Investigation On The Measurement Of Gas Content In Live Heavy Oil And The Degassing Method

Live heavy oil is usually dehydrated by dynamic settling, rising bubbles in the settling tank cause interference to the settlement of water droplets. Thus, the dehydration efficiency severely declined. Rising bubbles consist of stable micro-bubbles and micro-bubbles from phase change. The former is mainly composed of inorganic gas such as N2, CO2 and H2 S carried in the mining process and lighter organic components C1-C4 in live heavy oil, which are gaseous at room temperature and atmospheric pressure. The latter mainly includes C5 and C6 hydrocarbons, which change from liquid to gaseous as temperature increases.This paper theoretically analyzed the factors influencing the gas content in live heavy oil. When pressure and oil thickness are constant, increasing temperature can enhance micro-bubbles rise up and if heated enough time, they can be removed completely. Based on which vapor pressure method was innovatively put forward to accurately measure the micro-bubble content. According to gas state equation of the initial state, the end of heating state and the state cooled to initial temperature, the content of the stable micro-bubbles and the micro-bubbles from phase change can be obtained. Meanwhile, gas content measurement system was developed based on vapor pressure method.The influence of temperature on micro-bubble content was experimentally studied with gas content measurement system. And the degassing method by stir, ultrasonic wave and strong centrifugation were respectively studied. Mainly conclusions are as follows:(1) Micro-bubbles in live heavy oil are mainly micro-bubbles from phase change and stable micro-bubble content is small. Temperature is the main factor affecting micro-bubble content and increase of temperature can effectively promote phase change and thereby decrease the total micro-bubble content. However, increasing treating time has no obvious promotion.(2) Overall size of stable micro-bubbles increases with increasing temperature while the stable micro-bubble content first increases and then decreases. The turning temperature is 70℃ in the experiment. The stable micro-bubble content increases with increasing treating time and the increase trend diminishes at certain temperature which is also 70℃ in the experiment, while overall size of stable micro-bubbles decreases and the decrease trend also diminishes as temperature rises.(3) Stir treating can promote the removal of stable micro-bubbles, but it inhibits the removal of micro-bubbles from phase change at low oil temperature. The inhibition fades with rising temperature. With the increase of treating time, the stable micro-bubble content slightly decreases while the content of micro-bubbles from phase change slightly increases. Total micro-bubble content keeps constant. Increase of both stir speed and stir treating time can enlarge the overall size of stable micro-bubbles.(4) Mechanical vibration and thermal function of ultrasonic wave can enhance micro-bubbles assemble, collide and coalesce into larger bubbles and can also decrease the intensity of interfacial film, promoting micro-bubble removal. However, the mechanism of cavitation is unclear. Thus, as ultrasonic intensity and treating time increase, micro-bubble content and the overall size has indefinite regulation.(5) Appropriate strong centrifugal treating can accelerate the removal of stable micro-bubbles. There is a critical value of the centrifugal acceleration. In the range of the critical value, increase of centrifugal acceleration and treating time can enlarge the overall size of stable micro-bubbles. However, when centrifugal acceleration exceeds the critical value, increase of centrifugal acceleration and treating time play an opposite role. The critical value decreases as temperature increases and is approximate 1500 g in 70℃ heavy oil and 1000 g in 80℃ heavy oil.