Egyptian Journal of Petroleum xxx (2017) xxx–xxx Contents lists available at ScienceDirect Egyptian Journal of Petroleum journal homepage: www.sciencedirect.com Full Length Article Silica nanofluid flooding for enhanced oil recovery in sandstone rocks Magda I Youssif a, Rehab M El-Maghraby b,⇑, Sayed M Saleh c, Ahmed Elgibaly d a Petroleum Department and Gas Technology, Faculty of Engineering, British University, Egypt Chemical Engineering and Petroleum Refining Department, Faculty of Pet and Min Engineering, Suez University, Egypt c Department of Science and Mathematics, Faculty of Pet and Min Engineering, Suez University, Egypt d Petroleum Engineering Department, Faculty of Pet and Min Engineering, Suez University, Egypt b a r t i c l e i n f o Article history: Received 26 September 2016 Revised 26 December 2016 Accepted 24 January 2017 Available online xxxx Keywords: Enhanced oil recovery (EOR) Porous media Dispersed silica nanoparticle Nanoflooding Nanoparticles stability Nanofluid a b s t r a c t Enhanced oil recovery is proposed as a solution for declining oil production One of the advanced trends in the petroleum industry is the application of nanotechnology for enhanced oil recovery Silica nanoparticles (SiNPs) are believed to have the ability to improve oil production, while being environmentally friendly and of natural composition to sandstone oil reservoirs In our work, we investigated the effect of silica nanoparticles flooding on the amount of oil recovered Experiments were carried using commercial silica of approximately 20 nm in size We used sandstone cores in the core flooding experiments For one of the cores tertiary recovery is applied where brine imbibition was followed by nanofluid imbibition While in the other cores secondary recovery was applied where primary drainage is directly followed by nanofluid imbibition We investigated the effect of concentration of nanofluid on recovery; in addition, residual oil saturation was obtained to get the displacement efficiency Silica nanofluid of concentration 0.01 wt%, 0.05 wt%, 0.1 wt% and 0.5 wt% were studied The recovery factor improved with increasing the silica nanofluid concentration until optimum concentration was reached The maximum oil recovery was achieved at optimum silica nanoparticles concentration of 0.1 wt% The ultimate recovery of initial oil in place increased by 13.28% when using tertiary flooding of silica nanofluid compared to the recovery achieved by water flooding alone Based on our experimental study, permeability impairment was investigated by studying the silica nanoparticles concentration, and the silica nanofluid injection rate The permeability was measured before and after nanofluid injection This helped us to understand the behavior of the silica nanoparticles in porous media Results showed that silica nanofluid flooding is a potential tertiary enhanced oil recovery method after water flooding has ceased Ó 2017 Egyptian Petroleum Research Institute Production and hosting by Elsevier B.V This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Introduction Due to the declining oil production in many oil reservoirs, advanced techniques are necessary to continue oil production and to recover more oil in place [1] Among those techniques are the enhanced oil recovery techniques The use of nanotechnology for enhanced oil recovery is considered to be a new emerging trend This nanotechnology application began at the end of 1980’s and has been developed to synthesize new nanomaterials by rearranging atoms and molecules [2] Based on the small size of the nanoparticles (1–100 nm), the optical, thermal, chemical, Peer review under responsibility of Egyptian Petroleum Research Institute ⇑ Corresponding author E-mail addresses: magda.ibrahim@bue.edu.eg (M.I Youssif), rehab.elmaghraby@ suezuniv.edu.eg (R.M El-Maghraby), sayed.saleh@suezuniv.edu.eg (S.M Saleh), Elgibalya@yahoo.com (A Elgibaly) and structural properties of the nanomaterial differs totally from those displayed by either their atoms or the bulk materials [3] For enhanced oil recovery purpose, the smaller the nanoparticle size, the larger the surface area, and the larger the contact surface between the nanoparticles and the oil phase This allows better interaction between the nanoparticles and the oil phase for further recovery [4] The most commonly used nanoparticles in enhanced oil recovery are silica nanoparticle (SiNPs) About 99.8% of silica nanoparticle are silicone dioxide, which is the main component of sandstone Silica nanoparticles are an environmentally friendly material compared to other nanomaterials In addition, silica