The Measurement of Interfacial Forces During Crude Oil/water Immiscible Displacement
Authors: Brown C.E. , Jones T.J. , Neustadter E.L. , Whittingham K.P. 
Published: March 2010

Abstract
Direct measurement has been made of the forces acting during immiscible displacement in a capillary system of model geometry. The aim of this study is to obtain better understanding of the microscopic displacement mechanism, and to determine how these processes may be characterized in terms of the interfacial properties of the system. The parameters measured include the interfacial tension, the wettability and the interfacial rheology. A range of crude oil/aqueous phase systems representing a range of interfacial rheological characteristics has been examined. The implications of the various interfacial characteristics for immiscible displacement during oil recovery are discussed.

Introduction
The development and optimization of chemical Enhanced Oil Recovery (EOR) systems is based on our understanding of the mechanisms by which oil is displaced from a porous matrix, and of the parameters which control those mechanisms. Better insight into the displacement processes is required than is afforded by "black box" experiments such as displacement tests in sand packs. It is therefore necessary to carry out laboratory experiments concerned with specified system parameters, and to link the results of these experiments with displacement tests.
The most commonly applied measurement used in this way is of interfacial tension, which is linked to displacement tests via intuitive conceptual models of the displacement process.
In the development of EOR systems based on waterflooding, the generation of a very low interfacial tension is often considered to be of paramount importance(1.2). However, it is also recognized that a system with a low interfacial tension is not by itself certain of success as the basis of an EOR process(3,4). Hence, the measurement of an equilibrium (or steady-state) interfacial tension is a valuable screening test, but other parameters are also relevant to the dynamic process of oil recovery. This paper focusses attention on these dynamic processes. Its scope is limited to consideration of the local microscopic immiscible displacement mechanisms in capillary-size pores; thus, interfacial properties dominate the over-all system behaviour.
The use of model capillary systems is widely reported in the literature. Blake, Everett and Haynes(5) have previously pointed out that immiscible displacement in even a single cylindrical capillary is associated with radial flow near the interface, so that a dynamic interfacial tension will apply. Blake et al.(5) reported measurements of displacement rate as a function of dynamic contact angle and pressure gradient for pure oil/water systems in a single cylindrical glass capillary. Capillaries of the same geometry were used by Hansen and Toong(6), who reported displacement phenomena other than the piston-like mode. Templeton(7) described the break-up of a crude oil/water interface during displacement in a single capillary, and confirmed the applicability of Poiseuille's law in micron-size capillaries. The potential importance of hydrodynamic effects in the interfacial region and the paucity of information concerning them has been highlighted by Dussan(8), who emphasized the importance of this topic in understanding surfactant behaviour. None of the above studies were able to give an instantaneous measurement of displacement pressure, and hence they were unable to examine the effects of changes in capillary geometry.