▎ 摘　　要

NOVELTY - Preparing nano-graphene comprises: (i) reacting graphite, first oxidant and intercalating agent to obtain modified graphite; (ii) reacting modified graphite, acid and second oxidant to obtain graphene pre-product; and (iii) gas-stripping graphene pre-product. USE - The method is useful for preparing nano-graphene, which is used as plugging agent in oil-based drilling fluid (all claimed). ADVANTAGE - The nano-graphene as plugging material has good dispersing effect in oil-based drilling fluid, and strong bearing capacity, and is capable of effectively plugging nano-level pore in stratum at lower concentration, delaying pore pressure transmission, and improving stratum bearing capacity. The oil-based drilling fluid has good rheology, and high plugging rate, which can greatly improve well wall stabilizing ability, and has good quality, safety and high efficiency drilling. DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for: nano-graphene, prepared by above method, where the average particle diameter of the nano-graphene is 110-750 nm, preferably 110-600 nm; and oil-based drilling fluid, comprising nano-graphene.