| Hydraulic fracturing is a traditional reservoir reconstruction technology,which is often used in the development of low permeability oilfields.The fracturing effect is evaluated by fracture monitoring.The commonly used fracture monitoring methods have limited monitoring range,high requirements for monitoring formation conditions,and can not be quantitatively evaluated,which has certain pollution to operators,formation environment and produced crude oil.Therefore,it is necessary to study a kind of nano tracer which can quantitatively evaluate the fracture productivity.The tracer is composed of carrier and surface component.When it is pressed to the reservoir,the active component and carrier are separated and dissolved into the oil.After fracturing,according to the surface component concentration of oil phase and water phase in the backflow fluid to the production curve,the water production and oil production can be monitored at the same time,which provides technical support for on-site construction scheme design.Aiming at the problems of other kinds of tracers,Fe3O4 nanoparticles was used as raw material,and the surface of Fe3O4 nanoparticles was modified by initiator.The optimal conditions of polymer grafting modification were optimized by orthogonal design,and the active components were loaded on the modified particles.Application of infrared spectroscopy（FTIR）,X-ray photoelectron spectroscopy（XPS）,thermogravimetric analysis（TG）,transmission electron microscopy（TEM）and laser particle size analysis to characterize the main groups,coating effects,particle morphology and molecular size of nano magnetic tracer.The temperature and salt resistance,compatibility with fracturing fluid,formation adsorption,sensitivity and recovery of nano magnetic tracer were evaluated.The factors influencing the release of surface components of nano magnetic tracer were studied by orthogonal and single factor experiments,and the significance of each factor was evaluated.By monitoring the release rate of surface components under different influence factors,the release kinetics curve was fitted,and the release mechanism of surface components was explained.The effects of displacement rate,salinity and temperature of formation water on tracer production curve were studied by using displacement device.The production law of tracer was analyzed,and the productivity monitoring effect of nano magnetic tracer was evaluated.The results show that the particle size of the nano magnetic tracer prepared in the laboratory is about 500 nm,and the surface is grafted with PVA molecular chain,which has good temperature and salt resistance,and has little effect on the fracturing fluid.The long chain on the particle surface effectively reduces the adsorption of the tracer in the formation.In the magnetic field environment,the tracer presents a regular distribution and can be recycled.The results show that the effect of the factors is:reaction temperature>oil-water ratio>nano magnetic tracer dosage>mineralization>p H,and the first order dynamic equation fitting effect of release curve is the best.When the single fracture is single,the tracer mass concentration curve has only a sharp and high peak,and the area surrounded by y=x is larger without the cumulative output quality curve.The faster displacement speed is,the faster the surface component release is,the less the release is,the earlier the peak value appears,the weaker the peak intensity is;the higher the mineralization degree or the lower the temperature of the formation water,the slower the release speed of surface components,the later the peak time of the output curve.The instantaneous oil（water）contribution rate and dynamic oil production contribution rate are analyzed.The main oil production time of single fracture is the early stage of monitoring,and the main oil production time period of two fractures parallel is the middle period of monitoring,which provides a feasible method for fracture productivity monitoring. |
PDF Full Text Request