Increasing the Viscosity of CO₂ to Improve EOR Performance

Authors: D. Xing, NETL; R. Erick, NETL and University of Pittsburgh Department of Chemical and Petroleum Engineering; K. Trickett, J. Eastoe, M. Hollamby, and K.Mutch, Bristol University School of Chemistry; S. Rogers and R. Heenan, ISIS STFC, Rutherford Appleton Laboratory, Chilton, UK; and D. Steytler, University of East Anglia School of Chemical Sciences, Norwich, UK.

Venue: May 20, 2009, ISASF-ENSIC 9th International Symposium on Supercritical Fluids, Bordeaux, France, May 18-20, 2009. http://www.issf2009.cnrs.fr/ [external site]

Abstract: About 1.5 billion standard cubic feet of CO2 is injected into US oil fields each day, resulting in the recovery of about 200,000 barrels per day of oil, but the low viscosity of CO2 results in viscous fingering and poor volumetric sweep efficiency. If the viscosity of dense CO2 could be increased by a factor of 2-20, much less CO2 would be required to recover the oil. Further, there would be no need for the injection of alternating slugs of water into the reservoir to reduce the relative permeability of the CO2. Researchers have identified two polymeric thickeners for CO2: a fluoroacrylate-styrene copolymer and a vinyl acetate-styrene copolymer. They have also hypothesized that it is possible to increase the viscosity (thicken) dense, high-pressure CO2 via the self-assembly of CO2-soluble surfactants into rod-like micelles. Three semi-fluorinated surfactants have been synthesized in order to test this concept; one with a monovalent cation and a single twin-tail, Na+1((COOCH2C4F8H)2CH2CHSO3)-1, and two with a divalent cation and two twin-tails, Ni+2(((COOCH2C4F8H)2CH2CHSO3)-1)2 and Co+2(((COOCH2C4F8H)2CH2CHSO3)-1)2. Phase behavior results indicate that all three surfactants are soluble to at least 5 wt% in CO2 at 295K and pressures less than 20 MPa. SANS results indicate that only the surfactants with divalent metal ions and two twin tails form cylindrical micelles in CO2. No viscosity enhancement was detected for the surfactant with the monovalent cation. Falling cylinder viscometry results will illustrate the degree of “CO2 thickening” that was achieved by the formation of rod-like micelles at relatively high shear rates. The mobility of the surfactant solution flowing through Berea sandstone was also provided to determine the effectiveness of the thickener at extremely low shear rates characteristic of enhanced oil recovery projects. The performance of the copolymeric and surfactant thickeners will be compared. The strategy for the development of CO2-soluble non-fluorous surfactants capable of forming rod-like micelles will also be presented.

Related NETL Project
This presentation is related to the NETL project DE-FG26-04NT-15533 “Synthesis and Evaluation of CO2 Thickeners Designed with Molecular Modeling.” The goal of this project is to use molecular modeling and experimental results to design inexpensive, environmentally benign, CO2-soluble compounds that can decrease the mobility of CO2 at typical enhanced oil recovery reservoir conditions.

Project Contacts
NETL – Thomas Gruber (Thomas.Gruber@NETL.DOE.GOV)
U. of Pittsburgh – Robert Enick (enick@engr.pitt.edu or 412-624-9649)