Function Of Interfacial Tension Research Articles

A Visualization Study of Low-Tension Polymer Flooding for Viscous Oil Reservoirs

Summary Polymer flooding improves the sweep efficiency of viscous oil recovery over waterflooding. The low-tension polymer (LTP) flooding has the potential to improve the displacement efficiency due to low interfacial tension (IFT) without sacrificing sweep efficiency. Compared with ultralow tension (<0.001 mN/m) alkaline-surfactant-polymer (ASP) floods, LTP flooding uses a low concentration surfactant to moderately reduce the IFT (>0.01 mN/m). The objective of this research is to evaluate the performance of LTP floods as a function of IFT for a viscous oil in a 2D sandpack. Over 20 nonionic surfactants/cosolvents were tested. A series of sandpack flooding experiments were conducted in a custom-designed 2D visualization cell. The results show that short-hydrophobic surfactants 2EH-xPO-yEO can reduce the IFT to as low as 0.05 dyne/cm. Flooding experiments were performed in sandpacks with and without connate water saturation. The sandpack was water-wet for the experiments with connate water. For the experiments without connate water, the sandpack was oil-wet. A base-case secondary polymer flood (without any surfactant) with a viscosity ratio (µo/µp) of 10 showed a stable displacement and an oil recovery of 82% at the first pore volume injected (PVI). An LTP flood with an IFT of 0.1 dyne/cm also had a stable displacement front, but a higher oil recovery at 1 PVI [90% original oil in place (OOIP)]. Further reduction in IFT to 0.05 dyne/cm resulted in an unstable displacement and a lower recovery of 65% OOIP. For the experiments without connate water saturation, sandpack was oil-wet; the base-case polymer flood at a viscosity ratio of 10 showed severe fingering and a low oil recovery at 1 PVI (58% OOIP). Adding surfactants did not improve the oil recovery in oil-wet sandpacks.

Analytical solutions of critical oil film thickness of negative spreading coefficient in a capillary corner

In this paper, by combining applications of minimum surface free energy with capillary force balance equations, and considering that the total free energy change is zero at thermodynamic equilibrium, an analytical equation of the oil film critical thickness to spread over a water film in a three-dimensional capillary corner is derived. The derivation is based on the analysis proposed by Dong et al. [Journal of Colloid and Interface Science 172 (1995) 21–36]. This analytical solution allows the critical oil film thickness in three-phase systems to be calculated conveniently without lengthy calculation and be readily applied in simulation of three-phase systems in porous media using predictive models. The equation was examined by comparing the analytical solutions with the numerical results by Dong et al. Using the analytical solution, the reason why the oil phase spreads between the gas and water phases in three-phase systems in porous media was analyzed. The spreading of oil phase is controlled by the free energy change, and the spreading of oil phase only occurs in the system when the free energy change during the oil spreading process is negative. Also, there is a critical oil film thickness controlling this process that is a function of interfacial tension, contact angles, and corner angles. This analytical solution of critical oil film thickness can also be utilized to find the correlation of three-phase capillary pressure when the system is in thermodynamic equilibrium for water-wet porous media. This correlation should be useful in pore-scale simulation of three-phase flow of spreading oil.

Applying Grid partitioning based Fuzzy inference system method to estimate interfacial tension of brine and hydrocarbon

The oil recovery reservoirs and oil trapping in the reservoirs are extensively function of interfacial tension between brine and hydrocarbon, so estimation of interfacial tension becomes one of the interesting topics in petroleum industry. In this study, Grid partitioning based Fuzzy inference system method is utilized to forecast interfacial tension of hydrocarbon and brine based on various effective parameters such as ionic strength of brine, carbon number of hydrocarbon, pressure, and temperature. The estimated values of interfacial tension were compared with real interfacial tension of brine and hydrocarbon using graphical and statistical analyses. The determined coefficients of determination (R2) for training and testing phases were 0.9916 and 0.9447, respectively. The comparing analyses express that the Grid partitioning based Fuzzy inference system method has great ability in prediction of interfacial tension, and it can be used as an applicable tool in petroleum industry.

