A Study On Nanofluids Spreading On The Reservoir Cores Surface And Its Displacement Mechanism

At present, there are two problems in the process of oilfield exploitation at home and abroad. Firstly, the proportion of low permeability oilfields become more and more large. Secondly, crude oil recovery is low. With the continuous development of nanotechnology, nanoparticles have been speculated as good in-situ agents for enhancing oil recovery.In this paper, Si O2 nanoparticles have been collected as the additive of oil displacement agent due to it’s cheap, available and pollution-free. Choosing sol-gel method to prepare Si O2 nanoparticles by using TEOS as raw material. Conducted hydrophobic modification experiments on particles surface with dichlorodimethylsilane, compared the size, surface wettability and dispersion of modified nanoparticels with different modification methods. Then diverse hydrophilic/hydrophobic Si O2 nanoparticles were respectively dispersed in aqueous solution to form into different nanofluids displacement agent. In order to enhance oil recovery and explore the oil displacement mechanism of nanofluids, we carried out the research from two aspects. From microscopic perspective, observed the core inner surface by electron microscope after nanofluids are spreading. From macro perspective, tested interfacial tension between nanofluids and crude, performed core flooding experiments and evaluated the oil displacement effect.The results show that sol-gel preparation method can effectively control the size of Si O2 particles, reaction time and yield by adjusting the p H of mother liquor, stirring speed and other conditions. Especially when the p H of liquor is equal to 8, the reaction time is only 12 hours, yield up to 80% and the average size of synthetic spherical Si O2 nanoparticles is 38 nm. There existed striking differences in the size and hydrophobic degrees of Si O2 nanoparticles with different modified methods. The best effect is using dichlorodimethylsilane one-step method to do modification tests, the size of modified Si O2 nanoparticles is only 10 nm. When conducted oil displacement experiments, the mass fraction of 0.05% particles water-based dispersion, especially hydrophilic S-05, can significantly reduce interfacial tension and improve oil recovery.The oil displacement mechanism by nanofluids can be obtained base on the above results. As the Si O2 nanoparticles added, the oil-water interfacial tension has been greatly reduced and the oil washing efficiency of displacement has been improved. With the nanofluids enter the reservoir continuously, Si O2 particles can break through the hydration layer and oil layer which attached to the core surface. This part of Si O2 selective adsorbed and formed into micro-nanometer hydrophobic structure on some areas of core surface. The structure not only play a role of releasing crude oil, also could produce the effect of decreasing pressure and increasing injection rate in the late process of water injection.