Final Field Results Of True In Situ Oil Shale Retorting Demonstration Project In The Green River Formation Of Southwestern Wyoming
Authors: Goldstein Kenneth M. , Goldstein Linda F. 
Published: December 2007

The commercial production of oil from oil shades using true in-situ technology would allow recovery of vast national fossil fuel resources with minimal environmental impact. A demonstration project was completed recently under a contract funded by the U.S. Dept. of Energy (DOE), which indicated that no current true in-situ technology exists that will allow shale oil recovery on an economically feasible basis.

Introduction

Vast deposits of oil shales have been identified within the continental United States, primarily in Wyoming, Colorado, and Utah. The DOE estimates that nearly 3 trillion bbl (4.8 × 10(11) m3) of shale oil are contained in the Green River Formation of the Western U.S. The Eastern oil shales are not quantified as well, but the total potential quantity of domestic shale oil has been estimated at more than 5 trillion bbl (8 × 10(11) m3).

The Western oil shale deposits will provide much-needed fossil-fuel oil as soon as technology is developed to extract the oil with comparable economics to conventional oilwell production. There are three methods currently being researched to recover oil from shale. The oldest and least environmentally acceptable method requires mining of the shale, with above ground retorting and processing. The second method is a modified in-situ precess in which underground miners dig a room beneath the oil shale deposits. Explosives are used then to turn the shale formation into rubble and drop it into the mined room. Both of these methods require costly and environmentally detrimental excavations and tailings piles.

The third, or true in-situ, method entails fracturing of the oil shale formation in a manner similar to conventional oilwell processing. Water and hard frac sand are pumped into the formation at high pressures, causing near-horizontal pancake-shaped fractures to be propagated. These fractures provide a path for other fluids to follow at lower pressures. A slurried explosive then can be pumped into the fracture paths and detonated, rubblizing the formation and reducing particle sizes for increased retorting surface area. Because this method also requires a minimum of surface preparation and processing, it is the most environmentally processing, it is the most environmentally acceptable.

In both underground methods, combustion is started in the center of the rubblized volume. Air is pumped into the formation to allow continuing combustion. The heat of pyrolysis forces oil out of the shale and away from the center, where it is recovered from holes drilled at the periphery of the rubblized volume. Decreased particle sizing caused by rubblization allows radial flow of retorted oil to gravity-fed recovery sumps.

Under the DOE contract, Talley Energy Systems Inc. was the project manager, with Sandia Laboratories, M. D. Wood Inc., Systems, Science and Software, and Laramie Energy Technology Center (LETC) providing instrumentation and manpower.

The project was conducted from Aug. 1977 through Dec. 1978 on a 1-square-mile section, designated Site 17, located several miles east of Green River in southwestern Wyoming.

THEORY

True in-situ retorting of oil shale can be economically feasible only if the natural permeability of the shale formation can be increased by several orders of magnitude. The typical permeability of the Green River oil shale deposit was determined to be approximately 1 md (9.9 × 10(-4) um), indicating a highly competent formation. This ambient lack of natural fractures will not allow either combustion or mass transport of the produced shale oil for recovery.