Abstract
The spinning drop apparatus has been modified to measure interfacial tensions (IFT) at elevated pressures and temperatures. Interfacial tension properties of various surfactant solutions against a mineral oil and a California crude oil have been measured at elevated temperatures with this equipment. The surfactants included TRS 10–80, Igepal DM-730 and Petro step 465. The IFT of Igepal DM-730 against the crude oil shows a minimum at a temperature of 95°C and at a surfactant concentration of 5 g/l in a 10 g/l NaCl solution. With the same crude oil, Petro step 465 shows no temperature effect and the minimum IFT is obtained at a surfactant concentration of 2 g/l and a NaCl concentration of 10 g/l. The TRS 10–80 shows a somewhat similar behavior with respect to temperature, but the minimum IFT's and the corresponding salt and surfactanat concentrations to obtain them are different.
Introduction
The application of surfactant systems at elevated temperature has been the subject of several studies. Handy et al. described various aspects of usingsurfactants as additives in steam flooding. 1 In this application, the interfacial tension properties of surfactant-crude oil systems must beevaluated at elevated temperatures. Furthermore, data on the temperature dependence of the IFT of surfactants versus crude oil will be pertinent to careful design of chemical floods for reservoir temperatures above 100°C.
Two methods for measuring IFT properties of surfactant-oil systems have been described in the literature, the pendent drop and the spinning drop methods. The pendent drop method, developed by Andreas, Hauser, and Tucker2, has been modified for high pressure application by Harvey3 and for high temperature and pressure by Jennings4. Systems studied by these modified instruments have beenin IFT ranges significantly above the ultra-low IFT's required for improvingoil displacement with surfactants. The spinning drop method discussed byVannegut5, Silberberg6, Rosenthal7, Princen etal.8 was recently developed by Caylas et al.9 The proposed design included the capability for variable speed tensiometry. Gashand Parrish10 introduced a fixed speed spinning drop tensiometer and reported satisfactory results at a speed of 3600 RPM. No work has yet beenreported on the extension of the design of the spinning drop method for use at high temperatures.
In this study, problems associated with high temperature application of the spinning drop method were considered. The equipment was modified to extend the operation of a fixed speed system to temperatures up to 250°C. The modified quipment was used to study the IFT behavior of three surfactants versus a crude oil and one surfactant versus a mineral oil.
Apparatus
A constant speed (3600 RPM) spinning drop apparatus was modified for high temperature application by addition of a temperature air bath and the development of a technique for sealing the fluids within the capillary tubes to withstand high temperatures and pressures. As shown in Fig. 1, the capillarytubes operate within the air bath (A) made of a 3/4" thick Marinite mix (anasbestos-free insulator) with a capability of maintaining the temperature as high as 600°C (~1100°F). Vanes (B) placed inside the air bath were intended to maintain uniform temperature throughout the system. Temperature was measured beside the capillary tubes (E) using J type thermocouples (F) and read on a digital recorder (G).
The fluid content within the capillaries must be contained at high temperatures and pressures. The open end of the capillary tubes were sealed with a high temperature epoxy, Fig. 2. The epoxy hardens quickly and is capable of withstanding pressures up to 5.9 MPa. The epoxy seal can easily be drilled out to permit the re-use of the tubes.
Improving the Thermal Stability of Hydrophobic Associative Polymer Aqueous Solution Using a “Triple-Protection” Strategy