|Use of Polymers to Recover Viscous Oil from Unconventional Reservoirs
||Last Reviewed 11/1/2011
The goal of this three-year research project is to develop methods using water soluble polymers to recover viscous oil from unconventional reservoirs (e.g., on Alaska’s North Slope).
New Mexico Institute of Mining & Technology, Socorro, NM 87801
Alaska’s North Slope contains a very large unconventional oil resource—over 20 billion barrels of heavy/viscous oil. Conventional wisdom argues that thermal recovery methods are most appropriate for recovering viscous oils. However, for viscous oil reservoirs at Alaska’s North Slope, a number of factors complicate this thinking. The formations that hold vast viscous oil reserves— Ugnu, West Sak, and Schrader Bluff—are relatively shallow and therefore close to permafrost. Steam generation is prohibitive here due to severe cold weather on the surface, heat losses while pumping steam down through 700 to 2,200 ft of permafrost, heat losses when contacting the cold formation, and environmental considerations.
Miscible gas injection and water-alternating-gas have been proposed and attempted, with some success, as ways to reduce the viscosity and enhance displacement in some North Slope reservoirs. However, this displacement is characterized by a remarkably unfavorable mobility ratio. Therefore, the current technology is confined to the least viscous of the North Slope’s heavy oils. The availability of natural gas for miscible EOR purposes may be restricted by the potential construction of a gas pipeline to the lower 48 states.
This project will identify a wider range of conditions (especially regarding the limits of oil viscosity) for application of polymer flooding. It should specifically open opportunities for increased oil recovery in North Slope viscous oil reservoirs. New methods will be developed to improve injectivity during polymer injection for fractures/horizontal wells without compromising sweep efficiency. In fact, opportunities for enhancing sweep efficiency may be realized. The studies of polymer properties versus permeability will identify the most suitable polymer(s) for cost-effectively improving sweep in North Slope viscous oil reservoirs. The project will establish whether a newly identified mechanism using viscoelastic polymers can be useful for reducing residual oil saturations in North Slope reservoirs below the values possible from waterflooding. If induced fracturing or formation parting proves to be detrimental, the project will develop a means to correct these problems using gel treatments. This project will also compare the viability of a “Bright Water” type of process with that of normal polymer flooding when applied to North Slope reservoirs with viscous oils. All of the above information will be valuable in establishing the most cost-effective path forward to develop Alaska heavy oil resources.
- Extensively evaluated new hydrophobically associative polymers for use in enhanced oil recovery.
- Showed that it is important whether or not polymers reduce residual oil saturation.
- Demonstrated that a conventional HPAM polymer can reduce the residual oil saturation (for 190-cp North Slope crude) by up to 6 saturation percentage points at a fixed capillary number.
- Identified conditions when polymer flooding is superior to “Bright Water”.
- Prepared and presented two papers at the SPE/DOE IOR Symposium, one at the Arctic Technology Conference, and one at the SPE International Oilfield Chemistry Symposium.
- Four papers were accepted for publication: Two in SPE Reservoir Evaluation and Engineering, one in SPE Journal, and one in the American Oil and Gas Reporter.
- Using North Slope fluid and relative permeability data, used fractional flow calculations to show that polymer flooding may have considerable potential in recovering viscous North Slope crudes, even at $20/bbl.
- Characterized rheology in a viscometer and in porous media with permeabilities from 55 to 5120 md for nine commercially available polymers, including xanthan, diutan, and polyacrylamides.
- Injectivity reductions associated with injecting the above polymer solutions into North Slope horizontal and vertical wells were estimated.
- Demonstrated that the key limitation for polymer flood application is reduced injectivity, not chemical costs.
- Demonstrated that both xanthan and partially hydrolyzed polyacrylamide (HPAM) polymers have a very high molecular weight component that artificially causes high resistance factors and shear thinning behavior at low flux in short cores. This component is not expected to propagate deep into a reservoir.
- Demonstrated that shear thinning behavior does not significantly harm vertical sweep efficiency.
Current Status (October 2011)
The project has been completed and the final report is available below under "Additional Information".
Project Start: October 1, 2008
Project End: September 30, 2011
DOE Contribution: $1,012,035
Performer Contribution: $505,259
NETL – Sinisha (Jay) Jikich (Sinisha.Jikich@netl.doe.gov or 304-285-4320)
New Mexico Institute of Mining & Technology – Dr. Randy Seright (firstname.lastname@example.org or 575-835-5571)
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Final Project Report [PDF-1.82MB]