Nernst-Planck equation

A model is solved based on the Nernst Planck equation to calculate the diffusion and migration currents for a species in a thin layer (about 200 nm) confined between two electrodes. This is proposed to account for the current voltage behaviour of a memristor constructed in a similar fashion. At the working electrode, an electroactive species is oxidised and at the counter electrode, the same species is reduced. Upon application of a simple voltammetric waveform, the migration current exhibits a resistance profile at slow scan rates and hysteresis at faster scan rates, indicative of memristor behaviour.

A model is solved based on the Nernst Planck equation to calculate the diffusion and migration currents for a species in a thin layer (about 200 nm) confined between two electrodes. This is proposed to account for the current voltage behaviour of a memristor constructed in a similar fashion. At the working electrode, an electroactive species is oxidised and at the counter electrode, the same species is reduced. Upon application of a simple voltammetric waveform, the migration current exhibits a resistance profile at slow scan rates and hysteresis at faster scan rates, indicative of memristor behaviour.

This study was conducted to investigate the phenomenon of oil removal from inside pores using a selfdesigned microfluidic test kit. An artificial micromodel chip as a representation of porous rocks has been created with a uniform pore structure design and made of PMMA (Polymethyl Methacrylate) material. The micromodel chip has a porosity of 27.8% as well as a permeability of 2.7 Darcy. By using the microfluidic test kit, this study has investigated how low salinity water (LSW) injection with MgCl 2 divalent ions and the addition of anionic surfactant, linear alkylbenzene sulfonate mixed with nonionic surfactants, nonylphenol ethoxylate (NP-10) affects to oil recovery. The injection of LSW and surfactant solution was carried out with different injection stages, injection rates and surfactant solutions concentrations. Visual images during the injection process are recorded for analysis, which is the advantage of dynamic testing using this microfluidic test kit over conventional coreflooding. From this study, it is indicated that the selection of ions contained in LSW affects the success of LSW injection. Reducing the surfactant injection rate from 50 mL/min to 20 mL/min can increase the oil recovery from 1.27% to 4.29%. Oil recovery was also higher on surfactant injection which resulted in lower interfacial tension of the system based on the calculation of interfacial tension obtained from the Chun-Huh and Ghosh equations from the Winsor test. From all injection scenarios carried out in this study, the highest increase in oil recovery of 26.87% OOIP was obtained by injecting surfactant solutions directly in the secondary stage without prior LSW injection.

In recent years, controlling the salinity and composition of the injected water has become an emerging enhanced oil recovery (EOR) technique, often described as low salinity (LS) waterflooding. This work is done with the intention to contribute to the ongoing discussions about LS waterflooding mechanism(s). For this purpose, a series of different experiments were conducted. At first, the effect of salinity on the interfacial tension (IFT) and the contact angle was evaluated with a crude oil sample. Then to achieve more accurate results in observing oil/water interface, similar IFT experiments were also carried out on a synthetic oil containing asphaltenes. Thereafter, microscopic visualization using glass micromodel was performed on the interface of the synthetic oil and brine. Four brine solutions including Sea Water (SW), it's

The long-held industry view that the Low Salinity Effect (LSE) depends mainly on rock-fluid 10 interactions has led to failures and successes that can be explained by fluid-fluid interactions. 11 Therefore, elevating our knowledge about the microscopic interactions occurring in the 12 crude oil/brine/rock system appear to be of paramount importance. This paper chooses to 13 outline various analytical tools in combination with a microfluidic instrument (Micromodel) 14 to identify these interactions at simulated reservoir conditions for the first time 15 (temperature and pressure of 50 and 2000 psi). In this study, six crude oil samples have = 16 undergone testing for microdispersion quantification and surface charge evaluation. 17 Microdispersion is a term referring to the spontaneous formation of water clusters (in Page 1 of 55 ACS Paragon Plus Environment Energy & Fuels 2 18 micrometre sizes) within the crude oil during Low Salinity Water Injection (LSWI), which 19 will be elaborated in this study. Despite all samples showing the same trend regarding the 20 negative surface charges, they showed an entirely different propensity towards formation of 21 water microdispersion. The analysis of the oil/water interface by Fourier-Transform 22 Infrared spectroscopy (FT-IR), led to the understanding that conjugated acidic compounds 23 within the crude oil are the main compounds for creation of water microdispersions. The 24 Micromodel results revealed the predominant role of microdispersions in oil swelling and 25 wettability alteration in a porous media leading to an increase in the microscopic sweeping 26 efficiency thus leading to improved oil recovery. Also highlighted, is the pivotal importance 27 of water microdispersion as a screening method for oil reservoirs before waterflooding 28 operation. 29 1 Introduction 30 Low salinity water injection (LSWI) has gained attention over the past ten years being 31 recognised as a cost-effective Enhanced Oil Recovery (EOR) method 1. There is a consensus 32 about LSWI for sandstone reservoirs in which reduction of salinity to less than 5000 ppm 33 leads to a low salinity water effect (LSE) 1-5. In contrast, several reports are showing the 34 negligible influence of LSWI in carbonate reservoirs, meaning this EOR method is only 35 effective in sandstone reservoirs (usually with a high clay content 2, 6). Early studies have 36 attributed the role of clay minerals during LSWI, through which clay swelling and 37 incremental pressure drop was introduced as the main mechanism 7-13. Wickramathilaka et 38 al. 14 suggested that the incremental oil recovery by low salinity brine might be affected by 39 total clay content and clay type. Austad et al. 15 argued that oil recovery by low salinity water

