Interfacial Tensions and VisualInteractions of Crude Oil-Brine-CO2Systems Under Reservoir Conditions

摘要

In this paper, an experimental technique is developed tostudy the interfacial tension phenomenon and visualinteractions of crude oil-brine-CO2 systems at differentpressures and temperatures. The major component of thisexperimental set-up is a see-through windowed high-pressurecell. By using the axisymmetric drop shape analysis (ADSA)forthe pendant drop case, this new technique makes it possible todetermine the interfacial tension (IFT)and to visualize theinterfacial interactions among crude oil, brine and CO2 underpractical reservoir conditions. More specifically, IFT of thecrude oil-brine-CO2 system is measured as a function ofpressure and temperature, respectively. For the crude oil-CO2system, it is found that the dynamic IFT gradually reduces to aconstant value, I.e., the equilibrium IFT. Meanwhile, a numberof important physical phenomena are observed after the crudeoil is made in contact with CO2.In particular, the oil swellingeffect, light-ends extraction, initial turbulent mixing andwettability alteration are the major characteristics of the CO2flooding processes. There always exists a constant low IFT (I.e., partial miscibility)as long as the pressure is higher than athreshold value. No ultra low or zero IFT between the crude oiland CO2 is found, regardless of the operating pressures and temperatures tested in this study. For the crude oil-brine-CO2systems, wettability between crude oil and needle surroundedby CO2-saturated brine phase is different from that of the crudeoil-CO2 systems. In addition, immiscibility between CO2-saturated crude oil and CO2-saturated brine is still observed atP=28. 196 Mpa and T=58℃. Therefore, this laboratory studyshows that partial miscibility between the crude oil and CO2occurs in the reservoirs and that wettability alteration mayconsiderably improve the oil recovery in a water-wet reservoirduring CO2 flooding processes.