The invention relates to the technical field of oil gas well tracing monitoring, in particular to a preparation method and application of an oil gas well tracing monitoring magnetic nano tracer agent. Comprising the following steps: dissolving FeCl3, FeSO4. 7H2O and doped
metal salt in water, and introducing N2 to remove
oxygen; the initial
reaction temperature is 85 DEG C, rapidly adding
ammonia water, reacting to generate Fe3O4 nanoparticles,
doping elements, reducing the temperature to 60 DEG C, and firstly adding
sodium citrate for primary carboxyl modification; adding a
mixed solution of
oleic acid and PEG twice; the pH value of the
reaction system is controlled to be 9.5-10.5 in the whole process. The method has the beneficial effects that the
doping amount is remarkably increased, the
doping amount of doped elements is multiple times of that in the prior art, and the detection sensitivity is remarkably improved; in addition,
oleic acid / PEG composite modification is adopted instead of single
citric acid modification, so that the tracer is kept stably dispersed in high-
salinity formation water; the
superparamagnetism facilitates
magnetic separation and
recovery, and is suitable for harsh formation conditions.