Geography, Geology and the Environment

I graduated from Keele in 2010 with an undergraduate MGeoscience degree in geology with physics. My 4^th year masters thesis was based on fieldwork carried out in the Arches National Park, Utah, looking at complex fault geometries and accommodation zones in the hanging-walls of large extensional faults. This experience reinforced a developing interest in structural geology and basin analysis, and introduced me to the structural complexities posed by the presence of salt in basin settings.

I am currently studying for a PhD in Earth Science, looking at salt-controlled fault systems and accommodation zones in the Paradox Basin, Utah, U.S.A.

Positions/Affiliations:

• Fellow of the Geological Society of London (GSL)
• Student Member of the American Association of Petroleum Geologists (AAPG)
• Student Member of the Geological Society of America (GSA)
• Vice President – Keele University Student Chapter of the AAPG

Structural development of accommodation zones in host and suprajacent sediments associated with the development of salt walls: Implications for sub-surface hydrocarbon flow.

Supervisory team: Dr. Stu Clarke^1, Dr. Phil Richards², Prof. Graham Williams¹, Sue Stoker².

¹ Dept. Earth Science & Geography, Keele University, Staffordshire ST5 5BG.

² British Geological Survey, Murchison House, Edinburgh EH9 3LA

Project Summary:

Linear structures associated with salt diapirism, such as salt walls, salt anticlines and salt rollers, are common features in active hydrocarbon provinces including those of the UK North Sea, the West African Salt Basin and the Gulf of Mexico. They often present a wide range of structural styles along their lengths, with complex fault geometries which can be difficult to interpret meaningfully from seismic survey. Salt walls are known to end rather abruptly, or change their dominant deformational style over short distances, resulting in extremely complex accommodation zones where displacement is transferred between the different structural regimes. Given the potential for salt to provide both stratigraphical and structural closure to any reservoirs, and the importance of accommodation zones in offering migration pathways into potential trapping structures, understanding the complexity of salt-related accommodation zones is of paramount importance to the evaluating and risking any related hydrocarbon traps.

In key areas within the Paradox Basin, Utah, U.S.A., horst and graben deformational styles along, and adjacent to, the crests of salt walls give way to half-graben geometries, where displacement is accommodated on a single listric fault with an associated rollover anticline, over no more than a few hundred metres. Hanging-wall structures in these areas have been identified as exhumed palaeohydrocarbon traps, and it has even been suggested that charge may have been by way of accommodation zones. These exposures offer an ideal opportunity to evaluate the complexity of these salt-related accommodation zones, to compare them to geometries resolvable on seismic survey, and to assess the implications they might have for hydrocarbon migration and entrapment.

Geological map of the Moab-Spanish Valley, Utah (Utah Geological Survey, Map 180). Dominant deformational styles along the crest of a salt anticline change from a graben geometry in the south, to a half-graben in the north, with an associated rollover anticline in the hanging-wall. Accommodation of displacement between these structural styles takes place over approx. 200m.	Geological map of the Moab-Spanish Valley, Utah (Utah Geological Survey, Map 180). Dominant deformational styles along the crest of a salt anticline change from a graben geometry in the south, to a half-graben in the north, with an associated rollover anticline in the hanging-wall. Accommodation of displacement between these structural styles takes place over approx. 200m.

Aims and Objectives:

• Evaluate the 3D geometry of fault systems, sediment bodies and small scale deformational structures within complex salt-related deformation zones between opposing structural styles using excellently exposed examples from the Paradox Basin, Utah, U.S.A.
• Develop 3D summary models of structural styles present both immediately adjacent to and within those accommodation zones, that can be used to aid modelling of potential hydrocarbon traps from seismic data.
• Apply this field-based modelling to sub-surface analogues for the Utah exposures using well-imaged 3D seismic data from the Central North Sea.
• Develop 3D stochastic flow models for fluid migration through salt-related accommodation zones as a means of evaluating those parameters and uncertainties of the accommodation zone that effect hydrocarbon charge and trap risk.
• Elucidate the controlling-factors on the locii of accommodation zones within salt-controlled basins; What parameters control their position?

Preliminary Work:

Early work has focused on the three-dimensional geometry of sub-seismic scale fault systems in the rollover anticline of a large listric fault, which forms a half-graben geometry at the crest of the Salt Valley salt anticline, Cache Valley, Arches National Park, Utah. Preliminary results suggest a possible link between the development of en-echelon (stepping) hanging-wall fault systems and variation in displacement along the length of the listric fault.

• Randles, T.A., Clarke, S.M. and Tichards, P.C. The three-dimensional geometry and kinematics of brittle structures within the immediate hanging-wall of large extensional faults: Implications for subsurface hydrocarbon migration and entrapment. TSG 2011. TSG 2011 poster.