Interfacial Tension between Water and Oil under Reservoir Conditions

Abstract

The distribution and movement of fluids in oil reservoirs are influenced toa great extent by capillary forces, which depend upon the size and shape of thepores in the reservoir rock, the surface characteristics of the rock, and theinterfacial tension between the fluid phases. This paper presents the resultsof an investigation of the interfacial tension between salt water and crude oilcontaining dissolved gas under reservoir conditions. Apparatus and Procedure In the preliminary phases of this investigation, it was found that a scumformed at the oil-water interface, which made measurement of interfacialtension by either the ring or capillary rise methods unreliable. Accordingly, the drop-weight method, in which a fresh interface is continuously formed, wasselected. In this method, a tip through which drops of one fluid can beexpelled is immersed in a second fluid. At the instant that the drop becomeslarge enough to fall, the gravitational force tending to pull away the dropexactly balances the interfacial force tending to hold it. From the size of thedrop, the dimensions of the tip, and the density of the two fluid phases, theinterfacial tension may be calculated. The apparatus consists of a circulating pump for bringing the oil toequilibrium with gas at the desired pressure, a displacement pump for formingthe drops, an interfacial tension cell in which the drops are formed, and adensity cell to determine the density of the oil. The density of the water isdetermined separately in another apparatus. A flow diagram of the assembledequipment is shown in Fig. 1. The interfacial tension cell contains a stainless-steel dropping tip suspendedfrom the top and extending below the surface of the oil. The tip is acylindrical rod with a small hole in the center through which the water wasforced to form the drop on the lower face. T.P. 1006