OIL SHALE REVISITED

The US has three centuries' worth of coal. Make that three millennia: for most of it is never going to be used. Coal is labor-intensive and movable only by obsolescent transportation; no economical way of retrieving its energy without mining it (an in situ process) has yet been found. Such a process, resulting in a liquid or gaseous hydrocarbon would make it pipeline-transportable, and presumably also diminish its worst environmental drawbacks.

There were two major pilot projects to extract oil from shale: by Occidental and Colony Oil, both in the mountains near Rifle, Colo-rado. Occidental succeeded in an in situ process, and the Colony Project succeeded in retorting the shale; but the economics were miserable, and when oil prices collapsed, both were discontinued and are unlikely to be revived.

The Occidental process was not a full-fledged in situ process. It drilled into an outcropping, rubblized the shale above by explosives and then heated the rubble to make the oil flow out of the kerogen particles locked in the shale. In effect, they used the mountain as a retort, whereas Colony's retort was man-made and filled by mined shale before it was heated; but the Occidental process could not, for example, have been used on shale below extraction level. Apart from this difference, the two processes were essentially the same, and both used unpromisingly large amounts of heat to extract the energy contained in the retorted liquid.

The man who said there must be a better way was Dr Donald H. Nielson, professor of Metallurgy/Fuels Engineering at the Univer-sity of Utah. There must be a better way to get the heat into the shale, he figured; and the energy is just as good (or better) if it comes out carried by a liquid rather than a gas.