nanoparticles are cheap and their chemical behavior could be easily controlled by surface modification There are possible displacement mechanisms, by which silica nanoparticle could enhance oil production, are believed to occur The first mechanism is the disjoining pressure mechanism This mechanism occurs when silica nanoparticle are present in the dis- http://dx.doi.org/10.1016/j.ejpe.2017.01.006 1110-0621/Ó 2017 Egyptian Petroleum Research Institute Production and hosting by Elsevier B.V This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Please cite this article in press as: M.I Youssif et al., Silica nanofluid flooding for enhanced oil recovery in sandstone rocks, Egypt J Petrol (2017), http://dx doi.org/10.1016/j.ejpe.2017.01.006 M.I Youssif et al / Egyptian Journal of Petroleum xxx (2017) xxx–xxx persing medium, so these particles tend to rearrange themselves in a wedge-shaped film in contact with the discontinuous oil phase [5,6] The wedge film acts to detach the oil phase from the rock surface, hence recovering more oil as illustrated in Fig The disjoining pressure represents the pressure difference between the pressure in the wedge film region and that in the bulk liquid [7] This pressure is driven by Brownian motion and the electrostatic repulsion between molecules The second mechanism is the Log-Jamming mechanism Due to the smaller size of pore throats and the constant differential pressure in the pores, the velocity of the silica nanofluid will increase at the pore throat compared to the pore body This may cause the water molecules to move faster than the silica nanoparticles, causing the nanoparticles to accumulate and eventually block the pore entrance This may force the water flow to change pass to other non-invaded pores, possibly oil filled, resulting in more oil recovery The third mechanism is the wettability alteration mechanism Silica nanoparticles have the ability to change rock wettability and to reduce the interfacial tension and the contact angle between two immiscible fluids [1,8–10] Oil recovery by nanofluid flooding is affected by various parameters such as nanofluid concentration, particle size, injection rate, and slug size Nanofluid concentration is considered one of the major parameters to enhance oil recovery The goal of this study is to investigate the effect of silica nanofluids as an enhanced oil recovery agent in Sandstone rocks Materials and methodology 2.1 Materials Three Sandstone cores of different permeability ranges were used The properties of the cores are listed in Table Black oil of 32.5 API and 4.6 cp obtained from the North Sea was used in the flooding experiments The synthetic brine used is of concentration of 3.0 wt% NaCl (GPR grade, purity 99.5%, from Alpha Chemicals Company) Commercial hydrophilic mono dispersed silica (SiO2) nanoparticles of 370 m2/g specific area were used in the experiments The average particle size was 22 nm They consist of basically more than 99.8% of silicon dioxide (SiO2) (Al2O3) 60.06%, Titanium Dioxide (TiO2) 60.03%, Hydrogen Chloride (HCl) 60.028% and other traces elements Hydrophilic silica nanoparticles were suspended in wt% brine; this solution will be referred as silica nanofluid The Nanofluid was prepared with different concentrations, 0.01 wt%, 0.05 wt%, 0.1 wt %, 0.2 wt% and 0.5 wt% Each solution was mixed by using magnetic stirrer for several minutes To avoid precipitation of nanoparticles from solution, ultrasonic probe (400 W and 0.5 Hz) is used for h to assurance the homogeneity and stability of prepared solutions The properties of the used nanofluid at different silica nanoparticles concentrations are listed in Table 2.2 Methodology The equipment used for cores flooding was manufactured by Vinci Company, in France The experimental set-up is shown in Fig Two flooding scenarios were studied; one with silica nanofluid as a secondary recovery technique, and the other where silica nanofluid are used as a tertiary recovery technique In the first scenario, silica nanofluid were used as a tertiary recovery technique Core# was first cleaned and dried then placed in glass desiccator to be fully saturated with brine of wt % NaCl concentration The weight of the core was recorded many times until the weight remained constant The core was placed in the core holder and black oil injection took place The injection flow rate was increased until irreducible water saturation was reached At this point the core was saturated with oil Then imbibition process was initiated by using brine to displace oil at injection rate of 0.5 ml/min, and then continued until no more oil produced Pore volume of the