Fluid Systems around Salt Diapirs
Fischer, Mark P.; Kenroy, Philip; Smith, Adam
The geological environment surrounding salt diapirs is one of the more complex and challenging settings in which to conduct hydrocarbon exploration and production. A growing diapir can influence the nearby sedimentary environment and thereby control the geometry, distribution and quality of reservoir and seal facies in its vicinity. Depending on the mechanism of emplacement, dissolution, and subsequent deformation, diapirs can induce and/or concentrate significant faulting and fracturing of the strata surrounding them. These faults and fractures can serve as conduits for vertical flow and lead to abundant stacked pay zones, or they can serve as barriers to lateral flow, causing complex compartmentalization and limiting reservoir drainage areas. The high thermal conductivity and solubility of evaporites further complicates the fluid system in the vicinity of diapirs, and studies of borehole fluids have identified strong thermal and salinity gradients that appear to create complex thermohaline convective flow systems near diapirs.
To better understand the spatial and temporal variability of fluid systems around salt diapirs, we studied paleofluid systems in the vicinity of three surface-exposed structures: (1) the Onion Creek diapir in the Paradox Basin, eastern Utah, (2) the El Papalote diapir in the La Popa Basin, northeastern Mexico, and (3) the Bakio diapir in the Cantabrian Basin, northern Spain. These diapirs formed in depositional environments ranging from terrestrial/subaerial to shelfal and deep marine, and as a consequence allow us to assess the influence of depositional setting on fluid system structure. Our research approach focuses on paleofluids that moved through fault and fracture networks in the vicinity of these diapirs, and from which vein minerals precipitated. We used mesoscopic structural analysis to document the geometry and timing of fractures and faults in each study area, and then employed thin section petrography, SEM, fluid inclusion microthermometry, and C, O and Sr isotope geochemistry to characterize the fluids that formed the veins. Our results allow us to outline the general structure and evolution of diapir-related fluid systems, and to identify and rank the variables that exert the greatest influence on these systems in different depositional settings. Though the systems are similar in many ways, stratigraphic variables seem to exert the greatest influence on the distribution and movement of fluids.
AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013