Measurement of Interfacial Tensions And Contact Angles At High Temperature And Pressure

Abstract

Abstract An apparatus has been developed for measuring interfacial tensions and contact angles at pressures from atmospheric to 10,000 psia (680 atmospheres) and temperatures from 77 °P (2SC) to 320 °F (l60 °C). This capability is required for determining oil/water interfacial tensions and oil/water/solid wetting properties of both reservoir and laboratory fluids at conditions which include those encountered in most oil reservoirs. The prime component of this apparatus is the high-pressure optical cell in which the measurements are made. To minimize contamination of the liquids by the flow system components, the test fluids can only contact titanium alloy, fused silica, Teflon and the solid substrate used in the wetting test. Interfacial tension measurements for n-dodecane/water and n-octane/water are reported. In addition, contact angle behaviour on quartz and interfacial tensions were determined for three different refined oil/brine systems. These three liquid pairs had previously been used in some hot waterflooding experiments with sandstone cores; knowledge of the interfacial tension and quartz wetting behaviour, as a function of temperature, was required as an aid in the interpretation of the waterflooding results. For the above tests, experimental conditions varied from atmospheric pressure and 77 °F to 6000 psia and 300 °F. INTRODUCTION ONE OF THE RESEARCH PROJECTS at PRR [deals with the study of interfacial phenomena in porous media. It was therefore decided to develop an apparatus capable of measuring- contact angles and interfacial tensions for temperatures from 25 °C (77 °F) to 160 °C (320 °F) and pressures from 1 atmosphere to 10,000 psia. This apparatus permits the study of reservoir and laboratory fluids over a range of conditions which include those encountered in most hydrocarbon reservoirs. Wettability is recognized to have an important bearing on the multiphase flow properties of porous media (1,2) and some recent evidence points to the possibility that a large proportion of oil producing reservoirs cannot be classed as water-wet(3). The contact angle can be used as a measure of wettability(4), even though some difficulties may arise in performing and interpreting the measurements(4). Raza et al.(5) note that it is relatively easier to obtain untontaminated reservoir fluid samples as compared to core samples. This is a point in favour of can tact angle tests. The oil/water interfacial tension (γ) does not significantly affect laboratory-measured flow properties in porous rocks (6,7) as long as γ is not less than about 1 dyne/cm. Nevertheless, measurements of interfacial tension at reservoir conditions are useful both as an indication of the degree of surface activity of a given crude oil/brine system and for assessing the alteration in the interfacial tension when chemical additives are placed in either phase. This latter use is associated with the evaluation of enhanced recovery methods based on lowering interfacial tension. In addition, knowledge of interfacial tensions of reservoir and laboratory fluids is required for adjusting laboratory capillary pressure measurements to reservoir conditions. This paper describes equipment for measuring contact angles and interfacial tensions, and presents the results of some initial experiments.