Influence of a calcined clay and the temperature on the hydration of an oilwell cement

The influence of a calcined clay on the hydration of an oilwell cement was studied in slurries. The replacement grades of the cement (by weight of cement) were 5, 10 and 20% of the calcined clay. The slurries were prepared at a density of 1.80 g·cm⁻³ and hydrated in sealed containers at 30 and 60 °C during 24 h. A reference slurry was prepared where the cement was substituted by 5% of a zeolitic tuff. The water–to–solid ratio was 0.52 for each slurry. From the TGA and pozzolanic reactivity tests were shown that the calcined clay was more reactive than the zeolitic tuff. The isothermal calorimetry tests showed that the induction periods of the slurries were shorter when the cement was replaced by the calcined clay at both temperatures and they decreased with the increment of the temperature and the replacement level by the mineral addition, what could impact negatively the thickening time in real conditions. The MIP assays evidenced that the influence of the kind and the quantity of the mineral addition on the porosity of the hardened slurries is complex but in general it was observed a refinement of porosity and less total porosity when the slurries were hydrated at 60 °C. The XRD experiments showed that the phase assemblages when the slurries were cured at 60 °C were more complex and with more crystalline phases presents, which could have influences on the performance of the hardened slurries in real well conditions.