Oil & Natural Gas Projects
Exploration and Production Technologies
Inexpensive CO2 Thickening Agents for Improving Mobility Control of CO2 Floods
This project was selected in response to DOE's solicitation DE-PS26-01NT41048
(December 1, 2000). The objective of this part of the solicitation was to access
oil not recoverable by conventional methods by developing improved methods of
gas, chemical, and microbial flooding for light oil recovery.
The goal of this project was to identify an inexpensive polymer capable of dissolving
in carbon dioxide and increasing its viscosity, thereby enabling improved mobility
control of CO2 floods.
University of Pittsburgh
During the final stages of this project, computational tools developed in the
project were used to design CO2-soluble polymers. These tools allowed a qualitative
explanation of why certain polymers were (or were not) CO2-soluble. At the end
of the project, the design of a new polymer-poly(3-acetoxy oxetane), or PAO-that
should be more CO2-soluble than PVAc was identified.
An inexpensive, environmentally benign, safe, CO2 thickener composed of carbon,
hydrogen, and oxygen (sulfur and nitrogen are also acceptable) added to CO2
as it is being injected will increase oil recovery from CO2 injection. The thickener
prevents early breakthrough of CO2, reduces the amount of CO2 required to recover
a barrel of oil, increases the rate of oil production, and ultimately increases
the amount of oil that could be recovered from a formation. Use of effective
thickeners would eliminate the additional cost of conducting a water-alternating-gas
About 1.5 billion standard cubic feet per day of CO2 is injected in U.S. oil
reservoirs each day, accounting for production of 200,000 barrels per day of
oil per. Despite the maturity of this technology, its performance still has
much room for improvement. For example, about 8,000 standard cubic feet of CO2
is required for each barrel of oil recovered, which translates into the injection
of 3.5 barrels of dense CO2 at reservoir conditions for each barrel of oil produced.
Further, large slugs of water must be injected alternately with slugs of CO2
(water-alternating-gas, or WAG) in order to make the CO2 flow more uniformly
through the reservoir rather than "fingering" from the injection well
to the production well and bypassing large regions of oil-bearing rock. Sweep
efficiency problems are directly associated with the low viscosity of CO2 compared
with that of the oil to be displaced.
The University of Pittsburgh research group, under previous funding from DOE,
designed, synthesized, and evaluated the first CO2 thickener-poly(fluoroacrylate-styrene),
or polyFAST-in the laboratory. PolyFAST remains the only CO2 thickener that
has been reported. Although this result proved that a thickening agent could
be designed for CO2, it was not a practical thickener for field application.
Specifically, it was expensive, biologically and environmentally persistent,
and not available in large quantity. All of these negative attributes were directly
the result of the polymer having a high content of fluorine.
This project evaluated numerous polymers that contained no fluorine for this
CO2 thickening application. Rather than performing a trial-and-error study of
what dissolves in CO2, specific chemical groups that were known to have a strong
and favorable interaction with CO2 were selected. The design of a thickener
consists of two steps. First, a high molecular weight "base polymer"
that is extremely soluble in CO2 must be designed. Second, the base polymer
must be modified to become a thickener by adding a small amount of "CO2-phobic"
groups that cause the dissolved thickener molecules to interact with one another.
This type of interaction forms large, viscosity-increasing macro-molecules to
form in the CO2. Unfortunately, this modification always will make the thickener
less soluble in CO2 than the base polymer, so the base polymer must be soluble
in CO2 at pressures less than the minimum miscibility pressure (MMP), or the
pressure at which the CO2 flood is conducted.
This project focused on the first step-making the most CO2-soluble polymer
possible. Oxygen-rich hydrocarbons (chemical groups composed of carbon, hydrogen,
and oxygen) were determined to be the most promising "CO2-philic"
groups. Ether, carbonyl, and acetate groups were determined to be particularly
promising components for making a polymer that dissolves in CO2. Several low
molecular weight polymers (a.k.a. oligomers) of comparable CO2 solubility were
identified, including sugar acetates, polypropylene oxide, polymethyl acrylate,
and polyvinyl acetate. The CO2-solubility of high molecular weight versions
of these polymers varied dramatically. Poly(vinyl acetate), PVAc, was clearly
the most CO2 soluble, inexpensive, high molecular weight, commodity polymer
identified. For example, 5 wt % PVAc with a molecular weight of 600,000 could
dissolve in CO2. Unfortunately, the pressure required to dissolve PVAc was much
greater than the range of MMP values of CO2 floods. About 25 novel polymers
were designed. Each was a candidate for being a CO2-soluble base polymer. However,
none were more CO2-soluble than PVAc. After identifying PVAc, computing tools
were developed to design inexpensive polymers that are even more soluble in
Current Status (August 2005)
This project has been completed and the final report is available below under "Additional Information".
Project Start: September 1, 2001
Project End: August 31, 2005
Anticipated DOE Contribution: $977,000
Performer Contribution: $260,000 (21% of Total)
NETL - Dan Ferguson (email@example.com or 918-699-2047)
U. of Pittsburgh - Robert Enick (firstname.lastname@example.org or 412-624-9649)
Final Project Report [PDF-973KB]