We have developed a new technique that utilizes microwave energy to study the phase behavior of mixtures at the extreme temperatures and pressures encountered in petroleum and natural gas reservoirs. Our technique measures shifts in a static microwave energy field caused by changes in sample properties on a phase boundary. The appearance of a second phase produces detectable changes in the microwave resonant frequency and power. The new method does not involve inaccurate or unsafe procedures such as visual observation of samples, interpolation of isochoric slopes, or compositional analysis of samples drawn from the sample cell. Only small sample cell volumes (<10 cm3) are required.

The microwave technique is effective with all types of fluids, light and heavy, nonpolar and polar, inert and corrosive, and it performs well at extreme conditions of pressure and temperature. A magnetic mixing pump enables preparation of homogeneous mixtures of fluids within the apparatus at experimental conditions. Measurements can be made at constant volume or at constant temperature. At constant volume, the microwave technique can determine phase boundary temperatures to better than 0.1 K. Pressure accuracy depends on the method of measurement. Results for phase boundary determinations of acid-gas mixtures with small amounts of heavy oils at high pressures and temperatures are presented.

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