Oil & Natural Gas Projects
Exploration and Production Technologies
Stimuli-Responsive Copolymers with Enhanced Efficiency in Reservoir Recovery
The project was selected under the 2000 Program Solicitation DE-PS26-00NT40759.
The goal of this solicitation was to strengthen and advance fossil-fuel technologies
to improve domestic recovery.
The goal is to develop a new class of "smart" copolymers capable of
stimuli-responsive in situ rheology control. The objective was to synthesize
responsive systems, measure rheological properties of the resulting fluids including
behavior in fixed geometry flow through porous media, and tailor the final compositions
for rheology control under "triggered" conditions.
University of Southern Mississippi
The new "smart" copolymers developed can control fluid mobility and/or
conformance in oil recovery processes by altering viscosity and/or permeability
using triggers based on pH, salt or temperature variations. The polymer systems
developed may demonstrate superior performance as mobility control agents in
micellar enhanced EOR processes due to surfactant-induced viscosity enhancement.
The primary impact of "smart" copolymers will be to increase oil recovery
by producing bypassed oil. The model developed has identified the parameters
that are important to fluid mobility, thereby revealing methods to enhance solution
performance when using polyions solutions as displacing fluids in oil reservoirs.
The model was found to be valid for flexible polymer coils in aqueous salt solutions
where intermolecular interactions are minimal. The "smart" polymers
are designed to have "triggerable" properties such as changes in pH
and/or salt concentration, which enable them to react to reservoir conditions
to stimulate increased oil flow.
To date, the University of Southern Mississippi's synthetic research efforts
have been focused on the development of stimuli-responsive water-soluble polymers
designed for use in enhanced oil recovery applications. These model systems
are structurally tailored for potential methods. The goal of previous synthetic
work has been to design novel polymers that exhibit large dilute solution viscosities
in the presence of the adverse conditions normally encountered in oil reservoirs
(such as high salt concentrations, the presence of multivalent ions, and elevated
Polyzwitterions were investigated in previous research. A goal of the current
project is to investigate the interaction of surfactants with the hydrophobically
modified (HM) polyzwitterions. Surfactants are critical components in micellar
enhanced EOR processes because of their ability to reduce interfacial tension
and mobilize oil trapped in reservoir formations. The aim is to synthesize polymer
systems that will demonstrate synergistic increases in solution viscosity upon
the addition of surfactants.
A new relationship based on Yamakawa-Fujii and OSF theories was developed to
describe the contribution of electrostatic forces to the excluded volume of
a polyelectrtolyte in solution. The model is valid for flexible polymer coils
in aqueous salt solutions where intermolecular interactions are minimal.
As fluid passes through the channels of a porous medium, the fluid is continually
accelerating and decelerating. A fluid flowing under these conditions experiences
as extensional flow filed. The fluid drag forces that are applied to a polymer
coil in a fluid under extensional flow are proportional to the average extension
rate the fluid experiences. Although the fluid extension rate depends upon the
porous medium's channel geometry it always increases, regardless of channel
geometry, as the fluid flow rate increases.
When polymer solutions are used to flood an oil reservoir, very low fluid extension
rates exist at large distances away from the injection well-head. To be effective
in decreasing displacing fluid mobility during polymer flooding, polymer coils
must experience extension as they percolate through the porous media. An understanding
of which fluid flow conditions extend polymer coils is needed to control flooding
and improve oil recovery.
In this study a hypothesis was formulated that presumes polymer coils will extend
only when the rate of coil extension is greater than the rate of coil recovery.
A mathematical analysis was used to develop a relationship that predicts the
minimum fluid extension rate that produces coil extension. The minimum fluid
extension rate was shown to be inversely proportional to the coils hydrodynamic
This finding implies that in typical reservoir flooding where fluid extension
rates are very low, polymer coil extension that decreases displacing fluid mobility
and improves oil recovery will occur only if the coil hydrodynamic diameter
is extremely large. Large coil hydrodynamic diameters are formed when polymer
molecular weights are high and the polymer solution intrinsic viscosity is large
at the temperature conditions exist in the oil reservoir.
Current Status (September 2004)
The project is recently completed and the final report is in progress.
A related project was awarded under the PRIME solicitation in 2003, "Smart
Multifunctional Polymers" to follow up on knowledge learned in this project.
Semiannual Progress Reports are available at NETL, 918-699-2000.
Steady shear viscosity vs pH for DiC12AD and DiC14Am terpolymers at a concentration
of 0.5 g/dl. (Figure A.)
Model illustrating the effect of solution pH on terpolymer association behavior.
As referenced in figures A and B, for the DiC12AM terpolymer, a slight increase
in viscosity is observed between pHvalues of 5 and 7. At the lowest pH value,
the polymer is only marginally soluble in aqueous solution and likely exists
in a collapsed state with most hydrophobes participating in intrapolymer vs
interpolymer associates. As the pH is increased over this range (5 to 7), the
polymer becomes partially ionized and limited chain (backbone) extension occurs.
At pH values between 7 and 11, a larger change in viscosity for the DiC12AM
terpolymer is observed. Ionization of the carboxy functional groups into a conformationally
extended, energetically favorable state occurs. At these pH values the degrees
of ionization are sufficient to overcome hydrophobic forces and disrupt intrapolymer
aggregates, resulting in reordered, extended structures with more efficient
network formation. The less pronounced behavior of the DiC14AM terpolymer is
again likely due to its lower molecular weight and more hydrophobic nature.
Solvation and conformational rearrangements with increasing pH are not as favorable.
The pH responsive behavior of both terpolymers is illustrated in Figure B.
Project Start: May 21, 2004
Project End: August 31, 2004
Anticipated DOE Contribution: $998,864
Performer Contribution: $351,659 (26% of total)
NETL - Virginia Weyland (email@example.com or 918-699-2041)
U. of Southern Mississippi - Roger Hester (firstname.lastname@example.org or 601-266-4875)