A project researching the effectiveness of polymer injection for enhanced heavy oil recovery in the Milne Point field on Alaska’s North Slope is verifying significant benefits from the use of this injection technique. The $9.7 million project, primarily funded through a $7.1 million grant from the U.S. Department of Energy, is led by the University of Alaska Fairbanks and involves Milne Point operator Hilcorp Alaska, New Mexico Tech, Missouri S&T and the University of North Dakota.
“It’s a great example of government, academia and industry collaboration,” Abhijit Dandekar, professor and chair of petroleum engineering at UAF, told Petroleum News.
As previously reported by Petroleum News, Hilcorp has been implementing polymer injection at several well pads in the Milne Point field, to improve production of heavy oil from the Schrader Bluff formation. In parallel, the research project is using a four-well configuration - two horizontal production wells and two horizontal injection wells - at the Milne Point J pad, to determine and evaluate the characteristics of the injection technique. The research also involves building a reservoir model for designing the field tests and forecasting production results.
The fact that the wells being used were already in existence, operating using a waterflood oil production technique, has presented a major benefit for the project.
“It was a perfect opportunity to try out injecting polymer,” Dandekar said.
The research project began in June 2018 and is scheduled to run to the end of September 2022. Results to date indicate that polymer injection significantly increases oil production while also causing major reductions in the water cut from the production wells. The research team reported in February that the polymer injection technique could as much as double Schrader Bluff oil production, relative to the use of waterflood. Although the use of polymer involves additional operational costs, these costs are more than outweighed by the benefits from increased oil production and the reduced water cut.
Heavy oil on the North SlopeThere are huge quantities of heavy oil, oil with particularly high viscosity, under the North Slope, especially in the relatively shallow Schrader Bluff (or West Sak) and Ugnu formations. The oil is thought to have migrated from deeper rock formations into these shallower formations. Microbes, which become increasingly active at shallower depths, are thought to have degraded the oil in the shallow reservoirs, thus rendering the oil more viscous. The relatively low temperatures at shallow depths below the permafrost also impact the viscosity. And, with the Ugnu being shallower than the Schrader Bluff, the Ugnu oil is significantly more viscous than the Schrader Bluff oil.
But enticing this viscous oil to the surface through conventional oil wells presents major technical challenges.
A significant breakthrough in Schrader Bluff development at Milne Point came in 2001 with the use of long horizontal wells that could thread through the reservoir rock formation and hence access relatively large areas of oil reservoir surface. Jet pumps proved effective in moving the oil to the surface. A further development in subsequent years involved the drilling of injector wells, to use water injection to drive oil towards the production wells.
Water viscosityDandekar explained that a constraint in the use of waterflood in the Schrader Bluff arises from the fact that water has a significantly lower viscosity than the heavy oil. As a consequence, the mobility of the water reduces the efficiency with which the oil is driven towards a production well. However, the addition of a polymer of an appropriate composition to the water renders the fluid more viscous. This slows down the movement of the water, thus making the fluid more effective in pushing the oil through the rock formation.
According to a paper published in association with the research project an appropriate choice of polymer type and concentration is critical to improving the movement of oil through the reservoir, while ensuring that the polymer does not itself clog the reservoir pores.
Major benefitsThe wells at J pad have demonstrated an oil production increase of about 1,000 barrels per day as a consequence of using the polymer injection technique, Dandekar said. And, given the properties of the polymer laced injection fluid, the polymer has taken a little over two years to start appearing in the production fluids, having slowly flowed from the injection wells.
While the slow rate of polymer flow confirms the effectiveness of the polymer technique, the benefits from the polymer injection take a while to build up, with increasing benefits accruing as the polymer flood matures. The researchers are continuing to monitor what is happening and evaluating the benefits of the technique.
Dandekar also commented that, although there are several techniques for producing heavy oil, the polymer injection is the clear technique of choice at Milne Point. It is not, for example, possible to use steam injection on the North Slope because injecting steam from the surface would cause the subsurface permafrost to melt.
“That is something that is unthinkable here in Alaska, especially on the North Slope, because of the permafrost,” Dandekar said.
Gas injection is another possible technique, but lab tests have indicated some challenges with this method. Moreover, at Milne Point there is a source of low salinity water that supports the polymer injection approach, Dandekar said.
Hilcorp extending injection programMeanwhile, given the clear benefits of polymer use, Hilcorp has been forging ahead with its polymer injection program in the Schrader Bluff at Milne Point - in its latest Milne Point plan of development the company indicated an intention to extend Schrader Bluff polymer injection beyond the pads where the technique is already in use.
“We’re proud of our partnership with UAF and the Department of Energy on this first-of-its-kind Arctic heavy oil polymer flooding project,” said Dave Wilkins, Hilcorp senior vice president, Alaska. “UAF and DOE provide outstanding Arctic and industry expertise, as well as technical and project support. As we build on our initial success, we’re expanding polymer flooding to additional patterns and reservoirs at Milne Point and continue to evaluate new opportunities across the North Slope.”
Ugnu developmentProducing the thicker oil in the Ugnu formation is significantly more challenging than producing from the Schrader Bluff. In recent years Hilcorp has been producing a small amount of Ugnu oil through the S-203 horizontal well drilled from the S pad. The company has been evaluating the performance of this well, with a view to determining a possible future Ugnu development strategy.
Between 2011 and 2013 BP succeeded in producing Ugnu oil on a test basis at Milne Point S Pad, using a downhole pump to drive a slurry of oil and sand to the surface from the unconsolidated reservoir, and then separating the oil in a tank. But BP did not further pursue this endeavor.
- ALAN BAILEY