75083·3836. Telex, 730989 SPEDAL. group is applied to the same generic Minnelusa reservoir at a fixed injection References and figures at end of paper. 557 rate to yield oil production in time-rate format. Economics are run based on these two production functions.Results show the polymer flood is economic and recovers an additional 7.5% OOIP over the waterflood.The polymer plus equipment cost is less than $2.00 per incremental barrel of oil.

SPE Members Abstract The Minnelusa formation in Wyoming's Powder River Basin exhibits high Powder River Basin exhibits high permeability variations and adverse permeability variations and adverse mobility ratios. Polymer augmented waterflooding has been the chosen technology to overcome these conditions for the past 15 years. The idea is to first unify the permeability distribution by injecting cationic polymer, followed by anionic polymer and aluminum citrate crosslinker. Then straight anionic polymer is injected for mobility control. polymer is injected for mobility control. This paper compares the results of 31 Minnelusa polymer floods with 24 Minnelusa waterfloods. The paper has two parts. The first part compares oil recoveries, injection part compares oil recoveries, injection volumes, flood lives, and water productions of the two population groups productions of the two population groups at various recovery efficiency cutoffs. At equal oil recoveries, the polymer floods inject less water, produce less water and recover the oil quicker than the waterfloods. The second part of the paper determines the economics of a typical polymer flood. The cumulative injection polymer flood. The cumulative injection and the cumulative oil production of each field are plotted for both the waterfloods and the polymer floods. The points are curve-fitted to yield an equation which predicts oil recovery versus injection in predicts oil recovery versus injection in dimensionless form. The equation of each group is applied to the same generic Minnelusa reservoir at a fixed injection rate to yield oil production in time-rate format. Economics are run based on these two production functions. Results show the polymer flood is economic and recovers an additional 7.5% OOIP over the waterflood. The polymer plus equipment cost is less than $2.00 per plus equipment cost is less than $2.00 per incremental barrel of oil. Introduction The Minnelusa sandstone is located in the Powder River Basin of Northeastern Wyoming (see Figure 1). Waterflooding has been ongoing in the Minnelusa since the late 1960's. The reason Minnelusa reservoirs are excellent waterflood candidates is that primary recoveries are low (5 – 15% OOIP) due to a fluid expansion drive mechanism. Relative permeability to oil is high with a low permeability to oil is high with a low relative permeability to water and the formation is a clean sandstone with excellent porosity and permeability. Polymer augmented flooding is used because of high permeability variations, adverse mobility conditions and tax incentives. Dykstra-Parsons permeability variation coefficients ranging from 0.6 to 0.8 and mobility ratios ranging from 2.0 to 25.0 are common throughout the trend. Polymer slug sizes range from 10% to 40% Polymer slug sizes range from 10% to 40% pore volume. The State of Wyoming offers pore volume. The State of Wyoming offers a 2% reduction in severance tax for certified polymer floods. Polymer flooding in the Minnelusa is well documented. The problem is how to measure the effectiveness of these floods. P. 557