Water Blocks in Tight Formations: The Role of Matrix/Fracture Interaction in Hydrocarbon-Permeability Reduction and Its Implications in the Use of Enhanced Oil Recovery Techniques

Summary Hydraulic fracturing is used to obtain economical rates from tight and unconventional formations by increasing the surface area of the reservoir within the flowing distance to a high-conductivity pathway. However, a significant fraction of the fracturing fluid is never recovered, and thus may reduce the hydrocarbon permeability near the fracture. Here, we experimentally mimic the water-invasion process during fracturing, and measure the effective permeability changes in a low-permeability core. Measurements of water flowback and effective permeability as a function of interfacial tension (IFT), flow rate, and shut-in time suggest that water is being held at the fracture face because of the capillary discontinuity (i.e., when the water leaves the matrix and enters a space with minimal capillary pressure). This effect arises from the capillary interaction between the matrix and the fracture, and is akin to the capillary end effect in coreflood experiments. The results show that this effect, although only a laboratory experimental artifact for conventional reservoirs, can be a significant source of effective hydrocarbon-permeability reduction by fracturing-fluid invasion into the formation in unconventional and tight reservoirs.

Glass transitions in the cellular Potts model

We study the dynamical transition between a fluid-like and a solid-like phase in a confluent cell monolayer, by using the cellular Potts model and computer simulations. We map out the phase diagram as a function of interfacial tension and of cell motility. While in the fluid phase there is normal diffusion, in the solid phase we observe sub-diffusion, very slow relaxation, and ageing, thereby strongly suggesting that this phase is glassy. Our results complement previous theoretical work within the vertex model and show that the cellular Potts model can account for the experimentally observed glassy dynamics of some biological tissues.

Influence of aqueous ionic strength upon liquid:liquid interfacial structure and microsolvation

Ionic strength of an aqueous solution is often used to alter the efficacy of industrial processes that rely upon liquid:liquid phase boundaries (e.g. solvent extraction), however there is little understanding of how this condition may alter the properties of the phase boundary itself. The current work examines the interfacial structure and processes within the biphasic system (NaNO3)aq:n-hexane from 0 to 10M NaNO3 at 298K and 1atm pressure. The extent of ion-pairing was quantified, alongside the primary solvation environments of both water and ions. Ion concentration was found to be depressed in the interfacial region relative to the bulk, and as such there is less likelihood of the formation of contact ion-pairs or ion-clusters at the interface. This in turn, leads to the interesting observation of more hydrogen bonds per water at the interface than in the bulk. At 10M NaNO3 enough ions are present at the interface to severely perturb the mesoscopic interfacial properties of width and tension (the latter doubling in size relative to the neat water interface with n-hexane). Chemical theories, like the Kelvin equation and its analogs for liquid:vapor interfaces, would intuit that such a large change in interfacial tension should influence the microsolvation processes of the immiscible solvents (microsolvation being the rare event where water can penetrate n-hexane and n-hexane may penetrate and be fully solvated by water). However, there is no statistical difference between the concentrations of water and n-hexane in their respective co-solvents as a function of interfacial tension in these non-ideal solutions. Based upon these data, the ability of electrolyte concentration to alter transport across the interface does not appear to be related to the perturbation imparted by the electrolyte upon the interfacial properties themselves.

Capillary Curves for Ex‐situ Washing of Oil‐Coated Particles

AbstractThe oil removal efficiency for the ex situ extraction of bitumen from oil sands, or ex situ washing of oil‐contaminated sand and related processes is determined by the balance of forces at the oil/water and solid/fluid interfaces. The objective of this work is to estimate the balance of forces at the interface using dimensionless numbers, and their use in evaluating and engineering ex situ soil washing processes. To this end, bitumen was removed from bitumen‐coated sand particles using a two‐step process. In the first step, the particles were mixed with a suitable solvent (toluene) used, primarily, to reduce the viscosity of bitumen. The particles were then mixed with water or an aqueous surfactant solution capable of producing low interfacial tensions with the solvent‐bitumen mixture. The fraction of oil retained after washing was evaluated as a function of interfacial tension, solvent/bitumen ratio, mixing time, mixing velocity, and particle size. These ex situ washing conditions were normalized using dimensionless film and particle‐based Weber and Capillary numbers. The fraction of oil retained by the particles was plotted against these dimensionless numbers to generate capillary curves similar to those used in enhanced oil recovery. These curves reveal the existence of a critical film‐based Weber number and a particle‐based Capillary number that can be used in the design or evaluation of soil washing processes. The film‐based Weber number also explained literature data that associates interfacial tension with the removal of oil from oil‐based drill cuttings, as well as field observations on the role that particle size plays on the removal of oil in soil washing operations.

