Ross Chow

The electric properties of the bitumen/water interface Part II. Application of the ionizable surface-group model

Abstract The Ionizable Surface-Group Model has been applied to explain the electric properties of the bitumen/water interface. The model assumes that the surface charge of the bitumen is derived from the dissociation of acid groups on the surface and calculates their dissociation as a function of both bulk pH and electrolyte concentration. The theory predicts that the dissociation behavior of carboxyl groups at the bitumen/water interface depends strongly on the total surface density of charge groups and on the electrolyte concentration in the aqueous solution. The theory was subsequently tested by comparing the predicted and measured electrophoretic mobilities of bitumen particles in aqueous solutions ranging in bulk pH from 4 to 11 and in electrolyte concentration from 10−4 to 10−1M NaCl. The results indicate that the surface charge of the bitumen/water interface can be explained by the dissociation of carboxyl group moieties belonging to surfactants naturally present in bitumen. The measured electrophoretic mobilities in 10−4M NaCl also demonstrate the existence of a maximum in mobility at high zeta potentials which is due to the electrophoretic relaxation effect.

Probing surface charge potentials of clay basal planes and edges by direct force measurements.

The dispersion and gelation of clay suspensions have major impact on a number of industries, such as ceramic and composite materials processing, paper making, cement production, and consumer product formulation. To fundamentally understand controlling mechanisms of clay dispersion and gelation, it is necessary to study anisotropic surface charge properties and colloidal interactions of clay particles. In this study, a colloidal probe technique was employed to study the interaction forces between a silica probe and clay basal plane/edge surfaces. A muscovite mica was used as a representative of 2:1 phyllosilicate clay minerals. The muscovite basal plane was prepared by cleavage, while the edge surface was obtained by a microtome cutting technique. Direct force measurements demonstrated the anisotropic surface charge properties of the basal plane and edge surface. For the basal plane, the long-range forces were monotonically repulsive within pH 6-10 and the measured forces were pH-independent, thereby confirming that clay basal planes have permanent surface charge from isomorphic substitution of lattice elements. The measured interaction forces were fitted well with the classical DLVO theory. The surface potentials of muscovite basal plane derived from the measured force profiles were in good agreement with those reported in the literature. In the case of edge surfaces, the measured forces were monotonically repulsive at pH 10, decreasing with pH, and changed to be attractive at pH 5.6, strongly suggesting that the charge on the clay edge surfaces is pH-dependent. The measured force profiles could not be reasonably fitted with the classical DLVO theory, even with very small surface potential values, unless the surface roughness was considered. The surface element integration (SEI) method was used to calculate the DLVO forces to account for the surface roughness. The surface potentials of the muscovite edges were derived by fitting the measured force profiles with the surface element integrated DLVO model. The point of zero charge of the muscovite edge surface was estimated to be pH 7-8.

Electroacoustic method for monitoring the coalescence of water-in-oil emulsions

Abstract Ultrasound vibration potential which involves the application of an ultrasonic field and the detection of an electric field, was a well suited technique for electrokinetic measurements of colloidal systems in non-polar and non-transparent media. The technique was used to monitor the rate and extent of coalescence in water-in-crude oil emulsions. The effect of water content, demulsifier type and concentration was studied. The change in ultrasonic vibration signal correlated well with the results from centrifugation and photomicrography which were also used to follow the demulsification process. The results also showed that the use of a combination of a demulsifier and a surfactant was more effective in separation than the individual chemicals.

The stability of kaolinite-in-water dispersions

Abstract The stability of a kaolinite-in-water dispersion was investigated as a function of solution ph and electrolyte concentration. The stability of the sol was measured directly using a technique which monitors the alternating portion of the transmitted light. Comparison of the measured stability with model calculations was conducted by invoking a model which predicted the potential of the edge of the kaolinite particle using the Ionizable Surface-Group model and calculated the stability using the Derjaguin—Landau—Verwey—Overbeek (DLVO) theory. Agreement was favorable except at electrolyte concentration > 0.05 M and solution ph > 9.0.

The In Situ Formation Of Heavy Oil Emulsions

Heavy oil is commonly produced in the form of water-in-oil emulsions. It has long been debated whether the emulsions are formed in the reservoir, and if so, what effect they have on the recovery process. This work examines the conditions under which water-in-oil emulsions can form in situ, and their flow properties. A number of experiments have been carried out in which water and oil were injected as separate phases into a sandpack, and the produced oil analyzed for emulsified water content. We find that emulsified water content is small at low injection rates, but that above some threshold rate, the water content rises rapidly. Dependence of the threshold rate on oil type, oil viscosity, water :oil ratio, pack permeability and pack wettability have all been examined. Our results suggest that oil phase capillary number, N c , defined as (oil velocity)x(oil viscosity)/(oil-water IFT) is a natural dimensionless parameter to describe the emulsification threshold. For oil viscosity much greater than that of water, and permeability of the order of a few darcies, threshold N c is between 10 -4 and 10 -3 . Such capillary numbers are commonly encountered in near-wellbore flow during heavy oil recovery operations. Experiments comparing a reservoir oil with mineral oils show similar threshold capillary numbers. The threshold increases with permeability of the medium and is significantly lower in oil-wet compared with water-wet sand. Preliminary results indicate that a significant reduction in effective mobility of the oil phase occurs when emulsification takes place.

Coalescence Behavior of Water-in-Oil Emulsions

In this paper the use of electroacoustic techniques involving the application of a sonic field and the detection of an electric field, for monitoring coalescence of water droplets in non-polar media will be discussed. This technique was used to evaluate the rate and extent of dewatering in oil continuous emulsions when surface active chemicals were added. The results showed that a combination of an oil soluble demulsifier and water soluble surfactant was substantially more effective in causing droplet coalesence than the individual components. An explanation for these findings were based on studies of time-dependent interfacial tensions at the oil/water interface and electrokinetic properties. The results indicated that a direct relationship exists between the adsorption behavior at the oil/water interface (apparent rate of spreading) and emulsion stability.

A Physical Preventive Treatment of Crystallization and Precipitation in the Petroleum Industry

The plugging of tubings and pipelines by scale, asphaltene, and wax is a common problem in the oil production, transportation and refinery systems. Hot oiling, chemical wash and mechanical scraping have been used for many years to restore flow. There may be economic benefit to implement preventive treatments. We propose to consider the application of ultrasound as a potential preventive treatment. As a physical treatment, it is expected to be independent of the details of the chemical nature of the problem, i.e., it should be equally applicable to particles such as salt crystals, asphaltene precipitates, or wax. We will present experimental results showing the effects of application of ultrasound during precipitation and crystallization. Three systems were tested in this study; crystallization of salt from saturated aqueous solutions, re-dispersion of asphaltene in heptane, and pour point depression of diesel with different wax contents. The results show that, under the influence of ultrasound during the phase transition, there was a reduction of the size of the salt crystals, precipitated asphaltene was re-dispersed, and the temperature at the pour point of diesel with different wax contents was substantially lowered.