Experimental research has been performed on the viscosity change of crude oil during the process of water displacement. The diffusion of light hydrocarbons from crude oil into water was simulated. The effect of simulated formation water on crude oil viscosity after oilwater contact was determined. The results show that during water displacement process, the fact that light hydrocarbons dissolve into water and are output with water was an importance reason for the increase of crude oil viscosity. The results could be helpful for effectively controlling crude oil viscosity, decreasing water-oil mobility ratio and enhancing water displacement efficiency.
Viscosity is an important property for crude oil. Data from production has indicated that during flooding process the viscosity of crude oil increases with the extent of crude oil production. At some point, crude oil viscosity may be as twice as the original viscosity. The viscosity rise results in the increase of water-oil mobility ratio, which causes oil production more difficulty.
An experimental apparatus has been designed to carry out simulation study on this phenomenon. The results show that the component change in crude oil is the main reason for crude oil viscosity variation. The component change of the crude oil is caused by the fact that lighter hydrocarbon was dissolved in water and flowed out with output liquid. The study can be useful for effectively controlling crude oil viscosity, decreasing water-oil mobility ratio and enhancing water displacement efficiency in oil production.
There have been some reports on the phenomenon of crude oil viscosity increase during water displacement process, with the increase of water hold-up and the amount of oil produced. However, only qualitative analysis can be found but no research by quantity has been reported. Most research on crude oil viscosity change has been focused on the area of reducing crude oil viscosity by miscible phase injection and gas injection (including natural gas, carbon dioxide, nitrogen). Some research has been reported on improving crude oil mobility by mixing light hydrocarbon and crude oil, and on the relationship between gas solubility and crude oil viscosity . For instance, Bu Xing Han and et al studied that dissolving methane carbon dioxide and nitrogen into heavy oil to decrease crude oil viscosity and to enhance recovery ratio.
Data from production shows that crude oil viscosity has close relations with water holdup and oil recovery in water displacement process. For example, in Guan-Tao formation of Gu-Dao oil field, crude oil viscosity had increased 180% from 1975 to 1991. A similar phenomenon was observed in Sheng-Tuo oil field as well. In addition to pressure, temperature, oxidation and others factors, the crude oil viscosity variation could be significantly resulted from the decrease of light hydrocarbon in crude oil. As the light hydrocarbon dissolves in water and flows out with output liquid, thelight hydrocarbon in crude oil is decreased.