Graham H. Neale

Creeping flow over a composite sphere: Solid core with porous shell

Abstract Creeping flow past a solid sphere with a porous shell has been solved using the Stokes and Brinkman equations. The dimensionless solid core and shell radii, normalized by the square root of the shell permeability, are the two parameters that govern the flow. In the limiting cases, the analytical solution describing the flow past the composite sphere reduces to that for flow past a solid sphere and a homogeneous porous sphere. The settling rates of a solid sphere with attached threads are measured experimentally. This system can be considered a model for rigid linear molecules anchored or adsorbed onto a colloidal particle. The analytical solution for the composite sphere is in excellent agreement with the experimental results.

Dynamic interfacial tension behavior of acidified oil/surfactant-enhanced alkaline systems 1. Experimental studies

Abstract A mechanistic interpretation of the dynamic interfacial tension behavior arising from the interactions between acidic oil and surfactant-alkaline systems has been developed. A physico-chemical model, based on Nernstian theory of convective diffusion, Langmuir theory of interfacial sorption kinetics, and electrical phenomena, has been invoked to account for the dynamic nature of the interfacial tension. The results show that the interfacial tension arising from the interaction of these chemical combinations with model acidic oil exhibits a marked dynamic behavior. The magnitude of interfacial tension variations changes not only with alkali concentration but also with surfactant corcentration. The pertinent sorptive rate constants that characterize dynamic behavior are precisily estimated by correlating experimental interfacial tension data with the proposed model. A very good overall agreement is obtained between the experimental values and those predicted by the model. A better of the interactions between acidic oil and alkaline solutions has been developed. The improvement is mainly related to a modification of the adsorption isotherms as well as the kinetic equations. These changes allow for the co-adsorption of the un-ionized acid along with the ionized acid at the interface. The extension of the acidic oil/alkaline model to incorporate an additional pre-formed surfactant is also accomplished by a modification of the adsorption isotherms, of the micellar relationship and of the resulting equilibria.

Some aspects of wetting/dewetting of a porous medium

Abstract Various features of wetting/dewetting of porous media are examined. The phenomenon of capillary hysteresis is illustrated by a vertical capillary tube which consists of an alternating sequence of convergent—divergent conical sections. A study of the kinetics of wetting of this tube by a liquid shows that when the velocity of the liquid/vapour meniscus is plotted against the height of penetration, it oscillates about the Washburn velocity—distance curve and performs Haines jumps. A general macroscopic equation is derived for the rate of wetting/dewetting of a porous medium having randomly distributed, finely divided particles or pores. Use is made of the Forchheimer equation, which is an extension of Darcys equation to higher Reynolds numbers. Dissipative energy terms due to internal fluid calculaton and to irreversible movements of the meniscus strongly affect the initial rate of imbibition, but as the wetting progresses the Reynolds number decreases and Washburns equation prevails. The application of percolation theory to wetting/dewetting phenomena in porous media is studied. The use of percolation theory by Kirkpatrick and Stinchcombe to find the electrical conductivity of inhomogeneous solid mixtures is adapted to determining the permeability of a porous medium to fluid flow. It is also shown how the relation between the “precolation probability” and the concentration of “unblocked” channels or pores can be applied in calculating the capillary pressure—desaturation curve in drainage. In particular, percolation theory predicts that a threshold pressure or break-through pressure is required before a non-wetting fluid can displace a wetting fluid in a porous medium. It is often convenient to use tree-like or branching lattice networks as models of a porous medium, because these are amenable to exact solutions in regard to percolation probability and permeability. The percolation properties of porous medium models which consist of lattice networks of cylindrical channels with a distribution of cross-sections and also of randomly packed rotund particles are examined and their relevance to wetting/dewetting phenomena discussed.

Visualization of a Surfactant Flood of an Oil-Saturated Porous Medium

This paper discusses the viscous fingering that occurs when water or a surfactant solution displaces oil in a porous medium. Such floods were visualized in an oilwet porous medium composed of fused plastic particles. The flow structure changed significantly within the range of capillary numbers between 10/sup -4/ and 10/sup -3/. The addition of surfactant resulted in narrower fingers, which developed in a more dispersive fashion.

A modified pendant drop method for transient and dynamic interfacial tension measurement

Abstract An apparatus has been constructed based upon the drop shape method for the determination of surface and interficial tensions. The system, built around a commercial pendant drop instrument, incorporates computer-based video image analysis. A user interface is designed and built around the core subprograms. A filter routine using a global threshold is used along with an edge-tracing algorithm for the extraction of the drop profile. The tension is calculated using the Jennings and Pallas algorithm. The time needed to digitize a single frame and to extract the drop profile coordinates is about 0.5 s. The instrument is capable of measuring surface tension of water of 72.00 ± 0.07 mN m −1 . The method is suitable for measuring transient as well as dynamic interfacial tensions. The relaxation of surfactant adsorption layers at the oil/water interfaces can also be inferred from the data obtained.