Dynamics of step-emulsification: From a single to a collection of emulsion droplet generators

Microfluidics has proven to be an efficient tool for making fine and calibrated emulsion droplets. The parallelization of drop makers is required for producing large amounts. Here, we investigate the generation of emulsion drops along a series of shallow microchannels emerging in a deep one, in other words the step-emulsification process. The dynamics of a single drop maker is first characterized as a function of interfacial tension and viscosities of both phases. The characteristic time scale of drop formation, namely, the necking time that finally sets drop size, is shown to be principally governed by the outer phase viscosity to interfacial tension ratio with a minor correction linked to the viscosity ratio. The step emulsification process experiences a transition of fragmentation regime where both the necking time and drop size suddenly raise. This transition, that corresponds to a critical period of drop formation and thus defines a maximum production rate of small droplets, is observed to be ruled by the viscosity ratio of the two phases. When drops are produced along an array of microchannels with a cross flow of the continuous phase, a configuration comparable to a one-dimensional membrane having rectangular pores, a drop boundary layer develops along the drop generators. In the small drop regime, the local dynamics of drop formation is shown to be independent on the emulsion cross flow. Moreover, we note that the development of the drop boundary layer is even beneficial to homogenize drop size along the production line. On the other hand, in the large drop regime, drop collision can trigger fragmentation and thus lead to size polydispersity.

A New Methodology to Characterize Wettability Alteration in Network Modeling

abstract In network models, the characterization of wettability for porous media is of great significance. In this article, an index, F, called the wettability alteration index, is defined and applied to evaluate the degree of wettability change after drainage displacement. This new parameter is also analyzed as a function of interfacial tension, size and shape of pores, and capillary pressure. A new method to characterize the wettability of a porous medium after primary drainage is proposed. The imbibition relative permeability curves obtained using the wettability alteration index are compared to those obtained using traditional methods.

Exploring capillary trapping efficiency as a function of interfacial tension, viscosity, and flow rate

Abstract We present experimental results based on computed x-ray microtomography (CMT) for quantifying capillary trapping mechanisms as a function of fluid properties using several pairs of analog fluids to span a range of potential supercritical CO 2 -brine conditions. Our experiments areconducted in a core-flood apparatus using synthetic porous media and we investigate capillary trapping by measuring trapped non-wetting phase area as a function of varying interfacial tension, viscosity, and fluid flow rate. Experiments are repeated for a single sintered glass bead core using three different non-wetting phase fluids, and varying concentrations of surfactants, to explore and separate the effects of interfacial tension, viscosity, and fluid flow rate. Analysis of the data demonstrates distinct and consistent differences in the amount of initial (i.e. following CO 2 injection) and residual (i.e. following flood or WAG scheme) non-wetting phase occupancy as a function of fluid properties and flow rate. Further experimentation and analysis is needed, but these preliminary results indicate trends that can guide design of injection scenarios such that both initial and residual trapped gas occupancy is optimized.

Measuring and Modeling of Viscosity and Surface Properties in High Temperature Systems

In order to be able to understand and model the kinetics of heterogeneous reactions and transport phenomena it is necessary to have experimental data of physical properties like viscosity, surface energy and interfacial energy. In this study viscosity of high-melting slags containing chromium oxides were measured. Central results and observed relationships and modelling are described. The results showed that addition of chromium oxide into the slag decreases the viscosity but the influence becomes weaker at high CrOx contents. The viscosity–composition relation was evaluated by a modified Iida's model and a good agreement between the experimental and calculated results was observed.Interfacial phenomena between liquid metal and slag with gas bubbles entering through the metal–slag interface were investigated by X-ray transmission technique. Bubble behaviour at metal–slag interface and dispersion of metal droplets into the slag were measured as a function of interfacial tension, gas bubble size and slag viscosity. The effect of different parameters on metal entrainment is discussed.

