Reinterpretation of Wire-line Log Data in the Eastern Galilee Basin, Queensland: Stratigraphical and Hydrogeological Implications.

Abstract

The Bureau of Meteorology (BoM) to meet the role of compiling and delivering Australia’s water information under the conditions set out in the Federal Water Act 2007 developed the Australian Water Resource Information System (AWRIS) and the National Groundwater Information System (NGIS) to support AWRIS. Functionality of the NGIS relied on compiling state and territory groundwater databases. Completeness of the data contained in these databases was critical in facilitating data migration to the NGIS and groundwater bores in the Galilee Basin were identified as a priority target for addressing data gaps. Published wire-line log interpretation information was used to create and map structure surfaces for the Galilee Basin. These structure surfaces were used to create a 3D stratigraphic framework to visualise the basin architecture. Assessment of the 3D stratigraphic framework, structure surfaces and wire-line log interpretations identified numerous inconsistencies with the established basin stratigraphy. This is partially attributed to the large number of interpretation sources, exploration relevance and an incomplete understanding of facies variability. Additional areas of concern that were also identified included inconsistent surface geology mapping and a poor understanding of regional lineaments. To address these inconsistencies systematic reinterpretation of the published wire-line log data was undertaken to validate or reassign inconsistent existing stratigraphic interpretations in the Galilee Basin. The highest percentage of inconsistent interpretations was concentrated in the eastern Galilee Basin and this area was chosen as the priority focus area. Reinterpretation relied on utilising a suite of wire-line log data from multiple data sources that included stratigraphic drill holes, coal seam gas (CSG), oil and gas exploration drill holes and groundwater bores. The availability of gamma wire-line log data was the minimum data requirement. Reinterpretation of the wireline log data has resulted in producing revised stratigraphic formation data for the tops of the Moolayember Formation/Base Eromanga Basin, Rewan Group, Dunda beds, Clematis Group, Bandanna Formation/Betts Creek beds, Colinlea Sandstone and Joe Joe Group. This revision has shifted some of these formation tops vertically by up to 300m in some instances leading to significant modification of some structure contour surfaces and the lateral extents of some formations. The Clematis Group, Dunda beds and Rewan Group have undergone the greatest level of modification. Uncertainty over the internal architecture of the Galilee Basin has significant implications for understanding the hydrogeology of aquifer systems and springs in the basin. Reinterpretation by a single operator has assisted in removing some of this uncertainty and provided a consistent dataset of interpretations.