Charlotte Priddy

This project will evaluate the interactions and controlling mechanisms affecting linked ephemeral fluvial, playa and aeolian systems in outcrop and a sub-surface North Sea analogue. It will elucidate the relative impacts of climate change and tectonism on facies distributions and interactions in these systems, and provide a 3D fluid-flow model pertinent to migration and reservoir evaluation.

The Leman Sandstone comprises a sedimentary succession recording the interaction between ephemeral fluvial systems and aeolian and playa environments. The record is punctuated by numerous regional surfaces, the origin of which may have been mostly climatic, with periods of increased run-off resulting in fluvial incision, especially near active faults. However, the surfaces formed in a basin that was subsiding. Thus, even in a background of overall increasing accommodation space, climatic variation may have allowed for periods of significant erosion. The occurrence of significant erosion resulted in a sedimentary record that shows pronounced lateral as well as vertical facies variations.

The distribution of facies element geometries, their 3D interactions and relationships to regional erosive surfaces, and their dependence on climatic variation and active tectonism, are critical to understanding the distribution of petrophysical properties within the Leman Sandstone, and therefore to the distribution of fluid migration pathways for reservoir characterisation and management.  Interactions between fluvial and aeolian systems in arid continental basins have been the subject of past research, and these relationships have been related to a sequence-stratigraphical framework based upon climatic cyclicity. However, this past work does not account for a fluvial component that is strongly ephemeral, and upon which there is a strong control on facies distribution from active tectonism. North & Taylor (1996), and the present authors, have shown that in strongly ephemeral-fluvial systems elements show significantly more variability at all scales. Hence the distribution of ephemeral-fluvial deposits, and their interaction with other environments, will more strongly control permeability distributions and migration pathways than is the case for more stable fluvial settings.

This project will use extensive fieldwork of well-exposed sedimentary successions through arid continental depositional systems within the intra-cratonic basins of the Western USA, principally the Wingate, Moenave and Kayenta formations of the Colorado Plateau. As well as traditional methods of data gathering and analysis in the field, the project will make use of novel and developing 3D photogrammetric techniques to provide spatially accurate 3D models of the outcrop.  

The fieldwork will provide a well-constrained analogue for environmental interaction and facies distribution within the Leman Sandstone, which is undergoing a resurgence of successful exploration activity at present with new discoveries such as Pharos and nearby as yet undrilled exploration prospects.