Controls On Porosity Development And Preservation In The Acacia Sandstone, Southern Canning Basin.
Honours Degree, 1997
University of Adelaide
The lower Ordovician (Arenigian) Acacia Sandstone, located in the Southern Canning Basin was studied by various methods including log correlations, sequence stratigraphy, petrophysics, core description, petrography, SEM, XRD and cathodoluminescence. From these studies the diagenetic history, depositional environment, porosity distribution, and mechanisms for porosity development, preservation and destruction were determined.
The results of this study suggest that the most significant control on porosity development within the Acacia Sandstone is the precipitation and subsequent dissolution of various stages of carbonate cementation. Primary porosity was likely to have been entirely destroyed by an initial dolomitisation event, which subsequently aided in preserving the early intergranular relationships from the effects of compaction. Evidence from this study suggests most porosity present may be a rejuvenation of the primary porosity. Illite in the pore throats of the samples studied is detrimental to the permeability characteristics of this possible reservoir.
The study also suggested that the depositional environment of the Acacia Sandstone can be interpreted as a clastic wedge of sediment that prograded over a shallow broad carbonate platform in response to a local regression brought about by tectonism. The varying grain size, sorting and other sediment characteristics that are related to this depositional environment may also control porosity development and distribution.
There is some evidence that variation in the overlying evaporite sequence of the Carribuddy Group may have controlled porosity development. Local absence of this seal may have controlled migration pathways for groundwaters that affected carbonate dissolution.