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 over a wide range of high permeable zones at high temperature and high pressure conditions. The special emphasis of this study is to extend the usage of loss preventer material (LPM) as a component of fresh water sepiolite base mud that has never been investigated for this purpose before. The rheology and loss tests at 27−204 °C and 2070 or 6895 kPa revealed that the sepiolite drilling mud shows good rheology and high solid suspension capability at all temperatures except 149 °C, 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, showed 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 °C). The PPA experiment results were proved by the analysis using SEM and ideal packing theory. Key words: sepiolite drilling mud, loss circulation, plugging performance, thermal stability, calcium carbonate particle, HTHP drillin