Mechanisms for the interfacial reaction between acidic oils and alkaline reagents

Abstract Alkaline reagents are increasingly added to flood water as a means of improving cumulative oil recovery from heavy oil reservoirs. The effectiveness of these reagents rests with their ability to interact with reactive species (such as acids and phenols) resulting in the formation of surface-active soap species. The in situ produced surfactants are responsible for the lowering of the interfacial tension and the subsequent mobilization of residual oil. In this paper, a physico-chemical model based on convective diffusion, sorption kinetics and electrical interfacial phenomena has been proposed to account for dynamic interactions between single carboxylic acids and caustic reagents over a wide range of both acid and alkaline concentrations. The primary objective of the work is to obtain a mechanistic interpretation of the dynamic interfacial tension arising from simple reacting systems. In view of inadequate knowledge of crude oil chemistry, oleic and aqueous phases of known composition have been employed. The model equations applicable to single carboxylic acids such as oleic and lauric contacted with a spectrum of NaOH solutions have been fully developed. A novel combination of sensitivity analysis with nonlinear regression has resulted in reliable parameter estimates. The dynamic interfacial tension predicted by the model compares favorably with the experimental data over a wide range of acid and caustic concentrations.

Theory of the rate of wetting of a porous medium

The classic equations of Washburn and Rideal for the rate of penetration of a fluid into a capillary due to surface tension are re-examined and time-dependent solutions are obtained for large times in both horizontal and vertical flow. By applying Darcys law, a general theory of wetting of a porous medium is derived. The rate of fluid penetration is expressed in a form analogous to that for a capillary, in terms of fluid viscosity, surface tension, porosity and permeability. The permeability is calculated for the Happel–Kuwabara cell model of a porous medium, consisting of a swarm of identical spherical particles.

Evaluation of aqueous chemical systems for heavy oil recovery processes

Abstract The effects of temperature and certain chemical additives on the interfacial tension behaviour of a heavy oil (from Lloydminster, Alberta) with petroleum sulphonate surfactant solutions and alkaline solutions are investigated experimentally. Corresponding data for a light Canadian oil are included for comparison purposes. It is concluded that alkaline solutions are effective only in the recovery of heavy oils, while petroleum sulphonate surfactants are effective only for light oils. The effect of temperature on the minimum attainable interfacial tension is marginal in all cases. However, for alkaline solutions, temperature has a significant effect on the rate of rise of interfacial tension with time after attainment of the minimum value.

TRANSIENT INTERFACIAL TENSION BEHAVIOR BETWEEN ACIDIC OILS AND ALKALINE SOLUTIONS

Abstract A study of the dynamic interfacial tension behavior of reacting acidic oil/alkaline solutions has been conducted for both an artificially acidified synthetic oil and a real crude oil for four different alkalis at various concentrations. The IFT values between a 10 mM acidified synthetic oil and various 25 mM alkaline solutions, before the minimum IFT value was reached, were found to be in the descending order: KOH, NaOH, Na2SiO3 and LiOH. The corresponding IFT values between diluted Lloydminster heavy crude oil and the same alkaline solutions, again before the minimum was reached, were found to be in the descending order: LiOH, NaOH, Na2SiO3 and KOH. The crude oil exhibited lower minimum IFT values against alkaline solutions than the synthetic acidified oil. The general trend of decreasing IFT towards a minimum value followed by an increase in IFT thereafter was noted for all solutions tested.

The measurement of dynamic interfacial tension by photo-micropendography

Abstract A novel experimental technique called photo-micropendography has been developed for the precise and accurate measurement of the dynamic interfacial tension of finite reactive systems. Photo-micropendography is an integrated experimental/data analysis system which is essentially a modification of the classical pendant drop apparatus, but features also a numerical solution of the Young-Laplace equation. A complete range of coordinate measurements extending from the apex to the base of the drop is used for the numerical calculation of the boundary tension as well as the interfacial area and drop volume. This experimental scheme was used to study the interfacial behaviour of 0.3125 mM oleic acid in hexadecane in contact with various caustic solutions up to 25 mM. Tension values ranged from 2 to 44 mN/m and interfacial ages extended from 5 sec to 25 min depending on the specific caustic concentration. The accuracy of the dynamic interfacial tension data was well within 2%. Comparative dynamic tension measurements for the same working solutions were carried out by means of the ring and spinning drop tensiometers. The interfacial tension data obtained by the spinning drop tensiometer were largely inaccurate and imprecise at caustic concentrations below 12.5 mM, while data obtained from the ring tensiometer were grossly inaccurate at caustic concentrations above 2.5 mM. The micropendographic technique gave the most precise and consistent tension values of the three methods over the IFT range investigated.