Visualization Investigation of the Mechanisms of Higher Quality Heavy Oil Recovery by Dense CO2 Injection

摘要

The efficiency of primary recovery from heavy oil reservoirs is low due to their nature of high oil viscosities and low dissolved gas contents. Because of a substantial reduction in the oil viscosity,CO2 injection would be a potential solution to enhance recovery from heavy oil reservoirs. Many heavy oil reservoirs are shallow and likely to have a low temperature. Under the conditions of those reservoirs,CO2 would be a dense liquid or supercritical fluid. Another benefit of dense CO2 injection could be a favorable improvement in the physical properties of the recovered oil. It appears that the mechanism of extraction of light and intermediate components of the oil by CO2 causes the changes in the properties of recovered oil. To identify the processes that affect the physical properties of heavy oil,the contact between CO2 and heavy oil was visually investigated under reservoir conditions. In addition,several experiments were performed using a transparent micromodel setup to understand the impact of the extraction of oil components on the flow in porous media. As CO2 contacts the oil,the extraction of hydrocarbons,mostly methane at the beginning,from the oil starts immediately. The extraction of hydrocarbons by CO2 initially leads to a sudden swelling of the oil mainly because of the liberation of the dissolved gas from the oil. Consequently,an accumulation of the light and intermediate compounds of the oil takes place in the oil phase,near the interface of the oil and CO2. The results of the direct visualization of the flow reveal that the contact of CO2 and heavy oil results in the formation of a different oil-rich phase. This light and less viscous oil-rich phase has a relatively lighter color than the oil in contact with CO2 and it is significantly mobile in pore spaces.