Dryland Fluvial Reservoir Analogues: A Description of Lithofacies and Deposit Geometries for a System with Varying Planform Morphology
Mann, Sandra and Wadey, Carolyn
Engineering Honours Degree, 2013
University of Adelaide
Dryland fluvial deposits have the potential to form important hydrocarbon reservoirs and are a focus for petroleum exploration and production. However, the reservoir characteristics of these deposits, including porosity, permeability, connectivity and the distribution of baffles, barriers and seals, are generally not well understood. Detailed sediment logical analyses and interpretation of modern analogues can help to provide some insight into the properties of preserved ancient sediments in the geological record; including deposit architecture, geometries, connectivity and potential reservoir quality. The principal aims of this research were to investigate and describe the characteristics of and controls on the sedimentology of a dryland river of variable planform morphology and use these findings to understand the implications for petroleum exploration and production from ancient systems which share physical characteristics.
The studied modern fluvial deposit is on the ephemeral Peake Creek, approximately 100 km upstream and to the north west of its termination in Lake Eyre. The fluvial system exhibits multiple styles, changing from single channel to multiple channel downstream. Analysis of remotely sensed data, Real Time Kinematic GPS topographic transects, a quantitative grain size study and sediment observation and description were combined to define lithofacies and facies associations within the study area. A conceptual model for controls on sediment deposition in the study area was developed, a depositional element map produced and potential petroleum system elements evaluated.
Results show that classically accepted fluvial depositional models do not explain grain size distribution and deposit geometries in the study area. This has been interpreted to reflect different sediment transport and deposition characteristics relating to varying flow regimes within the study area. Primary controls on planform morphology can be related to floodplain width constriction and environmental conditions in the region. These results are consistent with a recent comparable study by Morón and Amos. It appears that the changes in fluvial planform morphology are formed through both avulsion and bifurcation, at locations controlled by downstream changes in flow hydraulics. These results have implications for hydrocarbon exploration and production. Reservoir and seal elements, as well as stratigraphic traps, can be found within multiple depositional elements within the study area. Understanding the characteristics of these elements can help to optimise field development, increase field productivity and mitigate potential production problems in analogous ancient reservoir deposits.