Extending thermal stability of calcium carbonate pills using sepiolite drilling fluid

The aim is to investigate the plugging ability of sepiolite clay water base drilling fluids before and after CaCO₃ added over a wide range of high permeable zones at high temperature and high pressure conditions, to verify the feasibility of CaCO₃ as loss preventer material (LPM) into the sepiolite drilling mud. The rheology and loss tests at 27-204℃ and 2 070 or 6 895 kPa reveal that the sepiolite drilling mud shows good rheology and high solid suspension capability at all temperatures except 149℃, and low loss circulation at high temperature and high pressure. The Permeability Plugging Apparatus (PPA) experiment, in which the 10-90 µm permeable ceramic plate was simulated as formation, shows that the sepiolite drilling mud without CaCO₃ can not plug the pores, while the sepiolite drilling mud with CaCO₃ can plug the pores quickly and keep the CaCO₃ particles suspended even at high temperature (up to 193℃). The PPA experiment results were proved by the analysis using SEM and ideal packing theory.