The long-held industry view that the Low Salinity Effect (LSE) depends mainly on rock-fluid 10 interactions has led to failures and successes that can be explained by fluid-fluid interactions. 11 Therefore, elevating our knowledge about the microscopic interactions occurring in the 12 crude oil/brine/rock system appear to be of paramount importance. This paper chooses to 13 outline various analytical tools in combination with a microfluidic instrument (Micromodel) 14 to identify these interactions at simulated reservoir conditions for the first time 15 (temperature and pressure of 50 and 2000 psi). In this study, six crude oil samples have = 16 undergone testing for microdispersion quantification and surface charge evaluation. 17 Microdispersion is a term referring to the spontaneous formation of water clusters (in Page 1 of 55 ACS Paragon Plus Environment Energy & Fuels 2 18 micrometre sizes) within the crude oil during Low Salinity Water Injection (LSWI), which 19 will be elaborated in this study. Despite all samples showing the same trend regarding the 20 negative surface charges, they showed an entirely different propensity towards formation of 21 water microdispersion. The analysis of the oil/water interface by Fourier-Transform 22 Infrared spectroscopy (FT-IR), led to the understanding that conjugated acidic compounds 23 within the crude oil are the main compounds for creation of water microdispersions. The 24 Micromodel results revealed the predominant role of microdispersions in oil swelling and 25 wettability alteration in a porous media leading to an increase in the microscopic sweeping 26 efficiency thus leading to improved oil recovery. Also highlighted, is the pivotal importance 27 of water microdispersion as a screening method for oil reservoirs before waterflooding 28 operation. 29 1 Introduction 30 Low salinity water injection (LSWI) has gained attention over the past ten years being 31 recognised as a cost-effective Enhanced Oil Recovery (EOR) method 1. There is a consensus 32 about LSWI for sandstone reservoirs in which reduction of salinity to less than 5000 ppm 33 leads to a low salinity water effect (LSE) 1-5. In contrast, several reports are showing the 34 negligible influence of LSWI in carbonate reservoirs, meaning this EOR method is only 35 effective in sandstone reservoirs (usually with a high clay content 2, 6). Early studies have 36 attributed the role of clay minerals during LSWI, through which clay swelling and 37 incremental pressure drop was introduced as the main mechanism 7-13. Wickramathilaka et 38 al. 14 suggested that the incremental oil recovery by low salinity brine might be affected by 39 total clay content and clay type. Austad et al. 15 argued that oil recovery by low salinity water

In recent years, controlling the salinity and composition of the injected water has become an emerging enhanced oil recovery (EOR) technique, often described as low salinity (LS) waterflooding. This work is done with the intention to contribute to the ongoing discussions about LS waterflooding mechanism(s). For this purpose, a series of different experiments were conducted. At first, the effect of salinity on the interfacial tension (IFT) and the contact angle was evaluated with a crude oil sample. Then to achieve more accurate results in observing oil/water interface, similar IFT experiments were also carried out on a synthetic oil containing asphaltenes. Thereafter, microscopic visualization using glass micromodel was performed on the interface of the synthetic oil and brine. Four brine solutions including Sea Water (SW), it's

(The parts in green have been added for correction.)
Regarding K. Mendelssohn's scientific career, one Internet site states that he studied under Max Planck, Walter Nernst, Erwin Schrödinger, and Albert Einstein, and received a doctorate in physics from the University of Berlin. Based on this description alone, it would be difficult to know what he learned under Nernst unless you read his book "The World of Walter Nernst: The Rise and Fall of German Science." The purpose of this material's author is to clarify the true nature of the Boltzmann relation while confirming the role of each researcher appeared in the book in the progress of physics and physical chemistry.

