Numerical Simulation of Electromagnetic Heating of Alaskan Tar Sands Using Horizontal Wells

Abstract

Abstract In an effort to develop a novel recovery technique for tar sand reservoirs of Ugnu in Alaska, electromagnetic heating using horizontal wells is proposed. One of the bigger technical problems with thermal injection on the North Slope is the large permafrost region. The permafrost reduces the effective heat that can be transmitted to a reservoir, even with insulated tubing. Applying the heat with a down-hole device, such as electromagnetic heating is a much more efficient process than conventional thermal recovery techniques. The horizontal well addresses another problem by heating and producing from the same well bore. The drainage radius is normally very limited due to the inability to conduct or convert heat away from the wellbore. A horizontal well, particularly one located at the bottom of a thick sand with vertical permeability, allows gravity drainage of a much larger reservoir volume. This paper presents numerical simulation results of such a process for Alaskan tar sand reservoirs using a horizontal well simulator. Numerical simulation results show oil recovery as high as 40% of the oil in place for tar sands. The recovery is even higher for heavy oil of moderate viscosity. Introduction The state of Alaska is estimated to contain some 70 billion barrels of oil in place. More than 50% of this reserve is in the form of heavy oil and tar sand in the Alaskan North Slope(1). Some 15 billion barrels of this reserve is in the form of tar sand in the Ugnu reservoir of the North Slope. With recent decline in oil production from the Prudhoe Bay light oil reservoir, there is a need to develop techniques for expanding oil production from other oil resources of Alaska. One such reservoir is the tar sand of Ugnu. Oil in the Ugnu reservoir was discovered by BP in the eastern region in the range of 828–994 m depth. Ever since the original discovery, there have been several drilling activities in the area during the 1970's. The Ugnu sand is divided into a lower and an upper zone. Figure 1 shows a cross sectional view of Ugnu and West Sak reservoirs. The lower Ugnu is mainly medium grained ranging from fine to coarse grained. The thickness of the lower Ugnu ranges from 75 to 92 m tbroughom most part of the northern Kuparak area. There are three to five major sand beds in the lower Ugnu interbedded with silts and muds. However, sand beds range from 3.5–10 m at the base to 20–31 m thick at the top of the member. The lower Ugnu is separated from underlying West Sak sands by a regionally extensive shale and mud sequence. FIGURE 1: Cross-sectional view of Ugnu and West Sak. (Available in full paper) The upper Ugnu sands are thicker than lower Ugnu sands and are mainly fine to medium grained. The upper Ugnu has an average thickness of 100 m in the Kuparak area and is composed of five to seven major sand beds. Each sand bed has an average thickness of 10–20 m.