Selection of proper drilling fluid is recognized as a challenging process in high temperature environments. Therefore, chemical and physical properties of drilling mud should be suitable at high temperatures to minimize mud and borehole instabilities. This study is aimed to characterize rheological and filtration properties of sepiolite based muds at high temperatures and to determine their plugging ability in permeable formations. Mud samples were aged up to 204 °C temperature and tested with viscometer and HTHP filter press. The filtration of sepiolite muds were customized through ceramic discs having various pore throat sizes using Permeability Plugging Apparatus (PPA) that simulates more realistic borehole conditions. PPA experiments were conducted at temperatures up to 204 °C and 2070 kPa pressure differential. CaCO3 was used as a lost circulation pill.
Experimental results reveal that customized sepiolite mud is not flocculated up to 204 ° C and yields suitable filtration rates from HTHP filter press. However, the fluid losses obtained from PPA were unacceptable. Therefore, result from HTHP filter press is not a decisive factor to select an effective mud. However, sepiolite muds with CaCO3 can effectively initiate the plugging phenomenon in relatively short time and give low fluid losses and extend the usage of CaCO3 as a loss circulation material.