CO2 convective mixing in water has been visualized in Hele-Shaw and PVT cell experiments but not at the pore scale. Furthermore, CO2 convective mixing in a three-phase system (i.e., CO2 in the presence of both water and oil) has not been visually investigated. A vertically placed micromodel setup was used to visualize CO2 convective mixing at 100 bar and 50 °C, representative of reservoir conditions. To the best of our knowledge, for the first time, we have visually investigated CO2 convective mixing in water at the pore scale and also CO2 convective mixing in a multiphase system (water and oil). CO2 mixing in water governed by both diffusion and convection mechanisms was observed. The vertical CO2 transport velocity was calculated to be 0.3 mm/min in both a 100% water saturation system and a residual oil-saturated system. First, CO2 always found the easiest path through the connected pores, and then CO2 was transported into less connected pores and dead-end pores. CO2 transport int...

Coreflooding experiments on aged Berea sandstone cores were performed to study the effect of divalent cations on the low-salinity-surfactant enhanced oil recovery (EOR). In the experiments where the core samples were aged for 4 weeks, replacement of a small amount of sodium with calcium in the injected low-salinity surfactant did not lead to higher tertiary recovery. However, the effects on wettability alteration and relative permeabilities were substantial. For the experiments with longer aging duration of 7 weeks, addition of calcium to the injected low salinity surfactant led to better oil recovery and the impact on wettability alteration was strong. Further addition of calcium led to lower oil recovery. Results of the injection experiments were discussed based on interfacial tension (IFT), surfactant adsorption, end-point relative permeabilities, and contact angles. A part of discussion was also dedicated to the effect of calcium on the secondary low-salinity water (LSW) injection. Although the oil recoveries by LSW injection in the absence and presence of calcium are similar, calcium causes late oil mobilization during low-rate LSW injection.

The implementation of polymer injection on a field scale needs a preliminary laboratory test to analyze the performance and flow behavior of polymer injection in a porous media. Compared to coreflooding method, micromodel provides the visualization of oil displacement mechanism and facilitating a more detailed process description. Understanding the effect of polymer concentration on the incremental of oil recovery factor and its displacement mechanism are essential to know the polymer injection performance with the intention of avoiding failures in the implementation of polymer injection at field scale. We used dry etching technique for the fabrication of acrylic micromodel with homogenous characteristic. In this work, pre-flush (waterflooding) is performed first before doing the polymer injection to determine the incremental oil recovery factor and analyze the effect of polymer concentration on oil recovery factor enhancement in homogenous porous media. They were positioned horizon...

Direct pore-scale visualizations using micromodels for low salinity water injection (LSWI) have revealed that the contact between low salinity water and crude oil can provoke formation of water-in-oil micro-dispersions. This experimental work, using a number of different crude oils, aims to visually study the link between micro-dispersion formation and pore surface wettability alteration by low salinity water injection. The effect of aging time on wettability alteration by LSWI was investigated. It was observed that mixed-wet conditions established with a moderate aging time would increase low salinity ability controlled by the oil characteristics. Moreover, under tertiary LSWI, the trapped oil was mobilized if the crude oils exhibited capabilities of forming micro-dispersions. Interestingly, when a crude oil with little or no propensity to form micro-dispersions was used, low salinity effects such as wettability alteration and improved oil recovery were absent. Also, micromodel experiments could enable the investigation of LSWI for waxy crude oil, which is difficult to do with other approaches. To demonstrate the impact of micro-dispersion formation on polar components of the oils, infrared analyses were performed indicating the importance of oil polar agents enriched in aromatics and sulfoxides on controlling the formation of the micro-dispersions. After using various crude oils, it was concluded that the effectiveness of LSWI as the method to increase oil recovery is predominantly controlled by two factors; (i) initial degree of wettability of pore surfaces and (ii) the propensity of crude oil to form micro-dispersions.

A preliminary enhanced oil recovery (EOR) screening was completed for the Ben Nevis Formation, Hebron Field, offshore Canada. Polymer flooding was determined to be the most viable methodology based on the oil and reservoir properties and known challenges with respect to sourcing potential injection gas. Digital image analysis and microscopic petrographic analysis were applied to investigate the pore system characterization in Ben Nevis formation sandstone cores, which were subjected to an experimental polymer injection at 62°C. Polymer Flopaam 5115 delivered the best performance in terms of oil recovery irrespective of the flooding sequence or permeability facies. Initial grain size before flooding has a profound impact on oil displacement efficiency. Pore network analyses before and after flooding indicate that the movement of fine grains potentially affects porosity postflooding, depending on the permeability facies.

A difference in salt concentration in two solutions separated by a membrane leads to an electrical potential difference across the membrane, also without applied current. A literature study is presented on proposed theories for the origin of this membrane potential (Φm). The most well-known theoretical description is Teorell-Meyer-Sievers (TMS) theory, which we analyze and extend. Experimental data for Φm were obtained using a cation exchange membrane (CMX, Neosepta) and NaCl solutions (salt concentration from 1 mM to 5 M). Deviations between theory and experiments are observed, especially at larger salt concentration differences across the membrane. At a certain salt concentration ratio, a maximum in Φm is found, not predicted by the TMS theory. Before the maximum, TMS theory can be used as a good estimate of ?m though it overestimates the actual value. To improve the theory, various corrections to TMS theory were considered: A) Using ion activities instead of ionic concentration i...

