Nanometer blocking agent for oil-based drilling fluid and preparation method of nanometer blocking agent

The invention provides a nanometer blocking agent for an oil-based drilling fluid and a preparation method of the nanometer blocking agent. The nanometer blocking agent comprises the following components in parts by weight: 10-40 parts of styrene, 20-60 parts of methyl methacrylate, 0.3-1.0 part of emulsifier, 130-150 parts of deionized water, 1.0-2.0 parts of cross-linking agent and 0.1-0.2 part of redox initiator. The preparation method of the nanometer blocking agent comprises the following steps of mixing the emulsifier, the cross-linking agent and deionized water and evenly stirring to obtain a mixture; adding styrene and methyl methacrylate into the mixture and emulsifying for 20-30 minutes to obtain a pre-emulsion; adding the redox initiator into the 20-35wt% pre-emulsion, raising the temperature to 60-80 DEG C, reacting for 20-30 minutes, dropwise adding the residual pre-emulsion and continuously reacting at 60-80 DEG C for 2-5 hours to obtain the nanometer blocking agent for the oil-based drilling fluid. Due to adoption of the nanometer blocking agent for the oil-based drilling fluid disclosed by the invention, the nanoscale microcrack can be effectively blocked and the problem that the well wall of a shale gas well easily collapses is solved and the nanometer blocking agent is simple in preparation method.