7092
Ind. Eng. Chem. Res. 2009, 48, 7092–7102
Determination of Water-in-Oil Emulsion Viscosity in Porous Media Mohamed Arhuoma,† Mingzhe Dong,‡ Daoyong Yang,*,† and Raphael Idem† Faculty of Engineering, UniVersity of Regina, Regina, SK, Canada S4S 0A2, and Department of Chemical and Petroleum Engineering, UniVersity of Calgary, Calgary, AB, Canada T2N 1N4
Experiments have been conducted to determine the viscosities of water-in-oil (W/O) emulsions in porous media. W/O emulsions were first prepared for different volume fractions of the dispersed phase and then characterized for their properties and rheological parameters including flow index and consistency constant. All prepared W/O emulsions with volume fractions between 6.78% and 33.48% were found to behave as non-Newtonian shear-thinning fluids at fairly high viscosities. The viscosities of the emulsions were measured during emulsion flow in three types of sandpacks. A correlation of the viscosities of the W/O emulsions in porous media was developed by performing a regression on the experimentally measured data. The newly developed correlation was validated, and a sensitivity analysis was performed to examine the effects of tortuosity and emulsion quality. The emulsion quality has a dominant effect on the viscosity of the W/O emulsions and has been included in the correlation for the first time to achieve accurate predictions of the viscosities of W/O emulsions in porous media. The existing correlations for oil-in-water (O/W) emulsions provide underestimated predictions for the viscosities of W/O emulsions, whereas the droplet size distribution does not have a significant impact on the viscosity of the W/O emulsions tested in this study. 1. Introduction Because heavy oils are often produced from subsurface reservoirs with water in the form of water-in-oil (W/O) emulsions, it is of great interest for petroleum engineers to understand how these mixtures behave during flow within porous media. Extensive efforts have been made to determine and quantify the viscosity of oil-in-water (O/W) emulsions in porous media both theoretically and experimentally. Few attempts, however, have been made to determine the viscosity of W/O emulsions, even though almost two-thirds of crude oil worldwide is mainly produced in the form of W/O emulsions.1 Therefore, it is of fundamental and practical importance to accurately determine and evaluate the viscosity of W/O emulsions in porous media. As an enhanced oil recovery (EOR) technique, alkaline flooding has been extensively studied for conventional oils, including numerous laboratory experiments and some field tests. Laboratory experiments showed that caustic flooding could significantly improve oil recovery of waterflood at a concentration of 0.1% NaOH.2 It is well-accepted that in situ O/W emulsions tend to plug growing water fingers and channels and, thus, divert flow to improve sweep efficiency. Recent research showed that waterflood recovery of Western Canadian heavy oils with viscosities from 1000 to over 10000 mPa · s could be improved considerably by alkaline flooding.3-7 This is ascribed to the fact that alkaline solutions can penetrate into heavy oil in porous media by forming W/O emulsions in situ. Because of the high viscosity of W/O emulsions, the resistance to water flow in the high water saturation zone can be increased significantly to improve sweep efficiency and thus oil recovery. In the literature, there exist two major groups of studies for determining emulsion viscosities. One determines the viscosity of an emulsion as a function of emulsion quality and the viscosities of the internal and external phases without considering porous media.1,8,9 The other considers the porous media * To whom correspondence should be addressed. Tel.: 1-306-3372660. Fax: 1-306-585-4855. E-mail:
[email protected]. † University of Regina. ‡ University of Calgary.
and emulsion properties, most of which are related to O/W emulsions rather than W/O emulsions.1,10,11 The power-law model is the simplest representation of the viscosity of nonNewtonian fluids. The O/W emulsion flow in glass beadpacks of several different meshes has been studied.10 A viscosity model has been developed to simulate the viscosity of an O/W emulsion, assuming that the emulsion is a single-phase and homogeneous fluid,12,13 and a model has been formulated to determine the effective viscosity of non-Newtonian fluids.1 Also, experiments have been conducted to study the flow mechanism of emulsions in porous media and to investigate the emulsion rheology and the blocking or capture effect of emulsions during displacement process.11 So far, no efforts have been made available to thoroughly study the viscosity of W/O emulsions in porous media. In addition, because experimentally determining the viscosities of emulsions is time-consuming, accurate and well-constructed correlations need to be developed for characterizing W/O emulsion flow in porous media. In this study, experiments were performed to determine the viscosities of W/O emulsions. The emulsions were first prepared by the so-called agent-in-water technique.14-16 Then, emulsion flow tests in sandpacks were performed at different flow rates, and the corresponding differential pressures were recorded when the flow reached the steady state so that the emulsion viscosities were determined accordingly. Subsequently, the experimental emulsion viscosity together with the other dependent parameters, namely, porosity, permeability, flow index, consistency constant, tortuosity, and flow rate, were used to develop a correlation. 2. Experimental Section 2.1. Materials. An oil sample from an Alberta heavy oil reservoir was used for the experiments; its properties are listed in Table 1. Oil viscosity was measured using a viscometer (DVII+Pro, Brookfield, Middleboro, MA) with a heating/cooling water bath. The viscometer was equipped with two spindles (CPE-42 and CPE-52) for low- and high-viscosity measurements, respectively. The crude oil used in this study was considered as a Newtonian fluid because the viscosity of the crude oil remains almost constant while being measured with a
10.1021/ie801818n CCC: $40.75 2009 American Chemical Society Published on Web 07/02/2009
Ind. Eng. Chem. Res., Vol. 48, No. 15, 2009 Table 1. Physical Properties of the Pelican Oil Sample property
value
density at 15 °C (kg/m3) density at 25 °C (kg/m3) viscosity at 15 °C (mPa · s) viscosity at 22 °C (mPa · s) viscosity at 25 °C (mPa · s) water content (%) acid number (mg of KOH/g)
970.9 964.2 2440 1360 1020
