SOME GEOPHYSICAL RESULTS ACROSS THE SIMPSON DESERT

Abstract

The subsurface geology of the Simpson Desert was unknown four years ago. Since then aeromagnetic, gravity and seismic reconnaissance surveys have been carried out by several oil companies, the B.M.R., and the South Australian Department of Mines.

Two different interpretations of the aeromag data show that this method, if not very accurate with regard to the depth of basement, does give very useful indications on the present basins and trends of basement.

The results of the reconnaissance helicopter gravity survey outlined the main sedimentary basins and made it possible to get the best possible location for the seismic lines, and extrapolate the seismic data, saving a lot of time and money in seismic operations.

The regional features of the Simpson Desert in the Mesozoic and Upper Paleozoic units are now well known; the limits of the formations can be drawn.

The 400-mile-long section across the Simpson Desert through Poeppel Corner incorporates all of the known geophysical data.

To overcome the main problem of defining the depth of the Pre-Devonian unconformity, the accurate and economical technique of reflection offset shooting was evolved. Below the unconformity no real continuous events can be followed, minimising the hope of defining Lower Paleozoic problems. Some examples of seismic section and offset shooting are shown.

A few stratigraphic wells on the edge of the Desert have beautifully confirmed the results of the geophysical data.

The estimated cost of the geophysical data in this area is very low compared with the knowledge of the regional geology obtained from these operations. Now is the time for detailed geophysical surveys to find structures and oil, but some slides show that it is not an easy-going area.