Abstract - Recent seismic and outcrop studies have revealed that the internal structure of lobe complexes is arranged hierarchically. Significant differences, however, exist between the hierarchical schemes proposed by different researchers in different distributary lobe systems. The scope of the present work is to synthesize and rationalize available descriptions of hierarchical lobe geometries within a consistent quantitative framework, and to augment this data with new outcrop studies of the Ross Sandstone lobe deposits. Amalgamation data measured from published correlation panels for a variety of lobe deposits at different hierarchical levels demonstrate a broad trend of increasing amalgamation at smaller scales. This new finding can have profound implications on our understanding of sandstone connectivity at the scale of hydrocarbon reservoirs, since if bed-scale amalgamation ratios are applied directly at the lobe scale, the resultant 3D lobe models are much more connected than if they are applied within an intermediate, less amalgamated, hierarchical level. Existing datasets of lobe dimensions are usually based on subsurface studies which, because they offer only limited scope for characterising thin mudstones and internal architecture, may result in overly simplistic hierarchical models. Conversely, well exposed outcrops provide high-resolution records of small thickness trends and lateral/ vertical amalgamations, but only over a limited portion of a lobe. We have examined a previously uncharacterised portion of the Ross Sandstone lobe deposits in eastern Kilbaha Bay, and have used 1D logs and 2D correlation panels to interpret 3D lobe bodies. One of our fieldwork objectives has been to quantitatively examine whether a hierarchical characterisation of this outcrop is compatible with global datasets. This comparison can benefit understanding the applicability of previous hierarchical schemes, as well as augmenting available constraining data for numerical modelling.
Abstract of talk given to:
Irish Geological Research Meeting, University of Ulster, March 2013.