Measurement of the WAT of waxy oil under the reservoir condition with ultrasonic method

To solve the problem that wax appearance temperature (WAT) acquired by conventional method is not suitable and effective to the subsurface live crude oil and dark oil, a way to measure the WAT of crude oil varying in properties is explored using the characteristics of ultrasonic transmission through media. In WAT measurement with ultrasonic, as the temperature of crude dropped, solid wax crystallized from the crude, the decline effect of crude oil to ultrasonic would be strengthened during the measurement by ultrasonic. The head wave frequency changed during the process; the frequency turning point was the wax precipitation point that could be obtained through segmental fitting of temperature and main frequency. This method was adopted to attain the WAT of the live oil at the reservoir condition and stock tank oil with high pour point and the results indicate that this method is reliable and not restricted by the color of oil. With the decrease of pressure, the WATs of live oil and dead oil both reduce, the WAT of live oil is 8 ℃ lower than that of dead oil under the same pressure. The WAT of live oil at the reservoir pressure measured by ultrasonic is about 3.7 ℃ lower than that of the stock tank oil measured by conventional method.