FAILURE ANALYSIS OF THE LAKE HOWE BLOWOUT STRUCTURE, WILLISTON BASIN

Christiansen et al. (1982) and Gasby et al. (2000) both proposed that Lake Howe, located in southeast Saskatchewan, is a Late Pleistocene (~ 12 ka) blow out structure associated with Wisconsin glacial loading. We hypothesize that during glacial loading, high pore pressures within the sand-silt dominated Mannville aquifer resulted in low effective stress conditions and failure within the overlying ultra-low permeability Pierre Shale. The Lake Howe blowout structure likely facilitated the rapid influx of relatively low salinity, isotopically depleted pore fluids. Analysis of isotopic profiles by Hendry et al. (2013) collected from a bore hole located over 100 km from where the Manville crops to the East suggests that glacial melt waters were likely emplaced much earlier than the formation of Lake Howe; between about 0.135 to 0.51 Ma. We speculate that there may have been many Lake Howe’s in the geologic past. We have constructed a cross-sectional hydrodynamic-geomechanical model that incorporates glacial loading, isotope and brine transport as well as a Mohr-Columb failure criteria. We have applied this model to the Williston basin in order to constrain the timing of blowout structure formation and emplacement of relatively freshwater, isotopically depleted meltwater into the Mannville Formation.