Three-dimensional modelling of a mixed-influence coastal environment in the Gulf of Carpentaria to test the effects of upscaling on field-scale heterogeneity.
Engineering Honours Degree 2009
University of Adelaide
The Mitchell River delta on the eastern coastline of the Gulf of Carpentaria in Queensland, Australia is a modern mixed-influence delta that has been selected as an analogue for shallow-marine reservoirs by the WAVE consortium and was the subject location for this study. Ancient fluviodeltaic reservoirs host a significant proportion of the world’s remaining hydrocarbon reserves and are often deposited under complex morphological processes that result in varying degrees of heterogeneity. Shallow-marine systems deposited by singleinfluence river-, tide- or wave-dominated processes are relatively well documented but a combination of these processes leads to significant changes in the coastal morphology and gives rise to complex heterogeneity that is less understood. Determining the lateral extent of this heterogeneity at the field-scale leads to better reservoir connectivity estimation. A threedimensional modelling approach was taken to provide information including, the shape, distribution and preferred orientations of sedimentary units relevant to mixed-influence systems. Geomorphological units were mapped from unambiguous satellite imagery at three different scales: element, set and complex. The resultant maps were inputted into a 3D grid and given artificial reservoir properties. The effects of lateral and vertical upscaling on the complex relationships between reservoir facies were tested and changes in reservoir volume and connectivity in the resultant upscaled models was assessed. Models based on element scale mapping captured the extent of the areal complexity in the system. Furthermore the element model was found to retain the complexity as it was laterally upscaled to 10m x 10m and 20m x 20m grids. Further upscaling resulted in a loss of relatively small-scale facies, often absorbed into reservoir facies leading to an overestimation in reservoir volume. The set level mapping was sufficient to model the reservoir connectivity and volume but did not contain the model the small-scale complexity. The set model could be upscaled to a 50m x 50m grid without any significant changes in reservoir volume. Complex scale modelling did not produce accurate results for either the reservoir volume or connectivity when compared to both the set and element models. Vertical upscaling resulted in a significant loss in detail, even when relatively small changes in the vertical resolution were made. Vertical upscaling should only be undertaken in sufficiently thick reservoirs.