Abstract

In an effort to develop a novel recovery technique for tar sand reservoirs of Ugnu in Alaska, electromagnetic heating using horizontal well 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 downhole device, such as electromagnetic heating is a much more efficient process than conventional thermal recovery techniques. The horizontal well addresses another problem with heating and producing the same wellbore. The drainage radius is normally very limited due to the inability to conduct or convect 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 resulls 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 Slope1. 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 Prudhoe Bay light oil reservoir, there is development techniques for expanding oil from other oil resources of Alaska 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 1970's. The Ugnu sand is divided into a lower and an upperzone. Figure 1 shows a cross sectional view of Ugnu and West Sal reservoirs.

The lower Ugnu is mainly medium grained ranging from fine to coarse grained. The thickness of the lower Ugnu ranges from 7S to 92 m throughout most port of the northern Kuparak area. There are 3 to 5 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 Wesk Sak sands by a regionally extensive shale and mud sequence.

The upper Ugnu sands are thicker tban lower Ugnu sands and are mainly fine [0 medium grained. The upper Ugnu bas an average thickness of 100 m in the Kuparak area and is composed of 5 to 7 major sand beds. Each sand bed has an average thickness of 10–20 m. Reservoir rock and fluid data for both upper and lower Ugnu arc given in Table 1.

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