Abstract

The results of the first 150 days of operation of an in-situ oil shale retorting experiment are presented. A zone of oil shale between 137 feet (42 m) and 177 feet (54 m) deep in the Tipton Member of the Green River Formation was retorted. The oil shale averaged 21.3 gallons per ton (89 litres per tonne) in the target zone. A section 70 feet (21.4 m) square with eight production wells was hydraulically fractured to produce three horizontal fractures. Slurry-type explosive was forced into the fractures and detonated to produce a bed of fractured oil shale.

The fractured oil shale bed was successfully ignited on April 5, 1976, using an electrical resistance heater to heat injection air supplemented with propane. Advance of the combustion front was monitored with a computer data acquisition system reporting temperatures, pressures, flows, and gas compositions each hour. It was found the flame front moved radically outward from the injection well as retorting progressed. The location of the air injection was moved from the central injection well to well 10 in the northeast part of the pattern on the 60th day of operation to increase oxygen utilization, which averaged 65 percent.

The effects of in-situ retorting upon air, surface, and ground waters were also monitored during the course of the test.

Material balance calculations indicated that 3,260 tons (2,964 tonnes) of oil shale were retorted, representing 21 percent of the target zone. Oil migration beyond the pattern was evidenced and only 2,483 gallons (9,300 litre) of shale oil, representing 1 percent of the total resource was recovered. Nitrogen balances show 93 percent recovery of injected air. The calorific value of effluent gas totaled 1,515 million Btu (1,600 million kj) of gas averaging 38 Btu per scf (1,415 kj/m3).

Core samples will be taken after the burn is completed. A complete evaluation of the experiment will be made at that time.

Introduction

An economically feasible method to recover oil from the vast oil shale resources of Wyoming, Colorado, and Utah has long been sought. Until the early 1960's, nearly all work was centered on techniques which mined the shale and recovered oil from the mined shale in aboveground retorts. That approach is useful for only the one-third of oil shale which is high grade and suited for conventional mining techniques. In the early 1960's, Laramie Energy Research Center initiated tests 1–3 to develop techniques for inducing the permeability necessary for recovery of oil by in situ processing. Successful implementation of in-situ recovery will make available the two-thirds of oil shale not suited for conventional mining. Oil produced by in-situ recovery can be an economic, environmentally sound contribution to American energy independence.

Early tests 4–6 showed that oil can be recovered from oil shale by in-situ processing. The test at Rock Springs site 4 was the most productive of the early tests, but high injection pressures were experienced and more than 60 percent of the product gas in the oil shale formation was lost.

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