In multispecies electrolyte solutions, each individual species can migrate according to its specific ionic properties. This process is called electrochemical migration or electro-diffusion and is well-described by the Nernst–Planck equation. The common approach for solving the corresponding mathematical system is based on the null current (NC) assumption, which expresses the electric potential in terms of charges and concentrations of chemical components. This assumption has a great advantage as it eliminates the electric potential from the Nernst–Planck equation. However, the NC assumption has limited capacities in describing electro-diffusion processes when the domain is subjected to an external electric field. The validity of the NC assumption could be questionable, even in the absence of an external electric field. This topic has never been investigated in the past. The main goal of this work is to evaluate the validity of the NC assumption and to understand its effect on the mo...

Low Salinity Waterflooding (LSW) is a promising technology for improving oil recovery in secondary and tertiary stages over the conventional waterflooding (HSW). As widely reported in the literature, this emerging recovery approach has relatively low operating costs and is more environmentally-friendly than conventional Enhanced Oil Recovery (EOR) methods. In fact, LSW is a multi-physics recovery process; however, most of the previous studies focused on wettability modification as the sole mechanism for the incremental oil recovery by LSW. Unfortunately, these studies often ignored other crucial factors that importantly affect the performance of LSW, e.g., fines transport under a low salinity injection environment. This paper introduces a robust modeling workflow to capture important recovery mechanisms occurred in LSW by integrating fines migration, wettability alteration, and geochemistry. The results showed that fines transport including fines deposition, fines migration, and fines plugging plays an important role in LSW process. Fines plugging by LSW can cause formation damage, but it also can be used as a mobility control agent. The LSW model equipped with fines transport shows an excellent agreement for incremental oil recovery and pressure drop against laboratory coreflooding. Finally, a novel concept of hybrid low salinity assisted gas flooding was proposed to overcome the existing technical challenges associated with the conventional CO 2 flooding.

The implementation of polymer injection on a field scale needs a preliminary laboratory test to analyze the performance and flow behavior of polymer injection in a porous media. Compared to coreflooding method, micromodel provides the visualization of oil displacement mechanism and facilitating a more detailed process description. Understanding the effect of polymer concentration on the incremental of oil recovery factor and its displacement mechanism are essential to know the polymer injection performance with the intention of avoiding failures in the implementation of polymer injection at field scale. We used dry etching technique for the fabrication of acrylic micromodel with homogenous characteristic. In this work, pre-flush (waterflooding) is performed first before doing the polymer injection to determine the incremental oil recovery factor and analyze the effect of polymer concentration on oil recovery factor enhancement in homogenous porous media. They were positioned horizon...

In situ mixing by dispersive transport of salt and viscous fingering between the injected low-salinity (LS) brine and high-salinity (HS) formation brine can jeopardize the performance of low-salinity waterflooding (LSWF). In our previous papers, we demonstrated that in situ mixing can be suppressed by polymerenhanced low-salinity waterflooding (PELS), in which a small amount of a viscosifying agent, such as a polymer, is added to the LS stream. Nevertheless, effective mixing control with PELS depends upon several factors and operational conditions, which have not yet been addressed. Therefore, this research focuses on the investigation of the impact of injection parameters, such as the polymer concentration, salinity difference, and injection rate, on the performance of PELS. In this regard, single-phase mixing experiments were performed using synthetic sandstone cores (sandpacks). The experimental results reveal that adding only 200 ppm of hydrolyzed polyacrylamide polymer (HPAM) lowers the salt dispersivity by up to 84%, depending upon the salinity difference. The results indicate that higher LS injection rates intensify the salt dispersivity and weaken the performance of PELS as a result of the dependency of polymer solution viscosity upon the share rate. The dependency of dispersivity upon the injection rate increases as the salinity difference increases. On the basis of our experimental data, we developed an empirical model to predict the required pore volume of PELS to displace the resident HS brine in the core as a function of the salinity difference and injection rate. A mathematical model based on the advection−dispersion theory is also presented to calculate the required volume of PELS for consecutive brine injection or slug injection. The results of this paper highlight that PELS is an effective method to increase the performance of formation brine displacement during LSWF and tackle the negative impact of salt dispersion on LSWF, particularly at a large scale. These results are also of use in hydrogeology and contaminant remediation.

