Abstract:

CO₂ enhanced oil recovery (CO₂-EOR) technique is a good choice that can not only limit global warming, but also cut the high cost of carbon capture and storage (CCS). CO₂ flooding produced fluid contains large amounts of CO₂ and a lot of foam will generate in the separation process due to decompression. To study the foaming characteristics of CO₂-crude oil system in oilfield separators, an experimental system was designed to simulate the real environment. Depressurization method was used to study the foam behavior in the tests. The foaming process of dissolved crude oil could be divided into depressurization stage and stable working pressure stage. Foam evolution from generation to attenuation was recorded by high-speed camera, and foam behaviors at different stages were summarized and analyzed. Foaming process could be divided into five stages: bubble formation, arrangement with single layer, bubble coalescence, bubble breakage and multilayer stack. As pressure decreased, the diameters of stable bubbles increased and the foam position moved upwards, and foaming behavior became more violent. In addition, foam form in crude oil belonged to spherical foam and the Gibbs-Marangoni effect of foam was found in the tests. The attenuation mechanism and influencing factors of CO₂ foam were analyzed and it was found that gas diffusion was the main mechanism for CO₂ foam attenuation. Furthermore, the effects of depressurization rate and stirring rate on the properties of foam were studied. The results show that the increase in depressurization rate had no obvious effect on the foaming behavior in depressurization process while it would aggravate the foaming behavior under stable working pressure. When the rotation speed is less than or equal to 120 r/min, the increase of the stirring rate will aggravate the foaming behavior in the depressurization stage, but accelerate the foam decay under stable working pressure.

Key words: carbon dioxide, petroleum, foam, separation, decompression, stirring

摘要：

为研究CO₂驱油田分离器内泡沫层产生及消除机理，设计了一套高压溶气原油泡沫测试系统，采用降压法研究了CO₂-原油体系的发泡特性。利用高速摄像机对泡沫产生至衰变的演变过程进行了记录，总结分析了不同降压阶段的气泡行为，研究了降压速率和搅拌速率对原油发泡特性的影响规律。研究发现，随压力降低，稳定存在气泡的直径增大，气泡位置上移，发泡行为更加剧烈；降压速率增加对降压阶段的发泡行为无明显影响，但会加剧稳定工作压力下的发泡行为；在转速小于等于120 r/min的条件下，搅拌速率增加会加剧降压阶段的发泡行为，但会加速稳定工作压力下的泡沫衰变。

关键词: 二氧化碳, 石油, 泡沫, 分离, 降压, 搅拌