injected brine was 1.77 PV At this stage, residual oil saturation (Sor1) was determined, and recovery factor was calculated The next step was to continue injection by nanofluid of different concentration at injection rate of 0.5 ml/min At this stage, residual oil saturation (Sor2) was determined again, and recovery factor was calculated to determine how much oil would be produced at this concentration The displacement efficiency was calculated from the following equation: Sor2 100 ED ẳ Sor1 1ị Fig Illustration of nanoparticle schematic and structural disjoining pressure gradient mechanism among solid, oil and nanofluids as aqueous phase Please cite this article in press as: M.I Youssif et al., Silica nanofluid flooding for enhanced oil recovery in sandstone rocks, Egypt J Petrol (2017), http://dx doi.org/10.1016/j.ejpe.2017.01.006 M.I Youssif et al / Egyptian Journal of Petroleum xxx (2017) xxx–xxx Table The properties of the sandstone cores used in our experiments a b Core No Length (cm) Diameter (cm) Pore volume (cc) Porositya % Permeabilityb md Swi % Core# Core# Core# 4.2 4.1 4.3 3.8 3.8 3.8 8.9 9.9 9.5 19.4 21.7 19.8 587 285 325 10.0 23.7 16.2 Porosity is measured by Helium Porosimeter Permeability is measured by Klinkenberg method Table Silica nanofluid properties Fluid Nanofluid Nanofluid Nanofluid Nanofluid 0.01 wt% 0.05 wt% 0.1 wt% 0.5 wt% Density, gm/cc Viscosity, cp 1.019 1.019 1.020 1.022 1.009 1.067 1.160 1.347 where, ED is displacement efficiency, Sor1 is residual oil saturation after brine floods, and Sor2 is residual oil saturation after nanofluid floods In the second scenario, Core # and Core# were tested using silica nanofluid as secondary recovery method The previous flooding steps mentioned in scenario were repeated The only difference was that the imbibition step using brine was not followed immediately by silica nanofluid imbibition Instead after the imbibition of the core with brine the core was cleaned, then dried and saturated with brine The drainage process was initiated by oil injection in the core till irreducible water saturation is reached, after which the silica nanofluid imbibition stared immediately till we reach residual oil saturation Different silica nanofluid concentration was investigated Injecting Silica nanoparticles through the pores of the cores may lead to particle retention in some cases [11] Consequently many parameters should be taken into consideration to eliminate permeability impairment to minimum level Concentration of nanoparticle suspension, well-dispersion solution, injection rate, and pore volume injected are the most important parameter affecting on the permeability impairment [12] The permeability was measured before and after nanofluid injection on Core# 1, Core# 2, and Core# to make sure that permeability impairment or other reduction in reservoir properties didn’t exceed a desired value Results & discussion Tertiary recovery is performed on Core# 1, after imbibition by water flooding; Core# was flooded by silica nanofluid of different concentration Fig showed the relation between PV injected and recovery factor at each concentration for Core# The residual saturation after water flooding and silica nanofluid flooding for core# and core# are listed in Table It was observed that the injection of silica nanofluid in the core enhances oil production, especially as the silica concentration increases The higher the silica concentration, the higher the amount of recovered oil up to an optimum silica nanofluid concentration after which the oil recovery decrease It is believed that permeability impairment was the cause of the reduction in oil recovery at high concentration because of the locking of the tiny pores of the core plug The use of silica nanoparticles following brine flooding increased the oil recovery factor from 53.1% in the case of water flooding alone to 66.40% following silica nanofluid injection at 0.1 wt% silica concentration as a tertiary recovery Secondary recovery is performed on Core# 2, where the primary drainage stage is followed by direct silica nanofluid imbibition Different silica nanoparticles concentrations were used to reach an optimum concentration that will maximize the oil recovery factor Fig Experimental set up schematic: (1) Graduated tube (2) Prep Pump (3) Injection pipe (4) Core holder (5) Core plug (6) Sleeve pressure (7) Fluid accumulator (8) Carry over fluid accumulator (9) Hydraulic pump Please cite this article in press as: M.I Youssif et al., Silica nanofluid flooding for enhanced oil recovery in sandstone rocks, Egypt J Petrol (2017), http://dx doi.org/10.1016/j.ejpe.2017.01.006 M.I Youssif et al / Egyptian Journal of Petroleum xxx (2017) xxx–xxx 70 Oil recovery of IOIP, % 60 50 WF NF, conc 0.01wt.