Fluid flow in porous media is affected by surface characteristics such as roughness and topography. In this work, to simulate the surface of natural porous structures in transparent interconnected media like micromodels, various degrees of roughness have been artificially created on flat glass substrates via different methods of laser ablation, cream etching, combination of laser ablation and cream etching, and hydrofluoric acid (HF) etching. The obtained surfaces by each method were characterized in detail via field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), energydispersive X-ray spectroscopy (EDX/EDS), and surface profilometry. The impact of high temperature, as often used during the thermal bonding step in micromodel fabrication, on the surface roughness and topography was also investigated. The results show that laser ablation leads to a homogenous distribution of roughness with an average value of 21.7 μm, not affected by temperature during the bonding step. In contrast, the chemical reaction of HF with the glass surface leads to a vast range of roughness values from 8.4 to 31.3 μm, with a heterogeneous distribution, varying with the exposure time. Applying etching cream on a laser-engraved surface reduces the previously created sharp hillocks as a result of a weak chemical reaction with the surface, resulting in a low roughness value of 5.5 μm. No significant changes were observed in the chemical composition of surfaces etched by the abovementioned methods, even in cases where a chemical reaction occurred on the surface, attributed to the water solubility of the reaction products. The novel findings of this study can be used for better controlling the surface characteristics in the fabrication of transparent porous structures to mimic the natural porous media and study the role of surface roughness and topography on fluid flow behavior.

The implementation of polymer injection on a field scale needs a preliminary laboratory test to analyze the performance and flow behavior of polymer injection in a porous media. Compared to coreflooding method, micromodel provides the visualization of oil displacement mechanism and facilitating a more detailed process description. Understanding the effect of polymer concentration on the incremental of oil recovery factor and its displacement mechanism are essential to know the polymer injection performance with the intention of avoiding failures in the implementation of polymer injection at field scale. We used dry etching technique for the fabrication of acrylic micromodel with homogenous characteristic. In this work, pre-flush (waterflooding) is performed first before doing the polymer injection to determine the incremental oil recovery factor and analyze the effect of polymer concentration on oil recovery factor enhancement in homogenous porous media. They were positioned horizon...

A preliminary enhanced oil recovery (EOR) screening was completed for the Ben Nevis Formation, Hebron Field, offshore Canada. Polymer flooding was determined to be the most viable methodology based on the oil and reservoir properties and known challenges with respect to sourcing potential injection gas. Digital image analysis and microscopic petrographic analysis were applied to investigate the pore system characterization in Ben Nevis formation sandstone cores, which were subjected to an experimental polymer injection at 62°C. Polymer Flopaam 5115 delivered the best performance in terms of oil recovery irrespective of the flooding sequence or permeability facies. Initial grain size before flooding has a profound impact on oil displacement efficiency. Pore network analyses before and after flooding indicate that the movement of fine grains potentially affects porosity postflooding, depending on the permeability facies.

In this study the laws of mechanics for multi-component systems are used to develop a theory for the diffusion of ions in the presence of an electrostatic field. The analysis begins with the governing equation for the species velocity and it leads to the governing equation for the species diffusion velocity. Simplification of this latter result provides a momentum equation containing three dominant forces: (a) the gradient of the partial pressure, (b) the electrostatic force, and (c) the diffusive drag force that is a central feature of the Maxwell-Stefan equations. For ideal gas mixtures we derive the classic Nernst-Planck equation. For liquid-phase diffusion we encounter a situation in which the Nernst-Planck contribution to diffusion differs by several orders of magnitude from that obtained for ideal gases.

In microfluidic studies of improved oil recovery, mostly pore networks with uniform depth and surface chemistry are used. To better mimic the multiple porosity length scales and surface heterogeneity of carbonate reservoirs, we coated a 2.5D glass microchannel with calcite particles. After aging with formation water and crude oil (CRO), high-salinity Water (HSW) was flooded at varying temperatures and durations. Time-resolved microscopy revealed the CRO displacements. Precise quantification of residual oil presented some challenges due to calcite-induced optical heterogeneity and brine–oil coexistence at (sub)micron length scales. Both issues were addressed using pixel-wise intensity calibration. During waterflooding, most of the ultimately produced oil gets liberated within the first pore volume (similar to glass micromodels). Increasing temperature from 22 °C to 60 °C and 90 °C produced some more oil. Waterflooding initiated directly at 90 °C produced significantly more oil than a...

In multispecies electrolyte solutions, each individual species can migrate according to its specific ionic properties. This process is called electrochemical migration or electro-diffusion and is well-described by the Nernst–Planck equation. The common approach for solving the corresponding mathematical system is based on the null current (NC) assumption, which expresses the electric potential in terms of charges and concentrations of chemical components. This assumption has a great advantage as it eliminates the electric potential from the Nernst–Planck equation. However, the NC assumption has limited capacities in describing electro-diffusion processes when the domain is subjected to an external electric field. The validity of the NC assumption could be questionable, even in the absence of an external electric field. This topic has never been investigated in the past. The main goal of this work is to evaluate the validity of the NC assumption and to understand its effect on the mo...

