The principle objective of the project is to characterize and test current and next generation high performance surfactants for improved chemical flooding technology, focusing on reservoirs in Pennsylvanian age (Penn) sands.
Oklahoma University Enhanced Oil Recovery Design Center, Norman, OK
Primary and secondary methods have produced approximately one-third of the 401 billion barrels of original-oil-in-place in the United States. Enhanced oil recovery (EOR) methods have shown potential to recover a fraction of the remaining oil. Surfactant EOR has seen an increase in activity in recent years due to increased energy demand and higher oil prices. In surfactant EOR the mobilization of the remaining (residual) oil is achieved through surfactants that can lower the oil-water interfacial tension to values that overcome capillary forces and allow oil to be displaced from pores. A new generation of surfactants is needed to achieve these goals.
Enhanced oil recovery currently provides about 13% of domestic oil production and is increasingly important for sustaining U.S. oil output as the nation’s oil fields continue to age and onshore oil production declines. The development and characterization of new surfactants will enhance the petroleum industry’s ability to economically recover oil remaining in mature fields using enhanced oil recovery applications. This will help to increase the volume of oil produced from domestic reservoirs and reduce the level of imports required to meet the energy demands of a growing economy.
This project focused on the following three aspects of a next generation of surfactants for chemical flooding EOR:
1. This project extended recent models relating surfactant structure to optimization of microemulsion formulation through the relationship between the theoretically accessible packing factor (Pf) calculation and the experimentally measurable characteristic curvature (Cc) of the surfactant membrane in a microemulsion. This was accomplished by extending the range of surfactants for which the Cc has been measured to surfactants typical of those used for EOR through the study of a suite of novel petroleum sulfonates, the recently commercialized extended surfactants (alkylethoxypropoxy sulfates), and a new series of disulfonates optimized for microemulsion formation The current Pf calculation was modified to better account for multiple and branched hydrophobes, which will improve the correlation between the calculated Pf and the measured Cc.
2. Researchers studied the relationships among new surfactants, co-surfactant (e.g., alcohol) concentrations, pH, and the use of sacrificial agents to minimize the surfactant adsorption at the brine/rock interface. While current surfactant concentrations for EOR are much lower than those used earlier, the ability to reduce those concentrations still further is limited by the high adsorption of the surfactant by the reservoir rock. Improving the ability to design low interfacial tension (IFT) formulations that have ultralow adsorption on reservoir rock would be a significant advance in improving the commercial viability of surfactant flooding technology.
3. Researchers also explored correlations among the optimal salinity, Cc of the surfactant, critical microemulsion concentration (CµC), and the achievement of ultralow interfacial tensions at concentrations below the CµC. It has been shown that ultralow IFT can be achieved without the formation of a microemulsion. If a correlation between ultralow IFT in the absence of microemulsion formation and the microemulsion phase diagram can be determined, then it will be possible to use recent design equations for microemulsion formulation to design surfactants to produce ultralow IFTs at concentrations below those required for the formation of a middle phase (Winsor Type III) microemulsion.
The results from a single-well tracer test (SWTT) completed in October 2011 determined that approximately 70% of the residual oil was mobilized in a single permeable zone.
The results from another SWTT conducted in November 2011 in a different reservoir resulted in an 87% residual oil recovery in the target zone after the analysis of pre-surfactant/polymer and post-surfactant/polymer data.
The project has been completed. The final report is available below under "Additional Information".
Final Project Report [PDF-1.91MB]