Stretch and Shape Distributions of Droplets with Interfacial Tension in Chaotic Mixing

Abstract A numerical simulation is developed to study the time-dependent shapes of droplets in chaotic mixing, as a function of interfacial tension and droplet-to-matrix viscosity ratio. The two-dimensional, time-periodic Newtonian flow between eccentric cylinders is used as a prototype mixing flow. The microstructure is modeled as three-dimensional ellipsoidal droplets, ignoring breakup and coalescence. A Lagrangian particle method is used to follow the microstructure. When interfacial tension is small (global capillary number is large), the major axes of the droplets exhibit the same stretching statistics as passive fluid elements and droplets with zero interfacial tension in chaotic flows: the geometric average of the stretch ratio grows exponentially with time, at a rate equal to the Lyapunov exponent of the flow, while the log of the major-axis stretch of the droplets, when scaled by its instantaneous mean and standard deviation, has a time-invariant, Gaussian global distribution and a non-uniform, fractal, and time-invariant spatial distribution. In this regime the stretch of the longest droplet axis is insensitive to interfacial tension, but the shape of the cross section is very sensitive: initially spherical droplets deform first into ribbons or sheets, but eventually transform into axisymmetric threads. The larger the global capillary number, the longer the sheet morphology persists, but sheet-like structures are always transient, and the sheets relax to threads if mixing goes on too long.

Improving the extraction of tetrachloroethylene from soil columns using surfactant gradient systems

In this work, we extend the recently developed gradient approach for surfactant-enhanced remediation of dense non-aqueous phase liquid (DNAPL)-impacted sites. The goal of the gradient approach is to maximize the DNAPL solubilization capacity in swollen micelles (Type I aqueous microemulsions) while at the same time minimizing the potential for DNAPL mobilization. In this work, we introduce a modified version of the capillary/trapping curve that we refer to as the gradient curve to help interpret and/or design the gradient approach. The gradient curve presents the residual DNAPL saturation as a function of interfacial tension and microemulsion viscosity. This approach demonstrates that keeping a low viscosity of the microemulsion phase is not only important for keeping a low head loss during surfactant flooding but also to prevent oil mobilization. Eight microemulsion systems were evaluated in this research; these systems were evaluated based on their tetrachloroethylene (PCE) solubilization capacity, interfacial tension (IFT), viscosity, density, and coalescence kinetics. Two of these systems were chosen for evaluation in site-specific column tests using an increasing electrolyte gradient to produce a decreasing IFT/increasing solubilization gradient system. The column studies were conducted with media from Dover Air Force Base in Dover, DE. Both solubilized and mobilized DNAPL were quantified. During the column studies, we observed that substantial PCE was mobilized when the residual level of PCE in the column was significantly higher than the steady-state residual saturation level being approach (as predicted from the gradient curve). Four column studies were performed, three of which were used to asses the validity of the gradient curve in predicting the residual saturation after each gradient step. From these tests we observed that starting IFTs of less than 1 mN/m all produced the same mobilization potential. In the last column, we used an additional gradient step with an initial IFT above 1 mN/m to dramatically reduce the amount of PCE mobilize. Based on the good agreement between column results and projections based on the gradient curve, we propose this as a preferred method for designing gradient surfactant flushing systems.

