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Oil Down Deep

The source of New Zealand's commercial hydrocarbons in the Taranaki Basin hides deep down below the level of most bores, according to Dr Jim Johnston of Victoria University's Chemistry Department.

Dr Johnston has spent the last few years looking at the chemical composition of organic molecules in oil and how they change during the oil formation process. As the original biomass goes through this process, some molecules remain unchanged or change in specific ways. These "biomarkers" can be used to identify the source rocks for the oil.

The research has led to some surprising results. Indications from the Kapuni field suggest that the oil there comes from a much deeper source than previously believed. The oil reservoir is found at 2,500 metres, but the biomarkers indicate that it comes from a depth of over 5,500 metres. Dr Johnston suggests that a fault passage has allowed the oil to migrate upwards.

"It went against preconceived ideas," says Dr Johnston, adding that it could have a "profound bearing" on where one should look for oil.