Low salinity water (LSW) flooding is a commonly used technique to recover remaining oil. Efficiency of this method can be improved by decreasing salinity of the injected fluid during LSW flooding. However, the environment of low salinity is unfavorable for fine-sized particles retention, and may result in fines migration and formation damage. In most sandstone reservoirs, migration and production of fines along with fluid is a major problem in oil and gas industry. Several methods can be used to control migration of fine-sized particles. One effective treatment is to use nanofluids. Nanofluids can affect surface charges and increase the attraction between the particles and sand surface. Fines are negatively charged while nanoparticles usually have positive charge. By attracting nanoparticles to surface of the sand, sand surface becomes more positive which leads to retention of fines. In previous studies, effect of nanoparticles on fines migration in aqueous media was investigated. Another parameter which can influence surface charges is presence of hydrocarbon. Crude oil is an organic substance which is negatively charged just like other organic substances. And this charge difference explains why the presence of oil can affect the performance of nanoparticles in fine migration control. The purpose of this experimental study is to investigate the effect of using SiO 2 nanoparticles on controlling fines migration caused by LSW injection in presence of hydrocarbon. In addition, the effect of fine particles stabilization on oil recovery was analyzed. A mixture of paraffin and decane was used as hydrocarbon. Experiments have been conducted in three different series. The first series of experiments aimed to select the best nanoparticle among Al 2 O 3 , SiO 2 , and MgO. The results showed that silica nanoparticles had a great potential to control fines migration during LSW flooding. In the second series, the impact of injected nanofluid concentration on fines migration was investigated. And, in the third series, the effect of soaking times of 6, 12, 24, and 48 hours was investigated. In addition, recovery of oil is measured in all tests. Silica oxide nanofluid in 0.1% wt. concentration shows the best performance in controlling fines migration and reducing the pressure drop in the porous media. In the third series of experiments, the soaking time of 24 hours for the SiO 2 nanofluid showed the best results for controlling fines migration. Also, our experiments showed that migration of fines cannot be considered as an effective mechanism of enhanced oil recovery during LSW flooding.

In multispecies electrolyte solutions, each individual species can migrate according to its specific ionic properties. This process is called electrochemical migration or electro-diffusion and is well-described by the Nernst–Planck equation. The common approach for solving the corresponding mathematical system is based on the null current (NC) assumption, which expresses the electric potential in terms of charges and concentrations of chemical components. This assumption has a great advantage as it eliminates the electric potential from the Nernst–Planck equation. However, the NC assumption has limited capacities in describing electro-diffusion processes when the domain is subjected to an external electric field. The validity of the NC assumption could be questionable, even in the absence of an external electric field. This topic has never been investigated in the past. The main goal of this work is to evaluate the validity of the NC assumption and to understand its effect on the mo...

Foam is consistently generated in situ in rough-walled, calcite fracture networks during experiments using surfactant-alternating-gas (SAG) and coinjection of gas and surfactant solution over a range of gas fractional flows. Boundary conditions are systematically changed including gas fractional flow, total flow rate, and liquid rates. Local sweep efficiency was evaluated through visualization of the propagation of the fluid front and compared for pure gas injection, SAG, and coinjection. Foam as a mobility control agent resulted in significantly improved sweep and delayed gas breakthrough. Gas mobility reduction factors varied from about 200 to more than 1000 consistent with observations of improved sweep. Shear-thinning foam-flow behavior was observed during coinjection over a range of gas fractional flow.

