مطالعه تجربی عبور جریان نانوسیالات از یک ریزمدل به عنوان محیط متخلخل Experimental Study of Nanofluids Flow in a Micromodel as Porous Medium

۱٫ INTRODUCTION Recent developments in nanotechnology and related manufacturing techniques have made possible the production of distant nanoparticles (i.e. particles typically smaller than 100 nm). By dispersing such particles into traditional fluids such as water, ethylene glycol, and engine oil a new class of nanotechnology based fluids are produced called nanofluids. Nanofluids become attractive due to their potential benefits and applications in important fields such as energy generation, medical, transportation, micro and nano electromechanical systems (MEMS & NEMS), etc [1]. Due to small sizes of nanoparticles, nanofluids can flow through the micro and nano scale throats. Therefore one of the interesting applications of nanofluids is using them as working fluid in the porous media. Fluid flow through porous media has considered scientific and technological interest [2-4]. To characterize flow at the pore scale, it is convenient to use simplified representations of porous media such as physical network models which can be constructed in the form of twodimensional networks. These models are a network of pores and throats which are prepared using the standard photolithography technique on a silicon, polymer or glass substrate. Glass network models are one of the most important tools for research and study about the flow in complicated geometries such as filters and oil reservoirs. One of the most important preferences of these models is that they can be made with pores which are comparable in shape and size to actual pore geometries. In real rocks, on the other hand, they can accept all of the arbitrary patterns. Network model techniques have been used to visualize a wide range of processes in porous media [5-6]. A number of researches have been dedicated to nanofluids as part of nanotechnology application in enhanced oil recovery (EOR) nowadays. Nanoparticles have been speculated as good in-situ agents for solving reservoir engineering problems. Suspensions based on nano-materials and nanoparticles (nanofluids) are used in oilfields to enhance injection processes by changing wettability of porous media, increasing the viscosity of injecting fluid and decreasing the interfacial tension between injection fluid and reservoir fluid [7]. One of the challenges for this novel approaches includes propagating these suspensions through a porous media. Nanoparticles are small enough to pass through pore throats in typical reservoirs, but they nevertheless can be retained by the rock. The ability to predict retention with distance traveled, and to predict the effect of different surface treatments on retention, is essential for developing field applications of such particles [8]. Compared to the emulsions stabilized by colloidal particles, nanofluids have better specifics. Nanoparticles are one hundred times smaller and emulsions stabilized by them can travel a longer distance through the pore throats. Some selected types of nanoparticles that are likely to be used include oxides of Aluminum, Zinc, Magnesium, Iron, Zirconium, Nickel, Tin and Silicon. It is therefore imperative to find out the effect of these nanoparticle oxides on oil recovery since this is the primary objective of the oil industry [9]. Binshan et al. [10] mentioned that Nanofluids based on polysilicon materials could change the wettability of porous surfaces. They used one kind of polysilicon with sizes ranging from 10~500nm in oilfields to enhance water injection by changing wettability of porous media. The mechanism of enhancing water injection is through improving relative permeability of the water-phase by changing wettability induced by adsorption of polysilicon on the porous surface of sandstone. On the other hand, the adsorption on the porous surface and plugging at the small pore throats of the polysilicon may lead to reduction in porosity and absolute permeability (K) of porous media. Thus the degree of success in well treatment is determined by the improvement of effective permeability of the water-phase. Yu et al. [11] showed that Silica nanoparticles could easily pass through the sandstone core without changing the core’s permeability. A little adsorption was noted as silica nanoparticles flooded limestone core, but the core permeability was not changed. Therefore, deposition and adsorption of nanoparticles at surface pores causes the blockage in pore throat of porous media and reduces the permeability. Hendraningrat et al. [12] investigated the deposition and pore-blockage of nanoparticles in glass micromodel. Hydrophilic nanoparticles and synthetic seawater (brine, NaCl 3 wt. %) as base fluid were chosen in their study. To obviate the challenge of the flow behavior of nanofluids in porous media, more studies are needed, especially in experiment. The aim of this article is to examine flow behavior of alumina-water nanofluids in a porous medium experimentally. For simulating flow and transport in porous medium a small-scale artificial model of porous medium which is called micromodel has been constructed. Several experiments have been conducted on horizontal glass micromodel at several fixed flow rate conditions. Such experiments didn’t report hitherto for alumina-water nanofluids in a glass micromodel. The permeability of the porous medium has been evaluated by using experimental data. Moreover, an analytic solution was used to develop a correlation for predicting the permeability of such porous medium.