N. Gurusinghe, G. Ramadan, M. Liebum, Q.P. Nguyen
The University of Texas at Austin, United States
pp. 80 - 83
Keywords: viscoelasticity, high salinity, porous media, apparent viscosity, new switchable surfactants, mobility control
The use of viscoelastic (VES) or polymer-like surfactant solutions are important in applications related to enhanced oil recovery and subsurface conformance control. VES resembles polymer where it acts as a mobility control agent to promote a better sweep efficiency by increasing the waterflood’s viscosity . However unlike polymer, VES is able to sustain viscoelasticity when encounter with high saline, high temperature reservoirs . In particular, viscoelastic properties of VES could be modified and controlled with different physical factors such as salinity, surfactant concentration, pH, and temperature of the solution . These characteristic can be decoupled systematically using a rheometer to measure the bulk rheology of the solution. The objective of this study is to determine if the bulk rheology data can predict the rheological behavior in porous media. This study was conducted to mathematically express the correlation between bulk viscosity and apparent viscosity in porous media for a novel switchable surfactant. Steady state shear rate in outcrop carbonate cores was derived from the injection rate applied to the core and bulk rheology. Therefore, comparisons can be established between both rheology sets at the same shear rates. The rheological behavior of the bulk and the core flood for a 0.5% wt. surfactant and 20% wt. NaCl solution was found to be contradicting of one another (Figure 1). Bulk rheology data resembles shear thinning behavior while apparent viscosity in the cores thickened with increasing shear rate. This thickening phenomenon could be attributed to the large pressure drops at high injection rates, permeability reduction, extensional flow, and surfactant retention in the carbonate rock . The observed non-newtonian rheology of this particular VES at high salinity is quite different from conventional polymeric solutions for subsurface applications whose rheology is quite consistent between bulk rheometry and core flood. These striking findings suggest that porous media applies complexity to rheological behavior, which requires thorough evaluation to define the underlying effects that alter the viscoelastic properties.