COMMERCIAL Tasman Gives Details Of Survey Work

Press, Volume CX, Issue 32381, 21 August 1970, Page 20

COMMERCIAL Tasman Gives Details Of Survey Work

(New Zealand Press Association) WELLINGTON. August 20. Within four years Tasman Petroleum, Ltd, may drill for oil in the Chatham Islands area, according to an information bulletin L. and M. Oil N.Z., Ltd, mailed to shareholders this week.

The mailing came only days, after the spudding in of Cook' 1. the next well in the Tasman concession area. Drilling of the first well, Tasman 1, ended unsuccessfully in a basement of hard red conglomerate on March 24, at 5345 ft. In both cases New Zealand Aquitaine Petroleum, Ltd. has been the operator, with Murphy Australia Oil Company, and Odeco N.Z., Inc., under a farmout agreement with Tasman Petroleum. L and M Oil N.Z., Ltd, holds 25 per cent of the capital in Tasman Petroleum.

As well as dealing at some length with the Tasman 1 findings. the L and M information bulletin also underlines the fact that Tasman Petroleum’s fortunes do not rely entirely on the results obtained in the offshore areas currently being probed for oil. Chatham Islands

The bulletin gives progress reports on work carried out In the other concessions, outside the farmout agreement with Aquitaine, including licence areas in the ReeftonGreymouth area, the Waimea Basin and Chatham Islands, Including Pitt Island. The bulletin says that Tastnan’s 12 petroleum prospecting licences in the Chatham area cover a total of 18,200 square miles, including all the land which makes up Chatham Island itself and the offshore areas immediately surrounding it and Pitt Island. Preliminary geological and geophysical surveys have been completed in the field in this' area, the bulletin says, and on Chatham Island gravity data has indicated the potential} for a relatively thick cretaceous Tertiary section: considerably more work is required'. on this to assess its oil pot-: ential.

“On Pitt Island the cretaceous coal measure is considered to have significant source beds and reservoir potential for hydrocarbon generation and accumulation. “Additional land gravity and magnetometer surveys are now planned as a preliminary to magnetic offshore surveys and extensive marine seismic work." Survey Expenses The bulletin adds that in the first year of its licence holding in the area Tasman has been obliged to spend $50,000 on geological and geophysical work, and further expenditure of about $250,000 will be required in the second and third years on further similar work, including a marine seismic reconnaissance survey. The following year further: extensive studies will be re-1 quired, mainly marine seismic.! The bulletin says these will! cost about $200,000.

i “In the fifth year one well is to be drilled if the results of the work carried out justify it” The bulletin makes it plain that unlike the drilling being carried out in the Tasman concession by Aquitaine, the bill for the sinking of a well in the Chatham area will have to be met entirely by Tasman, and that L and M will have to contribute 25 per cent However, no estimate of costs can be given at this stage, the publication says. Aquitaine and its partners have met all drilling costs to date in the Tasman concession.

On the subject of Tasman 1, the bulletin says that the most positive result of the drilling of this well was that it substantially increased the knowledge of the formations in the Tasman concession. No Reservoir

It adds: “The red conglomerate basement found was of cretaceous to permian age (90 million to 150 million years old), but the known occurrence of petroleum in New Zealand has been among younger rocks. “Because it was an older and compacted rock the Tasman No. 1 conglomerate was not suffciently porous to act as a reservoir for hydrocarbons and there is sufficient

available knowledge of these formations on land for it to be known that there was little chance of finding any reservoir rocks beneath it: drilling was therefore halted. Increase In Gas “However, almost 100 ft of reservoir sands with a high porosity were present near this level and also noticed was a very slight increase in gas—mostly methane—plus some oil coating of sand grains. But calculations from electric logs showed that the reservoir was completely saturated with salt water, not oil.

The bulletin adds that during drilling limestone was struck within a few hundred feet of where the seismic records had placed it on the Tasman structure. But because limestone is a very good reflector, the publication explains, it is also difficult to get energy through it to accurately predict tiie depth of basement, the point beyond which it is known to be impossible to strike oil. Two interpretations thus had to be placed on where the economic basement would be found and the more shallow proved correct Thus the drilling actually followed very closely the predictions of the technical experts, the bulletin says.