% 40 NF, Conc 0.05% 30 NF, conc 0.1wt.% NF,conc 0.5 wt.% 20 10 0 PV injected Fig Recovery factor (RF) vs pore volume (PV) injected for Core # Table Residual oil saturation (Sor) obtained after water flooding and Silica nanofluid flooding Oil saturation [ So], fraction Core No Before water flooding After water flooding After 0.01 wt% nanoflooding After 0.05 wt% nanoflooding After 0.1 wt% nanoflooding After 0.2 wt% nanoflooding After 0.5 wt% nanoflooding Core Core 0.9 0.763 0.422 0.447 0.408 – 0.34 0.383 0.302 0.351 – 0.397 0.416 0.465 As shown in Fig 4, the optimum silica concentration was 0.1 wt% At this concentration an oil recovery factor of 54% was achieved compared to an oil recovery factor of 41.3% in the case of water imbibition alone Introducing silica nanoparticles to the oil/water system was observed to lower the interfacial tension (IFT), then the potential to produce more trapped oil [13,14] This may be due to the hydrophilic part of the silica nanoparticles present in the aqueous phase and the hydrophobic part exists in the oil phase, so the adhesive forces between the two phases increases and the IFT decreases It was observed that within the range of silica nanoparticles concentration of 0.2 and 0.5 wt% there is a drop in the oil recovery when compared to the trend of other silica concentrations As silica surface is completely hydroxylated and each Si atom on the surface is surrounded by OH groups [15], the surface charge of the silica nanoparticles were determined in terms of protonation and depro- tonation of these silanol groups The resultant net charge of silica nanoparticles surface controls to which extent the repulsion forces keep particles dispersed in solution The drop in the oil recovery, in case of increasing the concentration of silica nanoparticles in presence of constant electrolyte concentration, may be due to the increment of the deprotonation process of silanol groups at the surface of nanoparticles which accelerates the coagulation process forming a cumulative particles that block the pores hindering oil production Comparing flooding in Core# and flooding in Core# we can see that there is no difference in the recovery when using silica nanofluid in a secondary recovery technique or in a tertiary recovery technique, as at the end we get nearly the same results As we can see from Fig an increase of 13.28% in the oil recovery was achieved when the silica tertiary recovery technique was followed by water secondary recovery technique in Core #1 We can also see RF , % 60 50 WF 40 NF, Conc 0.05wt.% NF, conc 0.1wt% 30 NF, conc 0.2wt% 20 NF, conc 0.5wt.% 10 0 PV injected Fig Recovery factor (RF) vs pore volume (PV) injected for Core # Please cite this article in press as: M.I Youssif et al., Silica nanofluid flooding for enhanced oil recovery in sandstone rocks, Egypt J Petrol (2017), http://dx doi.org/10.1016/j.ejpe.2017.01.006 M.I Youssif et al / Egyptian Journal of Petroleum xxx (2017) xxx–xxx from Fig 4, an increase of 12.7% in oil recovery factor was achieved when using silica nanofluid flooding as a secondary recovery technique compared to using water flooding as a secondary recovery technique in Core# This result will favour using water flooding as a secondary recovery technique due to its low price and feasibility at the start of the recovery, then silica nanofluid flooding can be used as a tertiary technique to utilize the benefit of silica nanoparticles in enhancing the oil production In addition, recovery achieved by nanofluid of concentration 0.5 wt% is less than that achieved by water flooding This is mainly due to the accumulation of the silica nanoparticles through the pores and pores throats, hence blocking the pores Consequently, this concentration could not be applicable as it could damage the rock morphology Core flooding is carried on Core# to investigate the effect of silica nanofluid on water breakthrough As shown in Fig 5, it was observed that silica nanofluid has an effect on delaying water breakthrough; hence volumetric sweep efficiency increase and more oil could be produced as confirmed also by Li and Torsaeter [10] The experiments were done at concentration of 0.1 wt% and at constant injection rate of 0.5 ml/min In general, when the concentration of the silica nanofluid increases within specific range, the random movement of particles increases [7], thereby repulsive forces between molecules increase and the rock wettability is strongly altered This will increase the amount of oil that could be recovered