|Small Molecular Associative Carbon Dioxide (CO2) Thickeners for Improved Mobility Control
||Last Reviewed 12/9/2014
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 on 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 CO2 breakthrough, 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 of its potential to eliminate water injection for mobility control. Some of the remaining 10 percent of 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 research aspiration. These factors contribute to increased oil recovery, better recovery economics, and fewer environmental impacts.
Letters of commitment have been obtained from Denbury Resources, Kinder Morgan, Tabula Rasa, and Conoco Phillips. Discussions are ongoing with Denbury Resources concerning the equipment requirements for a field trial because Denbury appears to be the company most interested in pursuing one. In fact, a small single-well test of high-pressure pumps and static mixers to introduce CO2-soluble additives was conducted at a Denbury field under Dr. Enick’s direction. Project personnel have made four presentations concerning this work at SPE, AIChE, and ACS conferences. Dr. Enick also received a request from Kinder Morgan, a major CO2 EOR operator, to consider recommending a natural gas liquid (NGL) (propane-heptane) thickener for a hydrocarbon miscible flood in the Yates field. Because propane is easier to thicken than CO2, and because many of the CO2-thickener candidates should work more readily in propane, plans are being made to deliver a recommendation for an NGL thickener to Kinder Morgan.
Current Status (December 2014)
Carbon dioxide EOR operators have been contacted for letters of commitment 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, Tabula Rasa, and Conoco Phillips have sent letters of commitment. Contact has been made with Daikin, the manufacturer of a new environmentally benign fluoroacrylate, which is the main component of the polyFAST thickener (which 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. Injection pumps and static mixers for use in adding a thickener to a CO2 pipeline were tested in association with Denbury Resources. Detailed plans for simulating EOR flooding in the laboratory using the most promising CO2 thickeners developed under ARPA-E funded research are also being developed. Phase 1 of this NETL project has been completed. A one-year no-cost extension to determine the optimal thickener (designed using ongoing ARPA-E funding) for use during Phase 2 of this NETL study (coreflood-intensive work) was requested and granted. Phase 2 required the identification of a CO2 thickener—present at 1wt. percent or less—capable of tripling the viscosity of CO2 flowing through a core. (One such compound has been identified thus far.)
Project Start: October 1, 2012
Project End: September 30, 2016
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]
Quarterly Research Progress Report [PDF-501KB]