Contamination of oil-well cement with conventional and microemulsion spacers

The performance of oil-well cement is altered if contaminated by spacers. Very few studies in the literature are found on this topic, in particular for newly developed microemulsion spacers. Therefore, it is worth investigating the properties of cement contaminated with spacers. In this study, material characterization techniques including chemical shrinkage, ultrasonic pulse velocity (UPV), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and nitrogen adsorption (NAD) were used to study the hydration and microstructure of contaminated cement. Results showed that the studied microemulsion spacer was less compatible with the cement slurry than the conventional one. The microemulsion spacer has complex effects on cement hydration: it slightly enhances hydration for the low dosage but can retard hydration at the early ages and accelerate hydration in the later ages with the increase of dosage. The conventional spacer caused early acceleration of cement hydration but had no effect at later ages. The presence of spacers in the cement slurry decreases the compressive strength and creates a more complex microstructure than is found for the neat cement. All these effects with the studied microemulsion spacer are worse than with the conventional spacer. Therefore, the presence of a microemulsion spacer in a cement slurry may cause long-term durability issues compromising the downhole zonal isolation.