Evalution of Chemical Flooding in the Minnelusa Formation, Powder River Basin, Wyoming
The choice of EOR techniques should be based on knowledge of prior efforts in similar settings. The Minnelusa Formation of Wyoming offers such an opportunity. The formation is a prolific producer with over 607 million barrels of oil cumulative to date from approximately 100 Minnelusa fields located in the Powder River basin. These fields are relatively small, eolian sandstone deposits with similar porosity and permeability, but have a wide range of production by field. About half of these fields have been subjected to some form of enhanced oil recovery, primarily with polymer floods. While some of these fields followed the traditional EOR sequence of primary, secondary and tertiary treatment, there were many cases where application of polymer was coincident with start of waterflooding. An evaluation of the effectiveness of all phases of recovery was performed using production data. The metric used was the incremental production after treatment where incremental was limited to that oil produced in addition to normal production activities. This metric provides the basis for estimating potential income to pay for the treatment. Almost all cases of water or chemical flooding produced positive results in terms of increased oil production.
Based on the incremental production metric, in-field drilling produced 50% incremental production, standard waterflooding, also positive for most cases, reached a maximum of 300% incremental production. Traditional post-waterflood application of polymer also showed mostly positive results with the best response generating more than 400% incremental production. However, application of polymer concurrent with the start of waterflooding produced the best results with incremental production as high as 1500%. These high values are partially related to low primary production potential, but other factors also play a role. The much larger range in chemical flood response was not strongly related to geological factors. Specific factors such as net pay, size and age of the field, ndepth/temperature, number of wells, cumulative production, oil gravity and formation water chemistry played some role in controlling the degree of success, but the most important variable was how soon the polymer was applied after field production was started. Application of chemical treatment in the first five years of the field produced significantly better results.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009