Experimental Study On Physical And Chemical Mechanisms Of Foamy Oil Formation

Some heavy oil reservoirs under primary recovery by solution gas drive exhibit anomalous behavior: high oil production rate,low production GOR,high oil recovery,which aroused a wide range of attention.Many researchers have done a lot of researches on this phenomenon and describe it as “foamy oil”.However,the reasons why foamy oil only appears in some special heavy oil reservoirs still cannot be explained.In addition,the inherent mechanisms that dissolved gas can be dispersed in crude oil in the form of tiny bubbles for a long time are lack of relevant research.Therfore,in-depth study of the physical and chemical mechanism of foamy oil formation is of great significance.In this paper,the micro-media experiments were carried out to simulate the solution gas drive process of three heavy crudes,and the bubbles’ flow characteristics were observed in these processes.Moreover,this paper designed a new experimental device to evaluate the stability of foamy oil oil-gas interface.Different influencing factors such as temperature,ambient gas type,film diameters,pressure,and oil fractions were considered in this experiment.On this base of film lifetime experiments,this paper presents a prediction model which is based on classical nucleation theory to simulate the rupturing process of the bubbles in foamy oil.At last,this paper measured the physical properties,chemical composition,and structural parameters of foamy oil,conventional heavy oils and their active components.Through the experimental results,the relationship between those charicteristics and the special oil-gas interface properties of the foamy oil were explored.Therefore,the machanisms of foamy oil formation were revealed.The results indicate that the foamy oil phenomenon is due to the stable oil-gas interface in the foamy oil heavy crude.And the interface stability decreases with the incresement of temperature and area.Asphaltene in heavy crudes,as a natural active component,plays a key role in stabilizing the oil-gas interface in the foamy oil phenomenon.High asphaltene concentration with more polar functional groups(hydroxyl groups,carboxylic groups,amine,and heterocyclic rings)could be the special nature of oil responsible for foamy oil formation.Meanwhile,the prediction model based on classical nucleation theory can be applied to study the rupture mechanism of single film.