The Basic Research Of Nanopolysilicon Material In The Exploration Of Low Permeability And Tight Oil Field

The rocks of low permeability and tight oil field are usually having the characteristics of high dense buried, tiny pore throat, small porosity, poor permeability, and low oil recovery rate, which has been become the worldwide problem. The permeability can be improved through the reservoir rock alteration and surface modification, and the efficiency of water flooding will be increasing in low permeability and tight reservoirs. Surface modification by hydrophobic nanopolysilicon adsorption in reservoir micro-channels is a new injection technology to decrease the injection pressure and increase the water injection in low permeability and tight oil field. In recent years, Henan University has developed a series of hydrophobic nanopolysilicon(silica) which have been widely adopted in field tests and significant injection was achieved during water extraction process in low permeability reservoir. In the preliminary study, a new kind of nanopolysilicon which is used as injection agent can be dispersed in water at room temperature, and the methods and techniques of chemical broken used for nanopolysilicon was establishment. Meanwhile, the quartz sand proppant which has high conductivity was prepared by surface modification with surface-modified nano-SiO2. The main research contents and results are as follows:1. The laser particle size distribution analyzer, transmission electron microscopy, field emission scanning electron microscopy, optical contact angle meter and core flooding experiments were selected as analysis and testing tools. The phase dispersion and phase separation behavior of NPS-W water-based nanopolysilicon was studied and the methods and techniques of chemical broken used for nanopolysilicon was establishment. The polysilicon nanoparticles was dispersed in water to form a stable micro-emulsion by chemical crushing and micro-emulsion dispersion technology, and its size can be controlled during the dispersion process. The effect of temperature, concentration, time, pressure on the adsorption behavior of nanopolysilicon on the surface rock were studied and the properties of decompression and augmented injection was carried out in core displacement experiments. Moreover, the mechanism of chemical-structure hydrophobic was explored and the water-based nanopolysilicon micro-emulsion was conducted with three times in order to examine the water phase permeability. The relation between the wettability and the critical pressure was investigated. Those results can provide a theoretical basis for the controlled application of water-based nanopolysilicon in low permeability and tight oil field.2. NPS-W water-based nanopolysilicon is a kind of white powder, it need a high-temperature about 80℃ during the process of dispersion which greatly cause some difficulties in petroleum industry. This article has been developed a high concentration nanopolysilicon emulsion with small particle size(denoted as NPS-L), which can be diluted with water at room temperature and a clear and transparent injection agent with average particle size of 6 ~ 7 nm was formed. The core displacement experiments of artificial core and natural core of Changqing oilfield were carried out in order to discuss the properties of decompression and augmented injection. The results show that the NPS-L injection agent has a obvious injection effect with a long-term flooding in ultra-low permeability cores, and the product has been well tested in Changqing Oilfield.3. The hydrophobic NPS-Z and the polysilicon nanoparticles which were washed form water-based NPS-W and NPS-L after chemical broken were compared using Fourier transform infrared spectroscopy, specific surface area and pore size analyzer and other testing methods. It was found that the hydrophobic polysilicon nanoparticles from NPS-W and NPS-L expose more reactive hydroxyl groups and have the specific surface area more than doubled, and show that they have interesting performance with amphiphilic and phase transfer function with a similar feature of surfactant. The amphiphilic nanoparticle with particular construction has selective adsorption properties: polar end groups can efficiently and strongly adsorb on the surface of polar rock, and the non-polar end groups were bared out to forming a hydrophobic surface and the effect of surface modification can be improved. Meanwhile, the amphiphilic nanoparticle has very important characteristics of migration, emulsification, adsorption so as to it is expected to function as a carrier compound and efficient flooding material.4. Hydraulic fracturing technology is pumping the high-pressure injection of fluids into a natural formation to create fissures in the rock, and quartz sand is selected as the proppant to support the fissures in order to avoid the closuring of fissures after releasing stress. In this paper, super-hydrophobic nano-SiO2 was adopted to modify quartz sand proppant so as to acquire hydrophobicity by surface-modification in situ. and improve the water-injection performance. We have analyzed the mechanism features of the quartz sands surface-modified by HMDS and by HMDS-modified nano-SiO2. In order to study the optimal condition for the surface modification of quartz sand, the impact of some important factors, such as temperature, time and concentration were systematically studied though contact angle measurements and micro-structure imaging. Moreover, laboratory displacement tests were conducted to estimate the water-injection performance of the quartz sand before and after surface-modified by nano-SiO2, with which the quartz sand proppant was filled into a glass tube and compacted, and then the rate of the water flowing through the compacted quartz sand was measured. And the results showed a better water phase conductivity performance of super-hydrophobic quartz sand and the increased rate reached 112.9%.