ) for H₂S and CO₂ corrosion resistance was determined through experiments and literature studies. Expansion cracks were prone to generate for original cement in the corrosion process, and the compressive strength decreased as well as the permeability increased with the growth of corrosion time. There was no generation of expansion cracks for designed cement, as well as the corrosion product and hydration products were relatively stable. Then the corrosion resistance of designed cement was much better than original cement.In the systems of cement - mineral admixture– bitumen and cement - mineral admixture– SBR, low activity and micro-aggregate effect of fly ash were favorable to inhibit expansion cracks. Under experimental temperature, SBR formed a complex network-like structure and bitumen got soft and expansivein designed cement, which were both beneficial to improve the pore structure as well as inhibit expansion cracks and loss of corrosion products.