Abstract

Oil recovery from the Athabasca tar sand was studied experimentally, employing a number of solvents with or without steam injection.

In the miscible type experiments, carbon tetrachloride, toluene, benzene, and naphtha employed as the displacing fluids, at flood advance rates of 2 to 42 ft/day. Highest recovery of 93.3% of the in-place bitumen was obtained in the case of carbon tetrachloride, while in the case of naphtha it was 37.2%. at a rate of 42 ft/day. Decrease in rate led to increase in recovery. For example, the recoveries increased to 72.8 and 75.2% at rates of 12 and 2 ft/day, in the case of naphtha.

A modification of the process tested consisted in recycling the produced solvent-tar mixture, with a view to improving the economics of the process. Experimental results showed that such a process can be highly efficient. For example, recycling two pore volumes of naphtha increased recovery to as high as 84.2%.

A number of experiments involved steam injection as well as injection of solvent slugs followed by steam. In the case of the more volatile solvents, the recovery was less than that for steam alone (e.g. 50.8% vs 73.4% for a 10% carbon tetrachloride slug). The reasons for such behavior are discussed, and conditions under which prior solvent injection would be effective are outlined.

Introduction

Tar sand deposits of the world, especially those of Athabasca, represent important hydrocarbon sources for the future. Some 45 percent of the 625 billion barrels of hydrocarbons contained in the Athabasca tar sands are considered to be recoverable by known methods. The surface mining methods, initiated in late 1967, can recover only a small fraction of these deposits, most of which must be recovered by in situ methods. One of the first attempts along these lines was made by Shell Canada in 1957 (1), employing fracture heating of the formation by steam, and emulsification of the bitumen drained by an alkaline solution. A figure of 38 percent was given for the bitumen recovery by this process.

The present work is the first of a series of research projects aimed at the recovery of bitumen from the Athabasca tar sand by use of miscible and thermal methods. The chief objective was to evaluate these methods in rather simple experiments, in order to plan a number of more specific studies now in progress.

BACKGROUND AND GENERAL CONSIDERATIONS

Steam injection in one or other form is recognized as an efficient means of recovering viscous oil. Similarly, many laboratory and field tests have been devoted to the use of solvents for oil recovery. Few investigations of this type relate to tar sand, however. Adams and Khan (2) and Bott (3) reported results of successful cyclic steam injection tests ion tar-bearing sands. Similar procedures in the case of the Athabasca tar sands seem to have met with little or no success.

As regards the use of solvents, Jacoby and Yarboreugh (4) referred to the sharp decrease in the viscosity of bitumen when propane was added.

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