Research on gas desorption characteristics of carbon dioxide in crude oil

摘要

After gas channeling during CO₂ flooding, CO₂ gas content in the produced liquid will gradually increase. Research on desorption law of CO₂ in crude oil has not yet appeared in the literature. In the design of gas-liquid separator, in order to desorb CO₂ gas effectively, the retention time of produced liquid in gas-liquid separator has to be prolonged appropriately just based on the experience, and the effect is usually not good, leading to serious corrosion of the follow-up equipment. In this paper, the study key point is the desorption law of CO₂ in crude oil. The gas desorption experimental device of CO₂ flooding produced liquid is set up, using the method of depressurization for desorption, gas desorption process of the produced liquid in gas liquid separator can be simulated in the condition of gathering temperature and pressure. How the CO₂ desorption rate and desorption percentage change with time is determined. Finally, the desorption rule of CO₂ in water and crude oil is obtained. The experimental results show that at the moment of the depressurization, high desorption rate peak of CO₂ appears with short duration. What's more, with the pressure rapidly reducing, desorption rate is falling rapidly. During most of the time when the pressure is the atmospheric pressure, which is the end of the desorption pressure, desorption rate of CO₂ in water and crude oil are both below 0.025 Ncm3/(cm2·s), and respectively after 20.9 min and 58.60 min, their desorption rates reduce to zero, the desorption percentage reaching only 62.13% and 22.92%. CO₂ gas desorption from crude oil is more difficult than that from the water, and the higher oil content in produced liquid is, the more difficult the CO₂ gas desorption is. So even if the retention time of produced liquid in the separator is far more than that stated in the specification, most of CO₂ still cannot desorb from the produced liquid. By studying the characteristics of desorption of CO₂ in crude oil, it is found clearly that only relying on stepdown desorption and prolonging retention time of produced liquid in the separator cannot solve the problem of effective desorption of CO₂. It is recommended to take some measures in the process of gas liquid separation to promote gas desorption. Thus, this paper provides a theoretical basis for the further research on methods of gas desorption.