Laboratory Monitoring of Surfactant Imbibition With Computerized Tomography

Summary Oil production from fractured reservoirs can occur by spontaneous water imbibition and oil expulsion from the matrix into the fracture network. Injection of dilute surfactant can recover additional oil by lowering oil/water interfacial tension (IFT) or altering rock wettability, thereby enhancing countercurrent movement and accelerating gravity segregation. Modeling of such recovery mechanisms requires knowledge of temporal and spatial fluid distribution within porous media. In this study, dilute surfactant imbibition tests performed for vertically oriented carbonate cores of the Yates field were found to produce additional oil over brine imbibition. Computerized tomography (CT) scans were acquired at times during the imbibition process to quantify spatial fluid movement and saturation distribution, and CT results were in reasonable agreement with material-balance information. Imbibition and CT-scan results suggest that capillary force and IFT gradient (Marangoni effect) expedited countercurrent movement in the radial direction within a short period, whereas vertical gravity segregation was responsible for a late-time ultimate recovery. Wettability indices, determined by the U.S. Bureau of Mines (USBM) centrifuge method, show that dilute surfactants have shifted the wetting characteristic of the Yates rocks toward less oil-wet. A numerical model was developed to simulate the surfactant imbibition experiments. A reasonable agreement between simulated and experimental results was achieved with surfactant diffusion and transitioning of relative permeability and capillary pressure data as a function of IFT and surfactant adsorption.

Relative Permeability at Near-Critical Conditions

SummaryWe have measured a series of two-phase drainage relative permeability curves at near-critical conditions by means of the displacement method. As a fluid system we have used the model system methanol/n-hexane that exhibits a critical point at ambient conditions. In the measurements we have varied the interfacial tension and the flow rate.Our results show a clear trend from immiscible relative permeability functions to miscible relative permeability lines with decreasing interfacial tension and increasing superficial velocity. The relative permeability measurements show that the controlling parameter is the ratio of viscous to capillary forces on a pore scale, denoted by the capillary number Nc=k‖∇Φ‖/ϕσ.To demonstrate the significance of using the proper relative permeability functions, we have calculated the well impairment due to liquid drop-out in a model gas condensate reservoir, for four different rock types showing four different relations between relative permeability and the capillary number. The calculations show that near-miscible relative permeability functions come into play in the vicinity of the well bore. This is contrary to what happens if the relative permeability would be a function of interfacial tension alone. In addition, the results show that well impairment by condensate drop-out may be significantly overestimated if the dependence of relative permeability on the capillary number is ignored.

Influence of carbon, silicon and molybdenum on the separating and emulsifying behaviour of steel and slag

The influence of C, Si, and Mo on the surface tension of Armco iron, and on the interfacial tension between Armco iron and a 40%CaO/40%SiO2/20%Al2O3 slag at 1550°C has been investigated. Surface tension was determined according to the drop weight method, and the interfacial tension by the drop detachment method. Based on these measurements, ternary interfacial tension diagrams are set up, which enable the separating and emulsifying tendencies of the related steel/slag/gas systems to be predicted. This is followed by the calculation of the meniscus radius as a function of interfacial tension in continuous casting, together with the assessment of its effect on lubrication.

Gas/Oil Capillary Pressure of Chalk at Elevated Pressures

Summary Accurate capillary pressure curves are essential for studying the recovery of oil by gas injection in naturally fractured chalk reservoirs. A simple and fast method to determine high-pressure drainage capillary pressure curves has been developed. The effect of gas/oil interfacial tension (IFT) on the capillary pressure of chalk cores has been determined for a methane/n-pentane system. Measurements on a 5-md outcrop chalk core were made at pressures of 70, 105, and 130 bar, with corresponding IFT's of 6.3, 3.2, and 1.5 mN/m. The results were both accurate and reproducible. The measured capillary pressure curves were not a linear function of IFT when compared with low-pressure centrifuge data. Measured capillary pressures were considerably lower than IFT-scaled centrifuge data. It appears that the deviation starts at an ΓFT of about 5 mN/m. According to the results of this study, the recovery of oil by gravity drainage in naturally fractured chalk reservoirs may be significantly underestimated if standard laboratory capillary pressure curves are scaled by EFT only. However, general conclusions cannot be made on the basis of only this series of experiments on one chalk core.

