DE-FE0003537

Goal
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.

Performer
Oklahoma University Enhanced Oil Recovery Design Center, Norman, OK

Background
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.

This project will focus on the following three aspects of a next generation of surfactants for chemical flooding EOR:

1. This project will extend 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 will be accomplished by extending the range of surfactants for which the Cc has been measured to surfactants typical of those used for EOR. This will include 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. In particular, the current Pf calculation will be modified to better account for multiple and branched hydrophobes, which will improve the correlation between the calculated Pf and the measured Cc.
2. Researchers will study 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 simultaneously have ultralow adsorptions on the reservoir rock would be a significant advance in improving the commercial viability of surfactant flooding technology.
3. Researchers will also explore 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 Design Institute laboratories are equipped to study both the phase behavior of the surfactant/oil/brine systems at conditions typical for EOR, and the adsorption of the surfactants at reservoir conditions, and to then take formulation design testing through the performance of core floods. Oklahoma University is partnering with Mid-Con Energy of Tulsa, Oklahoma (www.midcon-energy.com/) to perform a minimum of five single-well tests for chemical EOR.

Impact
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.

Accomplishments

• The results from the second single-well tracer test (SWTT) completed in October 2011 were reanalyzed. Initially it was thought that two perm zones existed within the well, but it has been determined that there is just a single perm zone. Approximately 87% of residual oil was mobilized.
• Three single-well tests have been conducted in a third reservoir located in Pennsylvanian age sands. The results from the first SWTT conducted in November 2011 suggested a problem with the well casing when an insufficient amount of the non-partitioning tracer was recovered. Project personnel decided to conduct the test at a second well within this reservoir. Two tests were conducted at this second well in March and April 2012, which again resulted in an insufficient amount of the non-partitioning tracer being recovered. In fact, increasing the shut-in time for the tracer from two days for the test conducted in March, to four days for the test conducted in April, resulted in a drop in recovery of the non-partitioning tracer from 40% to <10%. The results from these three SWTTs suggest reservoir factors may exist, and a need for further analysis.

Current Status (May 2012)
Discussions concerning a pilot-scale test in a 4- or 5-spot configuration in the same formation as the first single-well test (conducted at reservoir M) are on-going. Other potential reservoirs for conducting pilot-scale tests are being evaluated.

Current work continues to focus largely on establishing the minimum concentrations of surfactant and polymer required to mobilize the residual oil. Determining these minimum concentrations is now a standard part of the evaluation of the surfactant formulations being developed for a given reservoir.

The protocols used in conducting sandpack and coreflood tests to determine the suitability of surfactant formulations being evaluated for enhanced oil recovery application for a given reservoir have become well-established. Additionally, second- and third-generation researchers have been trained to conduct these tests.

Research is on-going to determine the characteristic curvatures of all of the surfactants used in the development of the surfactant formulations for enhanced oil recovery in the reservoirs examined in this project. The University of Oklahoma team is working with Huntsman, Sasol NA, Dow, and Pilot Chemical in the application of several of their commercially available surfactants for enhanced oil recovery, and on new surfactant designs for use in the oil recovery field.

Project Start: June 1, 2010
Project End: May 31, 2012

DOE Contribution: $481,000
Performer Contribution: $120,250

Contact Information:
NETL ? Sinisha (Jay) Jikich (sinisha.jikich@netl.doe.gov or 304-284-4320)
Oklahoma University ? Jeffrey Harwell (jharwell@ou.edu or 405-325-4375)
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