The goal of the multidisciplinary work presented by this study is to understand the geological and geophysical parameters that will affect the safe and efficient storage of CO2 at the proposed SW-Hub site in the Southern Perth Basin.
In particular, the areas of interest covered by this work are related to the characterisation of the geological units intersected by Harvey-1 in terms of storage capacity; injectivity and containment potential; elastic and mechanical properties and heterogeneity of the formations encountered.
The present work feeds into and supports a wider program aimed at the integrated evaluation of the SW-Hub encompassing a detailed analysis of the seismic data available in the region; an assessment of the potential for fault reactivation around the proposed injection area; a study of the possible fluid-rock interactions at reservoir conditions and the forward stratigraphic modelling of the area.
The outcomes of the work indicate significant differences between the Upper and Lower Members of the Lesueur Sandstone in terms of sedimentology, petrophysical, geomechanical and elastic properties. The deep saline aquifer equivalent to the Wonnerup Member of the Triassic Lesueur Sandstone represents the targeted reservoir, whereas the Yalgorup Member and the Basal Eneabba Shale may act as possible stratigraphic seals.
Good reservoir properties are recorded in the lower Member (Wonnerup 1380-2895m depth) of the Triassic Lesueur Sandstone with encouraging values of porosity (7 to 19%) and permeability (0.01 to 580 mD) and lithofacies homogeneity with depth. Permeability anisotropy measured in the laboratory can be very significant at the tentatively predicted injection levels: across bedding permeability ranges between 0.01 and 3mD while along bedding permeability ranges between 38-580mD, resulting in anisotropy of up to 3 orders of magnitude.
Core flooding tests also give positive indications for residual trapping (25 to 45%) as a principal containment mechanism. However, a marked decrease of permeability (up to 50%) was observed after sample flooding was also inferred from the tests. This phenomenon has been identified for future studies.
By contrast, the overlying Yalgorup (704-1380m) is far more heterogeneous and, due to poor core conditions of the shaly layers, the characterisation work only focused on the sandy intervals, and the results cannot be regarded as representative of the whole stratigraphic unit.
Uncertainties remain regarding the geomechanical properties and containment potential of the different lithofacies within the Yalgorup. Nevertheless, the presence of interbedded sands and shale layers could be beneficial in terms of storage.