Keywords: EOR, enhanced oil recovery, unconventional, CO2 injection, carbon dioxide, liquid–rich, oil reserves, reservoir simulation, numerical simulation, gas injection, oil wells, flow modelling
Gas injection to increase recovery from the Bakken formation
The Bakken formation, in the Williston Basin, has tremendous oil reserves estimated to be in the hundreds of billions of barrels. During the last decade, the Bakken has been rapidly developed with advances in horizontal drilling and improved multi–stage hydraulic fracturing. The primary recovery factor, however, has remained very low, around 5%–10% due in part to the extremely low permeability. Enhanced oil recovery, including gas injection, may be an essential process to increase the recovery factor and maximise the potential production from this formation. A numerical reservoir simulator is used to evaluate the performance of CO2 injection for the Bakken interval in a sector of the Sanish field. Future primary production performance of wells in the research area was predicted through flow modelling and confirmed the low primary recovery factors, which was less than 6% for this model. Several different scenarios of gas injection are tested to analyse gas injection performance. It appears that gas injection is suitable in such tight environments, as the recovery factors increased significantly for miscible CO2 injection. Depending on the scenario, the recovery factor increased between 5% and 21%. The best scenario involves drilling new injectors such that there are four new injectors around the three current producers.