Experimental Research On Heavy Oil Stability Evaluation Method Based On Asphaltene Phase Separation

Asphaltene is the largest molecular weight and the most polar component of the heavy oil. Asphaltene phase separation behavior caused by heavy oil instability brings many problems to the various processes in production industry, such as transportation, reserving, refining and so on. This problem has not been effectively solved up to now. Therefore, a simple and effective method needs to be established to inspect asphaltene stability and to support production industry.The first part of the paper describes about the theory of the decomposition mechanism of asphaltene. The deposition model is based on the macromolecular theory of polydisperse polymer, colloidal solutions, kinetics of aggregation and electrokinetic transport phenomena. N-alkane asphaltene precipitation mechanism shows that small alkane molecues cause the precipitation by changing the interaction between colloidal nucleus and solvent, while large molecules of alkane are making resin molecules by desorption from the asphaltene surface. Heavy oil asphaltene separation factors such as heavy oil composition, temperature and pressure as well as the precipitating agent are analyzed for knowing their influences.Secondly, evaluation method of heavy oil stability is studied through the experiment. Two kinds of heavy oil used on board are chosen as the research object. By studying on variation of asphaltene particle ratio during the separation process, the result shows that asphaltene particles whose sizes are beyond40μm deposit within1Ominutes, and these particles occupy the majority of the total number of particles. Thus, the transmittance is measured every0.04mm. According to the results, the changes of heavy oil transmittance during asphaltene phase separation process can be determined. The result shows that the initial low transmittance is due to the large particle asphaltene, and later the transmittance is increased, but small particles asphaltene still affect the transmittance. Build up a mathematical model between the heavy oil stability and change of transmittance to evaluate the stability of heavy oil. As asphaltene falls out of the solution, the transmittance increases. If the process is quick, resulting in a high separability number. A high separability number shows that the stability of heavy oil is poor. Finally the feasibility of the device is proved by showing the data of experiment is laying within the range of error limit.