Summary

The IIT Research Institute (IITRI) radio frequency (RF) process for tar sands consists of two steps:

  1. the deposit is volumetrically heated with RF energy to lower the viscosity of the bitumen, and

  2. the bitumen is produced by one of several petroleum recovery methods.

The RF heating step is accomplished by inserting tubular electrodes into boreholes and by energizing them with an RF power source. The electrode pattern is designed so that the deposit between the electrodes is uniformly heated with a minimum energy loss. The operating frequency is selected on the basis of the electromagnetic characteristics of the deposit. The recovery techniques that we investigated include replacing the heated bitumen with sodium silicate solutions, by gravity drainage, and by autogenously developed steam and hydrocarbon gases.

Two small-scale field experiments were conducted in the Asphalt Ridge tar sand deposit near Vernal, UT. About 25 m [33 cu yd] of the deposit was heated with RF energy, and about 35% of the total in-place bitumen was recovered during the 3-week test period.

Introduction

IITRI investigated the RF process for in-situ recovery of bitumen from Utah tar sands that are estimated to contain about 4 × 10 M [26 × 10 bb] of oil. Potential applications of the process to recover useful fuels from other hydrocarbonaceous resources (such as oil shale) are discussed elsewhere.

Economic recovery of bitumen from tar sand deposits is a technological problem for two reasons: the high viscosity of bitumen under native conditions, and the lack of any significant gas pressure in these deposits to push bitumen to the production wells. Hence, it is essential to increase the temperature of the deposits to lower the bitumen viscosity before it can be recovered by in-situ methods. So far, the surface processing of Utah tar sands has not proved to be economical and poses serious environmental problems.

Tar sand deposits are poor thermal conductors and nearly impermeable to fluids under native conditions. This makes transferring heat with conventional methods (such as steamflooding) difficult. We solved this problem by inventing an efficient volumetric RF power deposition technology suitable for heating very large volumes in situ. By inserting tubular electrodes into special patterns of boreholes and by applying RF energy to the conductors, we can heat the tar sand deposits uniformly. The conductor pattern and the operating frequency are matched to the electrical characteristics of the resource to ensure that virtually all the applied RF power is contained and does not leak out to cause interference. As opposed to other electrical methods that rely on the presence of moisture to establish ionic conduction paths to effect heating, the RF heating process can be adjusted to accommodate any moisture content. This is very important in view of the low moisture content of the Utah tar sands.

We describe the basic concept of the RF heating process and provide a brief discussion of its advantages over other electrical heating processes. Results of laboratory experiments, as well as two field experiments, on measurement of electrical and reservoir properties of tar sand samples and on recovery of bitumen from representative Utah tar sand deposits are reported.

Concept of the RF Process

The RF process for recovering bitumen from tar sand deposits can be described as follows: first, the deposit is uniformly heated to reduce bitumen viscosity; second, a petroleum recovery technique (such as gravity drainage or replacement with a surfactant solution as in the case of tertiary oil recovery techniques) is used; and third. the deposit is heated further until bitumen cracks in situ to form a light oil and carbon residue. We conducted laboratory experiments on core samples obtained from Utah tar sand deposits to establish the technical feasibility of all these recovery methods. These experiments indicate that between 50 and 80% of the total bitumen can be recovered. They also show that permeability to gas can be increased from less than 1 md at room temperature to more than 100 md by heating the core samples to more than 100 degrees C [373 K], which produces water and a small fraction of the bitumen. It is possible to use either steam or air injection to initiate a steam- or fireflood at this point.

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