The hydrophobic nanoparticles adsorption layer on core surface and its properties

The hydrophobic nanoparticles adsorption layer on core surface and itspropertiesXinliang Wang1,2,a, Qinfeng Di*1,2,b, Renliang Zhang1,2,Chunyuan Gu1,2, Weipeng Ding1,2 and Wei Gong1,21 Shanghai Institute of Applied Mathematics and Mechanics, Shanghai University,Shanghai 200072, China2 Shanghai Key Laboratory of Mechanics in Energy Engineering, Shanghai University,Shanghai 200072, Chinaa sea-wave007@,b qinfengd@Keywords: Core surfaces, HNPs adsorption layer, Surface properties, Drag reduction Abstract. A compact hydrophobic nanoparticles (HNPs) adsorption layer，which had miro- and nano- dual structural properties, can be built by adsorption of HNPs on core surfaces, and then the wettability of core surface can be change from hydrophilic into strong hydrophobic. Measurements validated that the maximum contact angle of HNPs adsorption surface was close to 150°. This method has a very good prospect for industrial application. The flow resistance can be significantly reduced when the water flow through the core micro-channel walls adsorbed HNPs. Core displacement experimental results show that the largest drag reduction rate can be up to 159%, and the average to 73.4%. The results have important significance to the studies of the HNPs drag reduction technology.IntroductionThe application of nanotechnology have attracted researchers much attention in recent years, and the application of super-hydrophobic surface in micro-flow related to micro-nanotechnology is very important one of them[1-7]. A successful practice of hydrophobic nanoparticles (HNPs) adsorption method[8, 9] to drag reduction technology solving the high-pressure and low-injecting problems is a perfect application of combination of nanomaterial and super-hydrophobic surfaces in petroleum engineering fields.HNPs adsorption method can build a micro- and nano- structural strong/super- hydrophobic surfaces on cores, and produce slip velocity of water flow on the surfaces in the purpose of reducing the flow resistance or water injection pressure and increasing water injection rate[10]. This paper aims to study the HNPs adsorption layer’s forming method and the characteristic of core surfaces and its application in HNPs drag reduction technology.Experimental detailsThe nanomaterial used in the experiments are innocuous and insipidness white SiO2powders modified by some modifier. There are many unsaturated impending bonds on nanomaterial surface and the material has good hydrophobic properties. The HNPs samples used in the experiments, named ShuNP2-10, are about 10nm in size. Fig. 1 shows a TEM image of the nanomaterial. The nano-scale powders appear to be amorphous crystal, some of which are aggregated or connected by short chains. The HNPs look like spheres with coarse surfaces.Fig. 1 TEM image of the nano-materialsPreparation of the HNPs adsorption layer on the core slice surfaces. The core slice samples which saturated brine (3%NH4Cl aqueous solution) were put into a vessel with the fine filtration diesel in which the Conclusions dispersed. In order to ensure the HNPs disperse uniformly, the diesel was stirred 10min with high-speed emulsifying machine. Then the vessel was placed into the water bath with the temperature of 80℃ for a certain time until the HNPs fully absorbed, then the core slices were fetched out and dried. Finally the core slice samples adsorbed HNPs were obtained.Preparation of the HNPs adsorption layer on the wall of micro channel of core samples. The core samples were saturated with the formation water and then putted into the core holder. Then the HNPs dispersion was injected into the core sample in a low-flow rate with a given temperature and confining pressure, The core samples adsorbed HNPs were obtained after 48h.Wettability test. An optic contact-angle apparatus (OCA30) was used to measure the contact angles of water drops on the surfaces of different core samples. The continuum testing method, by which 60 pictures of the contact angles were taken each second, was used to reduce the effect of the capillary pressure. Each sample was tested 3 times.Surface microstructure test. A Scanning Electron Microscope, SH-3000, was used to observe the microstructure of the samples.Results and discussionSEM results. The SEM images of different core samples with different magnification were shown in Fig. 2 and 3. Fig. 2 was the SEM image of the original core sample, and the sheets of quartz mineral with clear edges and corners can be seen clearly. Many surfaces of sub-areas are verysmooth.Fig. 2 SEM images of the original core sampleFig. 