Low-salinity water (LSW) flooding is one of the newest EOR techniques which has more advantageous over other EOR techniques. This research employed a heterogeneous synthetic three-dimensional reservoir to model LSW flooding for a two-phase system including brine (high salinity to low salinity) and oil. The obtained results show that exact determination of salinity threshold and its wettability alteration coefficients are very important since they affect the maximum value of oil recovery. The oil recovery has been varied between 55.79 and 60.34% for a given injection brine salinity (500 ppm) at different salinity threshold values. Furthermore, the result reveals that aging time has a low effect on oil recovery which is around 0.066% after more than 12 years of injection. However, the fine-grid 1D simulation of a small sample demonstrates that the aging time effect should be considered in small-scale models. Furthermore, we prove that there is an optimum value of injection brine salinity for each reservoir according to its salinity threshold. Highest recovery changes occur at the salinity of 5000, 3400 and 1200 ppm for three different salinity thresholds approximately. This paper demonstrates that before any implementation of LSW flooding, many laboratory tests must be done at reservoir condition to precisely detect wettability alteration coefficient, the best injection brine salinity and flow behavior from high-salinity water to LSW. Keywords Enhanced oil recovery • Wettability alteration • Low-salinity water flooding • Salinity threshold • Aging time List of symbols k rw Relative permeability to water k ro Relative permeability to oil S o Oil saturation S w Water saturation S orw Residual oil saturation S wr Residual water saturation k z Permeability of grid block in vertical direction C m Salt concentration of each block c b Brine compressibility k LSW rw Low-salinity water relative permeability k HSW ro High-salinity oil relative permeability P LSW c Low-salinity capillary pressure F 1 Weighting coefficient k x , k y Permeability of grid block in horizontal direction T Reservoir temperature p 0 Reference pressure (70 MPa) P c Capillary pressure k HSW rw High-salinity water relative permeability k LSW ro Low-salinity oil relative permeability P HSW c High-salinity capillary pressure Greek symbols Porosity of each block w Water viscosity st b Brine density at standard condition 0 w (20 o C) Water viscosity at temperature of 20 °C and zero pressure w0 Pure water density at reference pressure b0 Brine density at reference pressure b Brine density Abbreviations EOR Enhanced oil recovery HSW High-salinity water MIE Multiple ion exchange 1D One dimensional EDL Electrical double layer

Iron minerals are hydrophobic minerals predominately found in sandstone formations with their role in wettability alteration not fully understood. With the reservoir rock being a complex system of multiple minerals, the control of wettability alterations becomes difficult to manage due to the different surface chemistry of constituent minerals. This study presents for the first time the surface charge development of pyrite, magnetite, and hematite minerals in native reservoir environments and the effect of oilfield operations such as acidizing, water injection, polymerization, surfactant flooding, and alkaline flooding on iron minerals, surface charge development. This was achieved using zeta potential measurement, which depicts the type of surface charge and infers the propensity of precipitation. The experimental results show that pyrite, magnetite, and hematite behave similarly under reservoir conditions with all the minerals being positively charged although pyrite and hematite are negatively charged in seawater (SW). Results also show that the surface charge development is controlled by the electrical double-layer effect and ion adsorption on the mineral surfaces. These findings provide key insights into the role of iron minerals in wettability alteration as they provide surfaces that serve as a precursor for polar crude component adsorption. Also, the design of an ion-engineered fluid to control the surface charge of iron minerals was implemented, and the results showed that they behave differently. Furthermore, the effect of low-salinity water on the mineral surface charge was examined. The findings revealed that low-salinity water can produce a negatively charged surface, however, cannot mitigate the iron mineral precipitation challenge as the observed zeta potential values are near zero. Finally, slug and continuous injection of the ethylenediaminetetraacetic acid chelating agent was implemented as an iron mineral precipitation control strategy, with the continuous injection observed to significantly improve the colloidal stability of the iron minerals in the reservoir native state and after SW injection.

The results of many previous studies on low salinity/controlled ions water (CIW) flooding suggest that future laboratory and modeling investigations are required to comprehensively understand and interpret the achieved observations. In this work, the aim is co-optimization of the length of the injected slug and soaking time in the CIW flooding process. Furthermore, the possibility of the occurrence of several governing mechanisms is studied. Therefore, the experimental results were utilized to develop a compositional model, using CMG GEM software, in order to obtain the relative permeability curves by history matching. It was concluded that CIW slug injection, concentrated in the potential-determining ion, can increase oil recovery under a multi ion exchange (MIE) mechanism. The wettability of the carbonate rocks was changed from a mixed or oil wet state toward more water wetness. However, there is a CIW slug length, beyond which extending the length does not significantly improve the rock wettability, and consequently, the oil production, which is known as the optimum slug size. This implies that the optimization of the injection process, by minimizing the slug size, can decrease the need for the CIW supply, therefore lowering the process expenditure. Moreover, if the exposure time of the rock and CIW is increased (soaking), a higher level of ion substitution is probable, leading to more oil detachment and production. Rock dissolution/ precipitation (leading to a pH change) was found to have a negligible contribution.

After the publication of this article in 2018, we found that a similar set of methods to measure capillary pressure of paper membranes as a function of saturation was described by Buser 1 in a Ph.D. thesis in 2016. We request all researchers that cite our publication in Langmuir to also cite the work by Buser. 1

