The objective of the proposed research is to develop a low-cost, pH-triggered polymer for use in improved oil recovery (IOR) processes to enhance reservoir sweep efficiency and conformance in chemical flooding. The polymer solution, which has a low viscosity at low pH, preferentially flows into zones containing water because the effective permeability to water is highest in these zones. As the pH of the zone increases due to the buffering capacity of the reservoir rock, the polymer solution undergoes a liquid-to-gel transition, causing a sharp increase in the viscosity of the polymer solution in these zones. This allows operationally robust, in-depth conformance treatment of such water-bearing zones and better mobility control. The use of this polymer in conjunction with CO2 flooding will be investigated in detail, because a combination of the two offers some unique synergistic benefits.
University of Texas, Austin, TX
The work will combine rheological measurements with laboratory-scale core-flow experiments and reservoir modeling. The laboratory experiments include characterization of the pH-sensitive anionic polymer, rheological studies, core, and long sand-pack tests to obtain the conditions and factors that impact the gelling characteristics of the polymer solution. The optimum operating parameters for different lithologies for water shut-off and mobility control will be obtained from these experiments and geochemical modeling. The simulation studies will use these parameters to obtain practical operating conditions for the application of the pH-sensitive gel.
The overall objective of the proposed research is to develop a low-cost, pH-triggered polymer for use in polymer flooding to improve reservoir sweep efficiency and reservoir conformance in chemical flooding. The project’s main accomplishments over the first 9 months include rheological characterization of the polymers, proving the concept in the laboratory, and modeling the process geochemically.
Polymer injectivity is of great concern in polymer flooding and profile control, since large injection pressures are needed to inject viscous fluids. The use of pH sensitive polymers provides a way of reducing the injection pressures needed to inject the polymer solution. By injecting a pH buffered polymer solution at low pH, we can achieve significantly lower injection pressures since the polymer viscosity is low. As the pH of the solution increases, due to reaction with the rock, the polymer viscosity increases by at least an order of magnitude. This allows lower injection pressures in polymer injection wells.
Rheological characterization was completed for several types of polyacrylic acid polymers with different crosslink density and molecular weight, in order to select the optimum polymer. Eight polymers were evaluated, and the results tabulated. All polymer solutions have the same tendency for viscosity change as a function of pH. The cross-linked polymers are tightly coiled in a low-pH environment and begin uncoiling (swelling) at a high pH to increase the viscosity. As expected, a lower concentration of polymer in solution lowers the viscosity value over all ranges. The project’s main accomplishments include:
This project has been completed and the final report is available below under "Additional Information".
This project was selected in response to DOE’s Oil & Gas Master Solicitation, DEPS26-04NT15450.
$123,539 (24 percent of total)
Final Report [PDF-3.32MB]
Choi, S., Ermel, Y.M,, Bryant, S.L., Huh, C., Sharma, M.M., Transport of a pH-Sensitive Polymer in Porous Media for Novel Mobility-Control Applications, SPE 99656 presented at SPE/DOE Fifteenth Improved Oil Recovery Symposium in Tulsa, OK, April 2006.