3A~F shows the SEM images of the core samples after HNPs adsorption .From Fig. 3A~B, we can see that the HNPs adsorbed surface is covered entirely with ellipsoidal HNPs connected with each other tightly, and that many papillate dots appear on the surface continuously. The wholesurface appears nanopatterned but still has porous space, which indicates that the entire frameworkof the core is not changed by HNPs. From Fig. 3C, we can see that the HNPs aggregates are adsorbed entirely not only on the core surface but also on the pore throat, and from Fig. 3D, we can see the structures of core surfaces and pore throats after absorbed by these HNPs aggregates. From Fig. 3E, we can see that in non-smooth surface, there are more HNPs adsorbed, and manifest a typical multi adsorption; but in smooth surface, the distribution of the HNPs on the surface is relatively flat. Fig. 3F is the local enlarged drawing of Fig. 3E, and there is a dense HNPs adsorbed layer in the smooth surface and demonstrates single-layer adsorption.The experimental observations indicate clearly that the HNPs could adsorbed on the core surface, then covered with a layer of spherical HNPs aggregates with size of 200nm~400nm and spacing 0~150nm. But in our experiments, the particle size is only about 10nm; therefore, each HNPs aggregate must contain several single particles. This dual micro-, nano-structure surface has a structure similar to lotus leaf[11], which shows strong hydrophobic prosperities[12]. These features are critical not only for changing the wettability of the surface but also for preventing the claymineral from hydrating and inflating by separating water-phase from the core.A （×7000）B （×10000）C （×1500）D （×6000）E （×6000）F （×10000）Fig. 3 SEM images of the HNPs absorbed core samplesWettability results. The experiment shows that the contact-angles of water drops on the raw core surface are nearly 0°, which indicates that the core surface is hydrophilic. Fig. 4 shows that the HNPs-absorbed core surface is nearly super-hydrophobic because the contact-angles of 147.8°and 143.1° was tested respectively, which clearly indicates that the wettability of the core surfaces canbe changed from hydrophilic to hydrophobic by adsorption HNPs.(a) (b)Fig. 4 The images of contact angle on the HNPs absorbed core samplesThe evaluation of HNPs adsorption layer on core surface For the real core, actually, the HNPs adsorption layer not only generated on the core surfaces but also in the micro-channels after treated by HNPs dispersion. Due to the internal structure of the core cannot be observed directly, then whether the HNPs adsorption layer was formed and whether the wettability was changed cannot be determined. Therefore, the drag reduction effects were tested to verify the existence of HNPs adsorption layer indirectly by the core flow experiment.Table 1 shows the drag reduction effects of different cores after treated by ShuNP2-10 dispersion. From the table 1 we can see that the improve range of the water phase permeability is about 17%~159%, an average of 73.4%, which indicating a significant drag reduction effect was made , and the existence of HNPs adsorption layer was proved indirectly.Table 1 Drag reduction effects of different coresSerial number Water phase permeability [mDa] Permeability improving amplitude[％] Before treatedAfter treated 1 0.947 1.575 662 0.791 1.139 443 0.869 1.947 1244 1.071 1.977 855 1.352 2.789 1066 1.91 4.95 1597 0.225 0.298 478 12.42 16.58 569 0.502 0.585 1710 0.87 1.13 30average 2.0957 3.297 73.4SummaryIn conclusion, HNPs adsorption method can generate a compact layer on core surface with irregular HNPs aggregates, which is a dual micro- and nano- dual structure similar to lotus leaf . The HNPs adsorption method can turn the original strong hydrophilic surfaces into strong or superhydrophobic one, then produce velocity slip effect of water flow on the wall and then decrease the injection pressure. After treated by the HNPs dispersion, the improvement of the water phase permeability was about 17%~159%, with an average of 73.4%, which proved the existence of HNPs adsorption layer indirectly. This adsorption layer is equivalent to one kind of dense membrane, and can prevent the clay mineral from hydrating and inflating by separating water from the core.AcknowledgementsThis research is supported partly by the National Science Funding of China (50674065，50874071), the Chinese National Programs for High Technology Research and Development ( 2008AA06Z201 ), the Key Program of Science and Technology Commission of Shanghai Municipality(071605102), Shanghai Program for Innovative Research Team in Universities, the Innovation Fund Project for Graduate Student of Shanghai University (SHUCX101076), the Program for Changjiang Scholars and Innovative Research Team in University (IRT0844). References[1] Choi, C., U. Ulmanella, J. Kim, C. Ho, and C. Kim: Physics of Fluids, V ol. 18 (2006), p.087105.[2] Choi, C.H., K.J.A. Westin, and K.S. Breuer: Physics of Fluids, V ol. 15 (2003) No.10, p.2897.[3] Cottin, B., C., J.L. Barrat, L. Bocquet, and E. 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