DE-NT0006556

Goal
The objective of this project is to develop improved chemical oil recovery options for the Ugnu reservoir overlying the Milne Point unit in North Slope, Alaska.

Performers
University of Texas, Austin, TX 78712-1160

Background
The North Slope of Alaska has large (about 20 billion barrels) deposits of viscous oil in the Ugnu, West Sak, and Shraeder Bluff reservoirs. These shallow reservoirs overlie existing productive reservoirs such as Kuparuk and Milne Point. The viscosity of the Ugnu reservoir overlying Milne Point varies from 200 cp to 10,000 cp and the depth is about 3500 ft. The same reservoir extends to the west overlying the Kuparuk River Unit and on to the Beaufort Sea. The depth of the reservoir decreases and the viscosity increases toward the west. Currently, the operators are planning to test cold heavy oil production with sand (CHOPS) in Ugnu, but oil recovery is expected to be low (< 10%). Improved oil recovery techniques must be developed for these reservoirs. Proximity to the permafrost is an issue for thermal methods; thus non-thermal methods must be considered. In the past, gasflood and alkaline-surfactant-polymer methods have been developed for light oils and polymer methods have been developed for medium viscosity oil. Hydrocarbon gases are now available for injection into oil reservoirs to improve oil recovery, but their availability will be limited once a gas pipeline is constructed. Thus, the objective of this proposal is to develop chemical methods to recover oil from the Ugnu reservoir (overlying Milne Point) with a limited use of gas solvents.

Impacts
This project will identify the applicability of chemical techniques for heavy oil recovery at the laboratory-scale. Project personnel will evaluate mechanisms of heavy oil recovery in many new secondary recovery processes (e.g., alkaline-surfactant, alkaline-surfactant-polymer, and colloidal dispersion gel floods) as well as the sweep efficiency and the microscopic displacement efficiency of these processes. Mechanistic numerical models will be developed for each of these processes to explain laboratory results and determine field-scale implications. Research leading to a successful chemical recovery method could result in the economically viable recovery of many billions of barrels of oil from the Ugnu reservoir without damaging the permafrost. The scientific and technical insight gained from this project can potentially be applied to other heavy oil reservoirs.

Accomplishments

• Two papers were completed and will be presented at the SPE annual conference in Denver in November, 2011.
  • SPE 146839: Sweep Efficiency of Heavy Oil Recovery by Chemical Methods
  • SPE 146841: Viscous Fingering during Non-Thermal Heavy Oil Recovery
• Core floods have been conducted with alkali and surfactant systems that form emulsions with the 10,000 cp oil. Oil recovery is in the range of 50–75%. Injection of alkali and surfactant improves the 10,000 cp oil recovery significantly when compared to the waterflood recovery. Brine salinity affects the alkaline-surfactant process.
• Core floods have been conducted with alkali-surfactant-polymer systems that form microemulsions with the 330 cp oil. Injection of alkali-surfactant-polymer improves the 330 cp oil recovery significantly over the waterflood recovery; virtually 100% of the residual oil is recovered.
• A secondary polymer flood has been conducted in the same core. Injection of polymer improves the 330 cp oil recovery significantly over the waterflood recovery; about 90% of the initial oil is recovered.
• A displacement of the 10,000 cp oil by water and then alkaline surfactant formulation in a quarter 5-spot sand pack model has been completed. Recovery is lower (45%) than that of the coreflood. Displacement of the 330 cp oil in the quarter 5-spot is in progress.
• Two papers (SPE 129914, 135265) have been written on viscous oil recovery.
• The oils are very acidic and form soap in contact with an alkali. Macroemulsions can be formed by the addition of small concentrations of surfactants and alkali.
• The macroemulsion is an oil-in-water emulsion of a low viscosity.
• Silica nanoparticles do not form emulsions with this oil and brine.
• Core flood studies have been conducted to determine if the viscous oil can be extracted from cores by forming a low viscosity emulsion. These experiments show that oil recovery by waterflood is a function of injection rate.
• An imbibition mechanism has been recognized to model oil recovery during waterflood after finger breakthrough.

Current Status (October 2011)
Displacement of the 330 cp oil in the quarter 5-spot is in progress. Core flooding, micromodeling, and quarter five-spot model construction were conducted with the viscous oil, surfactants, and alkali prior to initiating the quarter 5-spot displacement. In linear waterfloods, a significant amount of oil was produced after water breakthrough. Post breakthrough oil recovery correlated with the square root of time. A model was developed based on imbibition of water from the water fingers and matches the experimental data. Micromodel displacements show that the finger pattern is a function of viscosity ratio. Oil was emulsified at the periphery of the fingers during alkaline-surfactant injection and removed through the water fingers. The high pressure quarter 5-spot has been saturated with oil and waterflooded. The oil recovery in the high pressure 5-spot is similar to that of the low pressure 5-spot. Sweep experiments and modeling will be conducted to understand and upscale this process

Project Start: October 1, 2008
Project End: March 31, 2012

DOE Contribution: $704,431
Performer Contribution: $180,061

Contact Information:
NETL – Chandra Nautiyal (Chandra.Nautiyal@NETL.DOE.GOV or 281-494-2488)
University of Texas at Austin – Kishore Mohanty (mohantyt@mail.utexas.edu or 512-471-3077)
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