Composite of carboxylized graphene oxide with nanosilica for shale plugging

Carboxylized graphene oxide (GO-COOH)-silica (SiO 2 ) composite (GO-COOH/SiO 2 ) was synthesized in two-steps, and can be applied as plugging additive during drilling operations of shale strata. In the synthetic rout, improved carboxylation method was adopted to have more carboxyl groups grafted on graphene oxide, and nanosilica was synthesized by sol–gel/emulsion technique. The preparation of GO-COOH/SiO 2 composite was achieved by dispersing SiO 2 nanoparticles in GO-COOH solution. XRD and Raman spectroscopy showed that the interlayer spacing of GO-COOH/SiO 2 was 1.36 nm, which was higher than that of GO (0.84nm) and GO-COOH (0.92nm). According to SEM and TEM, particle size of synthesized SiO 2 sphere was estimated to be 150 nm, and there were more grown SiO 2 spheres than wrapped SiO 2 particles in the GO-COOH/SiO 2 . The more carboxyl groups offers more nano SiO 2 distributed points. Compared to single nanosilica material, the SiO 2 particles in the composite was more evenly distributed and agglomeration was reduced. Plugging properties test results indicated that GO-COOH/SiO 2 composite had better sealing performance than SiO 2 , GO and GO-COOH. To evaluate influence of GO-COOH/SiO 2 addition on water-based drilling fluid properties, comparative tests were conducted. The experimental results revealed that introduction of GO-COOH/SiO 2 can reduce filtration loss and enhance plugging capability and thermal tolerance of water-based drilling fluid. Therefore, GO-COOH/SiO 2 can act as a promising nanoplugging additive for shale formation.