Thermal conductivity of rocks from SE New Brunswick and geothermal potential across stratigraphic successions containing salt chimneys and shale blankets

Reported bottom-hole temperatures (BHTs), resulting geothermal maps and, hence, potential for enhanced geothermal systems (EGS) were assessed for their reliability in SE New Brunswick (SENB), Canada, a region with very limited available geothermal information. Various boreholes with, and adjacent to, potential geothermal anomalies were also sampled to obtain thermal conductivity values for different lithologies encountered in the stratigraphic succession. Predictably, lowest conductivities correspond to the mudstone and particularly oil shale; intermediate values are associated with some sandstone and orthoconglomerate; and the highest values with anhydrite and halite. The most appropriate measured thermal conductivity values were then applied to each lithostratigraphic unit in a borehole's stratigraphic succession to model the geothermal profile in search of contacts between high thermal conductivity strata and overlying, insulating low-thermal conductivity strata. Such thermal chimney–thermal blanket associations enhance the local stratigraphic geothermal gradient relative to overall regional gradients that, in SENB, are well below the average global geothermal gradient. The modelling now also identifies several boreholes as unreliable because their reported BHTs had indicated thermal gradients anomalously higher than should be expected given the underlying stratigraphy. Accordingly, only minor thermal salt chimneys are identified in SENB boreholes, probably due to insufficient salt thickness, lack of a thick overlying insulating (shale) layer and/or thick thermal (oil-) shale blankets that underlie the salt deposits. An EGS potential may exist in SENB and elsewhere in locations where oil-shale blankets are at shallow depth and overlie sandstone that would then act as the thermal chimney.