Polymer Flooding the Minnelusa in the Powder River Basin of Wyoming

Polymer-augmented waterflooding of the Minnelusa in Wyoming has proven to be a successful method for improving production in most cases compared to normal waterfloods. Polymer is a lowcost, low-risk option when considering a method for enhancing production of a particular field. Its primary function is to improve the mobility ratio of the injected water by increasing its viscosity, thereby improving the volumetric sweep and conformance within the reservoir.

Advantages of using polymer include: (1) low cost, (2) preventing early water breakthrough, (3) improving volumetric sweep and conformance, (4) increasing oilwater ratios, (5) mobilizing oil that would likely have been bypassed under normal waterflood conditions, (6) mitigating heterogeneous permeabilities within the reservoir, and (7) other enhanced oil recovery injection technologies can still be applied after the polymer flood. Most, but not all, Minnelusa fields examined exhibited improved recoveries using polymer compared to fields under conventional waterfloods. Uneconomical polymer floods can be caused by a variety of factors, chief of which is the failure to properly understand the internal architecture of the reservoir prior to initiating the flood.

Understanding the distribution of flow units within a field, designing an efficient well pattern that fits the geometry of the flow units, identifying the problems that a polymer needs to address, and selecting the proper polymer to address those problems are all key factors for optimizing any type of polymer-augmented flood.

Associated chemical costs for the polymer, relative to the year 2020, can be as low as about $1.20 per incremental barrel of oil recovered (Manrique and Lantz, 2011), although most fields examined in this study exhibit slightly higher costs. Nevertheless, the economics of polymer flooding suggest that the method should be seriously considered for enhanced oil recovery (EOR) applications in Minnelusa reservoirs.

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