A mechanistic study on early hydration of oil based cement

Oil base cement slurries (OBCS) are an excellent water shutoff agent. The early hydration of oil base oilwell cement of grade G, original as received and finely ground, is studied using TAM Air 8 way calorimeter. The evolution of hydration heat proceeds much slower in OBCS than in an ordinary water base slurry; the hydration heat of cement in OBCS increases with the water to oil slurry (W/S) ratio; with finely ground cement taken in the OBCS, the hydration of cement accelerates but the hydration heat evolved decreases. There exists a notable induction period in cement hydration in OBCS and the larger the W/S ratio of OBCS the longer the induction period of hydration. Mechanical measurements show that the compressional strength of hardened oil base cement varies significantly with changing the W/S ratio of OBCS and the highest strength is observed at intermediate W/S ratios of 0.2:1-0.3:1; the early strength is higher when finely ground cement is taken in preparing OBCS. The loss on ignition measurements show that the hydration degree of hardened oil base cement is affected mainly by the W/S ratio of OBCS and in less extent by the curing temperature and the cement fineness and is low enough, accounting 33-64% in 7 days, for the hardened cement strength to develop further in some extent.