Interfacial Tensions and Visual Interactions of Crude Oil-Brine-CO Systems Under Reservoir Conditions

Abstract

In this paper, an experimental technique is developed to study the interfacial tension phenomenon and visual interactions of crude oil-brine-CO 2 systems at different pressures and temperatures. The major component of this experimental set-up is a see-through windowed high-pressure cell. By using the axisymmetric drop shape analysis (ADSA) for the pendant drop case, this new technique makes it possible to determine the interfacial tension (IFT) and to visualize the interfacial interactions among crude oil, brine and CO 2 under practical reservoir conditions. More specifically, IFT of the crude oil-brine-CO 2 system is measured as a function of pressure and temperature, respectively. For the crude oil-CO 2 system, it is found that the dynamic IFT gradually reduces to a constant value, i.e., the equilibrium IFT. Meanwhile, a number of important physical phenomena are observed after the crude oil is made in contact with CO 2 . In particular, the oil swelling effect, light-ends extraction, initial turbulent mixing and wettability alteration are the major characteristics of the CO 2 flooding processes. There always exists a constant low IFT (i.e., partial miscibility) as long as the pressure is higher than a threshold value. No ultra low or zero IFT between the crude oil and CO 2 is found, regardless of the operating pressures and temperatures tested in this study. For the crude oil-brine-CO 2 systems, wettability between crude oil and needle surrounded by CO 2 -saturated brine phase is different from that of the crude oil-CO 2 systems. In addition, immiscibility between CO 2 -saturated crude oil and CO 2 -saturated brine is still observed at P=28.196 MPa and T= 58°C. Therefore, this laboratory study shows that partial miscibility between the crude oil and CO 2 occurs in the reservoirs and that wettability alteration may considerably improve the oil recovery in a water-wet reservoir during CO 2 flooding processes.

Oil Recovery Performance of Immiscible and Miscible CO2 Huff-and-Puff Processes

“…Various studies have suggested that low IFT between the injected fluid and reservoir oil can improve sweep efficiency and reduce residual oil saturation. 18,19 In CO 2 -based EOR techniques, at specific thermodynamic conditions (i.e., pressure, temperature, and composition), the IFT of the crude oil−CO 2 system decreases to sufficiently low values which leads to a more favorable displacing process. 18 In this study, the axisymmetric drop shape analysis (ADSA) technique for the pendant drop case was applied to determine the IFT between the crude oil and CO 2 .…”

“…Interfacial tension (IFT) between an injected phase and reservoir oil in-place significantly affects the performance of EOR techniques. Various studies have suggested that low IFT between the injected fluid and reservoir oil can improve sweep efficiency and reduce residual oil saturation. , In CO 2 -based EOR techniques, at specific thermodynamic conditions (i.e., pressure, temperature, and composition), the IFT of the crude oil–CO 2 system decreases to sufficiently low values which leads to a more favorable displacing process …”

Evaluation of Polymers as Direct Thickeners for CO2 Enhanced Oil Recovery

“…It is well-known that during CO 2 flooding, the oil−CO 2 two-phase flow is largely controlled by their interfacial interactions, such as the interfacial tension (IFT) . However, no experimental tests were conducted to study the effect of a polymer or thickener dissolved into CO 2 phase on the equilibrium IFT of a crude oil−polymer-thickened CO 2 system.…”