A Simulation Study of Novel Thermal Recovery Methods in the Ugnu Tar Sand Reservoir, North Slope, Alaska

Abstract

Abstract The Ugnu reservoir, located in the Kuparuk River Unit on the North Slope of Alaska, is estimated to contain over 6 billion barrels of heavy oil in the form of tar and bitumen. Due to the extreme oil viscosities conventional enhanced oil recovery (EOR) methods are not readily applicable to the Ugnu sands. Additionally, high reservoir heterogeneity creates complications with EOR processes. A detailed simulation study was conducted to evaluate the performance of four novel thermal recovery methods in the Ugnu reservoir. These methods included steam assisted gravity drainage (SAGD) with horizontal injectors, SAGD with vertical injectors, SAGD with electrical preheating (EP-SAGD), and EP-SAGD with vertical injectors. A conventional steamflood was also simulated for comparison as the base case. The effects of various reservoir and process parameters such as well spacing, flood pattern, reservoir heterogeneity, and anisotropy on process performance were studied. The four SAGD based processes were found to be far superior to conventional steamflood, which performed very poorly. An optimum spacing between injector and producer for SAGD methods was determined. The EP-SAGD process was found to be thermally more efficient than SAGD, however, final oil recoveries were comparable for the two methods. Placement of horizontal producer was found to be more critical than placement of the injector.