|Small Molecular Associative Carbon Dioxide (CO2) Thickeners for Improved Mobility Control
||Last Reviewed 5/27/2014
The overall research goal is to test the effectiveness of a compound (CO2 thickener) that can induce very large changes in CO2 viscosity at typical injection and reservoir conditions associated with Carbon Dioxide Enhanced Oil Recovery (CO2-EOR).
The study consists of two phases. Phase 1 objectives are to (1) obtain commitment letters from CO2-EOR operators to provide field samples (oil, brine, and core) and field operating conditions from active or planned CO2-EOR floods and (2) develop laboratory test plans for Phase 2 testing. The Phase 2 objective is to assess compounds with a demonstrated ability to both dissolve in and thicken CO2 for CO2 mobility reduction and increased oil recovery over a wide range of operational and field conditions.
University of Pittsburgh, Pittsburgh, PA 15260
Although large-scale CO2-EOR is practiced domestically, the potential for expansion is enormous. The single greatest obstacle to fully realizing that potential is the inherently poor volumetric sweep efficiency of the process. The very low viscosity of high pressure CO2 is problematic for EOR projects by exacerbating CO2 gravity override and inducing viscous fingering, early breakthrough, poor sweep efficiency, and high CO2 injected to oil recovered ratios.
Most of the CO2-EOR projects in the U.S. are in carbonate reservoirs, which tend to have high- permeability layers or networks of very high permeability fractures intermixed with low permeability layers or zones. In these stratified formations, the low CO2 viscosity causes conformance control issues by promoting the flow of a significant portion of the injected CO2 into the higher permeability, watered-out zones while a much smaller fraction of the CO2 enters the lower permeability, oil-bearing zones of interest. High CO2 mobility within these portions of the reservoirs results in very low sweep efficiencies.
A recently completed DOE-sponsored extensive literature review of strategies for improved mobility and conformance control during CO2 floods indicated that the state-of-the-art technique for mitigating the unfavorable mobility ratio remains the water-alternating-gas (WAG) process. Rather than implementing WAG or SAG processes that require substantial amounts of water in an attempt to lower gas permeability, the University of Pittsburgh researchers intend to dissolve a dilute (<1wt percent) amount of a “thickener” or “viscosifier” in the CO2, thereby yielding a transparent, thermodynamically stable, high pressure CO2-rich phase that is significantly more viscous than pure CO2. This research is being funded through a DOE ARPA-E project which if successful, will provide the compounds for testing under NETL’s project FE0010799.
The focus of the project is to design, synthesize, and characterize a CO2 thickener that costs less than $10/lb yet can be manufactured at a large scale. By dissolving a dilute amount of a “thickener” or “viscosifier” in the CO2, a transparent, thermodynamically stable, high pressure CO2-rich phase is created that significantly increases viscosity over pure CO2. Carbon dioxide gravity override, viscous fingering, production well early CO2breakthrough, poor sweep efficiency, and high injected CO2 to oil recovered ratios are significantly reduced in the process.
More than 90 percent of CO2-EOR floods employ water-intensive WAG processes for mobility control creating a wide market for a CO2 thickener. A CO2 thickener has long been recognized as a game-changing, transformative technology because it has the potential to eliminate water injection for mobility control. Some of the remaining 10 percent CO2-EOR projects that do not employ WAG are still plagued by mobility control issues. Therefore the design of an economic CO2 thickener remains an extremely relevant aspiration for continued research. These factors contribute to increased oil recovery, better recovery economics, and reduced environmental impacts.
Final project negotiations were completed and the project was recently awarded. Letters of Commitment have been obtained from Denbury Resources, Kinder Morgan, and Tabula Rasa. Negotiations are in progress with Conoco Phillips for another Letter of Commitment. Discussions are ongoing with Denbury Resources concerning the equipment requirements for a field trial. Denbury appears to be the company most interested in pursuing a field trial.
Current Status (May 2014)
Carbon dioxide EOR operators have been contacted to obtain letters of commitment (from a minimum of three operators) to provide core, oil, and brine samples as well as the necessary field data (e.g., pressure and temperature) from representative field(s) where the thickener would potentially enhance oil recovery. The operators’ willingness to participate in a future field test—either a single well injectivity test or small-scale pilot test—will be determined to the extent possible. Denbury Resources, Kinder Morgan, and Tabula Rasa have sent letters of commitment. A non-disclosure agreement with Conoco Phillips has been completed and negotiations with them to obtain a letter of commitment are on-going. Contact has been made with Daikin, the manufacturer of a new environmentally benign fluoroacrylate, which is the main component of the polyFAST thickener (that was originally developed with a fluoroacrylate that was biopersistent and an environmental risk); Daikin representatives have visited the research group three times during the last year. Detailed laboratory testing plans that simulate EOR flooding for the most promising CO2 thickeners developed under APRA-E funded research are also being developed.
Project Start: October 1, 2012
Project End: September 30, 2015
DOE Contribution: $1,200,000
Performer Contribution: $300,000
NETL – Gary Covatch (email@example.com or 304-285-4589)
University of Pittsburgh – Robert Enick (firstname.lastname@example.org or 412-277-0154)
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Quarterly Research Progress Report [PDF-437KB]
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