ABSTRACT

Results from the analysis of over 8400 bottom-hole temperature values from petroleum exploration wells in the Williston Basin are reviewed. Estimates of geothermal gradients, thermal conductivities and heat flow values from the Mesozoic -Cenozoic and Upper Paleozoic units indicate that regional heat flow variations with depth occur and these are related to the hydrodynamics. Anomalously high geothermal gradients and heat flow values occur in the sedimentary interval below the Paleozoic erosional surface in the Weyburn area, but high values are not evident in the Mesozoic - Cenozoic sediments above. This anomaly cannot be completely explained by the blanketing effect of thick shaly units present there, and so there may be an anomalous contribution from the basement. The geothermal anomaly coincides with an electrical conductivity anomaly evident from magneto-telluric investigations. Two-dimensional numerical models with anomalous heat generation or anomalous thermal conductivity based on the structure indicated from magneto-tellurics give heat flow values that correspond to those observed. It is probable that enhanced radioactive heat generation related to mineralization occurs in the mid-upper crust resulting in the electrical and thermal anomalies.