In-Depth Drive Fluid Diversion Using an Evolution of Colloidal Dispersion Gels and New Bulk Gels: An Operational Case History of North Rainbow Ranch Unit

Abstract The North Rainbow Ranch Unit (NRRU) is located in Campbell County, Wyoming, and produces from the Minnelusa "A" Sand. In the absence of a strong water drive, primary production from the Minnelusa is generally less than 20% of the original oil in place (OOIP). Waterflooding the Minnelusa is an accepted procedure; however, sweep efficiencies can be poor due to high permeability variation. This variation can cause rapid water breakthrough, high producing water-oil ratios (WOR's), and low injection pressures. Polymer augmented waterflooding is utilized to improve reservoir conformance and can increase recoveries to over 45% of OOIP. Two different types of polymer-augmented systems have been used successfully on injection wells at NRRU. The first system was a long-term, in-depth colloidal dispersion gel (CDG). This process used cationic polyacrylamide and anionic polyacrylamide crosslinked with aluminum citrate. Fresh water was required for mixing. Incremental oil recovery from this process totaled 300,000 stock tank barrels of oil (STBO). The second system was a short-term bulk gel (BG) consisting of a new anionic polyacrylamide and chromium acetate combination. Produced water was used to mix the BG. Incremental oil recovery from this process is estimated at 155,000 STBO. This paper summarizes the design and performance of both systems and discusses operational issues encountered with the polymer augmented applications at NRRU.