However, as the concentration of nanoparticle in fluid increase the porosity and permeability is affected causing permeability impairment [12] Hence, the important to work at 0.1 wt% silica nanofluid concentration, to achieve the maximum oil recovery with minimum permeability impairment 3.1 Permeability impairment Permeability was calculated using Darcy equation The effect of nanoparticles concentration and injection rate on the permeability impairment was studied 3.1.1 Effect of concentration Based on the results shown in Table 4, as the concentration of silica nanofluid increases the absolute permeability decreases, at constant nanofluid injection rate of 0.5 ml/min Maximum permeability reduction of 60% due to nanofluid injection was observed at 0.5 wt% silica nanofluid concentrations This result justifies that at 0.5 wt% nanofluid concentration the oil recovery by silica nanofluid was the lowest of all concentration due to pore blockage 3.1.2 Effect of injection rate Nanoparticles retention is affected by the silica nanofluid injection rate Due to the high velocity and the difference in density 100 80 W/C , % WF 60 NF, conc 0.1wt.% 40 20 0 PV injected Fig Water cut vs pore volume (PV) injected for Core# Table Effect of silica nanoparticle concentration on permeability impairment at 0.5 ml/min injection rate Core No k absolute before nanofluid injection md Silica nanofluid concentration [%] k absolute after nanofluid injection md k reduction [%] Core# Core# Core# 285 325 587 0.05 0.1 0.5 231 195 233 19 40 60 Table Effect of silica nanoparticle injection rate on permeability impairment at 0.05 wt% silica concentration Core No k absolute before nanofluid injection md Silica nanofluid injection rate [cc/min] k absolute after nanofluid injection md k reduction [%] Core# Core# Core# 285 325 587 0.2 0.5 0.8 203 149 154 29 54 74 Please cite this article in press as: M.I Youssif et al., Silica nanofluid flooding for enhanced oil recovery in sandstone rocks, Egypt J Petrol (2017), http://dx doi.org/10.1016/j.ejpe.2017.01.006 M.I Youssif et al / Egyptian Journal of Petroleum xxx (2017) xxx–xxx between the silica nanoparticle and the brine, nanoparticles settle down causing pore blockage All the parameters are kept constant except injection rate Table showed that the permeability impairment increases as the injection rate increases Conclusions Silica nanofluid is environmentally compatible with sandstone rocks The amount of recovered oil with tertiary recovery using silica nanofluid is slightly higher than that obtained by secondary recovery method using silica nanofluid This makes water flooding followed by silica nanofluid flooding an effective recovery scenario and an economically wise Oil recovery factor increases by increasing the silica nanofluid concentration up to an optimum concentration of 0.1 wt% above, which the amount of recovered oil will decrease, with increasing the silica nanofluid concentration Silica nanofluid concentration of 0.1 wt% is the recommended concentration to achieve the maximum oil recovery with minimum permeability impairment, hence keeping the rock morphology undamaged Silica nanoparticles have the potential to increase oil recovery by delaying the water breakthrough hence more oil could be produced Injecting the silica nanofluid at low injection rate decreases permeability impairment, while using silica nanoparticles at high concentration will increase the permeability impairment but will increase oil recovery up to a certain value Acknowledgment Special thanks to Lab Engineer Walid, for his valuable assistance in the laboratory Laboratory work was conducted at the British University in Egypt References [1] G.S Dahle, Investigation of how Hydrophilic Silica Nanoparticles Affect Oil Recovery in Berea Sandstone, Petroleum Engineering and Applied Geophysics, NTNU, Trondheim, Master thesis (2014) [2] B Ju, D Shugao, L Zhian, Z Tiangoa, S Xiatao, Q Xiaofeng, A Study of Wettability and Permeability Change Caused by Adsorption of Nanometer Structured Polysilicon on the Surface of Porous Media, SPE Asia Pacific Oil and Gas Conference and Exhibition, Melbourne, Australia (2002) [3] R Kelsall, I 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SCA-Presented at the International Symposium of the Society of Core Analyst, Toronto, Canada (2005) [15] L.T Zhuravlev, Concentration of hydroxyl groups on the surface of amorphous silica, Langmuir (1987) 316–318 Please cite this article in press as: M.I Youssif et al., Silica nanofluid flooding for enhanced oil recovery in sandstone rocks, Egypt J Petrol (2017), http://dx doi.org/10.1016/j.ejpe.2017.01.006