Over The Horizon

Sounding for Oil

Victoria University geophysics student Mike Stevens is helping oil company Indo-Pacific Energy explore the 2.7 million acres of the Canterbury Plains.

Stevens' project results from the discovery of a major sedimentary basin that has been hidden under the gravel of the Canterbury Plains.

"The gravel has been shed by the Southern Alps, which are lifting upwards, over the last five million years," says Stevens. "Geologically that's young. But the gravel is around two kilometres thick and forms a formidable layer for oil explorers to deal with."

"We want to get a better picture of structures that appear to be a series of sedimentary basins similar to those in Taranaki, where oil production is well proven."

Dynamite is used to send sound waves into the earth. They reflect back and are recorded by listening devices on the earth's surface.

"By measuring the time the sound waves take to get back to you, you can work out the depth to the different layers. I then use a computer to organise the signals and construct a picture of the geological structure. It's a bit like an ultrasound."

The gravel sucks up the sound energy, making it hard to picture the sediments below, but new technology means it's now possible to get a good picture of what's beneath the gravel.

Stevens is comparing data from Indo-Pacific Energy and from a joint NZ-US project. Although they used different techniques, both found that the sedimentary basins under the Canterbury Plains were 3-4km thick, rather than the two kilometres previously estimated.

"This makes them a more exciting prospect for oil and gas exploration than previously thought."