Gridding Techniques and Qualitative Assessment of Sediment Thickness using Magnetics over the Pedirka Basin (central Australia)

Summary

Petroleum exploration of the Permo-Carboniferous Pedirka Basin (central Australia) has been limited due to the high costs of exploring in this region. Modern high resolution magnetics can be used as an effective tool to map major structures that may influence migration and trapping of hydrocarbons, but careful processing is needed because geologically sourced variations in TMI are comparatively small in the study area. Aeromagnetic data at 400m line spacing was collected in eleven datasets from government sources. The minimum curvature and bidirectional line gridding algorithms were applied on two datasets which were subsequently evaluated in the Fourier domain for undesired artefacts. The radially averaged power spectra highlighted power spikes related to the grid Nyquist frequency in the minimum curvature algorithm for grid cell sizes of 1/5, 1/4 and 1/3 the line spacing. These artefacts could be reduced with a value of 99.99999% for the % pass tolerance parameter. Bi-directional line gridding produced very good gridded results and exploited the high resolution along-line data. The separate grids were stitched together and were reduced to pole prior to the application of a vertical derivative filter. Textures of the resulting grid revealed five apparent depth-to-magneticsource zones. The deepest zone represents sediment thicknesses of the order of 1.5km – an area which includes the Eringa and Madigan troughs. Also visible in the vertical derivative filtered grid are stratigraphic features such as onlap margins, embayments and channel flows – all visible to moderate depths.

Key words::

• Pedirka
• magnetics
• gridding
• sediments
• interpretation.