Micro/nano structured oleophobic agent improving the wellbore stability of shale gas wells

Through embedding modified nano-silica particles on the surface of polystyrene using the method of Pickering emulsion polymerization, a kind of nano/micro oleophobic agent named OL-1 was developed. The effects of OL-1 on the rock surface properties and its performance in inhibiting the oil phase imbibition into the rock were explored. The performance and mechanisms of OL-1 in improving the wellbore stability of shale gas wells were evaluated and analyzed. OL-1 could absorb on the surface of the shale core to form a membrane with a micro-nano two-stage roughness, making the surface energy of the core decrease to 0.13 mN/m and the contact angle of the white oil on the core surface increase from 16.39° to 153.03°. Compared with the untreated capillary tube, when immersed into 3# white oil, the capillary tube treated by OL-1 had a reversal of capillary pressure from 273.76 Pa to -297.71 Pa, and the oil imbibition height inside the capillary tube decreased from 31 mm above the external liquid level to 33 mm below the external liquid level. The amount of oil invading into the rock core modified by OL-1 decreased by 64.29% compared with the untreated one. The shale core immersed into the oil-based drilling fluids with 1% OL-1 had a porosity reduction rate of only 4.5%. Compared with the core immersed in the drilling fluids without OL-1, the inherent force of the core treated by 1% OL-1 increased by 24.9%, demonstrating that OL-1 could effectively improve the rock mechanical stability by inhibiting oil phase imbibition.