利用超声波方法确定地层含气原油的析蜡点

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

针对目前常见的析蜡点测试方法不适于地层条件下含气原油及对颜色较深的原油测试效果差的问题,利用超声波在不同介质中传播的声学特性,探索适用于不同性质原油析蜡点测试的方法。采用超声波测试时,随着实验温度降低,固体蜡晶从原油中析出,原油体系对超声波的衰减作用增强,观察到的首波频率将发生变化,将温度与首波频率曲线进行分段拟合,即可得到频率随温度变化的拐点即原油的析蜡点。采用该方法对某高凝油田地层含气原油和地面脱气原油样品进行了析蜡点测定,结果表明:超声波方法适用于地层含气原油和地面脱气原油析蜡点的测定,且不受原油颜色限制;随着压力降低,含气原油和脱气原油析蜡点均呈下降趋势,相同压力条件下含气原油的析蜡点比脱气原油的析蜡点低8℃左右;采用超声波方法测得的地层压力下含气原油析蜡点比常规测试方法获得的地面原油析蜡点低约3.7℃。

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.