Abstract: To address the problem of low accuracy of wax precipitation point testing of high-pressure wax-bearing condensate gas in the gas phase, a set of high-pressure visualized fluid phase change observation device based on polarized light microscopy method was developed with reference to the preferred viscosity-temperature curve method, differential scanning calorimetry method and polarized light microscopy method to experimentally study on the wax precipitation point law of the wax-bearing condensate gas well fluid and gas-bearing oil under different pressures. The result shows: The wax precipitation point measured by polarized light microscopy method is more accurate than that by the viscosity-temperature curve method and differential scanning calorimetry method. The newly developed high-pressure visualized fluid phase change observation device can accurately test the wax precipitation point of wax-bearing condensate gas well fluid and gas-bearing oil. The wax precipitation point of the wax-bearing condensate gas well fluid first decreases and then increases with the increase of pressure, and then decreases after passing the dew point, and the wax precipitation line divides the well fluid wax precipitation phase diagram into such four parts as the single gas phase, gas-liquid phase, gas-solid phase and gas-liquid-solid phase; the wax precipitation point of gas-bearing oil first decreases with the increase of pressure, and begins to increase linearly when the pressure increases to the saturation pressure. The research results provide a new method for accurate test of the wax precipitation point of high-pressure wax-bearing condensate gas.

Key words: wax-bearing condensate gas, phase state, wax precipitation point, polarized light microscope, high-pressure gas reservoir