
he Alaska North Slope (ANS) is estimated to contain 20 Bbbl to 30 Bbbl of heavy oil. However, the development pace of that resource has been quite slow due to the high costs of development and the low oil recovery efficiency using conventional waterflood and EOR methods. Even after three decades of development efforts by multiple operators, the total heavy oil cumulative recovery from all ANS fields just reached 255 MMbbl, which was less than 1% of the total heavy oil in place in 2019.
The University of Alaska Fairbanks is leading a project being sponsored by the U.S. Department of Energy National Energy Technology Laboratory (NETL) and Hilcorp Alaska LLC. The project is a four-year field pilot project entitled, “First Ever Field Pilot on Alaska’s North Slope to Validate the Use of Polymer Floods for Heavy Oil Enhanced Oil Recovery (EOR).”
The objective of the project is to improve the oil recovery efficiency by polymer flooding in the Schrader Bluff heavy oil reservoir on the ANS. Polymer flooding has been widely applied to decrease the driving phase mobility and improve the sweep efficiency for conventional oil reservoirs. Recent theoretical results and field results have proved the effectiveness of this technology in viscous and heavy oil reservoirs. The current field pilot tests of the project also have shown encouraging results in the EOR performance of polymer flooding.
Many laboratory experiments and simulation studies have been conducted to understand the mechanisms behind the optimistic results in pilot tests in different environments. This paper will focus on the effect of polymer rheology on polymer flooding performance in ANS heavy oil reservoirs that are developed with horizontal well.
The use of horizontal wells for EOR in heavy oil reservoirs has increased in recent years. As the target formations in the ANS are relatively close to permafrost, steam generation is prohibitive considering the heat loss and environmental requirements. Thus, polymer flooding has been recommended and applied in the target heavy oil formation.
The horizontal model is located at 3,930 ft true vertical depth. The model contains a vertical high-permeability channel extended from injector to producer. Thus, the model contains two different permeabilities. The reservoir characteristics are listed in Table 1. The relative permeability was measured by laboratory experts using sandpack coreflooding from Schrader Bluff NB Formation.


Secondly, polymer flooding effectiveness was strongly influenced by reservoir heterogeneity.
In addition to the optimal recovery stage by waterflooding in heavy oil, polymer flooding can provide an extended period of optimal recovery with low WOR. For higher heterogeneity cases, this extended period was very limited for the bulk viscosity model but increased dramatically for the apparent viscosity model.
Lastly, the application of the apparent viscosity model in simulation shows significant benefit for the case study in heavy oil polymer flooding using horizontal wells to improve the sweep, reduce the WOR, overcome the negative effect by heterogeneity and extend the economic production.