The role of thermal conductivity measurements in modelling thermal histories in sedimentary basins

Abstract

Thermal conductivity is an important parameter in thermal maturity modelling, yet is often poorly constrained. Here we examine the consequences for thermal history models of incorporating imprecise and inaccurate thermal conductivity data. We adopt a formal inversion scheme to determine the heat flow history of Inigok 1, Colville Basin, Alaska, using an extensive suite of vitrinite reflectance measurements as calibration data. The initial model incorporates lithology-dependent matrix thermal conductivity values based on published data. Subsequently, we reran the inversion 100 times, using different matrix thermal conductivities generated by Monte Carlo sampling of normal distributions specified for each lithology. The mean of each distribution was set to the initial model value and standard deviation was set at 20% of the mean. The results show that the relative variation in palaeotemperatures associated with the inversion-generated thermal histories is considerably less than that used to generate the thermal conductivity samples. This is because the heat flow history compensates for the variations in thermal conductivity to satisfy the constraints afforded by downhole temperature measurements and downhole thermal indicator data. These results show that thermal histories modelled with the inversion scheme are robust to imprecise and inaccurate thermal conductivity data. However, if a meaningful estimate of the actual heat flow is required, then accurate thermal conductivity data are necessary.