Dan Mueller, BJ Services Co.
In recent years, the cementing industry has embraced the concept of right-angle-set as a desirable feature in the thickening time set profile of oilwell cements. Right-angle-set can be characterized as the rapid thickening of a cement slurry from a stabilized viscosity to a final set of 70-l 00 Bearden Units of Consistency (Bc). This is a dynamic-state phenomenon that usually takes place in the final 30-45 minutes of thickening time. Cement slurries exhibiting right-angle-set thickening time profiles were generally thought of as being preferable over slower "gel" type sets. However, within the practicalities of field operations, rarely is the cement still being placed while right-angle-set is occurring. More commonly, the cement slurry is mixed and displaced in only a fraction of the designed thickening time. How then does right-angle-set, a dynamic-state event late in the pumping history of the slurry, influence the static-state properties of the slurry, when placement is completed before the onset of right-angle-set? Presented are the results of conventional, low shear, and modified-hesitation-squeeze thickening time testing, combined with operating ultrasonic strength analysis, to quantify the differences in right-angle-set slurries as compared to cement designs with slower setting profiles.