Australian School of Petroleum

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https://hdl.handle.net/2440/84916
This collection contains Honours, Masters and Ph.D by coursework theses from University of Adelaide postgraduate students within the Australian School of Petroleum. The material has been approved as making a significant contribution to knowledge.

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Browsing Australian School of Petroleum by Advisors "Nanson, Rachel"

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    Controls on the morphology of fluvial and tidal influenced channels in the Gulf of Carpentaria, Australia.
    (2013) Okafor, Rosemary N.; Nanson, Rachel; Rarity, Frank; Australian School of Petroleum
    The influence of wave, tide and fluvial processes interact to control sediment erosion, transport and deposition in clastic coastal environments. This results in mixed-process coastal systems, which can form good quality, yet geometrically complex reservoir deposits. Channels in modern analogue mixed process environments provide useful insights into how wave, tide and fluvial processes affect paleochannels and can aid subsurface stratigraphic correlation and palaeoenvironmental reconstruction. The Gulf of Carpentaria is an epicontinental sea which formed as a result of sea level rise during the last marine transgression. Holocene deposits have prograded over low gradient bathymetry and display a range of channel forms. The channels that traverse these coastal plains cannot be satisfactorily characterised by simple morphological classification. They have morphologically complex patterns which have developed in response to the seasonal variations in fluvial, tide and wave energy. A numerical examination of the effects of fluvial, tidal and wave energy on the geometry and morphology of 70 single and distributary channels in the Gulf Carpentaria was undertaken using desktop based statistical analyses. Catchment area was used as a proxy for fluvial discharge in these largely ungagged catchments while wave height and tidal range was applied directly from available gauged data. These channels were divided into two subsets based on whether their channel mouths were best described by linear or exponential trends and by the channels being either distributary or single channels. These four groups were then tested separately to assess their geometrical characteristics, including the rate of decrease in channel width downstream of equi-width (fluvial) reaches, and the wave, tide and fluvial ratios. Of the analysed channels 65% where found to have a linear width profile, and their parallel banked profile was further enhanced by a strong positive correlation with catchment which exhibited very low slope of distance to equi-width. These parallel banked (linear) channels were found to be fluvial dominated while the other 35% had an exponential width profile with their entrance width visually exhibiting a strong funnelling characteristic, and the channels having a wider entrance width and a longer distance to equi-width. These exponential channels are more tidally dominated. There was a general decrease in tidal energy and wave influence with increase in distance to equivalent width in the channels, this relationship implies that a channel's distance to equivalent width can be used to identify where the fluvial energy is least effective moving downstream indicating that another process is dominant which is usually tidal or in some cases wave energy. It is also shown that there are characteristic relationships between geometric variables like entrance width at the channel mouth and the rate of decrease in channel width downstream of equivalent - width (slope) with proxies of fluvial influences and tidal range. These relationships may overlap as a result of the complex morphodynamic feedbacks between fluvial discharge, tidal propagation and wave height in this tropical monsoonal environment.
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    ItemOpen Access
    A facies atlas for the wave to tide-dominated Gulf St Vincent (South Australia)
    (2015) Swiatek, David; Nanson, Rachel; Rarity, Frank; Australian School of Petroleum
    Marginal marine depositional systems represent a significant proportion of the world’s known and exploitable hydrocarbons; however, they are complex environments containing varying modes of deposition and heterogeneity. Marginal marine process classifications have historically lacked adequate interpretation of the variability in mixed-process systems. Modern analogues provide the most accurate planform geometries of marginal marine elements for input into reservoir models. Observations made during deposition of similar systems can supplement seismic, core and geological outcrop datasets, thus improving 3D models. This research develops a facies atlas for Gulf St Vincent as a modern analogue, examining process variability of marginal marine elements resulting from wave and tide-dominant processes. Gulf St Vincent is a shallow, inverse estuary in South Australia that connects to the Southern Ocean. Gulf St Vincent was flooded by the most recent Holocene post-glacial marine transgression. The sediments that form the marginal marine deposits accumulated along the eastern coast of Gulf St Vincent are interpreted to be derived from the reworking of the gulf floor as the sea level transgressed to its present location. Analysis of data collected along the eastern coast of Gulf St Vincent displayed evidence that wave height and energy, along with tidal range, control the geomorphology of the shoreline and sediment heterogeneity. Depositional environments changed as the shoreline transitioned from wave to tide-dominated processes. The carbonate-rich sediments in the tide-dominated northern region indicate they were very different depositional environments from the homogeneous quartz-rich medium-grained sands produced in the wave-dominated areas to the south. The dominant process controls vary from wave through tide in a northerly direction.This research has determined that four types of depositional environments dominate the eastern coastline of Gulf St Vincent, which were linked to process controls and characterised by their shore face slope, sedimentary deposits and architecture. They were linked to distinct arrangements of depositional elements with their own sedimentary signatures. This study also suggests that the observed carbonate sediments can be classified using the Ainsworth et al. (2011) and Vakarelov and Ainsworth (2013) marginal marine mapping and classification systems. The facies atlas presented herein has the potential to inform hydrocarbon reservoir modellers by providing data on the internal architecture of 2D mapped depositional elements.