The efficiency of low salinity waterflooding, particularly during tertiary mode injection, is highly controlled by in situ mixing between the stagnant regions holding high salinity water (HSW) and the flowing regions containing low salinity water (LSW) because it impacts directly the electrokinetics of wettability alteration and the time scale of the low salinity effect. This study aims to address the effects of oil polarity and charged rock surfaces on the time scale of mixing and transport under two-phase flow conditions. A systematic series of micromodel experiments were performed. The micromodels were first saturated with high salinity formation brine and oil (both model and crude oil); thereafter, HSW and LSW were injected sequentially and the mixing time was carefully monitored. Besides, the polarity of model oils was manipulated by adding oleic acid as the representative for the acidic functional groups of crude oil. In addition to the experimental work, conceptual computational fluid dynamics (CFD) simulations were performed to get further insights into the experimental observations and to identify the dominant parameters on the time scale of mixing in stagnant regions. The experimental results show that the time scale of ionic transport in stagnant regions can be slowed down 10−16 times by the increase of the polar fractions of oil, where the time scale cannot be simply described by the Fickian diffusion. It is postulated that the stronger electrical field established in the water film by the increase of oil polarity lowers the solute transport rate according to the Poisson−Nernst−Planck theory. The results were further verified by using crude oil which is highly polar and contains complex types of polar components such as resins/asphaltenes. Experimental results clearly indicated the electrokinetics effect as the time scale was increased even further. Nevertheless, the mixing time does not vary linearly with the polar group fraction and follows a rather logarithmic trend. The CFD simulation confirms that the effective diffusion coefficient (which is influenced by the oil polarity and the induced electric field) is the predominant parameter determining the time scale of mixing. Other parameters such as film thickness/film length and salinity gradient have comparatively a lesser effect on the time scale of mixing in the stagnant regions.

The thermal energy equation plays two important roles in multi-component, reacting systems.  One role is to provide the governing equation for the temperature.  A second role is to provide information for the entropy transport equation.  In these notes the axiomatic statements concerning energy in multi-component systems are examined carefully and the results are compared to those developed half a century ago.

In this study the laws of mechanics for multi-component systems are used to develop a theory for the diffusion of ions in the presence of an electrostatic field. The analysis begins with the governing equation for the species velocity and it leads to the governing equation for the species diffusion velocity. Simplification of this latter result provides a momentum equation containing three dominant forces: (a) the gradient of the partial pressure, (b) the electrostatic force, and (c) the diffusive drag force that is a central feature of the Maxwell-Stefan equations. For ideal gas mixtures we derive the classic Nernst-Planck equation. For liquid-phase diffusion we encounter a situation in which the Nernst-Planck contribution to diffusion differs by several orders of magnitude from that obtained for ideal gases. The study of ion transport in fluids is an important topic with a wide range of applications. Some classic examples are batteries, fuel cells, electroplating, and protection of metal structures against corrosion 1. In addition to the traditional battery, the flow battery or rechargeable fuel cell 2,3 represents an important new technology involving the transport of ions. Ion exchange membranes have a wide range of applications 4 , and the underlying theory has been a matter of concern for several decades 5. Other examples of complex electro-chemical systems are the transport of charged particles in ion channels 6–8 , in protein channels 9 , and during the primordial conversion of light to metabolic energy 10. Often upscaling is necessary for a complete analysis of the transport of electrolytes in charged pores 11,12. Much of ion transport occurs at the nano-scale 13 , and most of the studies use the Nernst-Planck equation 14–16 to describe this type of phenomena. However, there are molecular dynamic simulations indicating that the Nernst-Planck equation does not always provide a complete description 17 , and there are experimental studies that lead to the same conclusion 18. The need to analyze the limits of the Nernst-Planck contribution to diffusion has been emphasized 19 in an exploration of the transport of divalent ions in ionic channels. The authors of this paper have not found a derivation of the Nernst-Planck equation that does not make use of the ideal gas assumption. To be precise we note that ideal gas behavior for mixtures is based on Dalton's laws (see page 114 in ref. 20) that we list as Some care must be taken with the interpretation of Eq. 2 since it applies to all Stokesian fluids and is therefore not limited to ideal gas mixtures (see Appendix B in ref. 21). Caution must also be used with the interpretation of Eq. 3 which is applicable to all ideal fluid mixtures. For example, Eq. 3 should provide reliable results for a liquid mixture of hexane and heptane, but it should not for a mixture of ethanol and water. Here it is important to emphasize that Eq. 1 can only describe a fluid composed of non-interacting particles. To provide a reliable framework in which a fluid is considered to be composed of interacting particles ̶ as in the case of a liquid ̶ it is necessary to understand the process of Nernst-Planck diffusion in a fluid different from an ideal gas. This is the problem under consideration in this paper. In this work we analyze the ion transport process from a fundamental point of view using an axiomatic mechanical perspective. Our analysis is for ideal fluid mixtures, and from the analysis we find that the classic

The mass-transport process that takes place in a Stefan diffusion tube has been used for decades as an example of diffusion through a stagnant film, and students often use this process in order to measure gas-phase molecular diffusivities. The traditional analysis of the Stefan diffusion tube leads to questions that are generally left unanswered, and in this paper we provide some answers on the basis of the species momentum equation. 0888-5885/91/2630-0978$02.50/0