Distribution of Facies and Sequence Stratigraphy of the Wyandra Sandstone, Eromanga Basin, Southwest Queensland
Siobhan Lee Walsh - 2014
Honours Degree of Bachelor of Science (Petroleum Geology & Geophysics)
Australian School of Petroleum
The University of Adelaide
Understanding the distribution patterns and paleoenvironments of the Wyandra Sandstone is essential in the delineation of one of the uppermost hydrocarbon targets in the Eromanga Basin. Within the exploration corporate database the Wyandra Sandstone is rarely defined even though it is a distinct sand prone unit within the uppermost Cadna-owie Formation. This thesis uses pre-existing Santos Ltd and third party well data from 398 wells within the south-west Queensland portion of the Eromanga Basin to demonstrate the sequence stratigraphic position and distribution of the Wyandra Sandstone.
This thesis uses a combination of the applications of isopach modelling, wireline analyses, lithological core analyses and palynology to reconstruct the distribution patterns, chronostratigraphic surfaces and to interpret the paleoenvironment of the Wyandra Sandstone. Chronostratigraphic surfaces of the CC10 and the CU00 mapped across the study area define; a lower fluvio-lacustrine flood plain of the "Lower Unnamed Cadna-owie Formation" bound by a regional unconformity, a fluvial low stand system tract of the Wyandra Sandstone and an upper transgressive to marginal marine system tract defined as the Wallumbilla/Bulldog Marine Shales.
To understand the subsurface distribution of the Wyandra Sandstone a transgressive, marginal marine and fluvial depositional analogue of the Newcastle Formation in Powder River Basin, are used to explain the distribution patterns observed within this thesis. The distribution of the Wyandra Sandstone was effected by a northeast to southwest paleotopographic high and low unconformably overlaying the "Lower Unnamed Cadna-owie Formation". The implication of the defined distribution pattern and the paleoenvironmental analysis is that the Wyandra Sandstone is genetically related to the overlying Wallumbilla/Bulldog Shales and should be formally defined as separate formation from the Cadna-owie Formation.