Trapping of Micellar Fluids in Berea Sandstone

Delshad, Mohammad
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The objective of this research was to experimentally investigate transport properties such as capillary trapping, relative permeability, dispersivity, and capacitance parameters of micellar fluids under single-and two-phase flow conditions. Low interfacial tension, brine-oil-surfactant-alcohol mixtures with different compositions and salinities were prepared at 30°C. Equilibrated phases (micellar fluids) were separated and used for displacements in Berea sandstone cores. The relation between residual phase saturation and capillary number of these micellar fluids was investigated. For all three types of phase environment, and regardless of which phase was the displacing phase, residual saturations and end-point relative permeabilities for each phase followed the same trend with capillary number. Residual microemulsion also followed the same trend with the capillary number when displaced simultaneously by excess-oil and brine. Steady-state two-phase flow relative permeabilities were measured at constant capillary number. The brine and oil relative permeability curves were concave up (positive second derivative) while that of microemulsion was concave down. The relative permeability curve for microemulsion was above those of brine and oil. Relative permeability data were compared with two relative permeability models. The first model is a simple Corey-type relative permeability model with the saturation exponents treated as adjustable parameters. The second model is a theoretical relative permeability model proposed by Foulser et al. [F5] called the droplet model. The parameter N (number of droplets in each capillary tube) was selected such that the standard error would be minimum. Comparisons were made over a range of capillary numbers and viscosity ratios. Continuous and slug displacement of radioactive tracers, both partitioning and non-partitioning, were also performed at steady-state. Effluent tracer profiles were compared to the numerical solution of a capacitance-dispersion model to estimate saturations, dispersivities, and capacitance parameters. Unlike brine and oil phases, the microemulsion phase did not show a capacitance behavior. Phase by-passing increased as the phase cut was decreased.