A Laboratory Study of Surfactant Flooding Performance Using a Modified Micromodel for Chemical Enhanced Oil Recovery (cEOR) Application: Capillary Desaturation Curve (CDC)

Abstract

Previous studies show that surfactant flooding in enhanced oil recovery substantially increases oil recovery due to the reduction of interfacial tension and alters the wettability of reservoir rock. The capillary desaturation curve (CDC) is often used to represent surfactant flooding performance in the laboratory study, which correlates the relationship between residual oil saturation changes and capillary number. There are many equations to define the capillary number. However, one well-known is the ratio between viscous force (fluid viscosity and injection rate) and capillary force (interfacial tension between two immiscible fluids).

In this study, two surfactant commercials have been analyzed to determine the surfactant flooding performance regarding the reduction of residual oil saturation as the effect of changes in capillary number. To increase the capillary number, we modify the interfacial tension between surfactants and crude oil until reaching the ultra-low IFT region so that the capillary number can increase up to three-five orders of magnitude. Then, the reduction of residual oil saturation, which leads to increased oil production, has been analyzed during the changes in capillary number.

In addition, we use a transparent modified micromodel that enables us to monitor the fluid moves in porous media lively. Advanced digital image analysis (DIA) was then used to quantify the residual oil saturation in the micromodel.The study is divided into two parts; static test (fluid-to-fluid compatibility) and dynamic test (fluid-to-rock interaction). The static test includes CMC-IFT which determine the optimum concentration to get the lowest IFT between surfactant solution and crude oil. Finally, dynamic tests for surfactant flooding have been observed using a modified micromodel to visualize the fluid displacement in the porous media. The analysis of initial oil saturation, residual oil saturation, water saturation and surfactant saturation are determined and calculated accurately using digital image analysis.

The result shows that the interfacial tension between surfactant solutions and crude oil directly impacts reducing oil saturation, leading to higher oil recovery. However, the lowest IFT does not guarantee the highest oil recovery, which might not conform to the existing fundamental theory. The laboratory result shows that a particular capillary number increment is adequate for higher oil recovery.

The study uses a modified micromodel that enables us to monitor the fluid moves in porous media lively. In addition, this method is quite simple and low-cost efficient but powerful, accurate, and fast compared to the conventional coreflood test. We also added quartz and cement to mimic the native core from the reservoir so that the detailed fluid-to-rock interaction can be captured in the study.