Abnormal gelation phenomenon of Class G oil well cement incorporating polycarboxylic additives and its countermeasures

Cementing security is endangered by the abnormal gelation phenomenon of cement slurry incorporating polycarboxylic additives occurred around 120 °C. The differences between gelatinous and non-gelatinous sections were investigated through various techniques. The polymer structural change around 120 °C could explain the abnormal gelation phenomenon by viscosity-temperature characterization. The other reasons are the polycarboxylic additives combine with Ca2+, SiO42− and aluminate hydrate by cross-linking reaction. The cross-linking structure developed flocs which was embedded in calcium silicate hydrate (C-S-H) gel and intertwined around stirring shaft. The practicable methods were proposed to relieve or solve the abnormal phenomenon of cement slurry.