Study On Preparation And Performance Of Nano-ferrofluids Used In Diagnostic Of Hydraulic Fracture

Microseism method is the most common fracture diagnostic method on oil field.In view of microseism method which cannot provide proppant distribution and effective fracture parameters,a diagnostic of hydraulic fracture method based on ferrofluids can make up for these disadvantages in principle and this method has a better application potential.Therefore,a kind of ferrofluids which has high magnetic susceptibility,stable performance,simple preparation method and can be applied to diagnostic of hydraulic fracture was prepared and its fluid properties and magnetic properties were studied.Using numerical simulation method,the effect of diagnostic of hydraulic fracture using nano-ferrofluids was studied,which provided the feasibility research of that with theoretical foundation.Fe₃O₄ nanoparticles was prepared by chemical coprecipitation method and according to size of particles and specific saturation magnetization,by orthogonal experiment,the optimal experiment parameters were as follows:reaction pH 10;Fe²⁺/Fe³⁺ratio 0.8¹.0;Fe³⁺concentration 0.2⁰.3mol/L;reaction temperature 50?;curing temperature 70?.X-ray diffraction?XRD?and scanning electron microscope?SEM?analysis indicated Fe₃O₄ particles composition of high purity,smaller and narrow particle size distribution about 20 nm;Hysteresis loop test showed that Fe₃O₄ nanoparticles have the property of superparamagnetism with saturation magnetization 53.6emu/g.On the basis,high stable water-based nano-ferrofluids is prepared with polyethylene glycol 4000?PEG-4000?as surface stabilizers.Performance experiment showed that nano-ferrofuids density was slightly larger than water and specific performance results were as follows:density 1.011¹.080 g/mL;Viscosity 2.84⁸.20 mPa s;Magnetic susceptibility 0.063⁰.244.At the same time,the convection-diffusion process of magnetic nanoparticles in the media of formation and fracture was studied by the method of numerical simulation and the simulation results indicated that in short period of injecting nano-ferrofluids,the magnetic nanoparticles are mainly distributed in the media of fracture and formation near the fracture surface;Injecting nano-ferrofluids could obviously improve the magnetic susceptibility of fracture domain,which was over 100 times greater than the magnetic susceptibility of formation.Based on the theory of static magnetic field,simulation results showed that under the earth magnetic field,nano-ferrofluids in the fracture domain could produce the induced magnetic field,which was influenced by injection time,fracture length,fracture height,fracture azimuth,etc.It is feasible that injecting nano-ferrofluids into fracture is used in diagnostic of hydraulic fracture,which has a better application potential.