Lipase Activity as a Function of Interfacial Tension Using the Rising Drop Method on a New Oil Drop Tensiometer

Lipase Activity as a Function of Interfacial Tension Using the Rising Drop Method on a New Oil Drop Tensiometer

Wettability Literature Survey- Part 4: Effects of Wettability on Capillary Pressure

Wettability Literature Survey- Part 4: Effects of Wettability Part 4: Effects of Wettability on Capillary Pressure Summary. The capillary-pressure/saturation relationship depends on the interaction of wettability, pore structure, initial saturation, and saturation history. No simple relationship exists that relates the capillary pressures determined at two different wettabilities. Therefore, the most accurate measurements are made with cores that have native reservoir wettability. In a uniformly wetted porous medium, pore geometry effects and the extremely rough surfaces of the porous medium make the capillary pressure curve insensitive to wettability for small contact angles (less than about 50 deg.[0.87 rad] for drainage capillary pressure curves and less than about 20 deg. [0.35 rad] for spontaneous-imbibition capillary pressure curves). When the porous medium has fractional or mixed wettability, both the amount and distribution of the oil-wet and water-wet surfaces are important in determining the capillary pressure curve, residual saturations, and imbibition behavior. Imbibition also depends on the interaction of wettability, pore structure, initial saturation, and saturation history. Because of these interactions, there is a large range of contact angles where neither oil nor water will imbibe freely into a uniformly wetted reservoir core. In contrast, it is sometimes possible for both fluids to imbibe freely into a core with fractional or mixed wettability. Contact Angles, Capillary Pressure, and Wettability This paper is the fourth in a series of literature surveys covering the effects of wettability on core analysis. Changes in the wettability of cores have been shown to affect electrical properties, capillary pressure, waterflood behavior, relative permeability, dispersion, simulated tertiary recovery, irreducible water saturation (IWS), and residual oil saturation (ROS). When oil and water are placed together on a surface, a curved interface between the oil and water is formed, with a contact angle at the surface that can range from 0 to 180 deg. [0 to 3.15 rad]. By convention, the contact angle, 0, is measured through the water. Generally, when 0 is between 0 and 60 to 75 deg. [0 and 1.05 to 1.31 rad], the system is defined as water-wet. When 0 is between 180 and 105 to 120 deg. [3.15 and 1.83 to 2.09 rad], the system is defined as oil-wet. In the middle range of contact angles, a system is neutrally or intermediately wet. It can be shown that whenever an oil/water interface is curved, the pressure will abruptly increase across the interface to balance the interfacial tension (IFT) forces. This pressure jump, which is the capillary pressure, is given by Laplace's equation : (1) where sigma = IFT, P = capillary pressure, p = pressure in the oil, p = pressure in the water, and r1, r2 = radii of curvature of the interface, measured perpendicular to each other. By convention, the capillary pressure is defined as po-pw. Because of this definition, a radius of curvature po-pw. Because of this definition, a radius of curvature directed into the oil is positive, while one directed into the water is negative. Depending on the curvature of the surface, the capillary pressure can be positive or negative. When the interface is flat, the capillary pressure is zero. When fluids other than oil and water are used, the capillary pressure is usually defined as (2) where pNW is the pressure in the nonwetting fluid and pWET is the pressure in the wetting fluid. pWET is the pressure in the wetting fluid. The radii of curvature of the interface, and hence the capillary pressure, are determined by local pore geometry, wettability, saturation, and saturation history. For most porous media, the equations for the interfacial curvature are much too complicated to be solved analytically, and capillary pressure must be determined experimentally. In these cases, a simple relationship between contact angle and capillary pressure cannot be derived. One geometry where capillary pressure can be calculated as a function of geometry, wettability, and IFT is a capillary tube. Laplace's equation can be used to solve for the capillary pressure as a function of IFT, contact angle, and rt, the radius of the tube. P. 1283

Numerical calculation of unstable immiscible fluid displacement in a two-dimensional porous medium or Hele-Shaw cell

AbstractA numerical procedure for calculating the evolution of a periodic interface between two immiscible fluids flowing in a two-dimensional porous medium or Hele-Shaw cell is described. The motion of the interface is determined in a stepwise manner with its new velocity at exach time step being derived as a numerical solution of a boundary integral equation. Attention is focused on the case of unstable displacement charaterised physically by the “fingering” of the interface and computationally by the growth of numerical errors regardless of the numerical method employed. Here the growth of such error is reduced and the usable part of the calculation extended to finite amplitudes. Numerical results are compared with an exact “finger” solution and the calculated behaviour of an initial sinusoidal displacement, as a function of interfacial tension, initial amplitude and wavelength, is discussed.