Fischer, Mark P.
M.S. (Master of Science)
Department of Geology and Environmental Geosciences
This thesis uses both numerical modeling and a field study to assess fluid systems associated with salt diapirs. I initially use the modeling software TOUGH2-MP to simulate coupled fluid and heat transport in the near salt environment. I use the software to conduct numerical simulations of coupled fluid and heat transport in a salt dome environment to determine the effects of advective heat transport in different scenarios. Model sets were designed to investigate (1) salt geometry, (2) depth dependent permeability, (3) geologic heterogeneity, and (4) a combined simulation to assess the relative influence of each of these factors.Decreasing the dip of the diapir induces advective heat transfer up the side of the diapir, elevating temperatures in the basin. The resulting fluid circulation causes flow up the diapir flank. Depth dependent permeability causes upwelling of warm waters in the basin. Heat is advected up the diapir in a narrower zone of upward-flowing warm water, and cold waters are advected deeper into the basin with isotherms nearly parallel to the salt sediment interface. The resulting fluid circulation pattern causes increased discharge at the diapir margin and fluid flow downward, above the crest of the diapir. Geologic heterogeneity decreases the overall effects of advective heat transfer. Sealing horizons reduce the vertical extent of convective cells and fluid flow is dominantly up the diapir flank. The combined effects of depth dependent permeability coupled with geologic heterogeneity provide the most realistic model. Conductive heat transfer dominates in the basal units, whereas advection of heat begins to affect the middle layers of the model and dominates the upper units of this model. Convection cells split by sealing layers develop within the upper units. Overall, my results indicate that fluid flow and the associated thermal advection are strongly controlled by salt geometry, permeable layer (i.e., reservoir) thickness, and permeability. Advective heat transport (i.e. thermal convection) likely dominates in the early phases of diapirism when sediments are relatively shallow and retain high porosity and permeability. As diapirism continues, and the salt sediment interface develops vertically, along with stratigraphic heterogeneity in the minibasin, conduction through the diapir will likely be the main heat transport mechanism with advection affecting the shallow, low permeability sediments. Further modeling is necessary to assess the relative influence of more complex structural geometries (i.e. megaflaps, salt shoulders, and other growth geometries), as well as these factors in the presence of salt dissolution. The third chapter of this thesis characterizes the fracture controlled paleohydrologic structure of two primary minibasins on ether side of Witchelina diapir in the Willouran Ranges of South Australia. I use a combination of structural and geochemical techniques to infer what the fluid system behavior was like when veins formed near the diapir. Fractures around Witchelina diapir are dominantly perpendicular to bedding despite significant rotations during salt diapirism and Delamerian deformation. Vein minerals were precipitated from a high temperature, high salinity, metamorphic fluid that entered the respective minibasins and rapidly cooled, precipitating quartz and dolomite upon fluid ascent. My data indicate that the fluid system around Witchelina diapir was metamorphic in origin and was fluid dominated, but host rock mediated, with the local stratigraphic architecture and fracture network playing a critical role in fluid compartmentalization and migration.
Canova, David Paul, "Comparing the paleohydrologic structure on either side of Witchelina Diapir, South Australia" (2017). Graduate Research Theses & Dissertations. 1858.
Northern Illinois University
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