ON THE IMPORTANCE OF MEASURING THERMAL-CONDUCTIVITIES FOR HEAT-FLOW DENSITY ESTIMATES - AN EXAMPLE FROM THE JEANNE DARC BASIN, OFFSHORE EASTERN CANADA

Temperature data from petroleum exploration wells can be used to study the thermal regimes of sedimentary basins. In this, it is common to c onsider many wells and to multiply the average geothermal gradient mea sured in each well by the effective thermal conductivity of the rocks across the interval over which the gradient is determined to obtain a heat flow density estimate for the location of each well. It is often not possible to measure the thermal conductivities of the rocks presen t in the basin, and the usual approach is to assign thermal conductivi ty values based on published values to those rocks. It is shown that, at least in the Jeanne d'Arc Basin, to use assumed thermal conductivit y values to calculate heat flow densities at the locations of the 35 w ells considered is misleading and results in heat flow density estimat es that can be one-half those found using thermal conductivities based on values obtained from measurements on rocks from some of the wells in the basin. These differences in heat flow densities can lead to dif ferences in the extrapolated temperatures using the two sets of therma l conductivities as high as 264 degrees C at 20 km depth. Higher tempe ratures are obtained when the measured thermal conductivity data set i s used.