The volume of heavy oil and bitumen in the oil sands deposits in Western Canada is similar to that of conventional crude oil in the Middle East. This resource is vast but difficult and energy intensive to extract because of its high oil/bitumen viscosity, over 1,000 to 10,000,000 cp at original reservoir conditions. Current commercial thermal recovery processes used are Steam Assisted Gravity Drainage (SAGD), Cyclic Steam Stimulation (CSS) and steam flood. In this study, the focus is on the SAGD process.
Currently most completion designs for SAGD are focused on wellbore and very near-wellbore regions and reservoir simulation history matching and forecasts are done using simple sink/source wellbores. In one case the complications of the geological and reservoir heterogeneity are not considered in the design, and in the latter, the impact of completion components on wellbore dynamics is ignored or oversimplified. This study shows that when reservoir and wellbore modeling are coupled, completion designs, history matching and forecasts may change significantly. The difference grows with increased reservoir heterogeneity and complex fluid saturation and properties distribution.
The impact of counter-current heat exchange in concentric configuration was found to be significant in reducing the energy delivered to a reservoir section during circulation. The application of Vacuum Insulated Tubing (VIT) with properly insulated couplings was shown to be promising in reducing the counter-current heat exchange.
Thermal energy distribution during thermal start up and true SAGD stages is key to obtaining high performance bitumen recovery. A synthetic parameter called Oil Production Potential (OPP) was derived to be used as a guide to distribute energy along the SAGD wells. A novel method/workflow was presented that identifies high and low potential reservoir sections to introduce heat to a reservoir accordingly. This workflow was used to design and implement SAGD wellbore completions in Senlac, Saskatchewan. The field results supported the design workflow and showed significant improvement over conventional completion design methodologies that emphasize on wellbore and very near-wellbore regions only.