AAPG Foundation 2019 Grants-in-Aid Projects

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The impact of base-salt relief and intra-salt heterogeneity on the structural development of traps on salt-influenced passive margins.

Abstract

Salt basins are widespread and typically hydrocarbon-rich (e.g. the Gulf of Mexico is estimated to hold recoverable reserves of 55.5 billion barrels of oil equivalent). However, such basins are structurally complex, difficult to image in seismic data, and thus challenging to explore. Classic models of gravitationally-driven salt tectonics divide passive margins into updip extensional and downdip contractional kinematic domains, with faults, folds and diapiric salt structures in both forming complex structural traps. These regionally defined domains are, however, too simplistic to explain the range and distribution of structural styles locally observed on many margins, and do not recognize that salt structures (and thus traps) may travel considerable distances (>10 km) downdip of where they initially formed. I am currently using 3D seismic datasets from offshore Angola and Lebanon to investigate how the development of salt-related traps may be impacted by: (i) base-salt relief, and (ii) the lithological heterogeneity of the evaporite sequence, both of which may locally affect salt flow and therefore overburden deformation. However, seismic data reveal only finite structural style, and in order to better understand how, when and where these structures evolve through time, I will run a series of physical analogue models. I will vary the base-salt relief and the rheological properties of the salt analogue in controlled experiments to isolate the effects of these conditions. By using a CT scanner to image the models, I will gain a unique insight into how salt structures evolve in 4D, allowing me to explore the extent to which base salt relief and intrasalt heterogeneity can redefine the distribution of structural and stratigraphic traps predicted by the classic models.