Application of Wormlike Micelles for Mobility Control in Chemical Enhanced Oil Recovery

Abstract

Mobility control is one of the most important parameters in chemical enhanced oil recovery (CEOR). Hydrolyzed polyacrylamide (HPAM) polymer, the standard mobility-control agent, is often degradable and causes poor sweep efficiency under changing shear rates and at temperatures above 140 °F. Under these conditions, HPAM solution loses more than 90% of its viscosity and is unable to sustain appropriate viscosity necessary for residual oil displacement. Therefore, a wormlike micellar (WLM) solution was developed as a substitute mobility polymer for CEOR applications. The WLM solution is composed of chains, bonded by electrostatic forces, which can deform and reform rather than permanently breaking down when subjected to high shear rates and temperature fluctuations.

In this study, two compositions of WLM solutions were chosen and prepared in the laboratory. For each of these two solutions, their effectiveness was determined by comprehensive thermal compatibility tests; interfacial tests (IFT); and rheological tests to evaluate the impact of concentration, shear rates, salinity (NaCl = 3.5%, CaCl2 = 0.05%, and MgCl2 = 0.05%), and temperature (86 to 158 °F) on viscosity. Next, the core displacement test was performed to examine the residual oil displacement by a mixed-surfactant WLM solution (zwitterionic surfactant 1.09% w/v, R = 0.55).

Test results determined that both of the tested WLM solutions showed great potential in high-salinity and high-temperature conditions. Each of the two WLM solutions was equally adaptable and unrestricted, despite differences between the components of each formulation. With the addition of salts, the WLM solutions were highly tolerant over the entire range of shear rates. At 158 °F, the thermal degradability of WLM solutions was less than HPAM polymer. In addition to this, IFT between crude oil and WLM solution was also observed to be very low compared to the typical water-and-oil system. Moreover, the WLM solution produced an additional oil recovery of 10.9% beyond secondary recovery during the coreflooding test. Hence, the results supported WLM solutions to be potential mobility control for CEOR.

WLM solutions have been successfully shown to perform beyond the salinity, temperature, and shear-rate limitations of HPAM polymers. This makes WLM solutions more flexible, not only for EOR applications, but also for well completion, well stimulation, and for coiled-tubing cleanout processes following gravel-pack operations.