Aquifer potential of the Coorikiana Sandstone, Eromanga Basin, Central Australia
Honours Degree, 2005
University of Adelaide
The aquifer potential of the Coorikiana Sandstone was studied with the aim of providing data for a potential amendment to the well abandonment guidelines regarding the hydraulic isolation of the Coorikiana Sandstone as outlined in Objective 6 of the Drilling and Well Completions Statement of Environmental Objectives (SEO). The SEO provides a list of objectives, and guidelines to meet the objectives under the South Australian Petroleum Act (2000) and its associated regulations.
The Coorikiana Sandstone is a thin, silty sandstone found in the otherwise siltstone-dominated lower to mid Cretaceous succession in the south western part of the Eromanga Basin in NE South Australia. The areal distribution and thickness variations of the Coorikiana Sandstone were mapped using formation tops from the Santos database. The permeability of the unit was determined using “rock-typing” techniques, supported by scanning electron microscopy, thin section and X-ray powder diffraction analyses, all with reference to a cored well. The regional extent and potential for natural communication with adjacent aquifers was examined using variance cube data from a series of 3D seismic volumes, regional seismic lines and water salinity analyses.
The permeability of the Coorikiana Sandstone is variable but generally very low, ranging from less than 0.1 millidarcies to greater than 7 millidarcies. The rocks with greatest permeability are found in the vicinity of the Murteree Horst but permeabilities decrease rapidly in all directions away from there.
Polygonal faulting compartmentalises the Cretaceous succession, but is most intense at the level of the Coorikiana Sandstone. The average size of the polygons is 0.5 km in diameter but they range in size from 0.2 km to around 4 km in some areas. The polygonal faults have been shown to be effective seals by gas production data from the Mudera and Marabooka Fields.
Possible aquifer contamination or pressure loss, via a well, involving the Coorikiana Sandstone would be confined to the fault polygon(s) that a well intersects. The study concludes that the Coorikiana Sandstone is not a regional aquifer and does not require isolation during the abandonment of a well.