Occurrences Of Oil Shales Here Worth Studying

Auckland Star, Volume LXXIII, Issue 88, 15 April 1942, Page 6

Occurrences Of Oil Shales Here Worth Studying

IT is not generally known that there * are other sources of oil than natural reservoirs of crude petroleum which have to be drilled. In the past considerable quantities of oil have been won from the so-called kerosene shales of New South Wales, the most profitable occurrence of which is in the Katoomba, Blue Mountains, district.

By A. W. B. Powell

These oil shales are a greyish rock rich in organic matter that yields considerable artificial petroleum by distillation.

New Zealand once had a shale oil mining and refining plant at Orepuki, in Southland. During the years 1899 to 1903 these works were in continuous operation, resulting in the mining of 14,000 tons of oil shale. Since 1903, however, the works have remained idle, and now only a few heaps of bricks and some rusty iron indicate the location. Sliale Still There 1 The abandoning of the mine was not due to a scarcity of the shale, but to the economic factors of high mining and working costs, coupled with the removal of duty on imported kerosene and paraffin. In a paper entitled "The Oil Shale Deposit of Orepuki, Southland," by Messrs. R. W. Willett and H. W. Wellman, published in the New Zealand Journal of Science and Technology, 1941, an interesting and valuable report on these shales is given. Unless a comprehensive/ scheme of drilling is undertaken it will be impossible to estimate with accuracy the quantity of oil shale available in the Orepuki area, for thicknesses vary between 4ft 6in and Sin. Also, the petroleum yield is subject to a variation range of from 12 gallons per ton to 60 gallons per ton, the average being a yield of 43 gallons of crude oil per ton. After considering the question of probable thicknesses of the shale seam over the whole area, the authors estimate that the quantity of shale present lies between a maximum of 6,769,000 tons and 1,770,850 tons. Economic Factors It is estimated that present-day mining costs would be in the vicinity of 20/ per ton for the Orepuki shales as compared with 15/ for a New South Wales mine. This means that for mining, retorting and refining the Orepuki oil would cost 11 id per gallon, there being the working costs, quite irrespective of plant, royalties, interest and depreciation.

In wartime, however, oil has a strategic value that can be far in excess of that of peace-time standards.

In 1911 plant for the Orepuki mine was recommended that would allow treatment of 100 tons every 24 hours. This would mean the treatment of 36,500 tons annually. At this rate, and assuming the maximum figure of over*6,ooo,ooo tons, as well as a 33 1-3 per cent recovery from the shale bed by mining, tne deposit would last approximately 55 years.

The modern treatment plant at Glen Davis, New South Wales, however, has a capacity of 35,000 gallons daily, which is considered the smallest possible economic unit. Such a unit, using Orepuki shale, would require 900 tons to be mined and treated daily, which would mean 328,000 tons annually. On the 33 1-3 per cent estimated recovery of shale, such operations would give a life of only six years to the Orepuki deposits.

It may be noted that Orepuki is not the only occurrence of oil shale in New Zealand, for it is known also from the Monowai River, further westward, as wejl as at Wakaia, Southland, several localities in Central Otago, Waihoa Valley, South Canterbury, near Blackball, West Coast and Pungaere Settlement, Northland.