CORE Geophysics and Drilling Collaborations Program Completed NSAMT survey at MMG's North Batten Project

Abstract

MMG applied for co-funding from Round 8 of the CORE Geophysics and Drilling Collaborations Program for a natural source audio magnetotellurics (NSAMT) survey at its North Batten Project in the McArthur Basin. The survey extended across the undercover northern extrapolation of the highly prospective Emu Fault zone. Conventional geophysical methods in the survey area have been found to have limitations, particularly their ability to differentiate prospective shale-rich sub-basins from false (conductivity) positives such as saline incursion and variable weathering profiles. This was the first trial of NSAMT in the McArthur region. The survey went as planned with the only significant issue encountered by the crew being highly conductive surface material that required the addition of large amounts of water and occasionally the addition of bentonite clays to retain water. The resulting 2D inversions of the AMT data produced consistent, spatially coherent responses which are able to be correlated relatively well with existing drilling and potential field geophysics. Several conductive near surface anomalies are imaged, and are interpreted to reflect potential shale accumulations in sub-basins. Like any electrical method, there is ambiguity in the results, with the incursion of saline groundwater and assumed conductive material in the Roper Group being examples of possible false positives. Overall, the results of the AMT survey are interpreted to have successfully imaged elements of the regional basin architecture, and in particular the location and geometry of shale accumulations within the undercover, relatively underexplored northern Batten Fault Zone.