Study on a Lyophobic Nanophase Plugging Agent for Oil Base Muds

Physical plugging with nanophase materials and wettability alteration of rock surface were used to solve the borehole wall stability problem encountered in shale gas drilling with oil base muds. The surface of the nanophase silica was modified sol-gel method, turning the silica into a lyophobic nanophase plugging agent, SNP-1. Molecule structure characterization with NMR and laboratory evaluation with SEM and natural imbibition revealed that SNP-1 gains the functional groups it was expected to have. With SNP-1, the contact angle of liquid on the surface of shale is greater than 150° and the additional capillary pressure is reversed to a force resisting the liquid phase from entering the pore throats of shales, further reducing the oil content of rocks through natural imbibition. The HTHP filtration rate and electrical stability of the oil base mud treated with SNP-1, after being aged at 150℃, were 2.4 mL and above 800 V, respectively, effectively hindering the pressure transmission through shale cores.